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-2
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@@ -43,8 +43,6 @@ Some aspects of the library can be configured by defining preprocessor macros **
- [**JSON_SKIP_UNSUPPORTED_COMPILER_CHECK**](https://json.nlohmann.me/api/macros/json_skip_unsupported_compiler_check/index.md) - do not warn about unsupported compilers
- [**JSON_USE_GLOBAL_UDLS**](https://json.nlohmann.me/api/macros/json_use_global_udls/index.md) - place user-defined string literals (UDLs) into the global namespace
- [**JSON_USE_SIMDUTF**](https://json.nlohmann.me/api/macros/json_use_simdutf/index.md) - use the simdutf library to accelerate UTF-8 validation
- [**JSON_VIEW_NO_SIMD**](https://json.nlohmann.me/api/macros/json_view_no_simd/index.md) - use only portable code in the parser of `json_view.hpp`
- [**JSON_VIEW_USE_SSSE3**](https://json.nlohmann.me/api/macros/json_view_use_ssse3/index.md) - validate non-ASCII strings with SSSE3 in the parser of `json_view.hpp`
## Library version
+2 -2
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@@ -38,7 +38,7 @@ Therefore, assertions can be switched off by defining `NDEBUG`.
```cpp
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using nlohmann::json;
int main()
{
@@ -64,7 +64,7 @@ Therefore, assertions can be switched off by defining `NDEBUG`.
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using nlohmann::json;
int main()
{
+4 -4
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@@ -1,8 +1,8 @@
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/macros/json_assert/" rel="canonical"><link href=../ rel=prev><link href=../json_brace_init_copy_semantics/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>JSON_ASSERT - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new 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xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> JSON_ASSERT </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark mode" type=radio 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6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9.5 5"/></Line truncated
</code></pre></div> <p>This macro controls which code is executed for <a href=../../../features/assertions/ >runtime assertions</a> of the library.</p> <h2 id=parameters>Parameters<a class=headerlink href=#parameters title="Permanent link">&para;</a></h2> <dl> <dt><code>x</code> (in)</dt> <dd>expression of a scalar type</dd> </dl> <h2 id=default-definition>Default definition<a class=headerlink href=#default-definition title="Permanent link">&para;</a></h2> <p>The default value is <a href="https://en.cppreference.com/w/cpp/error/assert"><code class=highlight><span class=n>assert</span><span class=p>(</span><span class=n>x</span><span class=p>)</span></code></a>.</p> <div class=highlight><pre><span></span><code><span class=cp>#define JSON_ASSERT(x) assert(x)</span>
</code></pre></div> <p>Therefore, assertions can be switched off by defining <code>NDEBUG</code>.</p> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <ul> <li>The library uses numerous assertions to guarantee invariants and to abort in case of otherwise undefined behavior (e.g., when calling <a href=../../basic_json/operator%5B%5D/ >operator[]</a> with a missing object key on a <code>const</code> object). See page <a href=../../../features/assertions/ >runtime assertions</a> for more information.</li> <li>Defining the macro to code that does not call <code>std::abort</code> may leave the library in an undefined state.</li> <li>The macro is undefined outside the library.</li> </ul> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example: default behavior</summary> <p>The following code will trigger an assertion at runtime:</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span>
<span class=p>{</span>
@@ -16,7 +16,7 @@
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span>
<span class=p>{</span>
@@ -24,4 +24,4 @@
<span class=w> </span><span class=k>auto</span><span class=w> </span><span class=n>v</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>j</span><span class=p>[</span><span class=s>"missing"</span><span class=p>];</span>
<span class=p>}</span>
</code></pre></div> <p>Output:</p> <div class=highlight><pre><span></span><code>assertion error in operator[]
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../../../features/assertions/ >Runtime Assertions</a> - overview documentation</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ul> <li>Added in version 3.9.0.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 2, 2026 09:32:15 UTC">October 2, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 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</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../../../features/assertions/ >Runtime Assertions</a> - overview documentation</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ul> <li>Added in version 3.9.0.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 25, 2026 11:07:51 UTC">October 25, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 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+2 -2
View File
@@ -35,7 +35,7 @@ The following code will trigger an assertion at runtime:
```
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using nlohmann::json;
int main()
{
@@ -61,7 +61,7 @@ The assertion reporting can be changed by defining `JSON_ASSERT(x)` differently.
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using nlohmann::json;
int main()
{
+2 -2
View File
@@ -79,7 +79,7 @@ The default value is `0` (disabled — existing behavior is preserved).
```cpp
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using nlohmann::json;
int main()
{
@@ -98,7 +98,7 @@ The default value is `0` (disabled — existing behavior is preserved).
#define JSON_BRACE_INIT_COPY_SEMANTICS 1
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using nlohmann::json;
int main()
{
@@ -1,14 +1,14 @@
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</code></pre></div> <p>When defined to <code>1</code>, single-element brace initialization of a <code>basic_json</code> value is treated as a copy/move of the element rather than wrapping it in a single-element array.</p> <h2 id=default-definition>Default definition<a class=headerlink href=#default-definition title="Permanent link">&para;</a></h2> <p>The default value is <code>0</code> (disabled — existing behavior is preserved).</p> <div class=highlight><pre><span></span><code><span class=cp>#define JSON_BRACE_INIT_COPY_SEMANTICS 0</span>
</code></pre></div> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <div class="admonition note"> <p class=admonition-title>Background</p> <p>C++ always prefers the <code>initializer_list</code> constructor over the copy/move constructor for brace initialization. This means that code like</p> <div class=highlight><pre><span></span><code><span class=n>json</span><span class=w> </span><span class=n>obj</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=p>{{</span><span class=s>"key"</span><span class=p>,</span><span class=w> </span><span class=s>"value"</span><span class=p>}};</span>
<span class=n>json</span><span class=w> </span><span class=n>j</span><span class=p>{</span><span class=n>obj</span><span class=p>};</span>
</code></pre></div> <p>creates a single-element <strong>array</strong> <code>[{"key":"value"}]</code> instead of a copy of <code>obj</code>. This behavior is compiler-dependent for older compilers (<abbr title="GNU Compiler Collection">GCC</abbr> wrapped, Clang did not), but starting from Clang 20, both compilers behave the same way.</p> <p>Enabling this macro opts into copy/move semantics for this case (see <a href="https://github.com/nlohmann/json/issues/5074">#5074</a>).</p> </div> <div class="admonition warning"> <p class=admonition-title>Opt-in only</p> <p>This macro must be defined <strong>before</strong> including <code>&lt;nlohmann/json.hpp&gt;</code>. Defining it after the include has no effect.</p> </div> <div class="admonition warning"> <p class=admonition-title>Applies to every single-element list</p> <p>The macro does not only affect a single <abbr title="JavaScript Object Notation">JSON</abbr> value in braces. <strong>Any</strong> single-element braced list is treated as its element, so it no longer creates a one-element array:</p> <div class=highlight><pre><span></span><code><span class=n>json</span><span class=w> </span><span class=n>j1</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=p>{</span><span class=mi>1</span><span class=p>};</span><span class=w> </span><span class=c1>// 1, not [1]</span>
<span class=n>json</span><span class=w> </span><span class=n>j2</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=p>{</span><span class=s>"text"</span><span class=p>};</span><span class=w> </span><span class=c1>// "text", not ["text"]</span>
<span class=n>json</span><span class=w> </span><span class=n>j3</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=p>{{</span><span class=mi>1</span><span class=p>,</span><span class=w> </span><span class=mi>2</span><span class=p>}};</span><span class=w> </span><span class=c1>// [1,2], not [[1,2]]</span>
</code></pre></div> <p>Code that relies on these producing arrays must use <code>json::array()</code> instead (see below). Lists with more than one element, and a single <code>[string, value]</code> pair <em>written as a braced list</em>, such as <code>{{"key", "value"}}</code>, which still creates an object, are not affected. This exception is based on how the pair is written, not on the shape of its value: an existing <abbr title="JavaScript Object Notation">JSON</abbr> value that happens to be a two-element array with a string as its first element, such as <code>json arr = {"key", 42};</code>, is still copied by <code>json j{arr};</code> rather than turned into an object. The library's own conversions are not affected either: for example, <code>std::tuple&lt;int&gt;{5}</code> still becomes <code>[5]</code>.</p> </div> <div class="admonition note"> <p class=admonition-title>ABI compatibility</p> <p>The value of this macro is encoded in the <a href=../../../features/namespace/ >namespace</a> (tag <code>_bics</code>), resulting in distinct symbol names. Translation units compiled with and without it can therefore be linked into the same program without One Definition Rule (ODR) violations, but they cannot exchange instances of library types.</p> </div> <div class="admonition tip"> <p class=admonition-title>Workaround without the macro</p> <p>To explicitly create a single-element array without enabling this macro, use <code>json::array()</code>:</p> <div class=highlight><pre><span></span><code><span class=n>json</span><span class=w> </span><span class=n>j</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>json</span><span class=o>::</span><span class=n>array</span><span class=p>({</span><span class=n>obj</span><span class=p>});</span><span class=w> </span><span class=c1>// always creates [obj]</span>
</code></pre></div> <p>Code that relies on these producing arrays must use <code>json::array()</code> instead (see below). Lists with more than one element, and a single <code>[string, value]</code> pair <em>written as a braced list</em>, such as <code>{{"key", "value"}}</code>, which still creates an object, are not affected. This exception is based on how the pair is written, not on the shape of its value: an existing <abbr title="JavaScript Object Notation">JSON</abbr> value that happens to be a two-element array with a string as its first element, such as <code>json arr = {"key", 42};</code>, is still copied by <code>json j{arr};</code> rather than turned into an object. The library's own conversions are not affected either: for example, <code>std::tuple&lt;int&gt;{5}</code> still becomes <code>[5]</code>.</p> </div> <div class="admonition note"> <p class=admonition-title><abbr title="Application Binary Interface">ABI</abbr> compatibility</p> <p>The value of this macro is encoded in the <a href=../../../features/namespace/ >namespace</a> (tag <code>_bics</code>), resulting in distinct symbol names. Translation units compiled with and without it can therefore be linked into the same program without One Definition Rule (<abbr title="One Definition Rule">ODR</abbr>) violations, but they cannot exchange instances of library types.</p> </div> <div class="admonition tip"> <p class=admonition-title>Workaround without the macro</p> <p>To explicitly create a single-element array without enabling this macro, use <code>json::array()</code>:</p> <div class=highlight><pre><span></span><code><span class=n>json</span><span class=w> </span><span class=n>j</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>json</span><span class=o>::</span><span class=n>array</span><span class=p>({</span><span class=n>obj</span><span class=p>});</span><span class=w> </span><span class=c1>// always creates [obj]</span>
</code></pre></div> </div> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example: default behavior (macro not defined)</summary> <p>Without the macro, single-element brace initialization wraps the value in an array:</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span>
<span class=p>{</span>
@@ -20,7 +20,7 @@
</code></pre></div> </details> <details class=example> <summary>Example: opt-in copy semantics (macro defined to 1)</summary> <p>With the macro, single-element brace initialization copies/moves the value:</p> <div class=highlight><pre><span></span><code><span class=cp>#define JSON_BRACE_INIT_COPY_SEMANTICS 1</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span>
<span class=p>{</span>
@@ -29,4 +29,4 @@
<span class=w> </span><span class=n>json</span><span class=w> </span><span class=n>j</span><span class=p>{</span><span class=n>obj</span><span class=p>};</span>
<span class=w> </span><span class=c1>// j is {"key":"value"} -- copy of obj</span>
<span class=p>}</span>
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../../../home/faq/#brace-initialization-yields-arrays><abbr title="Frequently Asked Questions">FAQ</abbr>: Brace initialization yields arrays</a></li> <li><a href=../../basic_json/basic_json/ ><strong>basic_json(initializer_list_t)</strong></a> - the affected constructor</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ul> <li>Added in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</li> <li>Planned to become the default (with the macro removed) in version 4.0.0.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 7, 2026 05:39:05 UTC">October 7, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 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</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../../../home/faq/#brace-initialization-yields-arrays><abbr title="Frequently Asked Questions">FAQ</abbr>: Brace initialization yields arrays</a></li> <li><a href=../../basic_json/basic_json/ ><strong>basic_json(initializer_list_t)</strong></a> - the affected constructor</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ul> <li>Added in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</li> <li>Planned to become the default (with the macro removed) in version 4.0.0.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 25, 2026 11:07:51 UTC">October 25, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 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@@ -66,7 +66,7 @@ Without the macro, single-element brace initialization wraps the value in an arr
```
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using nlohmann::json;
int main()
{
@@ -85,7 +85,7 @@ With the macro, single-element brace initialization copies/moves the value:
#define JSON_BRACE_INIT_COPY_SEMANTICS 1
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using nlohmann::json;
int main()
{
@@ -54,7 +54,7 @@ The default value is `0` (disabled, the deprecated functions can still be called
```cpp
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using nlohmann::json;
int main()
{
@@ -72,7 +72,7 @@ The default value is `0` (disabled, the deprecated functions can still be called
#define JSON_DELETE_DEPRECATED_FUNCTIONS 1
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using nlohmann::json;
int main()
{
@@ -1,8 +1,8 @@
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4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.52 6.52 0 0 1 9.5 16 6.Line truncated
</code></pre></div> <p>When defined to <code>1</code>, all <a href=../../../community/roadmap/#removal-of-deprecated-functions>deprecated functions</a> of the library are declared as deleted (<code>= delete</code>) instead of only being marked as deprecated. Code that still calls one of them no longer compiles. This way, you can find all calls that need to be replaced before version 4.0.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span> removes these functions; the <a href=../../../integration/migration_guide/#replace-deprecated-functions>migration guide</a> describes how.</p> <p>A deleted function, unlike a removed one, still takes part in overload resolution. A call that would select it therefore fails to compile instead of silently selecting another overload. This matters for the deprecated <code>from_*(ptr, len)</code> overloads of <a href=../../basic_json/from_cbor/ ><code>from_cbor</code></a>, <a href=../../basic_json/from_msgpack/ ><code>from_msgpack</code></a>, <a href=../../basic_json/from_ubjson/ ><code>from_ubjson</code></a>, <a href=../../basic_json/from_bjdata/ ><code>from_bjdata</code></a>, <a href=../../basic_json/from_bon8/ ><code>from_bon8</code></a>, and <a href=../../basic_json/from_bson/ ><code>from_bson</code></a>: without them, a call like <code>from_cbor(ptr, len)</code> would compile, read <code>ptr</code> as a NUL-terminated string, and convert <code>len</code> to the <code>strict</code> parameter.</p> <p>The macro does not affect the deprecated legacy comparison of discarded values, which is controlled by <a href=../json_use_legacy_discarded_value_comparison/ ><code>JSON_USE_LEGACY_DISCARDED_VALUE_COMPARISON</code></a>.</p> <h2 id=default-definition>Default definition<a class=headerlink href=#default-definition title="Permanent link">&para;</a></h2> <p>The default value is <code>0</code> (disabled, the deprecated functions can still be called, and the compiler warns about it).</p> <div class=highlight><pre><span></span><code><span class=cp>#define JSON_DELETE_DEPRECATED_FUNCTIONS 0</span>
</code></pre></div> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <div class="admonition info"> <p class=admonition-title>CMake option</p> <p>The macro can also be set with the CMake option <a href=../../../integration/cmake/#json_deletedeprecatedfunctions><code>JSON_DeleteDeprecatedFunctions</code></a> (<code>OFF</code> by default).</p> </div> <div class="admonition warning"> <p class=admonition-title>Opt-in only</p> <p>This macro must be defined <strong>before</strong> including <code>&lt;nlohmann/json.hpp&gt;</code>. Defining it after the include has no effect. Define it for the whole project to avoid different declarations of the same class in different translation units.</p> </div> <div class="admonition note"> <p class=admonition-title>ABI compatibility</p> <p>The macro only turns calls that compile into calls that do not; it does not change the layout or the behavior of any type. Its value is therefore not encoded in the <a href=../../../features/namespace/ >namespace</a>.</p> </div> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example: default behavior (macro not defined)</summary> <p>Without the macro, the deprecated overload is called, and the compiler warns about it:</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
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</code></pre></div> <p>When defined to <code>1</code>, all <a href=../../../community/roadmap/#removal-of-deprecated-functions>deprecated functions</a> of the library are declared as deleted (<code>= delete</code>) instead of only being marked as deprecated. Code that still calls one of them no longer compiles. This way, you can find all calls that need to be replaced before version 4.0.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span> removes these functions; the <a href=../../../integration/migration_guide/#replace-deprecated-functions>migration guide</a> describes how.</p> <p>A deleted function, unlike a removed one, still takes part in overload resolution. A call that would select it therefore fails to compile instead of silently selecting another overload. This matters for the deprecated <code>from_*(ptr, len)</code> overloads of <a href=../../basic_json/from_cbor/ ><code>from_cbor</code></a>, <a href=../../basic_json/from_msgpack/ ><code>from_msgpack</code></a>, <a href=../../basic_json/from_ubjson/ ><code>from_ubjson</code></a>, <a href=../../basic_json/from_bjdata/ ><code>from_bjdata</code></a>, <a href=../../basic_json/from_bon8/ ><code>from_bon8</code></a>, and <a href=../../basic_json/from_bson/ ><code>from_bson</code></a>: without them, a call like <code>from_cbor(ptr, len)</code> would compile, read <code>ptr</code> as a <abbr title="Null character (U+0000, byte value 0)">NUL</abbr>-terminated string, and convert <code>len</code> to the <code>strict</code> parameter.</p> <p>The macro does not affect the deprecated legacy comparison of discarded values, which is controlled by <a href=../json_use_legacy_discarded_value_comparison/ ><code>JSON_USE_LEGACY_DISCARDED_VALUE_COMPARISON</code></a>.</p> <h2 id=default-definition>Default definition<a class=headerlink href=#default-definition title="Permanent link">&para;</a></h2> <p>The default value is <code>0</code> (disabled, the deprecated functions can still be called, and the compiler warns about it).</p> <div class=highlight><pre><span></span><code><span class=cp>#define JSON_DELETE_DEPRECATED_FUNCTIONS 0</span>
</code></pre></div> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <div class="admonition info"> <p class=admonition-title>CMake option</p> <p>The macro can also be set with the CMake option <a href=../../../integration/cmake/#json_deletedeprecatedfunctions><code>JSON_DeleteDeprecatedFunctions</code></a> (<code>OFF</code> by default).</p> </div> <div class="admonition warning"> <p class=admonition-title>Opt-in only</p> <p>This macro must be defined <strong>before</strong> including <code>&lt;nlohmann/json.hpp&gt;</code>. Defining it after the include has no effect. Define it for the whole project to avoid different declarations of the same class in different translation units.</p> </div> <div class="admonition note"> <p class=admonition-title><abbr title="Application Binary Interface">ABI</abbr> compatibility</p> <p>The macro only turns calls that compile into calls that do not; it does not change the layout or the behavior of any type. Its value is therefore not encoded in the <a href=../../../features/namespace/ >namespace</a>.</p> </div> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example: default behavior (macro not defined)</summary> <p>Without the macro, the deprecated overload is called, and the compiler warns about it:</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span>
<span class=p>{</span>
@@ -13,7 +13,7 @@
</code></pre></div> </details> <details class=example> <summary>Example: deleted deprecated functions (macro defined to 1)</summary> <p>With the macro, the call does not compile:</p> <div class=highlight><pre><span></span><code><span class=cp>#define JSON_DELETE_DEPRECATED_FUNCTIONS 1</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span>
<span class=p>{</span>
@@ -21,4 +21,4 @@
<span class=w> </span><span class=k>auto</span><span class=w> </span><span class=n>j</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>json</span><span class=o>::</span><span class=n>from_cbor</span><span class=p>(</span><span class=n>v</span><span class=p>.</span><span class=n>data</span><span class=p>(),</span><span class=w> </span><span class=n>v</span><span class=p>.</span><span class=n>size</span><span class=p>());</span>
<span class=w> </span><span class=c1>// error: call to deleted function 'from_cbor'</span>
<span class=p>}</span>
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../../../community/roadmap/#removal-of-deprecated-functions>Roadmap: removal of deprecated functions</a> - the deprecated functions and the version they were deprecated in</li> <li><a href=../../../integration/migration_guide/#replace-deprecated-functions>Migration guide: replace deprecated functions</a> - how to replace each deprecated function</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ul> <li>Added in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</li> <li>Planned to be removed in version 4.0.0, which removes the deprecated functions. The deprecated <code>from_*(ptr, len)</code> overloads stay deleted in version 4.0.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 4, 2026 20:11:34 UTC">October 4, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 2013-2026 Niels Lohmann </div> </div> <div class=md-social> <a href="https://github.com/nlohmann" target="_blank" rel="noopener" title="github.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 512 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M173.9 397.4c0 2-2.3 3.6-5.2 3.6-3.3.3-5.6-1.3-5.6-3.6 0-2 2.3-3.6 5.2-3.6 3-.3 5.6 1.3 5.6 3.6m-31.1-4.5c-.7 2 1.3 4.3 4.3 4.9 2.6 1 5.6 0 6.2-2s-1.3-4.3-4.3-5.2c-2.6-.7-5.5.3-6.2 2.3m44.2-1.7c-2.9.7-4.9 2.6-4.6 4.9.3 2 2.9 3.3 5.9 2.6 2.9-.7 4.9-2.6 4.6-4.6-.3-1.9-3-3.2-5.9-2.9M252.8 8C114.1 8 8 113.3 8 252c0 110.9 69.8 205.8 169.5 239.2 12.8 2.3 17.3-5.6 17.3-12.1 0-6.2-.3-40.4-.3-61.4 0 0-70 15-84.7-29.8 0 0-11.4-29.1-27.8-36.6 0 0-22.9-15.7 1.6-15.4 0 0 24.9 2 38.6 25.8 21.9 38.6 58.6 27.5 72.9 20.9 2.3-16 8.8-27.1 16-33.7-55.9-6.2-112.3-14.3-112.3-110.5 0-27.5 7.6-41.3 23.6-58.9-2.6-6.5-11.1-33.3 2.6-67.9 20.9-6.5 69 27 69 27 20-5.6 41.5-8.5 62.8-8.5s42.8 2.9 62.8 8.5c0 0 48.1-33.6 69-27 13.7 34.7 5.2 61.4 2.6 67.9 16 17.7 25.8 31.5 25.8 58.9 0 96.5-58.9 104.2-114.8 110.5 9.2 7.9 17 22.9 17 46.4 0 33.7-.3 75.4-.3 83.6 0 6.5 4.6 14.4 17.3 12.1C436.2 457.8 504 362.9 504 252 504 113.3 391.5 8 252.8 8M105.2 352.9c-1.3 1-1 3.3.7 5.2 1.6 1.6 3.9 2.3 5.2 1 1.3-1 1-3.3-.7-5.2-1.6-1.6-3.9-2.3-5.2-1m-10.8-8.1c-.7 1.3.3 2.9 2.3 3.9 1.6 1 3.6.7 4.3-.7.7-1.3-.3-2.9-2.3-3.9-2-.6-3.6-.3-4.3.7m32.4 35.6c-1.6 1.3-1 4.3 1.3 6.2 2.3 2.3 5.2 2.6 6.5 1 1.3-1.3.7-4.3-1.3-6.2-2.2-2.3-5.2-2.6-6.5-1m-11.4-14.7c-1.6 1-1.6 3.6 0 5.9s4.3 3.3 5.6 2.3c1.6-1.3 1.6-3.9 0-6.2-1.4-2.3-4-3.3-5.6-2"/></svg> </a> <a href="https://www.linkedin.com/in/nielslohmann/" target="_blank" rel="noopener" title="www.linkedin.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 448 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M416 32H31.9C14.3 32 0 46.5 0 64.3v383.4C0Line truncated
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../../../community/roadmap/#removal-of-deprecated-functions>Roadmap: removal of deprecated functions</a> - the deprecated functions and the version they were deprecated in</li> <li><a href=../../../integration/migration_guide/#replace-deprecated-functions>Migration guide: replace deprecated functions</a> - how to replace each deprecated function</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ul> <li>Added in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</li> <li>Planned to be removed in version 4.0.0, which removes the deprecated functions. The deprecated <code>from_*(ptr, len)</code> overloads stay deleted in version 4.0.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 25, 2026 11:07:51 UTC">October 25, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 2013-2026 Niels Lohmann </div> </div> <div class=md-social> <a href="https://github.com/nlohmann" target="_blank" rel="noopener" title="github.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 512 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M173.9 397.4c0 2-2.3 3.6-5.2 3.6-3.3.3-5.6-1.3-5.6-3.6 0-2 2.3-3.6 5.2-3.6 3-.3 5.6 1.3 5.6 3.6m-31.1-4.5c-.7 2 1.3 4.3 4.3 4.9 2.6 1 5.6 0 6.2-2s-1.3-4.3-4.3-5.2c-2.6-.7-5.5.3-6.2 2.3m44.2-1.7c-2.9.7-4.9 2.6-4.6 4.9.3 2 2.9 3.3 5.9 2.6 2.9-.7 4.9-2.6 4.6-4.6-.3-1.9-3-3.2-5.9-2.9M252.8 8C114.1 8 8 113.3 8 252c0 110.9 69.8 205.8 169.5 239.2 12.8 2.3 17.3-5.6 17.3-12.1 0-6.2-.3-40.4-.3-61.4 0 0-70 15-84.7-29.8 0 0-11.4-29.1-27.8-36.6 0 0-22.9-15.7 1.6-15.4 0 0 24.9 2 38.6 25.8 21.9 38.6 58.6 27.5 72.9 20.9 2.3-16 8.8-27.1 16-33.7-55.9-6.2-112.3-14.3-112.3-110.5 0-27.5 7.6-41.3 23.6-58.9-2.6-6.5-11.1-33.3 2.6-67.9 20.9-6.5 69 27 69 27 20-5.6 41.5-8.5 62.8-8.5s42.8 2.9 62.8 8.5c0 0 48.1-33.6 69-27 13.7 34.7 5.2 61.4 2.6 67.9 16 17.7 25.8 31.5 25.8 58.9 0 96.5-58.9 104.2-114.8 110.5 9.2 7.9 17 22.9 17 46.4 0 33.7-.3 75.4-.3 83.6 0 6.5 4.6 14.4 17.3 12.1C436.2 457.8 504 362.9 504 252 504 113.3 391.5 8 252.8 8M105.2 352.9c-1.3 1-1 3.3.7 5.2 1.6 1.6 3.9 2.3 5.2 1 1.3-1 1-3.3-.7-5.2-1.6-1.6-3.9-2.3-5.2-1m-10.8-8.1c-.7 1.3.3 2.9 2.3 3.9 1.6 1 3.6.7 4.3-.7.7-1.3-.3-2.9-2.3-3.9-2-.6-3.6-.3-4.3.7m32.4 35.6c-1.6 1.3-1 4.3 1.3 6.2 2.3 2.3 5.2 2.6 6.5 1 1.3-1.3.7-4.3-1.3-6.2-2.2-2.3-5.2-2.6-6.5-1m-11.4-14.7c-1.6 1-1.6 3.6 0 5.9s4.3 3.3 5.6 2.3c1.6-1.3 1.6-3.9 0-6.2-1.4-2.3-4-3.3-5.6-2"/></svg> </a> <a href="https://www.linkedin.com/in/nielslohmann/" target="_blank" rel="noopener" title="www.linkedin.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 448 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M416 32H31.9C14.3 32 0 46.5 0 64.3v383.4Line truncated
@@ -41,7 +41,7 @@ Without the macro, the deprecated overload is called, and the compiler warns abo
```
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using nlohmann::json;
int main()
{
@@ -59,7 +59,7 @@ With the macro, the call does not compile:
#define JSON_DELETE_DEPRECATED_FUNCTIONS 1
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using nlohmann::json;
int main()
{
+3 -3
View File
@@ -75,7 +75,7 @@ When the macro is not defined, the library will define it to its default value.
#define JSON_DIAGNOSTIC_POSITIONS 1
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using nlohmann::json;
int main()
{
@@ -190,7 +190,7 @@ When the macro is not defined, the library will define it to its default value.
#define JSON_DIAGNOSTIC_POSITIONS 1
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using nlohmann::json;
/* Demonstration of type error exception with diagnostic positions support enabled */
int main()
@@ -236,7 +236,7 @@ When the macro is not defined, the library will define it to its default value.
#define JSON_DIAGNOSTIC_POSITIONS 1
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using nlohmann::json;
/* Demonstration of type error exception with diagnostic positions support enabled */
int main()
@@ -1,11 +1,11 @@
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</code></pre></div> <p>This macro enables position diagnostics for generated <abbr title="JavaScript Object Notation">JSON</abbr> objects.</p> <p>When enabled, two new member functions <a href=../../basic_json/start_pos/ ><code>start_pos()</code></a> and <a href=../../basic_json/end_pos/ ><code>end_pos()</code></a> are added to <a href=../../basic_json/ ><code>basic_json</code></a> values. If the value was created by calling the<a href=../../basic_json/parse/ ><code>parse</code></a> function, then these functions allow querying the byte positions of the value in the input it was parsed from. In case the value was constructed by other means, <code>std::string::npos</code> is returned.</p> <p><a href=../../basic_json/start_pos/ ><code>start_pos()</code></a> returns the position of the first character of a given value in the original <abbr title="JavaScript Object Notation">JSON</abbr> string, while <a href=../../basic_json/end_pos/ ><code>end_pos()</code></a> returns the position of the character <em>following</em> the last character. For objects and arrays, the first and last characters correspond to the opening or closing braces/brackets, respectively. For primitive values, the first and last character represents the opening and closing quotes (strings) or the first and last character of the field's numerical or predefined value (<code>true</code>, <code>false</code>, <code>null</code>), respectively.</p> <table> <thead> <tr> <th><abbr title="JavaScript Object Notation">JSON</abbr> type</th> <th>return value <a href=../../basic_json/start_pos/ ><code>start_pos()</code></a></th> <th>return value <a href=../../basic_json/end_pos/ ><code>end_pos()</code></a></th> </tr> </thead> <tbody> <tr> <td>object</td> <td>position of the opening <code>{</code></td> <td>position after the closing <code>}</code></td> </tr> <tr> <td>array</td> <td>position of the opening <code>[</code></td> <td>position after the closing <code>]</code></td> </tr> <tr> <td>string</td> <td>position of the opening <code>"</code></td> <td>position after the closing <code>"</code></td> </tr> <tr> <td>number</td> <td>position of the first character</td> <td>position after the last character</td> </tr> <tr> <td>boolean</td> <td>position of <code>t</code> for <code>true</code> and <code>f</code> for <code>false</code></td> <td>position after <code>e</code></td> </tr> <tr> <td>null</td> <td>position of <code>n</code></td> <td>position after <code>l</code></td> </tr> </tbody> </table> <p>Given the above, <a href=../../basic_json/end_pos/ ><code>end_pos()</code></a><code>-</code><a href=../../basic_json/start_pos/ ><code>start_pos()</code></a> for a <abbr title="JavaScript Object Notation">JSON</abbr> value provides the length of the parsed <abbr title="JavaScript Object Notation">JSON</abbr> string for that value, including the opening or closing braces, brackets, or quotes.</p> <p>Note that enabling this macro increases the size of every <abbr title="JavaScript Object Notation">JSON</abbr> value by two <code>std::size_t</code> fields and adds slight runtime overhead to parsing, copying <abbr title="JavaScript Object Notation">JSON</abbr> value objects, and the generation of error messages for exceptions. It also causes these values to be reported in those error messages.</p> <h2 id=default-definition>Default definition<a class=headerlink href=#default-definition title="Permanent link">&para;</a></h2> <p>The default value is <code>0</code> (position diagnostics are switched off).</p> <div class=highlight><pre><span></span><code><span class=cp>#define JSON_DIAGNOSTIC_POSITIONS 0</span>
</code></pre></div> <p>When the macro is not defined, the library will define it to its default value.</p> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <div class="admonition note"> <p class=admonition-title>CMake option</p> <p>Diagnostic positions can also be controlled with the CMake option <a href=../../../integration/cmake/#json_diagnostic_positions><code>JSON_Diagnostic_Positions</code></a> (<code>OFF</code> by default) which defines <code>JSON_DIAGNOSTIC_POSITIONS</code> accordingly.</p> </div> <div class="admonition note"> <p class=admonition-title>Availability</p> <p>Diagnostic positions are only available if the value was created by the <a href=../../basic_json/parse/ ><code>parse</code></a> function. The <a href=../../basic_json/sax_parse/ ><code>sax_parse</code></a> function or all other means to create a <abbr title="JavaScript Object Notation">JSON</abbr> value <strong>do not</strong> set the diagnostic positions and <a href=../../basic_json/start_pos/ ><code>start_pos()</code></a> and <a href=../../basic_json/end_pos/ ><code>end_pos()</code></a> will only return <code>std::string::npos</code> for these values.</p> </div> <div class="admonition warning"> <p class=admonition-title>Invalidation</p> <p>The returned positions are only valid as long as the <abbr title="JavaScript Object Notation">JSON</abbr> value is not changed. The positions are <em>not</em> updated when the <abbr title="JavaScript Object Notation">JSON</abbr> value is changed.</p> </div> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example: retrieving positions</summary> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<span class=cp>#define JSON_DIAGNOSTIC_POSITIONS 1</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span>
<span class=p>{</span>
@@ -105,7 +105,7 @@ Parsed string:
<span class=cp>#define JSON_DIAGNOSTIC_POSITIONS 1</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=cm>/* Demonstration of type error exception with diagnostic positions support enabled */</span>
<span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span>
@@ -138,7 +138,7 @@ Parsed string:
<span class=cp>#define JSON_DIAGNOSTIC_POSITIONS 1</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=cm>/* Demonstration of type error exception with diagnostic positions support enabled */</span>
<span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span>
@@ -57,7 +57,7 @@ Example: retrieving positions
#define JSON_DIAGNOSTIC_POSITIONS 1
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using nlohmann::json;
int main()
{
@@ -169,7 +169,7 @@ Example: using only diagnostic positions in exceptions
#define JSON_DIAGNOSTIC_POSITIONS 1
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using nlohmann::json;
/* Demonstration of type error exception with diagnostic positions support enabled */
int main()
@@ -215,7 +215,7 @@ Example: using extended diagnostics with positions enabled in exceptions
#define JSON_DIAGNOSTIC_POSITIONS 1
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using nlohmann::json;
/* Demonstration of type error exception with diagnostic positions support enabled */
int main()
+3 -3
View File
@@ -49,7 +49,7 @@ When the macro is not defined, the library will define it to its default value.
#include <iostream>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using nlohmann::json;
int main()
{
@@ -86,7 +86,7 @@ When the macro is not defined, the library will define it to its default value.
# define JSON_DIAGNOSTICS 1
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using nlohmann::json;
int main()
{
@@ -123,7 +123,7 @@ When the macro is not defined, the library will define it to its default value.
#define JSON_DIAGNOSTIC_POSITIONS 1
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using nlohmann::json;
/* Demonstration of type error exception with diagnostic positions support enabled */
int main()
+5 -5
View File
@@ -1,9 +1,9 @@
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<svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> JSON_DIAGNOSTICS </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark mode" type=radio 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15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.52 6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 Line truncated
</code></pre></div> <p>This macro enables <a href=../../../home/exceptions/#extended-diagnostic-messages>extended diagnostics for exception messages</a>. Possible values are <code>1</code> to enable or <code>0</code> to disable (default).</p> <p>When enabled, exception messages contain a <a href=../../json_pointer/json_pointer/ ><abbr title="JavaScript Object Notation">JSON</abbr> Pointer</a> to the <abbr title="JavaScript Object Notation">JSON</abbr> value that triggered the exception. Note that enabling this macro increases the size of every <abbr title="JavaScript Object Notation">JSON</abbr> value by one pointer and adds some runtime overhead.</p> <h2 id=default-definition>Default definition<a class=headerlink href=#default-definition title="Permanent link">&para;</a></h2> <p>The default value is <code>0</code> (extended diagnostics are switched off).</p> <div class=highlight><pre><span></span><code><span class=cp>#define JSON_DIAGNOSTICS 0</span>
</code></pre></div> <p>When the macro is not defined, the library will define it to its default value.</p> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <div class="admonition note"> <p class=admonition-title>ABI compatibility</p> <p>As of version 3.11.0, this macro is no longer required to be defined consistently throughout a codebase to avoid One Definition Rule (ODR) violations, as the value of this macro is encoded in the namespace, resulting in distinct symbol names. </p> <p>This allows different parts of a codebase to use different versions or configurations of this library without causing improper behavior.</p> <p>Where possible, it is still recommended that all code define this the same way for maximum interoperability.</p> </div> <div class="admonition hint"> <p class=admonition-title>CMake option</p> <p>Diagnostic messages can also be controlled with the CMake option <a href=../../../integration/cmake/#json_diagnostics><code>JSON_Diagnostics</code></a> (<code>OFF</code> by default) which defines <code>JSON_DIAGNOSTICS</code> accordingly. Note this only applies when building the library from source — see the pre-installed-package caveat on that page.</p> </div> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example: default behavior</summary> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
</code></pre></div> <p>When the macro is not defined, the library will define it to its default value.</p> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <div class="admonition note"> <p class=admonition-title><abbr title="Application Binary Interface">ABI</abbr> compatibility</p> <p>As of version 3.11.0, this macro is no longer required to be defined consistently throughout a codebase to avoid One Definition Rule (<abbr title="One Definition Rule">ODR</abbr>) violations, as the value of this macro is encoded in the namespace, resulting in distinct symbol names. </p> <p>This allows different parts of a codebase to use different versions or configurations of this library without causing improper behavior.</p> <p>Where possible, it is still recommended that all code define this the same way for maximum interoperability.</p> </div> <div class="admonition hint"> <p class=admonition-title>CMake option</p> <p>Diagnostic messages can also be controlled with the CMake option <a href=../../../integration/cmake/#json_diagnostics><code>JSON_Diagnostics</code></a> (<code>OFF</code> by default) which defines <code>JSON_DIAGNOSTICS</code> accordingly. Note this only applies when building the library from source — see the pre-installed-package caveat on that page.</p> </div> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example: default behavior</summary> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span>
<span class=p>{</span>
@@ -26,7 +26,7 @@
<span class=cp># define JSON_DIAGNOSTICS 1</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span>
<span class=p>{</span>
@@ -49,7 +49,7 @@
<span class=cp>#define JSON_DIAGNOSTIC_POSITIONS 1</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=cm>/* Demonstration of type error exception with diagnostic positions support enabled */</span>
<span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span>
+3 -3
View File
@@ -40,7 +40,7 @@ Example: default behavior
#include <iostream>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using nlohmann::json;
int main()
{
@@ -75,7 +75,7 @@ Example: extended diagnostic messages
# define JSON_DIAGNOSTICS 1
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using nlohmann::json;
int main()
{
@@ -110,7 +110,7 @@ Example: using only diagnostic positions in exceptions
#define JSON_DIAGNOSTIC_POSITIONS 1
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using nlohmann::json;
/* Demonstration of type error exception with diagnostic positions support enabled */
int main()
@@ -39,7 +39,7 @@ The default value is `0`.
#define JSON_DISABLE_ENUM_SERIALIZATION 1
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using nlohmann::json;
enum class Choice
{
@@ -66,7 +66,7 @@ The default value is `0`.
#define JSON_DISABLE_ENUM_SERIALIZATION 1
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using nlohmann::json;
enum class Choice
{
@@ -99,7 +99,7 @@ The default value is `0`.
#define JSON_DISABLE_ENUM_SERIALIZATION 1
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using nlohmann::json;
enum class Choice
{
@@ -1,9 +1,9 @@
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6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 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</code></pre></div> <p>When defined to <code>1</code>, default serialization and deserialization functions for enums are excluded and have to be provided by the user, for example, using <a href=../nlohmann_json_serialize_enum/ ><code>NLOHMANN_JSON_SERIALIZE_ENUM</code></a> (see <a href=../../../features/arbitrary_types/ >arbitrary type conversions</a> for more details).</p> <p>Parsing or serializing an enum will result in a compiler error.</p> <p>This works for both unscoped and scoped enums.</p> <h2 id=default-definition>Default definition<a class=headerlink href=#default-definition title="Permanent link">&para;</a></h2> <p>The default value is <code>0</code>.</p> <div class=highlight><pre><span></span><code><span class=cp>#define JSON_DISABLE_ENUM_SERIALIZATION 0</span>
</code></pre></div> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <div class="admonition hint"> <p class=admonition-title>CMake option</p> <p>Enum serialization can also be controlled with the CMake option <a href=../../../integration/cmake/#json_disableenumserialization><code>JSON_DisableEnumSerialization</code></a> (<code>OFF</code> by default) which defines <code>JSON_DISABLE_ENUM_SERIALIZATION</code> accordingly.</p> </div> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example: Disabled behavior</summary> <p>The code below forces the library <strong>not</strong> to create default serialization/deserialization functions <code>from_json</code> and <code>to_json</code>, meaning the code below <strong>does not</strong> compile.</p> <div class=highlight><pre><span></span><code><span class=cp>#define JSON_DISABLE_ENUM_SERIALIZATION 1</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=k>enum</span><span class=w> </span><span class=k>class</span><span class=w> </span><span class=nc>Choice</span>
<span class=p>{</span>
@@ -22,7 +22,7 @@
</code></pre></div> </details> <details class=example> <summary>Example: Serialize enum macro</summary> <p>The code below forces the library <strong>not</strong> to create default serialization/deserialization functions <code>from_json</code> and <code>to_json</code>, but uses <a href=../nlohmann_json_serialize_enum/ ><code>NLOHMANN_JSON_SERIALIZE_ENUM</code></a> to parse and serialize the enum.</p> <div class=highlight><pre><span></span><code><span class=cp>#define JSON_DISABLE_ENUM_SERIALIZATION 1</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=k>enum</span><span class=w> </span><span class=k>class</span><span class=w> </span><span class=nc>Choice</span>
<span class=p>{</span>
@@ -47,7 +47,7 @@
</code></pre></div> </details> <details class=example> <summary>Example: User-defined serialization/deserialization functions</summary> <p>The code below forces the library <strong>not</strong> to create default serialization/deserialization functions <code>from_json</code> and <code>to_json</code>, but uses user-defined functions to parse and serialize the enum.</p> <div class=highlight><pre><span></span><code><span class=cp>#define JSON_DISABLE_ENUM_SERIALIZATION 1</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=k>enum</span><span class=w> </span><span class=k>class</span><span class=w> </span><span class=nc>Choice</span>
<span class=p>{</span>
@@ -88,4 +88,4 @@
<span class=w> </span><span class=c1>// uses user-defined from_json function</span>
<span class=w> </span><span class=n>Choice</span><span class=w> </span><span class=n>ch</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>j</span><span class=p>.</span><span class=n>get</span><span class=o>&lt;</span><span class=n>Choice</span><span class=o>&gt;</span><span class=p>();</span>
<span class=p>}</span>
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../../../integration/cmake/#json_disableenumserialization><span class=twemoji><svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M11.769.066.067 23.206l12.76-10.843zm11.438 23.868L7.471 17.587 0 23.934zm.793-.198L12.298.463l1.719 19.24zM12.893 12.959l-5.025 4.298 5.62 2.248z"/></svg></span> JSON_DisableEnumSerialization</a> - CMake option to control the macro</li> <li><a href=../nlohmann_json_serialize_enum/ ><code>NLOHMANN_JSON_SERIALIZE_ENUM</code></a> - serialize/deserialize an enum</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ul> <li>Added in version 3.11.0.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 2, 2026 09:32:15 UTC">October 2, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 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</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../../../integration/cmake/#json_disableenumserialization><span class=twemoji><svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M11.769.066.067 23.206l12.76-10.843zm11.438 23.868L7.471 17.587 0 23.934zm.793-.198L12.298.463l1.719 19.24zM12.893 12.959l-5.025 4.298 5.62 2.248z"/></svg></span> JSON_DisableEnumSerialization</a> - CMake option to control the macro</li> <li><a href=../nlohmann_json_serialize_enum/ ><code>NLOHMANN_JSON_SERIALIZE_ENUM</code></a> - serialize/deserialize an enum</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ul> <li>Added in version 3.11.0.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 25, 2026 11:07:51 UTC">October 25, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 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@@ -34,7 +34,7 @@ The code below forces the library **not** to create default serialization/deseri
#define JSON_DISABLE_ENUM_SERIALIZATION 1
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using nlohmann::json;
enum class Choice
{
@@ -60,7 +60,7 @@ The code below forces the library **not** to create default serialization/deseri
#define JSON_DISABLE_ENUM_SERIALIZATION 1
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using nlohmann::json;
enum class Choice
{
@@ -92,7 +92,7 @@ The code below forces the library **not** to create default serialization/deseri
#define JSON_DISABLE_ENUM_SERIALIZATION 1
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using nlohmann::json;
enum class Choice
{
+2 -2
View File
@@ -92,7 +92,7 @@ The default value is `0`: streams are scanned in bulk.
#include <sstream>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using nlohmann::json;
int main()
{
@@ -115,7 +115,7 @@ The default value is `0`: streams are scanned in bulk.
#include <sstream>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using nlohmann::json;
int main()
{
@@ -1,10 +1,10 @@
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</code></pre></div> <p>When defined to <code>1</code>, parsing from a <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>istream</span></code> reads the input one character at a time through the stream buffer, as in version 3.12.0 and earlier, instead of scanning the characters that the stream buffer already holds in bulk.</p> <p>The macro is an escape hatch for stream buffers that do not follow the usual contract of <code>std::basic_streambuf</code> (see the requirements on the stream buffer in the notes below). It does not change any result: values, exceptions, and the position of the stream after parsing are the same either way. Only the speed differs.</p> <h2 id=default-definition>Default definition<a class=headerlink href=#default-definition title="Permanent link">&para;</a></h2> <p>The default value is <code>0</code>: streams are scanned in bulk.</p> <div class=highlight><pre><span></span><code><span class=cp>#define JSON_DISABLE_STREAM_BULK_SCAN 0</span>
</code></pre></div> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <div class="admonition note"> <p class=admonition-title>How streams are scanned</p> <p>A <code>std::streambuf</code> keeps the part of the input it has read but not yet handed out in its <em>get area</em>, the range from <code>gptr()</code> to <code>egptr()</code>. A <code>std::filebuf</code>, for instance, reads the file in blocks of a few kilobytes into its get area, and a <code>std::stringbuf</code> exposes its whole string as one get area.</p> <p>When parsing from a <code>std::istream</code>, the parser scans this get area directly, with the same fast paths that it uses for a <code>std::string</code>: runs of ordinary string characters, numbers, and indentation are recognized several bytes at a time instead of being requested from the stream buffer one character at a time. When the parser reaches the end of the get area, it asks the stream buffer for the next character as before, which makes the stream buffer refill its get area.</p> <p>The parser only reads characters that it would also have read one at a time, and it advances the stream buffer exactly over the characters it consumes. Nothing is read ahead, buffered elsewhere, or put back. Therefore, the stream is left exactly where it was left before:</p> <ul> <li><a href=../../operator_gtgt/ ><code>operator&gt;&gt;</code></a> and <a href=../../basic_json/sax_parse/ ><code>sax_parse</code></a> with <code>strict = false</code> can still read several values from one stream, and the stream can still be used with other <code>std::istream</code> functions after a value has been read.</li> <li>With <a href=../json_precise_stream_position/ ><code>JSON_PRECISE_STREAM_POSITION</code></a>, the stream is still positioned right after a parsed number.</li> <li>Exception messages, including the line, the column, and the last read token, are unchanged.</li> </ul> </div> <div class="admonition note"> <p class=admonition-title>Performance</p> <p>Parsing from a <code>std::ifstream</code> or <code>std::istringstream</code> is typically 1.5 to 2 times as fast as before, and reading many small values from one stream with <code>operator&gt;&gt;</code> 1.4 to 4 times as fast. Parsing from a stream is then within about 10 to 20 % of first reading the whole file into a <code>std::string</code> and parsing that.</p> <p>A stream buffer without a get area (one that only overrides <code>underflow()</code> and <code>uflow()</code> and hands out every character from there) offers nothing to scan in bulk, so it is read one character at a time as before.</p> </div> <div class="admonition note"> <p class=admonition-title>Requirements on the stream buffer</p> <p>The bulk scan relies on the following behavior, which every stream buffer of the standard library and every stream buffer that keeps its input in its get area has:</p> <ul> <li>When <code>sgetc()</code> returns a character while <code>gptr() &lt; egptr()</code>, that character is <code>*gptr()</code>; when <code>sbumpc()</code> returns one, it was at <code>gptr()</code> before the call.</li> <li>Characters in the get area are not changed while they are in the get area.</li> <li><code>underflow()</code> or <code>uflow()</code> either sets up a get area that holds the returned character at <code>gptr()</code> (or at <code>gptr() - 1</code> after <code>uflow()</code>), or leaves the get area empty.</li> </ul> <p>A stream buffer that returns characters from <code>uflow()</code> while leaving unrelated characters in its get area, or that changes the characters in its get area in place, does not meet these requirements. Define the macro to <code>1</code> for such stream buffers.</p> </div> <div class="admonition note"> <p class=admonition-title>ABI compatibility</p> <p>The value of this macro is encoded in the <a href=../../../features/namespace/ >namespace</a> (tag <code>_dsbs</code>), resulting in distinct symbol names. Translation units compiled with and without it can therefore be linked into the same program without One Definition Rule (ODR) violations, but they cannot exchange instances of library types.</p> </div> <div class="admonition note"> <p class=admonition-title>Other inputs</p> <p>Strings, string views, vectors, arrays, and pointer or iterator ranges over contiguous memory are scanned in bulk anyway. Reading from a <code class=highlight><span class=kt>FILE</span><span class=o>*</span></code> is not affected by this macro; see <a href=../json_disable_unlocked_file_io/ ><code>JSON_DISABLE_UNLOCKED_FILE_IO</code></a> for that input.</p> </div> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example: reading values from a stream (default)</summary> <p>The stream is scanned in bulk, and the values are read one after the other:</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span clLine truncated
</code></pre></div> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <div class="admonition note"> <p class=admonition-title>How streams are scanned</p> <p>A <code>std::streambuf</code> keeps the part of the input it has read but not yet handed out in its <em>get area</em>, the range from <code>gptr()</code> to <code>egptr()</code>. A <code>std::filebuf</code>, for instance, reads the file in blocks of a few kilobytes into its get area, and a <code>std::stringbuf</code> exposes its whole string as one get area.</p> <p>When parsing from a <code>std::istream</code>, the parser scans this get area directly, with the same fast paths that it uses for a <code>std::string</code>: runs of ordinary string characters, numbers, and indentation are recognized several bytes at a time instead of being requested from the stream buffer one character at a time. When the parser reaches the end of the get area, it asks the stream buffer for the next character as before, which makes the stream buffer refill its get area.</p> <p>The parser only reads characters that it would also have read one at a time, and it advances the stream buffer exactly over the characters it consumes. Nothing is read ahead, buffered elsewhere, or put back. Therefore, the stream is left exactly where it was left before:</p> <ul> <li><a href=../../operator_gtgt/ ><code>operator&gt;&gt;</code></a> and <a href=../../basic_json/sax_parse/ ><code>sax_parse</code></a> with <code>strict = false</code> can still read several values from one stream, and the stream can still be used with other <code>std::istream</code> functions after a value has been read.</li> <li>With <a href=../json_precise_stream_position/ ><code>JSON_PRECISE_STREAM_POSITION</code></a>, the stream is still positioned right after a parsed number.</li> <li>Exception messages, including the line, the column, and the last read token, are unchanged.</li> </ul> </div> <div class="admonition note"> <p class=admonition-title>Performance</p> <p>Parsing from a <code>std::ifstream</code> or <code>std::istringstream</code> is typically 1.5 to 2 times as fast as before, and reading many small values from one stream with <code>operator&gt;&gt;</code> 1.4 to 4 times as fast. Parsing from a stream is then within about 10 to 20 % of first reading the whole file into a <code>std::string</code> and parsing that.</p> <p>A stream buffer without a get area (one that only overrides <code>underflow()</code> and <code>uflow()</code> and hands out every character from there) offers nothing to scan in bulk, so it is read one character at a time as before.</p> </div> <div class="admonition note"> <p class=admonition-title>Requirements on the stream buffer</p> <p>The bulk scan relies on the following behavior, which every stream buffer of the standard library and every stream buffer that keeps its input in its get area has:</p> <ul> <li>When <code>sgetc()</code> returns a character while <code>gptr() &lt; egptr()</code>, that character is <code>*gptr()</code>; when <code>sbumpc()</code> returns one, it was at <code>gptr()</code> before the call.</li> <li>Characters in the get area are not changed while they are in the get area.</li> <li><code>underflow()</code> or <code>uflow()</code> either sets up a get area that holds the returned character at <code>gptr()</code> (or at <code>gptr() - 1</code> after <code>uflow()</code>), or leaves the get area empty.</li> </ul> <p>A stream buffer that returns characters from <code>uflow()</code> while leaving unrelated characters in its get area, or that changes the characters in its get area in place, does not meet these requirements. Define the macro to <code>1</code> for such stream buffers.</p> </div> <div class="admonition note"> <p class=admonition-title><abbr title="Application Binary Interface">ABI</abbr> compatibility</p> <p>The value of this macro is encoded in the <a href=../../../features/namespace/ >namespace</a> (tag <code>_dsbs</code>), resulting in distinct symbol names. Translation units compiled with and without it can therefore be linked into the same program without One Definition Rule (<abbr title="One Definition Rule">ODR</abbr>) violations, but they cannot exchange instances of library types.</p> </div> <div class="admonition note"> <p class=admonition-title>Other inputs</p> <p>Strings, string views, vectors, arrays, and pointer or iterator ranges over contiguous memory are scanned in bulk anyway. Reading from a <code class=highlight><span class=kt>FILE</span><span class=o>*</span></code> is not affected by this macro; see <a href=../json_disable_unlocked_file_io/ ><code>JSON_DISABLE_UNLOCKED_FILE_IO</code></a> for that input.</p> </div> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example: reading values from a stream (default)</summary> <p>The stream is scanned in bulk, and the values are read one after the other:</p> <div class=higLine truncated
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;sstream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span>
<span class=p>{</span>
@@ -20,7 +20,7 @@
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;sstream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span>
<span class=p>{</span>
@@ -31,4 +31,4 @@
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>string</span><span class=w> </span><span class=n>word</span><span class=p>;</span>
<span class=w> </span><span class=n>input</span><span class=w> </span><span class=o>&gt;&gt;</span><span class=w> </span><span class=n>word</span><span class=p>;</span><span class=w> </span><span class=c1>// "rest"</span>
<span class=p>}</span>
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../../basic_json/parse/ ><strong>parse</strong></a> - deserialize from a compatible input</li> <li><a href=../../operator_gtgt/ ><strong>operator&gt;&gt;</strong></a> - deserialize from stream</li> <li><a href=../../basic_json/sax_parse/ ><strong>sax_parse</strong></a> - generate <abbr title="Simple API for XML">SAX</abbr> events</li> <li><a href=../json_precise_stream_position/ ><strong>JSON_PRECISE_STREAM_POSITION</strong></a> - leave an input stream positioned right after a parsed number</li> <li><a href=../json_disable_unlocked_file_io/ ><strong>JSON_DISABLE_UNLOCKED_FILE_IO</strong></a> - read a <code>FILE*</code> with the locking stdio functions</li> <li><a href=../../../features/parsing/#input-sources-and-performance>Parsing: input sources and performance</a></li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ul> <li>Added in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 19, 2026 20:00:58 UTC">October 19, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 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</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../../basic_json/parse/ ><strong>parse</strong></a> - deserialize from a compatible input</li> <li><a href=../../operator_gtgt/ ><strong>operator&gt;&gt;</strong></a> - deserialize from stream</li> <li><a href=../../basic_json/sax_parse/ ><strong>sax_parse</strong></a> - generate <abbr title="Simple API for XML">SAX</abbr> events</li> <li><a href=../json_precise_stream_position/ ><strong>JSON_PRECISE_STREAM_POSITION</strong></a> - leave an input stream positioned right after a parsed number</li> <li><a href=../json_disable_unlocked_file_io/ ><strong>JSON_DISABLE_UNLOCKED_FILE_IO</strong></a> - read a <code>FILE*</code> with the locking stdio functions</li> <li><a href=../../../features/parsing/#input-sources-and-performance>Parsing: input sources and performance</a></li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ul> <li>Added in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 25, 2026 11:07:51 UTC">October 25, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 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@@ -65,7 +65,7 @@ The stream is scanned in bulk, and the values are read one after the other:
#include <sstream>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using nlohmann::json;
int main()
{
@@ -88,7 +88,7 @@ With the macro, the same program reads the stream one character at a time, with
#include <sstream>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using nlohmann::json;
int main()
{
@@ -72,7 +72,7 @@ The default value is `0` (disabled — existing behavior is preserved).
```cpp
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using nlohmann::json;
int main()
{
@@ -89,7 +89,7 @@ The default value is `0` (disabled — existing behavior is preserved).
#define JSON_DISABLE_TUPLE_REFERENCE_CONVERSION 1
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using nlohmann::json;
int main()
{
@@ -1,4 +1,4 @@
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1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.Line truncated
</code></pre></div> <p>When defined to <code>1</code>, a <code>basic_json</code> value can no longer be constructed from a one-element <code>std::tuple</code> whose element is a reference to that <code>basic_json</code> type, such as <code>std::tuple&lt;json&amp;&gt;</code>, <code>std::tuple&lt;const json&amp;&gt;</code>, or <code>std::tuple&lt;json&amp;&amp;&gt;</code>. These are the tuples created by <code>std::forward_as_tuple(j)</code>.</p> <h2 id=default-definition>Default definition<a class=headerlink href=#default-definition title="Permanent link">&para;</a></h2> <p>The default value is <code>0</code> (disabled — existing behavior is preserved).</p> <div class=highlight><pre><span></span><code><span class=cp>#define JSON_DISABLE_TUPLE_REFERENCE_CONVERSION 0</span>
</code></pre></div> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <div class="admonition note"> <p class=admonition-title>Background</p> <p>By default, <code>basic_json</code> can be constructed from any <code>std::tuple</code> whose elements can be converted to <abbr title="JavaScript Object Notation">JSON</abbr>; the result is an array. This includes <code>std::tuple&lt;json&amp;&gt;</code>, which becomes a one-element array.</p> <p><code>std::tuple</code> only converts another tuple element by element if its element type cannot be constructed from the whole source tuple. Because <code>json</code> <em>can</em> be constructed from <code>std::tuple&lt;json&amp;&gt;</code>, <code>std::tuple</code> instead converts the whole tuple into a single <code>json</code> value. This has two surprising effects:</p> <div class=highlight><pre><span></span><code><span class=n>json</span><span class=w> </span><span class=n>j</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=nb>true</span><span class=p>;</span>
@@ -13,7 +13,7 @@
<span class=n>json</span><span class=w> </span><span class=n>b</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>json</span><span class=o>::</span><span class=n>array</span><span class=p>({</span><span class=n>j</span><span class=p>});</span><span class=w> </span><span class=c1>// use this instead: [true]</span>
</code></pre></div> <p>Tuples holding a <abbr title="JavaScript Object Notation">JSON</abbr> value (<code>std::make_tuple(j)</code>), tuples with more than one element, and tuples holding references to other types (including other <code>basic_json</code> specializations) are converted to arrays as before.</p> </div> <div class="admonition hint"> <p class=admonition-title>CMake option</p> <p>This behavior can also be controlled with the CMake option <a href=../../../integration/cmake/#json_disabletuplereferenceconversion><code>JSON_DisableTupleReferenceConversion</code></a> (<code>OFF</code> by default) which defines <code>JSON_DISABLE_TUPLE_REFERENCE_CONVERSION</code> accordingly.</p> </div> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example: default behavior (macro not defined)</summary> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span>
<span class=p>{</span>
@@ -25,7 +25,7 @@
</code></pre></div> </details> <details class=example> <summary>Example: conversion disabled (macro defined to 1)</summary> <div class=highlight><pre><span></span><code><span class=cp>#define JSON_DISABLE_TUPLE_REFERENCE_CONVERSION 1</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span>
<span class=p>{</span>
@@ -37,4 +37,4 @@
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>tuple</span><span class=o>&lt;</span><span class=k>const</span><span class=w> </span><span class=n>json</span><span class=o>&amp;&gt;</span><span class=w> </span><span class=n>r</span><span class=p>(</span><span class=n>std</span><span class=o>::</span><span class=n>forward_as_tuple</span><span class=p>(</span><span class=n>j</span><span class=p>));</span>
<span class=w> </span><span class=c1>// std::get&lt;0&gt;(r) refers to j</span>
<span class=p>}</span>
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../../basic_json/basic_json/ ><strong>basic_json(CompatibleType&amp;&amp;)</strong></a> - the affected constructor</li> <li><a href=../../../integration/cmake/#json_disabletuplereferenceconversion><span class=twemoji><svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M11.769.066.067 23.206l12.76-10.843zm11.438 23.868L7.471 17.587 0 23.934zm.793-.198L12.298.463l1.719 19.24zM12.893 12.959l-5.025 4.298 5.62 2.248z"/></svg></span> JSON_DisableTupleReferenceConversion</a> - CMake option to control the macro</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ul> <li>Added in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</li> <li>Planned to become the default (with the macro removed) in version 4.0.0.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 4, 2026 20:11:34 UTC">October 4, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 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</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../../basic_json/basic_json/ ><strong>basic_json(CompatibleType&amp;&amp;)</strong></a> - the affected constructor</li> <li><a href=../../../integration/cmake/#json_disabletuplereferenceconversion><span class=twemoji><svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M11.769.066.067 23.206l12.76-10.843zm11.438 23.868L7.471 17.587 0 23.934zm.793-.198L12.298.463l1.719 19.24zM12.893 12.959l-5.025 4.298 5.62 2.248z"/></svg></span> JSON_DisableTupleReferenceConversion</a> - CMake option to control the macro</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ul> <li>Added in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</li> <li>Planned to become the default (with the macro removed) in version 4.0.0.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 25, 2026 11:07:51 UTC">October 25, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 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@@ -62,7 +62,7 @@ Example: default behavior (macro not defined)
```
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using nlohmann::json;
int main()
{
@@ -79,7 +79,7 @@ Example: conversion disabled (macro defined to 1)
#define JSON_DISABLE_TUPLE_REFERENCE_CONVERSION 1
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using nlohmann::json;
int main()
{
+2 -2
View File
@@ -73,7 +73,7 @@ The default value is `0`: the file is locked once and read with the unlocked std
#include <cstdio>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using nlohmann::json;
int main()
{
@@ -92,7 +92,7 @@ The default value is `0`: the file is locked once and read with the unlocked std
#include <cstdio>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using nlohmann::json;
int main()
{
@@ -1,9 +1,9 @@
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</code></pre></div> <p>When defined to <code>1</code>, parsing from a <code class=highlight><span class=kt>FILE</span><span class=o>*</span></code> reads every character with <code>std::fgetc</code>, as in version 3.12.0 and earlier, instead of locking the file once and reading it with the unlocked stdio functions.</p> <p>It does not change any result: values, exceptions, and the position of the file after parsing are the same either way. Only the speed and the locking of the file differ (see the notes on locking below).</p> <p>Builds with MemorySanitizer use <code>std::fgetc</code> automatically, because the inline <code>getc_unlocked</code> of glibc reads the stdio buffer directly, which glibc (not instrumented) filled, and MemorySanitizer would report it as uninitialized.</p> <h2 id=default-definition>Default definition<a class=headerlink href=#default-definition title="Permanent link">&para;</a></h2> <p>The default value is <code>0</code>: the file is locked once and read with the unlocked stdio functions where they are available.</p> <div class=highlight><pre><span></span><code><span class=cp>#define JSON_DISABLE_UNLOCKED_FILE_IO 0</span>
</code></pre></div> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <div class="admonition note"> <p class=admonition-title>Background</p> <p>The C standard library makes every <code>std::fgetc</code> call thread-safe by locking and unlocking the <code>FILE</code> object. When parsing from a <code>FILE*</code>, the parser reads one character at a time, so this happens for every character of the input.</p> <p>Instead, the parser locks the file once when parsing starts and unlocks it when parsing ends - also when an exception is thrown - and reads the characters in between without locking:</p> <table> <thead> <tr> <th>C library</th> <th>functions</th> </tr> </thead> <tbody> <tr> <td>glibc (Linux), Apple (macOS, iOS), Android, FreeBSD, NetBSD, OpenBSD, DragonFly BSD</td> <td><code>flockfile</code>, <code>getc_unlocked</code>, <code>funlockfile</code> (POSIX)</td> </tr> <tr> <td>Microsoft (<abbr title="Microsoft Visual C++">MSVC</abbr>, clang-cl)</td> <td><code>_lock_file</code>, <code>_fgetc_nolock</code>, <code>_unlock_file</code></td> </tr> <tr> <td>others (e.g., musl, MinGW, newlib)</td> <td><code>std::fgetc</code>, as before</td> </tr> </tbody> </table> <p>This makes parsing from a <code>FILE*</code> 3 to 4 times as fast with the Apple C library and 1.1 to 1.3 times as fast with glibc, whose locking is cheaper. The binary formats (<a href=../../basic_json/from_cbor/ ><code>from_cbor</code></a>, <a href=../../basic_json/from_msgpack/ ><code>from_msgpack</code></a>, ...) read from a <code>FILE*</code> the same way.</p> </div> <div class="admonition note"> <p class=admonition-title>Locking</p> <p>While a value is parsed from a <code>FILE*</code>, the parsing thread holds the file's lock. The lock is recursive, so the parsing thread itself - for instance, a <a href=../../json_sax/ ><abbr title="Simple API for XML">SAX</abbr></a> handler or a <a href=../../basic_json/parser_callback_t/ >parser callback</a> - can keep using the file with stdio functions such as <code>std::ftell</code>. Other threads that use the same <code>FILE</code> object wait until the parser is done. Before, they could interleave their reads with the parser's, which made the parsed input unpredictable anyway.</p> <p>A program in which a <abbr title="Simple API for XML">SAX</abbr> handler or parser callback waits for <strong>another</strong> thread that uses the <strong>same</strong> <code>FILE</code> object would deadlock. Define the macro to <code>1</code> for such programs.</p> </div> <div class="admonition note"> <p class=admonition-title>ABI compatibility</p> <p>The value of this macro is encoded in the <a href=../../../features/namespace/ >namespace</a> (tag <code>_dufio</code>), resulting in distinct symbol names. Translation units compiled with and without it can therefore be linked into the same program without One Definition Rule (ODR) violations, but they cannot exchange instances of library types.</p> </div> <div class="admonition note"> <p class=admonition-title>Other inputs</p> <p>Reading from a <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>istream</span></code> is not affected by this macro; see <a href=../json_disable_stream_bulk_scan/ ><code>JSON_DISABLE_STREAM_BULK_SCAN</code></a> for that input.</p> </div> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example: parsing from a <code>FILE*</code> (default)</summary> <p>The file is locked once while it is parsed:</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;cstdio&gt;</span>
</code></pre></div> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <div class="admonition note"> <p class=admonition-title>Background</p> <p>The C standard library makes every <code>std::fgetc</code> call thread-safe by locking and unlocking the <code>FILE</code> object. When parsing from a <code>FILE*</code>, the parser reads one character at a time, so this happens for every character of the input.</p> <p>Instead, the parser locks the file once when parsing starts and unlocks it when parsing ends - also when an exception is thrown - and reads the characters in between without locking:</p> <table> <thead> <tr> <th>C library</th> <th>functions</th> </tr> </thead> <tbody> <tr> <td>glibc (Linux), Apple (macOS, iOS), Android, FreeBSD, NetBSD, OpenBSD, DragonFly BSD</td> <td><code>flockfile</code>, <code>getc_unlocked</code>, <code>funlockfile</code> (POSIX)</td> </tr> <tr> <td>Microsoft (<abbr title="Microsoft Visual C++">MSVC</abbr>, clang-cl)</td> <td><code>_lock_file</code>, <code>_fgetc_nolock</code>, <code>_unlock_file</code></td> </tr> <tr> <td>others (e.g., musl, <abbr title="Minimalist GNU for Windows">MinGW</abbr>, newlib)</td> <td><code>std::fgetc</code>, as before</td> </tr> </tbody> </table> <p>This makes parsing from a <code>FILE*</code> 3 to 4 times as fast with the Apple C library and 1.1 to 1.3 times as fast with glibc, whose locking is cheaper. The binary formats (<a href=../../basic_json/from_cbor/ ><code>from_cbor</code></a>, <a href=../../basic_json/from_msgpack/ ><code>from_msgpack</code></a>, ...) read from a <code>FILE*</code> the same way.</p> </div> <div class="admonition note"> <p class=admonition-title>Locking</p> <p>While a value is parsed from a <code>FILE*</code>, the parsing thread holds the file's lock. The lock is recursive, so the parsing thread itself - for instance, a <a href=../../json_sax/ ><abbr title="Simple API for XML">SAX</abbr></a> handler or a <a href=../../basic_json/parser_callback_t/ >parser callback</a> - can keep using the file with stdio functions such as <code>std::ftell</code>. Other threads that use the same <code>FILE</code> object wait until the parser is done. Before, they could interleave their reads with the parser's, which made the parsed input unpredictable anyway.</p> <p>A program in which a <abbr title="Simple API for XML">SAX</abbr> handler or parser callback waits for <strong>another</strong> thread that uses the <strong>same</strong> <code>FILE</code> object would deadlock. Define the macro to <code>1</code> for such programs.</p> </div> <div class="admonition note"> <p class=admonition-title><abbr title="Application Binary Interface">ABI</abbr> compatibility</p> <p>The value of this macro is encoded in the <a href=../../../features/namespace/ >namespace</a> (tag <code>_dufio</code>), resulting in distinct symbol names. Translation units compiled with and without it can therefore be linked into the same program without One Definition Rule (<abbr title="One Definition Rule">ODR</abbr>) violations, but they cannot exchange instances of library types.</p> </div> <div class="admonition note"> <p class=admonition-title>Other inputs</p> <p>Reading from a <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>istream</span></code> is not affected by this macro; see <a href=../json_disable_stream_bulk_scan/ ><code>JSON_DISABLE_STREAM_BULK_SCAN</code></a> for that input.</p> </div> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example: parsing from a <code>FILE*</code> (default)</summary> <p>The file is locked once while it is parsed:</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;cstdio&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span>
<span class=p>{</span>
@@ -15,7 +15,7 @@
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;cstdio&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span>
<span class=p>{</span>
@@ -23,4 +23,4 @@
<span class=w> </span><span class=n>json</span><span class=w> </span><span class=n>j</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>json</span><span class=o>::</span><span class=n>parse</span><span class=p>(</span><span class=n>f</span><span class=p>);</span><span class=w> </span><span class=c1>// std::fgetc for every character</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>fclose</span><span class=p>(</span><span class=n>f</span><span class=p>);</span>
<span class=p>}</span>
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../../basic_json/parse/ ><strong>parse</strong></a> - deserialize from a compatible input</li> <li><a href=../../basic_json/sax_parse/ ><strong>sax_parse</strong></a> - generate <abbr title="Simple API for XML">SAX</abbr> events</li> <li><a href=../json_disable_stream_bulk_scan/ ><strong>JSON_DISABLE_STREAM_BULK_SCAN</strong></a> - read a <code>std::istream</code> one character at a time</li> <li><a href=../../../features/parsing/#input-sources-and-performance>Parsing: input sources and performance</a></li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ul> <li>Added in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 21, 2026 08:22:50 UTC">October 21, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 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</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../../basic_json/parse/ ><strong>parse</strong></a> - deserialize from a compatible input</li> <li><a href=../../basic_json/sax_parse/ ><strong>sax_parse</strong></a> - generate <abbr title="Simple API for XML">SAX</abbr> events</li> <li><a href=../json_disable_stream_bulk_scan/ ><strong>JSON_DISABLE_STREAM_BULK_SCAN</strong></a> - read a <code>std::istream</code> one character at a time</li> <li><a href=../../../features/parsing/#input-sources-and-performance>Parsing: input sources and performance</a></li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ul> <li>Added in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 25, 2026 11:07:51 UTC">October 25, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 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@@ -58,7 +58,7 @@ The file is locked once while it is parsed:
#include <cstdio>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using nlohmann::json;
int main()
{
@@ -77,7 +77,7 @@ With the macro, every character is read with `std::fgetc`, with the same result:
#include <cstdio>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using nlohmann::json;
int main()
{
+1 -1
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@@ -1,4 +1,4 @@
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<span class=cp>#define JSON_HAS_CPP_14</span>
<span class=cp>#define JSON_HAS_CPP_17</span>
<span class=cp>#define JSON_HAS_CPP_20</span>
+2 -2
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<span class=cp>#define JSON_HAS_EXPERIMENTAL_FILESYSTEM </span><span class=cm>/* value */</span>
</code></pre></div> <p>When compiling with C++17, the library provides conversions from and to <a href="https://en.cppreference.com/w/cpp/filesystem/path"><code>std::filesystem::path</code></a>. As compiler support for filesystem is limited, the library tries to detect whether <a href="https://en.cppreference.com/w/cpp/header/filesystem"><code>&lt;filesystem&gt;</code>/<code>std::filesystem</code></a> (<code>JSON_HAS_FILESYSTEM</code>) or <a href="https://en.cppreference.com/w/cpp/header/experimental/filesystem"><code>&lt;experimental/filesystem&gt;</code>/<code>std::experimental::filesystem</code></a> (<code>JSON_HAS_EXPERIMENTAL_FILESYSTEM</code>) should be used. To override the built-in check, define <code>JSON_HAS_FILESYSTEM</code> or <code>JSON_HAS_EXPERIMENTAL_FILESYSTEM</code> to <code>1</code>.</p> <h2 id=default-definition>Default definition<a class=headerlink href=#default-definition title="Permanent link">&para;</a></h2> <p>The default value is detected based on the preprocessor macros <code class=highlight><span class=n>__cpp_lib_filesystem</span></code>, <code class=highlight><span class=n>__cpp_lib_experimental_filesystem</span></code>, <code class=highlight><span class=n>__has_include</span><span class=p>(</span><span class=o>&lt;</span><span class=n>filesystem</span><span class=o>&gt;</span><span class=p>)</span></code>, or <code class=highlight><span class=n>__has_include</span><span class=p>(</span><span class=o>&lt;</span><span class=n>experimental</span><span class=o>/</span><span class=n>filesystem</span><span class=o>&gt;</span><span class=p>)</span></code>.</p> <div class="admonition info"> <p class=admonition-title>Known compiler/stdlib exclusions</p> <p>Even when the feature-test macro indicates filesystem support is available, the library disables it on the following broken toolchains:</p> <ul> <li><strong>MinGW + <abbr title="GNU Compiler Collection">GCC</abbr> 8</strong> — disabled entirely (broken <code>std::filesystem</code> implementation; <a href="https://sourceforge.net/p/mingw-w64/bugs/737/">MinGW-w64 bug 737</a>)</li> <li><strong><abbr title="GNU Compiler Collection">GCC</abbr> (non-Clang) &lt; 8</strong> — disabled (no filesystem support)</li> <li><strong>Clang &lt; 7</strong> — disabled (no filesystem support)</li> <li><strong><abbr title="Microsoft Visual C++">MSVC</abbr> &lt; 19.14</strong> — disabled (no filesystem support)</li> <li><strong>iOS &lt; 13</strong> — disabled (no filesystem support)</li> <li><strong>macOS &lt; Catalina (10.15)</strong> — disabled (no filesystem support)</li> </ul> <p>If <code>JSON_HAS_FILESYSTEM</code> or <code>JSON_HAS_EXPERIMENTAL_FILESYSTEM</code> is <code>0</code> despite <code>__cpp_lib_filesystem</code> being defined, one of the exclusions above likely applies to your toolchain.</p> </div> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <ul> <li>Note that older compilers or older versions of libstdc++ also require the library <code>stdc++fs</code> to be linked to for filesystem support.</li> <li>Both macros are undefined outside the library.</li> </ul> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The code below forces the library to use the header <code>&lt;experimental/filesystem&gt;</code>.</p> <div class=highlight><pre><span></span><code><span class=cp>#define JSON_HAS_EXPERIMENTAL_FILESYSTEM 1</span>
</code></pre></div> <p>When compiling with C++17, the library provides conversions from and to <a href="https://en.cppreference.com/w/cpp/filesystem/path"><code>std::filesystem::path</code></a>. As compiler support for filesystem is limited, the library tries to detect whether <a href="https://en.cppreference.com/w/cpp/header/filesystem"><code>&lt;filesystem&gt;</code>/<code>std::filesystem</code></a> (<code>JSON_HAS_FILESYSTEM</code>) or <a href="https://en.cppreference.com/w/cpp/header/experimental/filesystem"><code>&lt;experimental/filesystem&gt;</code>/<code>std::experimental::filesystem</code></a> (<code>JSON_HAS_EXPERIMENTAL_FILESYSTEM</code>) should be used. To override the built-in check, define <code>JSON_HAS_FILESYSTEM</code> or <code>JSON_HAS_EXPERIMENTAL_FILESYSTEM</code> to <code>1</code>.</p> <h2 id=default-definition>Default definition<a class=headerlink href=#default-definition title="Permanent link">&para;</a></h2> <p>The default value is detected based on the preprocessor macros <code class=highlight><span class=n>__cpp_lib_filesystem</span></code>, <code class=highlight><span class=n>__cpp_lib_experimental_filesystem</span></code>, <code class=highlight><span class=n>__has_include</span><span class=p>(</span><span class=o>&lt;</span><span class=n>filesystem</span><span class=o>&gt;</span><span class=p>)</span></code>, or <code class=highlight><span class=n>__has_include</span><span class=p>(</span><span class=o>&lt;</span><span class=n>experimental</span><span class=o>/</span><span class=n>filesystem</span><span class=o>&gt;</span><span class=p>)</span></code>.</p> <div class="admonition info"> <p class=admonition-title>Known compiler/stdlib exclusions</p> <p>Even when the feature-test macro indicates filesystem support is available, the library disables it on the following broken toolchains:</p> <ul> <li><strong><abbr title="Minimalist GNU for Windows">MinGW</abbr> + <abbr title="GNU Compiler Collection">GCC</abbr> 8</strong> — disabled entirely (broken <code>std::filesystem</code> implementation; <a href="https://sourceforge.net/p/mingw-w64/bugs/737/"><abbr title="Minimalist GNU for Windows">MinGW</abbr>-w64 bug 737</a>)</li> <li><strong><abbr title="GNU Compiler Collection">GCC</abbr> (non-Clang) &lt; 8</strong> — disabled (no filesystem support)</li> <li><strong>Clang &lt; 7</strong> — disabled (no filesystem support)</li> <li><strong><abbr title="Microsoft Visual C++">MSVC</abbr> &lt; 19.14</strong> — disabled (no filesystem support)</li> <li><strong>iOS &lt; 13</strong> — disabled (no filesystem support)</li> <li><strong>macOS &lt; Catalina (10.15)</strong> — disabled (no filesystem support)</li> </ul> <p>If <code>JSON_HAS_FILESYSTEM</code> or <code>JSON_HAS_EXPERIMENTAL_FILESYSTEM</code> is <code>0</code> despite <code>__cpp_lib_filesystem</code> being defined, one of the exclusions above likely applies to your toolchain.</p> </div> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <ul> <li>Note that older compilers or older versions of libstdc++ also require the library <code>stdc++fs</code> to be linked to for filesystem support.</li> <li>Both macros are undefined outside the library.</li> </ul> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The code below forces the library to use the header <code>&lt;experimental/filesystem&gt;</code>.</p> <div class=highlight><pre><span></span><code><span class=cp>#define JSON_HAS_EXPERIMENTAL_FILESYSTEM 1</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=p>...</span>
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</code></pre></div> <p>This macro indicates whether a <abbr title="JavaScript Object Notation">JSON</abbr> array can be constructed directly from a C++20 range view (<code>std::ranges::view</code>), such as the result of <code>std::views::filter</code> or <code>std::views::transform</code>. Possible values are <code>1</code> when supported or <code>0</code> when unsupported.</p> <h2 id=default-definition>Default definition<a class=headerlink href=#default-definition title="Permanent link">&para;</a></h2> <p>The default value is <code>1</code> if <a href=../json_has_ranges/ ><code>JSON_HAS_RANGES</code></a> is <code>1</code> and the compiler is not MinGW (that is, <code class=highlight><span class=n>__MINGW32__</span></code> is not defined), and <code>0</code> otherwise.</p> <p>When the macro is not defined, the library will define it to its default value.</p> <div class="admonition info"> <p class=admonition-title>Known compiler/stdlib exclusions</p> <ul> <li><strong>MinGW</strong> -- disabled, because its <code>std::ranges</code> support is incomplete (<a href="https://github.com/nlohmann/json/issues/4916">issue #4916</a>).</li> <li>All toolchains for which <a href=../json_has_ranges/#default-definition><code>JSON_HAS_RANGES</code></a> is disabled.</li> </ul> </div> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The code below forces the library to disable the conversion from range views:</p> <div class=highlight><pre><span></span><code><span class=cp>#define JSON_HAS_RANGE_VIEW_CONVERSION 0</span>
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/macros/json_has_range_view_conversion/" rel="canonical"><link href=../json_has_filesystem/ rel=prev><link href=../json_has_ranges/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>JSON_HAS_RANGE_VIEW_CONVERSION - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new 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data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> JSON_HAS_RANGE_VIEW_CONVERSION </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo 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6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 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</code></pre></div> <p>This macro indicates whether a <abbr title="JavaScript Object Notation">JSON</abbr> array can be constructed directly from a C++20 range view (<code>std::ranges::view</code>), such as the result of <code>std::views::filter</code> or <code>std::views::transform</code>. Possible values are <code>1</code> when supported or <code>0</code> when unsupported.</p> <h2 id=default-definition>Default definition<a class=headerlink href=#default-definition title="Permanent link">&para;</a></h2> <p>The default value is <code>1</code> if <a href=../json_has_ranges/ ><code>JSON_HAS_RANGES</code></a> is <code>1</code> and the compiler is not <abbr title="Minimalist GNU for Windows">MinGW</abbr> (that is, <code class=highlight><span class=n>__MINGW32__</span></code> is not defined), and <code>0</code> otherwise.</p> <p>When the macro is not defined, the library will define it to its default value.</p> <div class="admonition info"> <p class=admonition-title>Known compiler/stdlib exclusions</p> <ul> <li><strong><abbr title="Minimalist GNU for Windows">MinGW</abbr></strong> -- disabled, because its <code>std::ranges</code> support is incomplete (<a href="https://github.com/nlohmann/json/issues/4916">issue #4916</a>).</li> <li>All toolchains for which <a href=../json_has_ranges/#default-definition><code>JSON_HAS_RANGES</code></a> is disabled.</li> </ul> </div> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The code below forces the library to disable the conversion from range views:</p> <div class=highlight><pre><span></span><code><span class=cp>#define JSON_HAS_RANGE_VIEW_CONVERSION 0</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=p>...</span>
+3 -3
View File
@@ -1,6 +1,6 @@
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/macros/json_has_ranges/" rel="canonical"><link href=../json_has_range_view_conversion/ rel=prev><link href=../json_has_static_rtti/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>JSON_HAS_RANGES - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new URL("../../..",location),__md_hash=e=>[...e].reduce(((e,_)=>(e<<5)-e+_.charCodeAt(0)),0),__md_get=(e,_=localStorage,t=__md_scope)=>JSON.parse(_.getItem(t.pathname+"."+e)),__md_set=(e,_,t=localStorage,a=__md_scope)=>{try{t.setItem(a.pathname+"."+e,JSON.stringify(_))}catch(e){}}</script></head> <body dir=ltr data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo> <input class=md-toggle data-md-toggle=drawer type=checkbox id=__drawer autocomplete=off> <input class=md-toggle data-md-toggle=search type=checkbox id=__search autocomplete=off> <label class=md-overlay for=__drawer></label> <div data-md-component=skip> <a href=#json_has_ranges class=md-skip> Skip to content </a> </div> <div data-md-component=announce> </div> <header class=md-header data-md-component=header> <nav class="md-header__inner md-grid" aria-label=Header> <a href=../../.. title="JSON for Modern C++" class="md-header__button md-logo" aria-label="JSON for Modern C++" data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> JSON_HAS_RANGES </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark mode" type=radio 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15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.52 6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 1Line truncated
</code></pre></div> <p>This macro indicates whether the standard library has any support for ranges. Implies support for concepts. Possible values are <code>1</code> when supported or <code>0</code> when unsupported.</p> <h2 id=default-definition>Default definition<a class=headerlink href=#default-definition title="Permanent link">&para;</a></h2> <p>The default value is detected based on the preprocessor macro <code class=highlight><span class=n>__cpp_lib_ranges</span></code>.</p> <p>When the macro is not defined, the library will define it to its default value.</p> <div class="admonition info"> <p class=admonition-title>Known compiler/stdlib exclusions</p> <p>Even when the feature-test macro <code>__cpp_lib_ranges</code> indicates ranges support is available, the library disables it on the following incomplete or broken toolchains:</p> <ul> <li><strong><abbr title="GNU Compiler Collection">GCC</abbr> 11.1.0</strong> — disabled (the shipped <code>&lt;ranges&gt;</code> header has a syntax error; <a href="https://github.com/nlohmann/json/issues/4440">issue #4440</a>)</li> <li><strong>libstdc++ &lt; 11</strong> — disabled (incomplete C++20 ranges support; <a href="https://github.com/nlohmann/json/issues/4440">issue #4440</a>)</li> <li><strong>Clang &lt; 16 with libstdc++</strong> — disabled (incomplete ranges support; <a href="https://github.com/nlohmann/json/issues/5161">issue #5161</a>)</li> <li><strong>libc++ &lt; 160000</strong> — disabled (incomplete C++20 ranges support; <a href="https://github.com/nlohmann/json/issues/4440">issue #4440</a>)</li> <li><strong>nvcc (CUDA) 12.0.x and 12.1.x</strong> — disabled (the <code>enable_borrowed_range</code> variable-template syntax triggers a parse error under these two toolkit versions; fixed in CUDA 12.2; <a href="https://github.com/nlohmann/json/issues/3907">issue #3907</a>)</li> </ul> <p>If <code>JSON_HAS_RANGES</code> is <code>0</code> despite <code>__cpp_lib_ranges</code> being defined, one of the exclusions above likely applies to your toolchain.</p> </div> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The code below forces the library to enable support for ranges:</p> <div class=highlight><pre><span></span><code><span class=cp>#define JSON_HAS_RANGES 1</span>
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/macros/json_has_ranges/" rel="canonical"><link href=../json_has_range_view_conversion/ rel=prev><link href=../json_has_static_rtti/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>JSON_HAS_RANGES - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new URL("../../..",location),__md_hash=e=>[...e].reduce(((e,_)=>(e<<5)-e+_.charCodeAt(0)),0),__md_get=(e,_=localStorage,t=__md_scope)=>JSON.parse(_.getItem(t.pathname+"."+e)),__md_set=(e,_,t=localStorage,a=__md_scope)=>{try{t.setItem(a.pathname+"."+e,JSON.stringify(_))}catch(e){}}</script></head> <body dir=ltr data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo> <input class=md-toggle data-md-toggle=drawer type=checkbox id=__drawer autocomplete=off> <input class=md-toggle data-md-toggle=search type=checkbox id=__search autocomplete=off> <label class=md-overlay for=__drawer></label> <div data-md-component=skip> <a href=#json_has_ranges class=md-skip> Skip to content </a> </div> <div data-md-component=announce> </div> <header class=md-header data-md-component=header> <nav class="md-header__inner md-grid" aria-label=Header> <a href=../../.. title="JSON for Modern C++" class="md-header__button md-logo" aria-label="JSON for Modern C++" data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> JSON_HAS_RANGES </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark mode" type=radio 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</code></pre></div> <p>This macro indicates whether the standard library has any support for ranges. Implies support for concepts. Possible values are <code>1</code> when supported or <code>0</code> when unsupported.</p> <h2 id=default-definition>Default definition<a class=headerlink href=#default-definition title="Permanent link">&para;</a></h2> <p>The default value is detected based on the preprocessor macro <code class=highlight><span class=n>__cpp_lib_ranges</span></code>.</p> <p>When the macro is not defined, the library will define it to its default value.</p> <div class="admonition info"> <p class=admonition-title>Known compiler/stdlib exclusions</p> <p>Even when the feature-test macro <code>__cpp_lib_ranges</code> indicates ranges support is available, the library disables it on the following incomplete or broken toolchains:</p> <ul> <li><strong><abbr title="GNU Compiler Collection">GCC</abbr> 11.1.0</strong> — disabled (the shipped <code>&lt;ranges&gt;</code> header has a syntax error; <a href="https://github.com/nlohmann/json/issues/4440">issue #4440</a>)</li> <li><strong>libstdc++ &lt; 11</strong> — disabled (incomplete C++20 ranges support; <a href="https://github.com/nlohmann/json/issues/4440">issue #4440</a>)</li> <li><strong>Clang &lt; 16 with libstdc++</strong> — disabled (incomplete ranges support; <a href="https://github.com/nlohmann/json/issues/5161">issue #5161</a>)</li> <li><strong>libc++ &lt; 160000</strong> — disabled (incomplete C++20 ranges support; <a href="https://github.com/nlohmann/json/issues/4440">issue #4440</a>)</li> <li><strong>nvcc (<abbr title="Compute Unified Device Architecture">CUDA</abbr>) 12.0.x and 12.1.x</strong> — disabled (the <code>enable_borrowed_range</code> variable-template syntax triggers a parse error under these two toolkit versions; fixed in <abbr title="Compute Unified Device Architecture">CUDA</abbr> 12.2; <a href="https://github.com/nlohmann/json/issues/3907">issue #3907</a>)</li> </ul> <p>If <code>JSON_HAS_RANGES</code> is <code>0</code> despite <code>__cpp_lib_ranges</code> being defined, one of the exclusions above likely applies to your toolchain.</p> </div> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The code below forces the library to enable support for ranges:</p> <div class=highlight><pre><span></span><code><span class=cp>#define JSON_HAS_RANGES 1</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=p>...</span>
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../json_has_cpp_11/ >JSON_HAS_CPP_11 / JSON_HAS_CPP_14 / JSON_HAS_CPP_17 / JSON_HAS_CPP_20 / JSON_HAS_CPP_23 / JSON_HAS_CPP_26</a> - set supported C++ standard</li> <li><a href=../json_has_range_view_conversion/ >JSON_HAS_RANGE_VIEW_CONVERSION</a> - control construction from <code>std::ranges</code> views</li> <li><a href=../json_has_std_format/ >JSON_HAS_STD_FORMAT</a> - a similar feature-detection macro, for <code>std::format</code>/<code>std::formatter</code> support</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ul> <li>Added in version 3.11.0.</li> <li>Added the exclusions for libstdc++ &lt; 11, Clang &lt; 16 with libstdc++, libc++ &lt; 16, and nvcc (CUDA) 12.0.x and 12.1.x in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>. 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</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../json_has_cpp_11/ >JSON_HAS_CPP_11 / JSON_HAS_CPP_14 / JSON_HAS_CPP_17 / JSON_HAS_CPP_20 / JSON_HAS_CPP_23 / JSON_HAS_CPP_26</a> - set supported C++ standard</li> <li><a href=../json_has_range_view_conversion/ >JSON_HAS_RANGE_VIEW_CONVERSION</a> - control construction from <code>std::ranges</code> views</li> <li><a href=../json_has_std_format/ >JSON_HAS_STD_FORMAT</a> - a similar feature-detection macro, for <code>std::format</code>/<code>std::formatter</code> support</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ul> <li>Added in version 3.11.0.</li> <li>Added the exclusions for libstdc++ &lt; 11, Clang &lt; 16 with libstdc++, libc++ &lt; 16, and nvcc (<abbr title="Compute Unified Device Architecture">CUDA</abbr>) 12.0.x and 12.1.x in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>. 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</code></pre></div> <p>This macro indicates whether the standard library has any support for <abbr title="Runtime Type Information">RTTI</abbr> (run time type information). Possible values are <code>1</code> when supported or <code>0</code> when unsupported.</p> <h2 id=default-definition>Default definition<a class=headerlink href=#default-definition title="Permanent link">&para;</a></h2> <p>The default value is detected based on the preprocessor macro <code class=highlight><span class=n>_HAS_STATIC_RTTI</span></code>.</p> <p>When the macro is not defined, the library will define it to its default value.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The code below forces the library to enable support for libraries with <abbr title="Runtime Type Information">RTTI</abbr> dependence:</p> <div class=highlight><pre><span></span><code><span class=cp>#define JSON_HAS_STATIC_RTTI 1</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
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4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 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</code></pre></div> <p>This macro indicates whether the standard library has support for <code>std::format</code>/<code>std::formatter</code> (that is, the <code>&lt;format&gt;</code> header). Possible values are <code>1</code> when supported or <code>0</code> when unsupported.</p> <h2 id=default-definition>Default definition<a class=headerlink href=#default-definition title="Permanent link">&para;</a></h2> <p>The default value is detected based on the preprocessor macros <code class=highlight><span class=n>JSON_HAS_CPP_20</span></code> and <code class=highlight><span class=n>__cpp_lib_format</span></code>.</p> <p>When the macro is not defined, the library will define it to its default value.</p> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <div class="admonition info"> <p class=admonition-title>Enabled functionality</p> <p>When this macro evaluates to <code>1</code>, the library provides a <a href=../../basic_json/std_formatter/ ><code>std::formatter&lt;basic_json&gt;</code></a> specialization so <abbr title="JavaScript Object Notation">JSON</abbr> values can be used directly with <code>std::format</code>.</p> </div> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The code below forces the library to disable support for <code>std::format</code>, even if the standard library would otherwise support it:</p> <div class=highlight><pre><span></span><code><span class=cp>#define JSON_HAS_STD_FORMAT 0</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
@@ -1,4 +1,4 @@
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</code></pre></div> <p>This macro indicates whether the compiler and standard library support 3-way comparison. Possible values are <code>1</code> when supported or <code>0</code> when unsupported.</p> <h2 id=default-definition>Default definition<a class=headerlink href=#default-definition title="Permanent link">&para;</a></h2> <p>The default value is detected based on the preprocessor macros <code class=highlight><span class=n>__cpp_impl_three_way_comparison</span></code> and <code class=highlight><span class=n>__cpp_lib_three_way_comparison</span></code>.</p> <p>When the macro is not defined, the library will define it to its default value.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The code below forces the library to use 3-way comparison:</p> <div class=highlight><pre><span></span><code><span class=cp>#define JSON_HAS_THREE_WAY_COMPARISON 1</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
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</code></pre></div> <p>When defined, <code>&lt;nlohmann/json.hpp&gt;</code> does not include <code>&lt;nlohmann/json_literals.hpp&gt;</code>, so the user-defined string literals <a href=../../operator_literal_json/ ><code>operator""_json</code></a> and <a href=../../operator_literal_json_pointer/ ><code>operator""_json_pointer</code></a> are not declared. Include <code>&lt;nlohmann/json_literals.hpp&gt;</code> in the files that use them.</p> <p>The literals are ordinary inline functions whose bodies call the parser, so every translation unit that includes them instantiates the parser — even if it never parses anything itself. Defining <code>JSON_NO_AUTOMATIC_UDLS</code> for a whole project avoids this cost in translation units that do not parse (e.g., ones that only define types and conversions or pass <code>json</code> values around) and reduces their compile time.</p> <h2 id=default-definition>Default definition<a class=headerlink href=#default-definition title="Permanent link">&para;</a></h2> <p>By default, <code class=highlight><span class=n>JSON_NO_AUTOMATIC_UDLS</span></code> is not defined, and <code>&lt;nlohmann/json.hpp&gt;</code> includes <code>&lt;nlohmann/json_literals.hpp&gt;</code>.</p> <div class=highlight><pre><span></span><code><span class=cp>#undef JSON_NO_AUTOMATIC_UDLS</span>
</code></pre></div> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <div class="admonition info"> <p class=admonition-title>Header <code>&lt;nlohmann/json_literals.hpp&gt;</code></p> <p>The header includes <code>&lt;nlohmann/json.hpp&gt;</code> itself and places the literals according to <a href=../json_use_global_udls/ ><code>JSON_USE_GLOBAL_UDLS</code></a>. It is part of the multi-header sources (<code>include/nlohmann</code>) and of the single-header sources (<code>single_include/nlohmann</code>), next to <code>json.hpp</code>.</p> </div> <div class="admonition info"> <p class=admonition-title>C++ modules</p> <p>The <code>nlohmann.json</code> <a href=../../../features/modules/ >module</a> always exports the literals, regardless of this macro.</p> </div> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The code below includes the library without the literals and adds them in a single translation unit.</p> <div class=highlight><pre><span></span><code><span class=c1>// compiled with -DJSON_NO_AUTOMATIC_UDLS for the whole project</span>
@@ -11,4 +11,4 @@
<span class=w> </span><span class=k>auto</span><span class=w> </span><span class=n>j</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=sa>R</span><span class=s>"</span><span class=dl>(</span><span class=s>{"foo": 42}</span><span class=dl>)</span><span class=s>"</span><span class=n>_json</span><span class=p>;</span>
<span class=w> </span><span class=k>return</span><span class=w> </span><span class=n>j</span><span class=p>.</span><span class=n>at</span><span class=p>(</span><span class=s>"/foo"</span><span class=n>_json_pointer</span><span class=p>)</span><span class=w> </span><span class=o>==</span><span class=w> </span><span class=mi>42</span><span class=w> </span><span class=o>?</span><span class=w> </span><span class=mi>0</span><span class=w> </span><span class=o>:</span><span class=w> </span><span class=mi>1</span><span class=p>;</span>
<span class=p>}</span>
</code></pre></div> <p>Without the include of <code>&lt;nlohmann/json_literals.hpp&gt;</code>, the code would fail to compile.</p> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../../operator_literal_json/ ><code>operator""_json</code></a></li> <li><a href=../../operator_literal_json_pointer/ ><code>operator""_json_pointer</code></a></li> <li><a href=../json_use_global_udls/ ><code>JSON_USE_GLOBAL_UDLS</code></a> - place user-defined string literals (UDLs) into the global namespace</li> <li><a href=../../../integration/compile_times/ >Compile times</a> - options to reduce compile times</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ul> <li>Added in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 4, 2026 10:23:53 UTC">October 4, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 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</code></pre></div> <p>Without the include of <code>&lt;nlohmann/json_literals.hpp&gt;</code>, the code would fail to compile.</p> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../../operator_literal_json/ ><code>operator""_json</code></a></li> <li><a href=../../operator_literal_json_pointer/ ><code>operator""_json_pointer</code></a></li> <li><a href=../json_use_global_udls/ ><code>JSON_USE_GLOBAL_UDLS</code></a> - place user-defined string literals (<abbr title="User-defined literals">UDLs</abbr>) into the global namespace</li> <li><a href=../../../integration/compile_times/ >Compile times</a> - options to reduce compile times</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ul> <li>Added in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 4, 2026 10:23:53 UTC">October 4, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 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xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> JSON_NO_IO </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark mode" type=radio 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</code></pre></div> <p>When defined, headers <code>&lt;cstdio&gt;</code>, <code>&lt;ios&gt;</code>, <code>&lt;iosfwd&gt;</code>, <code>&lt;istream&gt;</code>, and <code>&lt;ostream&gt;</code> are not included and parse functions relying on these headers are excluded. This is relevant for environments where these I/O functions are disallowed for security reasons (e.g., Intel Software Guard Extensions (SGX)).</p> <h2 id=default-definition>Default definition<a class=headerlink href=#default-definition title="Permanent link">&para;</a></h2> <p>By default, <code class=highlight><span class=n>JSON_NO_IO</span></code> is not defined.</p> <div class=highlight><pre><span></span><code><span class=cp>#undef JSON_NO_IO</span>
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/macros/json_no_io/" rel="canonical"><link href=../json_noexception/ rel=prev><link href=../json_no_simd/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>JSON_NO_IO - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new 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15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.52 6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9.5 5"/></svg> Line truncated
</code></pre></div> <p>When defined, headers <code>&lt;cstdio&gt;</code>, <code>&lt;ios&gt;</code>, <code>&lt;iosfwd&gt;</code>, <code>&lt;istream&gt;</code>, and <code>&lt;ostream&gt;</code> are not included and parse functions relying on these headers are excluded. This is relevant for environments where these I/O functions are disallowed for security reasons (e.g., Intel Software Guard Extensions (<abbr title="Software Guard Extensions">SGX</abbr>)).</p> <h2 id=default-definition>Default definition<a class=headerlink href=#default-definition title="Permanent link">&para;</a></h2> <p>By default, <code class=highlight><span class=n>JSON_NO_IO</span></code> is not defined.</p> <div class=highlight><pre><span></span><code><span class=cp>#undef JSON_NO_IO</span>
</code></pre></div> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The code below forces the library not to use the headers <code>&lt;cstdio&gt;</code>, <code>&lt;ios&gt;</code>, <code>&lt;iosfwd&gt;</code>, <code>&lt;istream&gt;</code>, and <code>&lt;ostream&gt;</code>.</p> <div class=highlight><pre><span></span><code><span class=cp>#define JSON_NO_IO 1</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
+4 -2
View File
@@ -5,7 +5,8 @@
```
When defined, the library uses only portable C++ code where it would otherwise use vector instructions: when scanning
strings during parsing, and when writing floating-point numbers during serialization.
strings during parsing, and when writing floating-point numbers during serialization. This includes the parser of
[`basic_json_document`](../basic_json_document/index.md) (`<nlohmann/json_view.hpp>`).
The macro is an escape hatch, for example for toolchains that cannot compile the vector code, for sanitizers or
analyzers that do not understand it, or to compare the speed of both variants. It does not change any result: values,
@@ -61,7 +62,7 @@ By default, `#!cpp JSON_NO_SIMD` is not defined, and vector instructions are use
#include <iostream>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using nlohmann::json;
int main()
{
@@ -77,6 +78,7 @@ By default, `#!cpp JSON_NO_SIMD` is not defined, and vector instructions are use
- [**JSON_USE_SIMDUTF**](json_use_simdutf.md) - use the simdutf library to accelerate UTF-8 validation
- [**JSON_DISABLE_STREAM_BULK_SCAN**](json_disable_stream_bulk_scan.md) - read a `std::istream` one character at a time
- [Parsing: input sources and performance](../../features/parsing/index.md#input-sources-and-performance)
- [json_view](../../features/json_view.md) - the zero-copy view, whose parser the macro also affects
## Version history
+5 -5
View File
@@ -1,14 +1,14 @@
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/macros/json_no_simd/" rel="canonical"><link href=../json_no_io/ rel=prev><link href=../json_no_thread_local/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>JSON_NO_SIMD - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new 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name=__palette id=__palette_0> <label class="md-header__button md-icon" title="Switch to dark mode" for=__palette_1 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a4 4 0 0 0-4 4 4 4 0 0 0 4 4 4 4 0 0 0 4-4 4 4 0 0 0-4-4m0 10a6 6 0 0 1-6-6 6 6 0 0 1 6-6 6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> <input class=md-option data-md-color-media="(prefers-color-scheme: dark)" data-md-color-scheme=slate data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to light mode" type=radio name=__palette id=__palette_1> <label class="md-header__button md-icon" title="Switch to light mode" for=__palette_0 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 18c-.89 0-1.74-.2-2.5-.55C11.56 16.5 13 14.42 13 12s-1.44-4.5-3.5-5.45C10.26 6.2 11.11 6 12 6a6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.52 6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9.5 5Line truncated
</code></pre></div> <p>When defined, the library uses only portable C++ code where it would otherwise use vector instructions: when scanning strings during parsing, and when writing floating-point numbers during serialization.</p> <p>The macro is an escape hatch, for example for toolchains that cannot compile the vector code, for sanitizers or analyzers that do not understand it, or to compare the speed of both variants. It does not change any result: values, exceptions, and error positions are the same either way. Only the speed differs.</p> <h2 id=default-definition>Default definition<a class=headerlink href=#default-definition title="Permanent link">&para;</a></h2> <p>By default, <code class=highlight><span class=n>JSON_NO_SIMD</span></code> is not defined, and vector instructions are used where the target has them.</p> <div class=highlight><pre><span></span><code><span class=cp>#undef JSON_NO_SIMD</span>
</code></pre></div> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <div class="admonition note"> <p class=admonition-title>Which instructions are used</p> <ul> <li><strong>x86-64:</strong> SSE2, which every x86-64 CPU has, finds the end of runs of plain string characters 16 bytes at a time and writes the digits of floating-point numbers. The <abbr title="Unicode Transformation Format">UTF</abbr>-8 check of non-<abbr title="American Standard Code for Information Interchange">ASCII</abbr> text needs SSSE3, which is not part of x86-64: it is compiled for SSSE3 with a function attribute and used when the CPU has SSSE3 (every x86-64 CPU since about 2011), else the portable check. Code compiled for SSSE3 anyway (e.g., with <code>-mssse3</code> or <code>-march=native</code>) skips this check of the CPU. 32-bit x86 uses SSE2 for strings when the compiler targets it.</li> <li><strong>AArch64:</strong> NEON, which every 64-bit Arm CPU has, checks <abbr title="Unicode Transformation Format">UTF</abbr>-8 text and long runs of plain string characters 16 bytes at a time, and writes the digits of floating-point numbers. With <abbr title="Microsoft Visual C++">MSVC</abbr>, only the floating-point digits use NEON.</li> <li><strong>Other targets:</strong> portable code only.</li> </ul> <p>Strings are only scanned this way for contiguous input and for the characters a <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>istream</span></code> holds in its stream buffer (see <a href=../json_disable_stream_bulk_scan/ ><code>JSON_DISABLE_STREAM_BULK_SCAN</code></a>); other inputs are read one character at a time.</p> </div> <div class="admonition note"> <p class=admonition-title>Interaction with <code>JSON_USE_SIMDUTF</code></p> <p>With <a href=../json_use_simdutf/ ><code>JSON_USE_SIMDUTF</code></a>, runs of string characters are first validated by simdutf; the code described here is used for what simdutf does not accept, so that errors are reported at the same position. <code>JSON_NO_SIMD</code> does not affect simdutf.</p> </div> <div class="admonition note"> <p class=admonition-title>ABI compatibility</p> <p>The macro selects between two definitions of the library's internal scanning and formatting functions. Whether it is defined is encoded in the <a href=../../../features/namespace/ >namespace</a> (tag <code>_ns</code>), resulting in distinct symbol names. Translation units compiled with and without it can therefore be linked into the same program without One Definition Rule (ODR) violations, but they cannot exchange instances of library types.</p> </div> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example: switching off vector instructions</summary> <p>The program parses and serializes the same values with and without the macro:</p> <div class=highlight><pre><span></span><code><span class=cp>#define JSON_NO_SIMD</span>
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/macros/json_no_simd/" rel="canonical"><link href=../json_no_io/ rel=prev><link href=../json_no_thread_local/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>JSON_NO_SIMD - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new URL("../../..",location),__md_hash=e=>[...e].reduce(((e,_)=>(e<<5)-e+_.charCodeAt(0)),0),__md_get=(e,_=localStorage,t=__md_scope)=>JSON.parse(_.getItem(t.pathname+"."+e)),__md_set=(e,_,t=localStorage,a=__md_scope)=>{try{t.setItem(a.pathname+"."+e,JSON.stringify(_))}catch(e){}}</script></head> <body dir=ltr data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo> <input class=md-toggle data-md-toggle=drawer type=checkbox id=__drawer autocomplete=off> <input class=md-toggle data-md-toggle=search type=checkbox id=__search autocomplete=off> <label class=md-overlay for=__drawer></label> <div data-md-component=skip> <a href=#json_no_simd class=md-skip> Skip to content </a> </div> <div data-md-component=announce> </div> <header class=md-header data-md-component=header> <nav class="md-header__inner md-grid" aria-label=Header> <a href=../../.. title="JSON for Modern C++" class="md-header__button md-logo" aria-label="JSON for Modern C++" data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> JSON_NO_SIMD </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark mode" type=radio name=__palette id=__palette_0> <label class="md-header__button md-icon" title="Switch to dark mode" for=__palette_1 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a4 4 0 0 0-4 4 4 4 0 0 0 4 4 4 4 0 0 0 4-4 4 4 0 0 0-4-4m0 10a6 6 0 0 1-6-6 6 6 0 0 1 6-6 6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> <input class=md-option data-md-color-media="(prefers-color-scheme: dark)" data-md-color-scheme=slate data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to light mode" type=radio name=__palette id=__palette_1> <label class="md-header__button md-icon" title="Switch to light mode" for=__palette_0 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 18c-.89 0-1.74-.2-2.5-.55C11.56 16.5 13 14.42 13 12s-1.44-4.5-3.5-5.45C10.26 6.2 11.11 6 12 6a6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.52 6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9.5 5Line truncated
</code></pre></div> <p>When defined, the library uses only portable C++ code where it would otherwise use vector instructions: when scanning strings during parsing, and when writing floating-point numbers during serialization. This includes the parser of <a href=../../basic_json_document/ ><code>basic_json_document</code></a> (<code>&lt;nlohmann/json_view.hpp&gt;</code>).</p> <p>The macro is an escape hatch, for example for toolchains that cannot compile the vector code, for sanitizers or analyzers that do not understand it, or to compare the speed of both variants. It does not change any result: values, exceptions, and error positions are the same either way. Only the speed differs.</p> <h2 id=default-definition>Default definition<a class=headerlink href=#default-definition title="Permanent link">&para;</a></h2> <p>By default, <code class=highlight><span class=n>JSON_NO_SIMD</span></code> is not defined, and vector instructions are used where the target has them.</p> <div class=highlight><pre><span></span><code><span class=cp>#undef JSON_NO_SIMD</span>
</code></pre></div> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <div class="admonition note"> <p class=admonition-title>Which instructions are used</p> <ul> <li><strong>x86-64:</strong> <abbr title="Streaming SIMD Extensions 2">SSE2</abbr>, which every x86-64 <abbr title="Central Processing Unit">CPU</abbr> has, finds the end of runs of plain string characters 16 bytes at a time and writes the digits of floating-point numbers. The <abbr title="Unicode Transformation Format">UTF</abbr>-8 check of non-<abbr title="American Standard Code for Information Interchange">ASCII</abbr> text needs <abbr title="Supplemental Streaming SIMD Extensions 3">SSSE3</abbr>, which is not part of x86-64: it is compiled for <abbr title="Supplemental Streaming SIMD Extensions 3">SSSE3</abbr> with a function attribute and used when the <abbr title="Central Processing Unit">CPU</abbr> has <abbr title="Supplemental Streaming SIMD Extensions 3">SSSE3</abbr> (every x86-64 <abbr title="Central Processing Unit">CPU</abbr> since about 2011), else the portable check. Code compiled for <abbr title="Supplemental Streaming SIMD Extensions 3">SSSE3</abbr> anyway (e.g., with <code>-mssse3</code> or <code>-march=native</code>) skips this check of the <abbr title="Central Processing Unit">CPU</abbr>. 32-bit x86 uses <abbr title="Streaming SIMD Extensions 2">SSE2</abbr> for strings when the compiler targets it.</li> <li><strong><abbr title="64-bit execution state of the Arm architecture">AArch64</abbr>:</strong> <abbr title="Arm SIMD instruction set extension">NEON</abbr>, which every 64-bit Arm <abbr title="Central Processing Unit">CPU</abbr> has, checks <abbr title="Unicode Transformation Format">UTF</abbr>-8 text and long runs of plain string characters 16 bytes at a time, and writes the digits of floating-point numbers. With <abbr title="Microsoft Visual C++">MSVC</abbr>, only the floating-point digits use <abbr title="Arm SIMD instruction set extension">NEON</abbr>.</li> <li><strong>Other targets:</strong> portable code only.</li> </ul> <p>Strings are only scanned this way for contiguous input and for the characters a <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>istream</span></code> holds in its stream buffer (see <a href=../json_disable_stream_bulk_scan/ ><code>JSON_DISABLE_STREAM_BULK_SCAN</code></a>); other inputs are read one character at a time.</p> </div> <div class="admonition note"> <p class=admonition-title>Interaction with <code>JSON_USE_SIMDUTF</code></p> <p>With <a href=../json_use_simdutf/ ><code>JSON_USE_SIMDUTF</code></a>, runs of string characters are first validated by simdutf; the code described here is used for what simdutf does not accept, so that errors are reported at the same position. <code>JSON_NO_SIMD</code> does not affect simdutf.</p> </div> <div class="admonition note"> <p class=admonition-title><abbr title="Application Binary Interface">ABI</abbr> compatibility</p> <p>The macro selects between two definitions of the library's internal scanning and formatting functions. Whether it is defined is encoded in the <a href=../../../features/namespace/ >namespace</a> (tag <code>_ns</code>), resulting in distinct symbol names. Translation units compiled with and without it can therefore be linked into the same program without One Definition Rule (<abbr title="One Definition Rule">ODR</abbr>) violations, but they cannot exchange instances of library types.</p> </div> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example: switching off vector instructions</summary> <p>The program parses and serializes the same values with and without the macro:</p> <div class=highlight><pre><span></span><code><span class=cp>#define JSON_NO_SIMD</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span>
<span class=p>{</span>
<span class=w> </span><span class=k>const</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=n>j</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>json</span><span class=o>::</span><span class=n>parse</span><span class=p>(</span><span class=sa>R</span><span class=s>"</span><span class=dl>(</span><span class=s>{"name": "日本語 text", "pi": 3.141592653589793}</span><span class=dl>)</span><span class=s>"</span><span class=p>);</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>j</span><span class=p>.</span><span class=n>dump</span><span class=p>()</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=sc>'\n'</span><span class=p>;</span><span class=w> </span><span class=c1>// {"name":"日本語 text","pi":3.141592653589793}</span>
<span class=p>}</span>
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../../basic_json/parse/ ><strong>parse</strong></a> - deserialize from a compatible input</li> <li><a href=../../basic_json/dump/ ><strong>dump</strong></a> - serialization</li> <li><a href=../json_use_simdutf/ ><strong>JSON_USE_SIMDUTF</strong></a> - use the simdutf library to accelerate <abbr title="Unicode Transformation Format">UTF</abbr>-8 validation</li> <li><a href=../json_disable_stream_bulk_scan/ ><strong>JSON_DISABLE_STREAM_BULK_SCAN</strong></a> - read a <code>std::istream</code> one character at a time</li> <li><a href=../../../features/parsing/#input-sources-and-performance>Parsing: input sources and performance</a></li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ul> <li>Added in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 21, 2026 18:00:50 UTC">October 21, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 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</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../../basic_json/parse/ ><strong>parse</strong></a> - deserialize from a compatible input</li> <li><a href=../../basic_json/dump/ ><strong>dump</strong></a> - serialization</li> <li><a href=../json_use_simdutf/ ><strong>JSON_USE_SIMDUTF</strong></a> - use the simdutf library to accelerate <abbr title="Unicode Transformation Format">UTF</abbr>-8 validation</li> <li><a href=../json_disable_stream_bulk_scan/ ><strong>JSON_DISABLE_STREAM_BULK_SCAN</strong></a> - read a <code>std::istream</code> one character at a time</li> <li><a href=../../../features/parsing/#input-sources-and-performance>Parsing: input sources and performance</a></li> <li><a href=../../../features/json_view/ >json_view</a> - the zero-copy view, whose parser the macro also affects</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ul> <li>Added in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 26, 2026 19:13:31 UTC">October 26, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 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+3 -2
View File
@@ -4,7 +4,7 @@
#define JSON_NO_SIMD
```
When defined, the library uses only portable C++ code where it would otherwise use vector instructions: when scanning strings during parsing, and when writing floating-point numbers during serialization.
When defined, the library uses only portable C++ code where it would otherwise use vector instructions: when scanning strings during parsing, and when writing floating-point numbers during serialization. This includes the parser of [`basic_json_document`](https://json.nlohmann.me/api/basic_json_document/index.md) (`<nlohmann/json_view.hpp>`).
The macro is an escape hatch, for example for toolchains that cannot compile the vector code, for sanitizers or analyzers that do not understand it, or to compare the speed of both variants. It does not change any result: values, exceptions, and error positions are the same either way. Only the speed differs.
@@ -45,7 +45,7 @@ The program parses and serializes the same values with and without the macro:
#include <iostream>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using nlohmann::json;
int main()
{
@@ -61,6 +61,7 @@ int main()
- [**JSON_USE_SIMDUTF**](https://json.nlohmann.me/api/macros/json_use_simdutf/index.md) - use the simdutf library to accelerate UTF-8 validation
- [**JSON_DISABLE_STREAM_BULK_SCAN**](https://json.nlohmann.me/api/macros/json_disable_stream_bulk_scan/index.md) - read a `std::istream` one character at a time
- [Parsing: input sources and performance](https://json.nlohmann.me/features/parsing/#input-sources-and-performance)
- [json_view](https://json.nlohmann.me/features/json_view/index.md) - the zero-copy view, whose parser the macro also affects
## Version history
+2 -2
View File
@@ -1,6 +1,6 @@
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/macros/json_no_thread_local/" rel="canonical"><link href=../json_no_simd/ rel=prev><link href=../json_precise_stream_position/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>JSON_NO_THREAD_LOCAL - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new 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data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> JSON_NO_THREAD_LOCAL </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo 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</code></pre></div> <p>When defined, the library does not use <code class=highlight><span class=k>thread_local</span></code> storage. This is relevant for the few environments whose toolchain does not support it.</p> <p>Copying a value and comparing two values both descend into the first levels by letting the containers copy or compare themselves, and finish whatever is nested deeper than that without the call stack, so that neither can exhaust the stack however deeply the values are nested. Each counts the levels it has descended into in a <code class=highlight><span class=k>thread_local</span></code> variable, as a counter shared between threads would be raced.</p> <p>Without those counters, no descent can be bounded safely, so objects and arrays are copied and compared without the call stack right away. Both keep working exactly as they do otherwise - the same values come out, the same comparisons hold, and deeply nested values are handled just as safely - but both are slower, because the containers no longer copy or compare themselves. Copying the benchmark documents takes 9% (<code>canada.json</code>) to 34% (<code>twitter.json</code>) longer, and comparing two equal ones 10% (<code>citm_catalog.json</code>) to 90% (<code>canada.json</code>) longer.</p> <h2 id=default-definition>Default definition<a class=headerlink href=#default-definition title="Permanent link">&para;</a></h2> <p>By default, <code class=highlight><span class=n>JSON_NO_THREAD_LOCAL</span></code> is not defined.</p> <div class=highlight><pre><span></span><code><span class=cp>#undef JSON_NO_THREAD_LOCAL</span>
</code></pre></div> <p>The library defines it by itself for Clang targeting MinGW, which does not survive the <code class=highlight><span class=k>thread_local</span></code> storage: copying a value segfaults there, with both old and current Clang versions, while <abbr title="GNU Compiler Collection">GCC</abbr> targeting MinGW is unaffected. Copying and comparing fall back to working without the call stack there, as they do whenever the macro is defined.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The code below forces the library not to use <code class=highlight><span class=k>thread_local</span></code> storage.</p> <div class=highlight><pre><span></span><code><span class=cp>#define JSON_NO_THREAD_LOCAL 1</span>
</code></pre></div> <p>The library defines it by itself for Clang targeting <abbr title="Minimalist GNU for Windows">MinGW</abbr>, which does not survive the <code class=highlight><span class=k>thread_local</span></code> storage: copying a value segfaults there, with both old and current Clang versions, while <abbr title="GNU Compiler Collection">GCC</abbr> targeting <abbr title="Minimalist GNU for Windows">MinGW</abbr> is unaffected. Copying and comparing fall back to working without the call stack there, as they do whenever the macro is defined.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The code below forces the library not to use <code class=highlight><span class=k>thread_local</span></code> storage.</p> <div class=highlight><pre><span></span><code><span class=cp>#define JSON_NO_THREAD_LOCAL 1</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=p>...</span>
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</code></pre></div> <p>Exceptions can be switched off by defining the symbol <code>JSON_NOEXCEPTION</code>. When defining <code>JSON_NOEXCEPTION</code>, <code class=highlight><span class=k>try</span></code> is replaced by <code class=highlight><span class=k>if</span><span class=w> </span><span class=p>(</span><span class=nb>true</span><span class=p>)</span></code>, <code class=highlight><span class=k>catch</span></code> is replaced by <code class=highlight><span class=k>if</span><span class=w> </span><span class=p>(</span><span class=nb>false</span><span class=p>)</span></code>, and <code class=highlight><span class=k>throw</span></code> is replaced by <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>abort</span><span class=p>()</span></code>.</p> <p>The same effect is achieved by setting the compiler flag <code>-fno-exceptions</code>.</p> <h2 id=default-definition>Default definition<a class=headerlink href=#default-definition title="Permanent link">&para;</a></h2> <p>By default, the macro is not defined.</p> <div class=highlight><pre><span></span><code><span class=cp>#undef JSON_NOEXCEPTION</span>
</code></pre></div> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <p>The explanatory <a href="https://en.cppreference.com/w/cpp/error/exception/what"><code>what()</code></a> string of exceptions is not available for <abbr title="Microsoft Visual C++">MSVC</abbr> if exceptions are disabled, see <a href="https://github.com/nlohmann/json/discussions/2824">#2824</a>.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The code below switches off exceptions in the library.</p> <div class=highlight><pre><span></span><code><span class=cp>#define JSON_NOEXCEPTION 1</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
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@@ -94,7 +94,7 @@ The default value is `0` (disabled — existing behavior is preserved).
#include <sstream>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using nlohmann::json;
int main()
{
@@ -115,7 +115,7 @@ The default value is `0` (disabled — existing behavior is preserved).
#include <sstream>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using nlohmann::json;
int main()
{
@@ -1,4 +1,4 @@
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</code></pre></div> <p>When defined to <code>1</code>, <a href=../../operator_gtgt/ ><code>operator&gt;&gt;</code></a> and <a href=../../basic_json/sax_parse/ ><code>sax_parse</code></a> with <code>strict = false</code> leave a <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>istream</span></code> positioned right after the parsed value for every value type. By default, the character that terminates a number is consumed as well.</p> <p>The macro only affects reading from a <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>istream</span></code> when the rest of the stream is not required to be consumed. <a href=../../basic_json/parse/ ><code>parse</code></a>, <a href=../../basic_json/accept/ ><code>accept</code></a>, and all other inputs (strings, iterators, containers, <code class=highlight><span class=kt>FILE</span><span class=o>*</span></code>) are never affected.</p> <h2 id=default-definition>Default definition<a class=headerlink href=#default-definition title="Permanent link">&para;</a></h2> <p>The default value is <code>0</code> (disabled — existing behavior is preserved).</p> <div class=highlight><pre><span></span><code><span class=cp>#define JSON_PRECISE_STREAM_POSITION 0</span>
</code></pre></div> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <div class="admonition note"> <p class=admonition-title>Background</p> <p>A number is the only <abbr title="JavaScript Object Notation">JSON</abbr> value whose end can be detected solely by reading the character that follows it. By default, that character is consumed and not put back, so the stream is left one byte too far after a number, and only after a number:</p> <div class=highlight><pre><span></span><code><span class=n>std</span><span class=o>::</span><span class=n>istringstream</span><span class=w> </span><span class=n>input</span><span class=p>(</span><span class=s>"1true"</span><span class=p>);</span>
<span class=n>json</span><span class=w> </span><span class=n>j</span><span class=p>;</span>
@@ -13,11 +13,11 @@
<span class=n>input</span><span class=w> </span><span class=o>&gt;&gt;</span><span class=w> </span><span class=n>j</span><span class=p>;</span>
<span class=n>std</span><span class=o>::</span><span class=n>getline</span><span class=p>(</span><span class=n>input</span><span class=p>,</span><span class=w> </span><span class=n>line</span><span class=p>);</span><span class=w> </span><span class=c1>// default: "foo"</span>
<span class=w> </span><span class=c1>// with the macro: "" (like after reading an int with &gt;&gt;)</span>
</code></pre></div> <p>In both cases, the behavior with the macro is what you already get today when the value is not a number: <code>"a","b"</code> fails at the <code>,</code>, and <code>std::getline</code> after <code>{}</code> returns an empty string. This macro offers an opt-in path to the consistent behavior ahead of version 4.0.0, where it is planned to become the default.</p> </div> <div class="admonition warning"> <p class=admonition-title>Opt-in only</p> <p>This macro must be defined <strong>before</strong> including <code>&lt;nlohmann/json.hpp&gt;</code>. Defining it after the include has no effect.</p> </div> <div class="admonition note"> <p class=admonition-title>ABI compatibility</p> <p>The value of this macro is encoded in the <a href=../../../features/namespace/ >namespace</a> (tag <code>_psp</code>), resulting in distinct symbol names. Translation units compiled with and without it can therefore be linked into the same program without One Definition Rule (ODR) violations, but they cannot exchange instances of library types.</p> </div> <div class="admonition note"> <p class=admonition-title>Bulk scanning</p> <p>The parser scans the characters in the stream buffer in bulk (see <a href=../json_disable_stream_bulk_scan/ ><code>JSON_DISABLE_STREAM_BULK_SCAN</code></a>), but it never reads ahead. The stream is left at the same position with and without bulk scanning, in both modes of this macro.</p> </div> <div class="admonition tip"> <p class=admonition-title>Workaround without the macro</p> <p>Separate the values in the stream with whitespace. The character consumed after a number is then the separator, and whitespace before the next value is skipped anyway.</p> </div> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example: default behavior (macro not defined)</summary> <p>Without the macro, the character after a number is consumed:</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
</code></pre></div> <p>In both cases, the behavior with the macro is what you already get today when the value is not a number: <code>"a","b"</code> fails at the <code>,</code>, and <code>std::getline</code> after <code>{}</code> returns an empty string. This macro offers an opt-in path to the consistent behavior ahead of version 4.0.0, where it is planned to become the default.</p> </div> <div class="admonition warning"> <p class=admonition-title>Opt-in only</p> <p>This macro must be defined <strong>before</strong> including <code>&lt;nlohmann/json.hpp&gt;</code>. Defining it after the include has no effect.</p> </div> <div class="admonition note"> <p class=admonition-title><abbr title="Application Binary Interface">ABI</abbr> compatibility</p> <p>The value of this macro is encoded in the <a href=../../../features/namespace/ >namespace</a> (tag <code>_psp</code>), resulting in distinct symbol names. Translation units compiled with and without it can therefore be linked into the same program without One Definition Rule (<abbr title="One Definition Rule">ODR</abbr>) violations, but they cannot exchange instances of library types.</p> </div> <div class="admonition note"> <p class=admonition-title>Bulk scanning</p> <p>The parser scans the characters in the stream buffer in bulk (see <a href=../json_disable_stream_bulk_scan/ ><code>JSON_DISABLE_STREAM_BULK_SCAN</code></a>), but it never reads ahead. The stream is left at the same position with and without bulk scanning, in both modes of this macro.</p> </div> <div class="admonition tip"> <p class=admonition-title>Workaround without the macro</p> <p>Separate the values in the stream with whitespace. The character consumed after a number is then the separator, and whitespace before the next value is skipped anyway.</p> </div> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example: default behavior (macro not defined)</summary> <p>Without the macro, the character after a number is consumed:</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;sstream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span>
<span class=p>{</span>
@@ -31,7 +31,7 @@
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;sstream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span>
<span class=p>{</span>
@@ -40,4 +40,4 @@
<span class=w> </span><span class=n>input</span><span class=w> </span><span class=o>&gt;&gt;</span><span class=w> </span><span class=n>j1</span><span class=p>;</span><span class=w> </span><span class=c1>// j1 == 1</span>
<span class=w> </span><span class=n>input</span><span class=w> </span><span class=o>&gt;&gt;</span><span class=w> </span><span class=n>j2</span><span class=p>;</span><span class=w> </span><span class=c1>// j2 == true</span>
<span class=p>}</span>
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../../operator_gtgt/ ><strong>operator&gt;&gt;</strong></a> - deserialize from stream</li> <li><a href=../../basic_json/sax_parse/ ><strong>sax_parse</strong></a> - generate <abbr title="Simple API for XML">SAX</abbr> events</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ul> <li>Added in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</li> <li>Planned to become the default (with the macro removed) in version 4.0.0.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 19, 2026 20:00:58 UTC">October 19, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 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</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../../operator_gtgt/ ><strong>operator&gt;&gt;</strong></a> - deserialize from stream</li> <li><a href=../../basic_json/sax_parse/ ><strong>sax_parse</strong></a> - generate <abbr title="Simple API for XML">SAX</abbr> events</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ul> <li>Added in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</li> <li>Planned to become the default (with the macro removed) in version 4.0.0.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 25, 2026 11:07:51 UTC">October 25, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 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@@ -77,7 +77,7 @@ Without the macro, the character after a number is consumed:
#include <sstream>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using nlohmann::json;
int main()
{
@@ -98,7 +98,7 @@ With the macro, the stream is positioned right after the number:
#include <sstream>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using nlohmann::json;
int main()
{
@@ -1,6 +1,6 @@
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/macros/json_skip_library_version_check/" rel="canonical"><link href=../json_precise_stream_position/ rel=prev><link href=../json_skip_unsupported_compiler_check/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>JSON_SKIP_LIBRARY_VERSION_CHECK - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new 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<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/macros/json_skip_library_version_check/" rel="canonical"><link href=../json_precise_stream_position/ rel=prev><link href=../json_skip_unsupported_compiler_check/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>JSON_SKIP_LIBRARY_VERSION_CHECK - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new 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</code></pre></div> <p>When defined, the library will not create a compiler warning when a different version of the library was already included.</p> <h2 id=default-definition>Default definition<a class=headerlink href=#default-definition title="Permanent link">&para;</a></h2> <p>By default, the macro is not defined.</p> <div class=highlight><pre><span></span><code><span class=cp>#undef JSON_SKIP_LIBRARY_VERSION_CHECK</span>
</code></pre></div> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <div class="admonition danger"> <p class=admonition-title>ABI compatibility</p> <p>Mixing different library versions in the same code can be a problem as the different versions may not be ABI compatible.</p> </div> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example: switch off the version check</summary> <p>The code below switches off the warning about including a different version of the library.</p> <div class=highlight><pre><span></span><code><span class=cp>#define JSON_SKIP_LIBRARY_VERSION_CHECK 1</span>
</code></pre></div> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <div class="admonition danger"> <p class=admonition-title><abbr title="Application Binary Interface">ABI</abbr> compatibility</p> <p>Mixing different library versions in the same code can be a problem as the different versions may not be <abbr title="Application Binary Interface">ABI</abbr> compatible.</p> </div> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example: switch off the version check</summary> <p>The code below switches off the warning about including a different version of the library.</p> <div class=highlight><pre><span></span><code><span class=cp>#define JSON_SKIP_LIBRARY_VERSION_CHECK 1</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=p>...</span>
@@ -1,4 +1,4 @@
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</code></pre></div> <p>When defined, the library will not create a compile error when a known unsupported compiler is detected. This allows using the library with compilers that do not fully support C++11 and may only work if unsupported features are not used.</p> <h2 id=default-definition>Default definition<a class=headerlink href=#default-definition title="Permanent link">&para;</a></h2> <p>By default, the macro is not defined.</p> <div class=highlight><pre><span></span><code><span class=cp>#undef JSON_SKIP_UNSUPPORTED_COMPILER_CHECK</span>
</code></pre></div> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The code below switches off the check whether the compiler is supported.</p> <div class=highlight><pre><span></span><code><span class=cp>#define JSON_SKIP_UNSUPPORTED_COMPILER_CHECK 1</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
+2 -2
View File
@@ -64,7 +64,7 @@ The default value is `0` (disabled, the behavior of version 3.12.0 and earlier i
```cpp
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using nlohmann::json;
int main()
{
@@ -81,7 +81,7 @@ The default value is `0` (disabled, the behavior of version 3.12.0 and earlier i
#define JSON_STRICT_BINARY_UTF8 1
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using nlohmann::json;
int main()
{
@@ -1,8 +1,8 @@
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</code></pre></div> <p>When defined to <code>1</code>, the <code>error_handler</code> parameter of the binary writers <a href=../../basic_json/to_cbor/ ><code>to_cbor</code></a>, <a href=../../basic_json/to_ubjson/ ><code>to_ubjson</code></a>, <a href=../../basic_json/to_bjdata/ ><code>to_bjdata</code></a>, and <a href=../../basic_json/to_bson/ ><code>to_bson</code></a> defaults to <a href=../../basic_json/error_handler_t/ ><code>error_handler_t::strict</code></a> instead of <code>error_handler_t::keep</code>. These writers then check every string value and object key for valid <abbr title="Unicode Transformation Format">UTF</abbr>-8 and throw <a href=../../../home/exceptions/#jsonexceptiontype_error316><code>type_error.316</code></a> for ill-formed <abbr title="Unicode Transformation Format">UTF</abbr>-8, like <a href=../../basic_json/dump/ ><code>dump</code></a> does. Without it, they write the bytes unchanged. An <code>error_handler</code> passed explicitly always takes precedence.</p> <p>The macro does not affect:</p> <ul> <li><a href=../../basic_json/to_msgpack/ ><code>to_msgpack</code></a>: the MessagePack specification allows a <code>str</code> value to contain bytes that are not valid <abbr title="Unicode Transformation Format">UTF</abbr>-8, so its <code>error_handler</code> always defaults to <code>keep</code>.</li> <li><a href=../../basic_json/to_bon8/ ><code>to_bon8</code></a>: <abbr title="Binary Object Notation 8">BON8</abbr> always checks, because the <abbr title="Unicode Transformation Format">UTF</abbr>-8 lead bytes mark where a string ends.</li> <li>The binary readers (<a href=../../basic_json/from_cbor/ ><code>from_cbor</code></a>, <a href=../../basic_json/from_msgpack/ ><code>from_msgpack</code></a>, <a href=../../basic_json/from_ubjson/ ><code>from_ubjson</code></a>, <a href=../../basic_json/from_bjdata/ ><code>from_bjdata</code></a>, <a href=../../basic_json/from_bson/ ><code>from_bson</code></a>): none of these formats requires a decoder to reject ill-formed <abbr title="Unicode Transformation Format">UTF</abbr>-8, so by default they return the bytes unchanged (<code>error_handler_t::keep</code>), independent of this macro. Pass an <code>error_handler</code> argument explicitly to validate or sanitize the strings they read.</li> <li><a href=../../basic_json/from_bon8/ ><code>from_bon8</code></a>: <abbr title="Binary Object Notation 8">BON8</abbr> always validates, because the <abbr title="Unicode Transformation Format">UTF</abbr>-8 lead bytes mark where a string ends.</li> </ul> <h2 id=default-definition>Default definition<a class=headerlink href=#default-definition title="Permanent link">&para;</a></h2> <p>The default value is <code>0</code> (disabled, the behavior of version 3.12.0 and earlier is preserved).</p> <div class=highlight><pre><span></span><code><span class=cp>#define JSON_STRICT_BINARY_UTF8 0</span>
</code></pre></div> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <div class="admonition note"> <p class=admonition-title>Background</p> <p><abbr title="Concise Binary Object Representation">CBOR</abbr>, <abbr title="Universal Binary JSON">UBJSON</abbr>, <abbr title="Binary JData">BJData</abbr>, and <abbr title="Binary JSON">BSON</abbr> all require strings to be <abbr title="Unicode Transformation Format">UTF</abbr>-8. Up to version 3.12.0, the writers did not check this, so they could produce output that other decoders reject. Checking by default would break code that stores other encodings (for instance <abbr title="International Organization for Standardization">ISO</abbr> 8859-1) in a string and only ever writes it to a binary format. You can pass <code>error_handler_t::strict</code> to each call, or use this macro to check by default ahead of version 4.0.0, where <code>strict</code> is planned to become the default (see <a href="https://github.com/nlohmann/json/issues/5529">#5529</a> and <a href="https://github.com/nlohmann/json/issues/5651">#5651</a>).</p> </div> <div class="admonition warning"> <p class=admonition-title>Opt-in only</p> <p>This macro must be defined <strong>before</strong> including <code>&lt;nlohmann/json.hpp&gt;</code>. Defining it after the include has no effect.</p> </div> <div class="admonition note"> <p class=admonition-title>ABI compatibility</p> <p>The value of this macro is encoded in the <a href=../../../features/namespace/ >namespace</a> (tag <code>_sbu8</code>), resulting in distinct symbol names. Translation units compiled with and without it can therefore be linked into the same program without One Definition Rule (ODR) violations, but they cannot exchange instances of library types.</p> </div> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example: default behavior (macro not defined)</summary> <p>Without the macro, the bytes are written unchanged:</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
</code></pre></div> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <div class="admonition note"> <p class=admonition-title>Background</p> <p><abbr title="Concise Binary Object Representation">CBOR</abbr>, <abbr title="Universal Binary JSON">UBJSON</abbr>, <abbr title="Binary JData">BJData</abbr>, and <abbr title="Binary JSON">BSON</abbr> all require strings to be <abbr title="Unicode Transformation Format">UTF</abbr>-8. Up to version 3.12.0, the writers did not check this, so they could produce output that other decoders reject. Checking by default would break code that stores other encodings (for instance <abbr title="International Organization for Standardization">ISO</abbr> 8859-1) in a string and only ever writes it to a binary format. You can pass <code>error_handler_t::strict</code> to each call, or use this macro to check by default ahead of version 4.0.0, where <code>strict</code> is planned to become the default (see <a href="https://github.com/nlohmann/json/issues/5529">#5529</a> and <a href="https://github.com/nlohmann/json/issues/5651">#5651</a>).</p> </div> <div class="admonition warning"> <p class=admonition-title>Opt-in only</p> <p>This macro must be defined <strong>before</strong> including <code>&lt;nlohmann/json.hpp&gt;</code>. Defining it after the include has no effect.</p> </div> <div class="admonition note"> <p class=admonition-title><abbr title="Application Binary Interface">ABI</abbr> compatibility</p> <p>The value of this macro is encoded in the <a href=../../../features/namespace/ >namespace</a> (tag <code>_sbu8</code>), resulting in distinct symbol names. Translation units compiled with and without it can therefore be linked into the same program without One Definition Rule (<abbr title="One Definition Rule">ODR</abbr>) violations, but they cannot exchange instances of library types.</p> </div> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example: default behavior (macro not defined)</summary> <p>Without the macro, the bytes are written unchanged:</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span>
<span class=p>{</span>
@@ -12,11 +12,11 @@
</code></pre></div> </details> <details class=example> <summary>Example: opt-in check (macro defined to 1)</summary> <p>With the macro, ill-formed <abbr title="Unicode Transformation Format">UTF</abbr>-8 is rejected:</p> <div class=highlight><pre><span></span><code><span class=cp>#define JSON_STRICT_BINARY_UTF8 1</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span>
<span class=p>{</span>
<span class=w> </span><span class=k>auto</span><span class=w> </span><span class=n>v</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>json</span><span class=o>::</span><span class=n>to_cbor</span><span class=p>(</span><span class=n>json</span><span class=p>(</span><span class=s>"</span><span class=se>\xFF</span><span class=s>"</span><span class=p>));</span>
<span class=w> </span><span class=c1>// throws type_error.316: invalid UTF-8 byte at index 0: 0xFF</span>
<span class=p>}</span>
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../../basic_json/to_cbor/ ><strong>to_cbor</strong></a> - create a <abbr title="Concise Binary Object Representation">CBOR</abbr> serialization of a <abbr title="JavaScript Object Notation">JSON</abbr> value</li> <li><a href=../../basic_json/to_ubjson/ ><strong>to_ubjson</strong></a> - create a <abbr title="Universal Binary JSON">UBJSON</abbr> serialization of a <abbr title="JavaScript Object Notation">JSON</abbr> value</li> <li><a href=../../basic_json/to_bjdata/ ><strong>to_bjdata</strong></a> - create a <abbr title="Binary JData">BJData</abbr> serialization of a <abbr title="JavaScript Object Notation">JSON</abbr> value</li> <li><a href=../../basic_json/to_bson/ ><strong>to_bson</strong></a> - create a <abbr title="Binary JSON">BSON</abbr> serialization of a <abbr title="JavaScript Object Notation">JSON</abbr> value</li> <li><a href=../../basic_json/error_handler_t/ ><strong>error_handler_t</strong></a> - how <a href=../../basic_json/dump/ ><code>dump</code></a> treats ill-formed <abbr title="Unicode Transformation Format">UTF</abbr>-8</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ul> <li>Added in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</li> <li>Planned to become the default (with the macro removed) in version 4.0.0.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 11, 2026 06:21:51 UTC">October 11, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 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</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../../basic_json/to_cbor/ ><strong>to_cbor</strong></a> - create a <abbr title="Concise Binary Object Representation">CBOR</abbr> serialization of a <abbr title="JavaScript Object Notation">JSON</abbr> value</li> <li><a href=../../basic_json/to_ubjson/ ><strong>to_ubjson</strong></a> - create a <abbr title="Universal Binary JSON">UBJSON</abbr> serialization of a <abbr title="JavaScript Object Notation">JSON</abbr> value</li> <li><a href=../../basic_json/to_bjdata/ ><strong>to_bjdata</strong></a> - create a <abbr title="Binary JData">BJData</abbr> serialization of a <abbr title="JavaScript Object Notation">JSON</abbr> value</li> <li><a href=../../basic_json/to_bson/ ><strong>to_bson</strong></a> - create a <abbr title="Binary JSON">BSON</abbr> serialization of a <abbr title="JavaScript Object Notation">JSON</abbr> value</li> <li><a href=../../basic_json/error_handler_t/ ><strong>error_handler_t</strong></a> - how <a href=../../basic_json/dump/ ><code>dump</code></a> treats ill-formed <abbr title="Unicode Transformation Format">UTF</abbr>-8</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ul> <li>Added in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</li> <li>Planned to become the default (with the macro removed) in version 4.0.0.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 25, 2026 11:07:51 UTC">October 25, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 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+2 -2
View File
@@ -44,7 +44,7 @@ Without the macro, the bytes are written unchanged:
```
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using nlohmann::json;
int main()
{
@@ -61,7 +61,7 @@ With the macro, ill-formed UTF-8 is rejected:
#define JSON_STRICT_BINARY_UTF8 1
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using nlohmann::json;
int main()
{
+2 -2
View File
@@ -92,7 +92,7 @@ The default value is `0` (disabled — existing behavior is preserved).
```cpp
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using nlohmann::json;
int main()
{
@@ -109,7 +109,7 @@ The default value is `0` (disabled — existing behavior is preserved).
#define JSON_STRICT_NUL_HANDLING 1
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using nlohmann::json;
int main()
{
@@ -1,22 +1,22 @@
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/macros/json_strict_nul_handling/" rel="canonical"><link href=../json_strict_binary_utf8/ rel=prev><link href=../json_use_global_udls/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>JSON_STRICT_NUL_HANDLING - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new 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</code></pre></div> <p>When defined to <code>1</code>, a <code>'\0'</code> (NUL) byte in <abbr title="JavaScript Object Notation">JSON</abbr> text input is rejected with <code>parse_error.101</code>, like any other unexpected byte, instead of being silently treated as end of input.</p> <p>The macro only affects the <abbr title="JavaScript Object Notation">JSON</abbr> text parser (<a href=../../basic_json/parse/ ><code>parse</code></a>, <a href=../../basic_json/accept/ ><code>accept</code></a>, <a href=../../basic_json/sax_parse/ ><code>sax_parse</code></a>, and <a href=../../operator_gtgt/ ><code>operator&gt;&gt;</code></a>). There are three cases where a NUL byte is still not rejected:</p> <ul> <li>The binary formats (<a href=../../basic_json/from_bjdata/ ><code>from_bjdata</code></a>, <a href=../../basic_json/from_bon8/ ><code>from_bon8</code></a>, <a href=../../basic_json/from_bson/ ><code>from_bson</code></a>, <a href=../../basic_json/from_cbor/ ><code>from_cbor</code></a>, <a href=../../basic_json/from_msgpack/ ><code>from_msgpack</code></a>, <a href=../../basic_json/from_ubjson/ ><code>from_ubjson</code></a>) are never affected: there, <code>0x00</code> is ordinary data.</li> <li>A bare <code>const char*</code> pointer has no length of its own, so its length is still determined with <code>strlen()</code>. The first NUL byte therefore still marks the end of the input, and nothing after it is read.</li> <li>One trailing <code>'\0'</code> at the end of a <code>char</code>, <code>wchar_t</code>, <code>char16_t</code>, <code>char32_t</code>, or (C++20) <code>char8_t</code> array (e.g., a string literal) is trimmed; see the warning below.</li> </ul> <h2 id=default-definition>Default definition<a class=headerlink href=#default-definition title="Permanent link">&para;</a></h2> <p>The default value is <code>0</code> (disabled — existing behavior is preserved).</p> <div class=highlight><pre><span></span><code><span class=cp>#define JSON_STRICT_NUL_HANDLING 0</span>
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</code></pre></div> <p>When defined to <code>1</code>, a <code>'\0'</code> (<abbr title="Null character (U+0000, byte value 0)">NUL</abbr>) byte in <abbr title="JavaScript Object Notation">JSON</abbr> text input is rejected with <code>parse_error.101</code>, like any other unexpected byte, instead of being silently treated as end of input.</p> <p>The macro only affects the <abbr title="JavaScript Object Notation">JSON</abbr> text parser (<a href=../../basic_json/parse/ ><code>parse</code></a>, <a href=../../basic_json/accept/ ><code>accept</code></a>, <a href=../../basic_json/sax_parse/ ><code>sax_parse</code></a>, and <a href=../../operator_gtgt/ ><code>operator&gt;&gt;</code></a>). There are three cases where a <abbr title="Null character (U+0000, byte value 0)">NUL</abbr> byte is still not rejected:</p> <ul> <li>The binary formats (<a href=../../basic_json/from_bjdata/ ><code>from_bjdata</code></a>, <a href=../../basic_json/from_bon8/ ><code>from_bon8</code></a>, <a href=../../basic_json/from_bson/ ><code>from_bson</code></a>, <a href=../../basic_json/from_cbor/ ><code>from_cbor</code></a>, <a href=../../basic_json/from_msgpack/ ><code>from_msgpack</code></a>, <a href=../../basic_json/from_ubjson/ ><code>from_ubjson</code></a>) are never affected: there, <code>0x00</code> is ordinary data.</li> <li>A bare <code>const char*</code> pointer has no length of its own, so its length is still determined with <code>strlen()</code>. The first <abbr title="Null character (U+0000, byte value 0)">NUL</abbr> byte therefore still marks the end of the input, and nothing after it is read.</li> <li>One trailing <code>'\0'</code> at the end of a <code>char</code>, <code>wchar_t</code>, <code>char16_t</code>, <code>char32_t</code>, or (C++20) <code>char8_t</code> array (e.g., a string literal) is trimmed; see the warning below.</li> </ul> <h2 id=default-definition>Default definition<a class=headerlink href=#default-definition title="Permanent link">&para;</a></h2> <p>The default value is <code>0</code> (disabled — existing behavior is preserved).</p> <div class=highlight><pre><span></span><code><span class=cp>#define JSON_STRICT_NUL_HANDLING 0</span>
</code></pre></div> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <div class="admonition note"> <p class=admonition-title>Background</p> <p>By default, a <code>'\0'</code> byte anywhere in the input is treated the same as the real end of the input, rather than as an ordinary (and, outside of a string, invalid) byte. Everything from that byte onward is silently ignored, without a parse error - including further, otherwise well-formed <abbr title="JavaScript Object Notation">JSON</abbr>:</p> <div class=highlight><pre><span></span><code><span class=n>json</span><span class=o>::</span><span class=n>parse</span><span class=p>(</span><span class=n>std</span><span class=o>::</span><span class=n>string</span><span class=p>(</span><span class=s>"123"</span><span class=p>)</span><span class=w> </span><span class=o>+</span><span class=w> </span><span class=sc>'\0'</span><span class=p>);</span><span class=w> </span><span class=c1>// == 123, no error</span>
<span class=n>json</span><span class=o>::</span><span class=n>parse</span><span class=p>(</span><span class=n>std</span><span class=o>::</span><span class=n>string</span><span class=p>(</span><span class=s>"123"</span><span class=p>)</span><span class=w> </span><span class=o>+</span><span class=w> </span><span class=sc>'\0'</span><span class=w> </span><span class=o>+</span><span class=w> </span><span class=s>"true"</span><span class=p>);</span><span class=w> </span><span class=c1>// == 123, the "true" is silently ignored too</span>
</code></pre></div> <p>This falls out of the same convention used when no explicit input length is given at all: parsing from a <code>const char*</code> already stops at the first NUL byte via <code>strlen()</code>, since a bare pointer has no length of its own. The library applies that same NUL-terminated-C-string convention uniformly, rather than only when a length is genuinely unavailable - so a <code>std::string</code>, iterator range, or container whose content happens to include a NUL byte is affected the same way a raw <code>const char*</code> would be (see the <a href=../../../home/faq/#nul-bytes-in-the-input><abbr title="Frequently Asked Questions">FAQ</abbr> entry</a> for a fuller explanation).</p> <p>This was not fixed unconditionally, because doing so is backwards-incompatible for any caller who happens to depend on the current behavior - even unknowingly, for instance because their input already contains trailing padding they never noticed was being discarded (see <a href="https://github.com/nlohmann/json/issues/5530">#5530</a>). This macro instead offers an opt-in path to the corrected behavior ahead of version 4.0.0, where it is planned to become the default.</p> </div> <div class="admonition warning"> <p class=admonition-title>Opt-in only</p> <p>This macro must be defined <strong>before</strong> including <code>&lt;nlohmann/json.hpp&gt;</code>. Defining it after the include has no effect.</p> <p>Enabling it also changes how an array of a text-literal element type (<code>char</code>, <code>wchar_t</code>, <code>char16_t</code>, <code>char32_t</code>, or, since C++20, <code>char8_t</code> - including a string literal, e.g. <code>json::parse("123")</code> or <code>json::parse(L"123")</code>) is read: such an array normally carries a trailing <code>'\0'</code> contributed by the compiler, not by the source text. With this macro enabled, that one trailing element is trimmed if present so that parsing a string literal keeps working, for any of these character types; every other element in the array - including any <code>'\0'</code> that is not the very last element - is read as real data and rejected like any other unexpected byte. Arrays of any other element type (<code>unsigned char</code>, <code>std::uint8_t</code>, ...), as used for <abbr title="Concise Binary Object Representation">CBOR</abbr> or MessagePack, are never affected by this trimming; their full extent - including a genuine trailing <code>0x00</code> - is always preserved, in both states of this macro.</p> </div> <div class="admonition note"> <p class=admonition-title>ABI compatibility</p> <p>The value of this macro is encoded in the <a href=../../../features/namespace/ >namespace</a> (tag <code>_snul</code>), resulting in distinct symbol names. Translation units compiled with and without it can therefore be linked into the same program without One Definition Rule (ODR) violations, but they cannot exchange instances of library types.</p> </div> <div class="admonition tip"> <p class=admonition-title>Workaround without the macro</p> <p>To reject a NUL byte without enabling this macro, trim your input yourself before calling <code>parse()</code>:</p> <div class=highlight><pre><span></span><code><span class=n>s</span><span class=p>.</span><span class=n>resize</span><span class=p>(</span><span class=n>s</span><span class=p>.</span><span class=n>find</span><span class=p>(</span><span class=sc>'\0'</span><span class=p>));</span><span class=w> </span><span class=c1>// drop everything from the first NUL onward, if any</span>
</code></pre></div> <p>This falls out of the same convention used when no explicit input length is given at all: parsing from a <code>const char*</code> already stops at the first <abbr title="Null character (U+0000, byte value 0)">NUL</abbr> byte via <code>strlen()</code>, since a bare pointer has no length of its own. The library applies that same <abbr title="Null character (U+0000, byte value 0)">NUL</abbr>-terminated-C-string convention uniformly, rather than only when a length is genuinely unavailable - so a <code>std::string</code>, iterator range, or container whose content happens to include a <abbr title="Null character (U+0000, byte value 0)">NUL</abbr> byte is affected the same way a raw <code>const char*</code> would be (see the <a href=../../../home/faq/#nul-bytes-in-the-input><abbr title="Frequently Asked Questions">FAQ</abbr> entry</a> for a fuller explanation).</p> <p>This was not fixed unconditionally, because doing so is backwards-incompatible for any caller who happens to depend on the current behavior - even unknowingly, for instance because their input already contains trailing padding they never noticed was being discarded (see <a href="https://github.com/nlohmann/json/issues/5530">#5530</a>). This macro instead offers an opt-in path to the corrected behavior ahead of version 4.0.0, where it is planned to become the default.</p> </div> <div class="admonition warning"> <p class=admonition-title>Opt-in only</p> <p>This macro must be defined <strong>before</strong> including <code>&lt;nlohmann/json.hpp&gt;</code>. Defining it after the include has no effect.</p> <p>Enabling it also changes how an array of a text-literal element type (<code>char</code>, <code>wchar_t</code>, <code>char16_t</code>, <code>char32_t</code>, or, since C++20, <code>char8_t</code> - including a string literal, e.g. <code>json::parse("123")</code> or <code>json::parse(L"123")</code>) is read: such an array normally carries a trailing <code>'\0'</code> contributed by the compiler, not by the source text. With this macro enabled, that one trailing element is trimmed if present so that parsing a string literal keeps working, for any of these character types; every other element in the array - including any <code>'\0'</code> that is not the very last element - is read as real data and rejected like any other unexpected byte. Arrays of any other element type (<code>unsigned char</code>, <code>std::uint8_t</code>, ...), as used for <abbr title="Concise Binary Object Representation">CBOR</abbr> or MessagePack, are never affected by this trimming; their full extent - including a genuine trailing <code>0x00</code> - is always preserved, in both states of this macro.</p> </div> <div class="admonition note"> <p class=admonition-title><abbr title="Application Binary Interface">ABI</abbr> compatibility</p> <p>The value of this macro is encoded in the <a href=../../../features/namespace/ >namespace</a> (tag <code>_snul</code>), resulting in distinct symbol names. Translation units compiled with and without it can therefore be linked into the same program without One Definition Rule (<abbr title="One Definition Rule">ODR</abbr>) violations, but they cannot exchange instances of library types.</p> </div> <div class="admonition tip"> <p class=admonition-title>Workaround without the macro</p> <p>To reject a <abbr title="Null character (U+0000, byte value 0)">NUL</abbr> byte without enabling this macro, trim your input yourself before calling <code>parse()</code>:</p> <div class=highlight><pre><span></span><code><span class=n>s</span><span class=p>.</span><span class=n>resize</span><span class=p>(</span><span class=n>s</span><span class=p>.</span><span class=n>find</span><span class=p>(</span><span class=sc>'\0'</span><span class=p>));</span><span class=w> </span><span class=c1>// drop everything from the first NUL onward, if any</span>
<span class=n>json</span><span class=o>::</span><span class=n>parse</span><span class=p>(</span><span class=n>s</span><span class=p>);</span>
</code></pre></div> </div> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example: default behavior (macro not defined)</summary> <p>Without the macro, a NUL byte silently ends parsing at that point:</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
</code></pre></div> </div> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example: default behavior (macro not defined)</summary> <p>Without the macro, a <abbr title="Null character (U+0000, byte value 0)">NUL</abbr> byte silently ends parsing at that point:</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span>
<span class=p>{</span>
<span class=w> </span><span class=n>json</span><span class=w> </span><span class=n>j</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>json</span><span class=o>::</span><span class=n>parse</span><span class=p>(</span><span class=n>std</span><span class=o>::</span><span class=n>string</span><span class=p>(</span><span class=s>"123"</span><span class=p>)</span><span class=w> </span><span class=o>+</span><span class=w> </span><span class=sc>'\0'</span><span class=w> </span><span class=o>+</span><span class=w> </span><span class=s>"true"</span><span class=p>);</span>
<span class=w> </span><span class=c1>// j is 123 -- the '\0' and everything after it is silently ignored</span>
<span class=p>}</span>
</code></pre></div> </details> <details class=example> <summary>Example: opt-in strict handling (macro defined to 1)</summary> <p>With the macro, a NUL byte is rejected like any other unexpected byte:</p> <div class=highlight><pre><span></span><code><span class=cp>#define JSON_STRICT_NUL_HANDLING 1</span>
</code></pre></div> </details> <details class=example> <summary>Example: opt-in strict handling (macro defined to 1)</summary> <p>With the macro, a <abbr title="Null character (U+0000, byte value 0)">NUL</abbr> byte is rejected like any other unexpected byte:</p> <div class=highlight><pre><span></span><code><span class=cp>#define JSON_STRICT_NUL_HANDLING 1</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span>
<span class=p>{</span>
@@ -27,4 +27,4 @@
<span class=w> </span><span class=n>json</span><span class=w> </span><span class=n>ok</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>json</span><span class=o>::</span><span class=n>parse</span><span class=p>(</span><span class=s>"123"</span><span class=p>);</span>
<span class=w> </span><span class=c1>// ok is 123 -- parsing from a string literal still works</span>
<span class=p>}</span>
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../../../integration/cmake/#json_strictnulhandling><span class=twemoji><svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M11.769.066.067 23.206l12.76-10.843zm11.438 23.868L7.471 17.587 0 23.934zm.793-.198L12.298.463l1.719 19.24zM12.893 12.959l-5.025 4.298 5.62 2.248z"/></svg></span> JSON_StrictNulHandling</a> - CMake option to control the macro</li> <li><a href=../../../home/faq/#nul-bytes-in-the-input><abbr title="Frequently Asked Questions">FAQ</abbr>: NUL bytes in the input</a></li> <li><a href=../../basic_json/parse/ ><strong>parse</strong></a> - deserialize from a compatible input</li> <li><a href=../../basic_json/accept/ ><strong>accept</strong></a> - check if the input is valid <abbr title="JavaScript Object Notation">JSON</abbr></li> <li><a href=../../operator_gtgt/ ><strong>operator&gt;&gt;</strong></a> - deserialize from stream</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ul> <li>Added in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</li> <li>Planned to become the default (with the macro removed) in version 4.0.0.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 2, 2026 09:32:15 UTC">October 2, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 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</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../../../integration/cmake/#json_strictnulhandling><span class=twemoji><svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M11.769.066.067 23.206l12.76-10.843zm11.438 23.868L7.471 17.587 0 23.934zm.793-.198L12.298.463l1.719 19.24zM12.893 12.959l-5.025 4.298 5.62 2.248z"/></svg></span> JSON_StrictNulHandling</a> - CMake option to control the macro</li> <li><a href=../../../home/faq/#nul-bytes-in-the-input><abbr title="Frequently Asked Questions">FAQ</abbr>: <abbr title="Null character (U+0000, byte value 0)">NUL</abbr> bytes in the input</a></li> <li><a href=../../basic_json/parse/ ><strong>parse</strong></a> - deserialize from a compatible input</li> <li><a href=../../basic_json/accept/ ><strong>accept</strong></a> - check if the input is valid <abbr title="JavaScript Object Notation">JSON</abbr></li> <li><a href=../../operator_gtgt/ ><strong>operator&gt;&gt;</strong></a> - deserialize from stream</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ul> <li>Added in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</li> <li>Planned to become the default (with the macro removed) in version 4.0.0.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 25, 2026 11:07:51 UTC">October 25, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 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+2 -2
View File
@@ -63,7 +63,7 @@ Without the macro, a NUL byte silently ends parsing at that point:
```
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using nlohmann::json;
int main()
{
@@ -80,7 +80,7 @@ With the macro, a NUL byte is rejected like any other unexpected byte:
#define JSON_STRICT_NUL_HANDLING 1
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using nlohmann::json;
int main()
{
+1 -1
View File
@@ -1,4 +1,4 @@
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/macros/json_throw_user/" rel="canonical"><link href=../json_brace_init_copy_semantics/ rel=prev><link href=../json_diagnostics/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>JSON_CATCH_USER, JSON_THROW_USER, JSON_TRY_USER - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new 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URL("../../..",location),__md_hash=e=>[...e].reduce(((e,_)=>(e<<5)-e+_.charCodeAt(0)),0),__md_get=(e,_=localStorage,t=__md_scope)=>JSON.parse(_.getItem(t.pathname+"."+e)),__md_set=(e,_,t=localStorage,a=__md_scope)=>{try{t.setItem(a.pathname+"."+e,JSON.stringify(_))}catch(e){}}</script></head> <body dir=ltr data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo> <input class=md-toggle data-md-toggle=drawer type=checkbox id=__drawer autocomplete=off> <input class=md-toggle data-md-toggle=search type=checkbox id=__search autocomplete=off> <label class=md-overlay for=__drawer></label> <div data-md-component=skip> <a href=#json_catch_user-json_throw_user-json_try_user class=md-skip> Skip to content </a> </div> <div data-md-component=announce> </div> <header class=md-header data-md-component=header> <nav class="md-header__inner md-grid" aria-label=Header> <a href=../../.. title="JSON for Modern C++" class="md-header__button md-logo" aria-label="JSON for Modern 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1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 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<span class=cp>#define JSON_CATCH_USER(exception) </span><span class=cm>/* value */</span>
<span class=c1>// (2)</span>
<span class=cp>#define JSON_THROW_USER(exception) </span><span class=cm>/* value */</span>
+4 -4
View File
@@ -1,6 +1,6 @@
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/macros/json_use_global_udls/" rel="canonical"><link href=../json_strict_nul_handling/ rel=prev><link href=../json_use_implicit_conversions/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>JSON_USE_GLOBAL_UDLS - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new 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</code></pre></div> <p>When defined to <code>1</code>, the user-defined string literals (UDLs) are placed into the global namespace instead of <code>nlohmann::literals::json_literals</code>.</p> <h2 id=default-definition>Default definition<a class=headerlink href=#default-definition title="Permanent link">&para;</a></h2> <p>The default value is <code>1</code>.</p> <div class=highlight><pre><span></span><code><span class=cp>#define JSON_USE_GLOBAL_UDLS 1</span>
</code></pre></div> <p>When the macro is not defined, the library behaves as if it were defined to its default value.</p> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <div class="admonition info"> <p class=admonition-title>Future behavior change</p> <p>The user-defined string literals will be removed from the global namespace in the next major release of the library.</p> <p>To prepare existing code, define <code>JSON_USE_GLOBAL_UDLS</code> to <code>0</code> and bring the string literals into scope where needed. Refer to any of the <a href=#see-also>string literals</a> for details.</p> <p>See the <a href=../../../integration/migration_guide/#import-namespace-literals-for-udls>migration guide</a> for how to update existing code.</p> </div> <div class="admonition hint"> <p class=admonition-title>CMake option</p> <p>The placement of user-defined string literals can also be controlled with the CMake option <a href=../../../integration/cmake/#json_globaludls><code>JSON_GlobalUDLs</code></a> (<code>ON</code> by default) which defines <code>JSON_USE_GLOBAL_UDLS</code> accordingly.</p> </div> <div class="admonition info"> <p class=admonition-title>Leaving out the literals</p> <p>If <a href=../json_no_automatic_udls/ ><code>JSON_NO_AUTOMATIC_UDLS</code></a> is defined, the literals are only declared where <code>&lt;nlohmann/json_literals.hpp&gt;</code> is included; this macro then applies to that header.</p> </div> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example: Default behavior</summary> <p>The code below shows the default behavior using the <code>_json</code> UDL.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/macros/json_use_global_udls/" rel="canonical"><link href=../json_strict_nul_handling/ rel=prev><link href=../json_use_implicit_conversions/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>JSON_USE_GLOBAL_UDLS - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new 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data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> JSON_USE_GLOBAL_UDLS </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo 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6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 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</code></pre></div> <p>When defined to <code>1</code>, the user-defined string literals (<abbr title="User-defined literals">UDLs</abbr>) are placed into the global namespace instead of <code>nlohmann::literals::json_literals</code>.</p> <h2 id=default-definition>Default definition<a class=headerlink href=#default-definition title="Permanent link">&para;</a></h2> <p>The default value is <code>1</code>.</p> <div class=highlight><pre><span></span><code><span class=cp>#define JSON_USE_GLOBAL_UDLS 1</span>
</code></pre></div> <p>When the macro is not defined, the library behaves as if it were defined to its default value.</p> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <div class="admonition info"> <p class=admonition-title>Future behavior change</p> <p>The user-defined string literals will be removed from the global namespace in the next major release of the library.</p> <p>To prepare existing code, define <code>JSON_USE_GLOBAL_UDLS</code> to <code>0</code> and bring the string literals into scope where needed. Refer to any of the <a href=#see-also>string literals</a> for details.</p> <p>See the <a href=../../../integration/migration_guide/#import-namespace-literals-for-udls>migration guide</a> for how to update existing code.</p> </div> <div class="admonition hint"> <p class=admonition-title>CMake option</p> <p>The placement of user-defined string literals can also be controlled with the CMake option <a href=../../../integration/cmake/#json_globaludls><code>JSON_GlobalUDLs</code></a> (<code>ON</code> by default) which defines <code>JSON_USE_GLOBAL_UDLS</code> accordingly.</p> </div> <div class="admonition info"> <p class=admonition-title>Leaving out the literals</p> <p>If <a href=../json_no_automatic_udls/ ><code>JSON_NO_AUTOMATIC_UDLS</code></a> is defined, the literals are only declared where <code>&lt;nlohmann/json_literals.hpp&gt;</code> is included; this macro then applies to that header.</p> </div> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example: Default behavior</summary> <p>The code below shows the default behavior using the <code>_json</code> <abbr title="User-defined literal">UDL</abbr>.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
@@ -11,7 +11,7 @@
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>j</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>endl</span><span class=p>;</span>
<span class=p>}</span>
</code></pre></div> <p>Output:</p> <div class=highlight><pre><span></span><code><span class=mi>42</span>
</code></pre></div> </details> <details class=example> <summary>Example: Namespaced UDLs</summary> <p>The code below shows how UDLs need to be brought into scope before using <code>_json</code> when <code>JSON_USE_GLOBAL_UDLS</code> is defined to <code>0</code>.</p> <div class=highlight><pre><span></span><code><span class=cp>#define JSON_USE_GLOBAL_UDLS 0</span>
</code></pre></div> </details> <details class=example> <summary>Example: Namespaced <abbr title="User-defined literals">UDLs</abbr></summary> <p>The code below shows how <abbr title="User-defined literals">UDLs</abbr> need to be brought into scope before using <code>_json</code> when <code>JSON_USE_GLOBAL_UDLS</code> is defined to <code>0</code>.</p> <div class=highlight><pre><span></span><code><span class=cp>#define JSON_USE_GLOBAL_UDLS 0</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
@@ -1,4 +1,4 @@
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</code></pre></div> <p>When defined to <code>0</code>, implicit conversions are switched off. By default, implicit conversions are switched on. The value directly affects <a href=../../basic_json/operator_ValueType/ ><code>operator ValueType</code></a> and the <a href=../../basic_json/basic_json/ >converting constructor</a> from a <code>basic_json</code> specialization with a different string type (overload 4).</p> <h2 id=default-definition>Default definition<a class=headerlink href=#default-definition title="Permanent link">&para;</a></h2> <p>By default, implicit conversions are enabled.</p> <div class=highlight><pre><span></span><code><span class=cp>#define JSON_USE_IMPLICIT_CONVERSIONS 1</span>
</code></pre></div> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <div class="admonition info"> <p class=admonition-title>Future behavior change</p> <p>Implicit conversions will be switched off by default in the next major release of the library.</p> <p>You can prepare existing code by already defining <code>JSON_USE_IMPLICIT_CONVERSIONS</code> to <code>0</code> and replace any implicit conversions with calls to <a href=../../basic_json/get/ ><code>get</code></a>.</p> <p>See the <a href=../../../integration/migration_guide/#replace-implicit-conversions>migration guide</a> for how to update existing code.</p> </div> <div class="admonition tip"> <p class=admonition-title>Automatic migration</p> <p>The community-maintained clang-tidy check <code>modernize-nlohmann-json-explicit-conversions</code> rewrites implicit conversions into explicit calls to <a href=../../basic_json/get/ ><code>get</code></a>; for example, <code class=highlight><span class=kt>int</span><span class=w> </span><span class=n>i</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>j</span><span class=p>;</span></code> becomes <code class=highlight><span class=kt>int</span><span class=w> </span><span class=n>i</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>j</span><span class=p>.</span><span class=n>get</span><span class=o>&lt;</span><span class=kt>int</span><span class=o>&gt;</span><span class=p>();</span></code>. The check is not part of clang-tidy itself, and it does not catch every case (for example, constructing a <code>std::optional</code> from a <abbr title="JavaScript Object Notation">JSON</abbr> value), so review the result. See <a href="https://github.com/nlohmann/json/discussions/4610">discussion #4610</a> for how to build and use it.</p> </div> <div class="admonition hint"> <p class=admonition-title>CMake option</p> <p>Implicit conversions can also be controlled with the CMake option <a href=../../../integration/cmake/#json_implicitconversions><code>JSON_ImplicitConversions</code></a> (<code>ON</code> by default) which defines <code>JSON_USE_IMPLICIT_CONVERSIONS</code> accordingly.</p> </div> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example: implicit and explicit conversions</summary> <p>This is an example for an implicit conversion:</p> <div class=highlight><pre><span></span><code><span class=n>json</span><span class=w> </span><span class=n>j</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=s>"Hello, world!"</span><span class=p>;</span>
<span class=n>std</span><span class=o>::</span><span class=n>string</span><span class=w> </span><span class=n>s</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>j</span><span class=p>;</span>
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</code></pre></div> <p>This macro enables the (incorrect) legacy comparison behavior of discarded <abbr title="JavaScript Object Notation">JSON</abbr> values. Possible values are <code>1</code> to enable or <code>0</code> to disable (default).</p> <p>When enabled, comparisons involving at least one discarded <abbr title="JavaScript Object Notation">JSON</abbr> value yield results as follows:</p> <table> <thead> <tr> <th><strong>Operator</strong></th> <th><strong>Result</strong></th> </tr> </thead> <tbody> <tr> <td><code>==</code></td> <td><code class=highlight><span class=nb>false</span></code></td> </tr> <tr> <td><code>!=</code></td> <td><code class=highlight><span class=nb>true</span></code></td> </tr> <tr> <td><code>&lt;</code></td> <td><code class=highlight><span class=nb>false</span></code></td> </tr> <tr> <td><code>&lt;=</code></td> <td><code class=highlight><span class=nb>true</span></code></td> </tr> <tr> <td><code>&gt;=</code></td> <td><code class=highlight><span class=nb>true</span></code></td> </tr> <tr> <td><code>&gt;</code></td> <td><code class=highlight><span class=nb>false</span></code></td> </tr> </tbody> </table> <p>Otherwise, comparisons involving at least one discarded <abbr title="JavaScript Object Notation">JSON</abbr> value yield <code class=highlight><span class=nb>false</span></code>, except for <code>!=</code>, which is the negation of <code>==</code> and yields <code class=highlight><span class=nb>true</span></code>.</p> <h2 id=default-definition>Default definition<a class=headerlink href=#default-definition title="Permanent link">&para;</a></h2> <p>The default value is <code>0</code>.</p> <div class=highlight><pre><span></span><code><span class=cp>#define JSON_USE_LEGACY_DISCARDED_VALUE_COMPARISON 0</span>
</code></pre></div> <p>When the macro is not defined, the library will define it to its default value.</p> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <div class="admonition warning"> <p class=admonition-title>Inconsistent behavior in C++20 and beyond</p> <p>When targeting C++20 or above, enabling the legacy comparison behavior is <em>strongly</em> discouraged.</p> <ul> <li>The 3-way comparison operator (<code>&lt;=&gt;</code>) will always give the correct result (<code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>partial_ordering</span><span class=o>::</span><span class=n>unordered</span></code>) regardless of the value of <code>JSON_USE_LEGACY_DISCARDED_VALUE_COMPARISON</code>.</li> <li>Overloads for the equality and relational operators emulate the legacy behavior.</li> </ul> <p>Code outside your control may use either 3-way comparison or the equality and relational operators, resulting in inconsistent and unpredictable behavior.</p> <p>See <a href=../../basic_json/operator_spaceship/ ><code>operator&lt;=&gt;</code></a> for more information on 3-way comparison.</p> </div> <div class="admonition warning"> <p class=admonition-title>Deprecation</p> <p>The legacy comparison behavior is deprecated and may be removed in a future major version release.</p> <p>New code should not depend on it and existing code should try to remove or rewrite expressions relying on it.</p> <p>See the <a href=../../../integration/migration_guide/#miscellaneous-functions>migration guide</a> for how to update existing code.</p> </div> <div class="admonition hint"> <p class=admonition-title>CMake option</p> <p>Legacy comparison can also be controlled with the CMake option <a href=../../../integration/cmake/#json_legacydiscardedvaluecomparison><code>JSON_LegacyDiscardedValueComparison</code></a> (<code>OFF</code> by default) which defines <code>JSON_USE_LEGACY_DISCARDED_VALUE_COMPARISON</code> accordingly.</p> </div> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The code below switches on the legacy discarded value comparison behavior in the library.</p> <div class=highlight><pre><span></span><code><span class=cp>#define JSON_USE_LEGACY_DISCARDED_VALUE_COMPARISON 1</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
@@ -77,7 +77,7 @@ The default value is `0` (disabled — existing behavior is preserved).
#include <map>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using nlohmann::json;
enum TaskState { TS_STOPPED, TS_RUNNING, TS_COMPLETED };
@@ -105,7 +105,7 @@ The default value is `0` (disabled — existing behavior is preserved).
#include <map>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using nlohmann::json;
enum TaskState { TS_STOPPED, TS_RUNNING, TS_COMPLETED };
@@ -1,11 +1,11 @@
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</code></pre></div> <p>When defined to <code>1</code>, maps whose keys are enums (such as <code>std::map&lt;E, T&gt;</code> or <code>std::unordered_map&lt;E, T&gt;</code>) are stored as <abbr title="JavaScript Object Notation">JSON</abbr> objects, using the enum's own conversion for the keys. By default, they are stored as arrays of <code>[key, value]</code> pairs.</p> <h2 id=default-definition>Default definition<a class=headerlink href=#default-definition title="Permanent link">&para;</a></h2> <p>The default value is <code>0</code> (disabled — existing behavior is preserved).</p> <div class=highlight><pre><span></span><code><span class=cp>#define JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS 0</span>
</code></pre></div> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <div class="admonition note"> <p class=admonition-title>Background</p> <p><abbr title="JavaScript Object Notation">JSON</abbr> object keys are strings, so a map is only stored as an object if its keys can be converted to a string type. Enums are not, even if <a href=../nlohmann_json_serialize_enum/ ><code>NLOHMANN_JSON_SERIALIZE_ENUM</code></a> maps them to strings, so a map with enum keys becomes an array of <code>[key, value]</code> pairs:</p> <div class=highlight><pre><span></span><code><span class=p>[[</span><span class=s2>"stopped"</span><span class=p>,</span><span class=w> </span><span class=s2>"aa"</span><span class=p>],</span><span class=w> </span><span class=p>[</span><span class=s2>"completed"</span><span class=p>,</span><span class=w> </span><span class=s2>"bb"</span><span class=p>]]</span>
</code></pre></div> <p>With this macro, the same map becomes an object (see <a href="https://github.com/nlohmann/json/issues/4378">#4378</a>):</p> <div class=highlight><pre><span></span><code><span class=p>{</span><span class=nt>"completed"</span><span class=p>:</span><span class=w> </span><span class=s2>"bb"</span><span class=p>,</span><span class=w> </span><span class=nt>"stopped"</span><span class=p>:</span><span class=w> </span><span class=s2>"aa"</span><span class=p>}</span>
</code></pre></div> </div> <div class="admonition note"> <p class=admonition-title>Maps with non-unique keys</p> <p>Maps that allow duplicate keys, such as <code>std::multimap&lt;E, T&gt;</code> or <code>std::unordered_multimap&lt;E, T&gt;</code>, are not affected by the macro and are still stored as arrays of <code>[key, value]</code> pairs, as an object cannot hold duplicate keys.</p> </div> <div class="admonition note"> <p class=admonition-title>Reading</p> <p>Reading is not affected by the macro: a map with enum keys can always be read from both an array of pairs and an object. For the latter, each key is converted to the enum with its <code>from_json</code> function, e.g., the one defined by <a href=../nlohmann_json_serialize_enum/ ><code>NLOHMANN_JSON_SERIALIZE_ENUM</code></a>. Data written without the macro can therefore still be read after enabling it.</p> </div> <div class="admonition warning"> <p class=admonition-title>Keys must serialize to distinct strings</p> <p>Each key is converted with the enum's <code>to_json</code> function. If a key is not converted to a string (for instance, an enum without <a href=../nlohmann_json_serialize_enum/ ><code>NLOHMANN_JSON_SERIALIZE_ENUM</code></a>, which is stored as an integer, or an enumerator mapped to <code>nullptr</code>), <a href=../../../home/exceptions/#jsonexceptiontype_error302><code>type_error.302</code></a> is thrown. If two keys are converted to the same string (for instance, because <a href=../nlohmann_json_serialize_enum/ ><code>NLOHMANN_JSON_SERIALIZE_ENUM</code></a> maps an unlisted enumerator to the first entry), <a href=../../../home/exceptions/#jsonexceptiontype_error318><code>type_error.318</code></a> is thrown. In both cases, the target value is not changed.</p> </div> <div class="admonition warning"> <p class=admonition-title>Opt-in only</p> <p>This macro must be defined <strong>before</strong> including <code>&lt;nlohmann/json.hpp&gt;</code>. Defining it after the include has no effect.</p> </div> <div class="admonition note"> <p class=admonition-title>ABI compatibility</p> <p>The value of this macro is encoded in the <a href=../../../features/namespace/ >namespace</a> (tag <code>_ekmo</code>), resulting in distinct symbol names. Translation units compiled with and without it can therefore be linked into the same program without One Definition Rule (ODR) violations, but they cannot exchange instances of library types.</p> </div> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example: default behavior (macro not defined)</summary> <p>Without the macro, a map with enum keys is stored as an array of pairs:</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;map&gt;</span>
</code></pre></div> </div> <div class="admonition note"> <p class=admonition-title>Maps with non-unique keys</p> <p>Maps that allow duplicate keys, such as <code>std::multimap&lt;E, T&gt;</code> or <code>std::unordered_multimap&lt;E, T&gt;</code>, are not affected by the macro and are still stored as arrays of <code>[key, value]</code> pairs, as an object cannot hold duplicate keys.</p> </div> <div class="admonition note"> <p class=admonition-title>Reading</p> <p>Reading is not affected by the macro: a map with enum keys can always be read from both an array of pairs and an object. For the latter, each key is converted to the enum with its <code>from_json</code> function, e.g., the one defined by <a href=../nlohmann_json_serialize_enum/ ><code>NLOHMANN_JSON_SERIALIZE_ENUM</code></a>. Data written without the macro can therefore still be read after enabling it.</p> </div> <div class="admonition warning"> <p class=admonition-title>Keys must serialize to distinct strings</p> <p>Each key is converted with the enum's <code>to_json</code> function. If a key is not converted to a string (for instance, an enum without <a href=../nlohmann_json_serialize_enum/ ><code>NLOHMANN_JSON_SERIALIZE_ENUM</code></a>, which is stored as an integer, or an enumerator mapped to <code>nullptr</code>), <a href=../../../home/exceptions/#jsonexceptiontype_error302><code>type_error.302</code></a> is thrown. If two keys are converted to the same string (for instance, because <a href=../nlohmann_json_serialize_enum/ ><code>NLOHMANN_JSON_SERIALIZE_ENUM</code></a> maps an unlisted enumerator to the first entry), <a href=../../../home/exceptions/#jsonexceptiontype_error318><code>type_error.318</code></a> is thrown. In both cases, the target value is not changed.</p> </div> <div class="admonition warning"> <p class=admonition-title>Opt-in only</p> <p>This macro must be defined <strong>before</strong> including <code>&lt;nlohmann/json.hpp&gt;</code>. Defining it after the include has no effect.</p> </div> <div class="admonition note"> <p class=admonition-title><abbr title="Application Binary Interface">ABI</abbr> compatibility</p> <p>The value of this macro is encoded in the <a href=../../../features/namespace/ >namespace</a> (tag <code>_ekmo</code>), resulting in distinct symbol names. Translation units compiled with and without it can therefore be linked into the same program without One Definition Rule (<abbr title="One Definition Rule">ODR</abbr>) violations, but they cannot exchange instances of library types.</p> </div> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example: default behavior (macro not defined)</summary> <p>Without the macro, a map with enum keys is stored as an array of pairs:</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;map&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=k>enum</span><span class=w> </span><span class=nc>TaskState</span><span class=w> </span><span class=p>{</span><span class=w> </span><span class=n>TS_STOPPED</span><span class=p>,</span><span class=w> </span><span class=n>TS_RUNNING</span><span class=p>,</span><span class=w> </span><span class=n>TS_COMPLETED</span><span class=w> </span><span class=p>};</span>
@@ -26,7 +26,7 @@
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;map&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=k>enum</span><span class=w> </span><span class=nc>TaskState</span><span class=w> </span><span class=p>{</span><span class=w> </span><span class=n>TS_STOPPED</span><span class=p>,</span><span class=w> </span><span class=n>TS_RUNNING</span><span class=p>,</span><span class=w> </span><span class=n>TS_COMPLETED</span><span class=w> </span><span class=p>};</span>
@@ -46,4 +46,4 @@
<span class=w> </span><span class=k>auto</span><span class=w> </span><span class=n>m2</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>j</span><span class=p>.</span><span class=n>get</span><span class=o>&lt;</span><span class=n>std</span><span class=o>::</span><span class=n>map</span><span class=o>&lt;</span><span class=n>TaskState</span><span class=p>,</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>string</span><span class=o>&gt;&gt;</span><span class=p>();</span>
<span class=w> </span><span class=c1>// m2 == m</span>
<span class=p>}</span>
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../../../features/enum_conversion/ >Specializing enum conversion</a></li> <li><a href=../nlohmann_json_serialize_enum/ ><strong>NLOHMANN_JSON_SERIALIZE_ENUM</strong></a> - serialize/deserialize an enum</li> <li><a href=../nlohmann_json_serialize_enum_strict/ ><strong>NLOHMANN_JSON_SERIALIZE_ENUM_STRICT</strong></a> - serialize/deserialize an enum with exceptions</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ul> <li>Added in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 6, 2026 05:22:55 UTC">October 6, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 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</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../../../features/enum_conversion/ >Specializing enum conversion</a></li> <li><a href=../nlohmann_json_serialize_enum/ ><strong>NLOHMANN_JSON_SERIALIZE_ENUM</strong></a> - serialize/deserialize an enum</li> <li><a href=../nlohmann_json_serialize_enum_strict/ ><strong>NLOHMANN_JSON_SERIALIZE_ENUM_STRICT</strong></a> - serialize/deserialize an enum with exceptions</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ul> <li>Added in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 25, 2026 11:07:51 UTC">October 25, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 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@@ -60,7 +60,7 @@ Without the macro, a map with enum keys is stored as an array of pairs:
#include <map>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using nlohmann::json;
enum TaskState { TS_STOPPED, TS_RUNNING, TS_COMPLETED };
@@ -88,7 +88,7 @@ With the macro, the same map is stored as an object:
#include <map>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using nlohmann::json;
enum TaskState { TS_STOPPED, TS_RUNNING, TS_COMPLETED };
+2 -2
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@@ -1,5 +1,5 @@
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/macros/json_use_simdutf/" rel="canonical"><link href=../json_use_objects_for_enum_keyed_maps/ rel=prev><link href=../json_view_no_simd/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>JSON_USE_SIMDUTF - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new 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<svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> JSON_USE_SIMDUTF </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark mode" type=radio 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15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.52 6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 Line truncated
</code></pre></div> <p>When defined, the parser validates the <abbr title="Unicode Transformation Format">UTF</abbr>-8 content of <abbr title="JavaScript Object Notation">JSON</abbr> strings that come from a <strong>contiguous byte input</strong> (<code>std::string</code>, <code>std::vector&lt;char&gt;</code>/<code>&lt;std::uint8_t&gt;</code>, string literals, <code>const char*</code> ranges, …) using the <a href="https://github.com/simdutf/simdutf">simdutf</a> library instead of the built-in validator (which uses SSSE3 or NEON where available, see <a href=../json_no_simd/ ><code>JSON_NO_SIMD</code></a>). On text with many non-<abbr title="American Standard Code for Information Interchange">ASCII</abbr> characters (e.g. CJK or emoji) this can validate faster, depending on the CPU.</p> <p>This is an <strong>opt-in external dependency</strong>. The library itself remains header-only and its behavior is unchanged: the same input is accepted or rejected either way, and every parse error is reported at the same position with the same message (simdutf is only used to fast-path <em>valid</em> runs; anything it flags falls back to the scalar path so the exact diagnostic is preserved). A <code>std::istream</code> uses simdutf for the characters its stream buffer holds (see <a href=../json_disable_stream_bulk_scan/ ><code>JSON_DISABLE_STREAM_BULK_SCAN</code></a>); other streaming inputs (<code>FILE*</code>, wide strings, user-defined adapters) always use the scalar path.</p> <p>When <code>JSON_USE_SIMDUTF</code> is defined you must make the <code>simdutf.h</code> header available on the include path and link the simdutf library. When it is not defined, no simdutf header is included and there is no dependency.</p> <div class="admonition note"> <p class=admonition-title>Requires C++17</p> <p>simdutf requires C++17 and its header rejects older standards with an <code class=highlight><span class=cp>#error</span></code>. The backend is therefore only compiled in from C++17 on. In C++11 and C++14 the macro has no effect and the scalar validator is used, which accepts and rejects exactly the same input -- only throughput differs. Setting the macro project-wide is therefore safe even when some translation units are built with an older standard.</p> </div> <div class="admonition warning"> <p class=admonition-title>Define consistently</p> <p>The macro selects between two definitions of the same inline validation function. It must therefore be defined identically for <strong>every</strong> translation unit that includes the library; mixing translation units that define it with ones that do not is an ODR violation. Prefer setting it as a compile definition on the target rather than with <code class=highlight><span class=cp>#define</span></code> in individual source files.</p> </div> <h2 id=default-definition>Default definition<a class=headerlink href=#default-definition title="Permanent link">&para;</a></h2> <p>By default, <code class=highlight><span class=n>JSON_USE_SIMDUTF</span></code> is not defined and the portable C++11 scalar validator is used.</p> <div class=highlight><pre><span></span><code><span class=cp>#undef JSON_USE_SIMDUTF</span>
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/macros/json_use_simdutf/" rel="canonical"><link href=../json_use_objects_for_enum_keyed_maps/ rel=prev><link href=../nlohmann_define_derived_type/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>JSON_USE_SIMDUTF - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new 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<svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> JSON_USE_SIMDUTF </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark mode" type=radio 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15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.52 6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2Line truncated
</code></pre></div> <p>When defined, the parser validates the <abbr title="Unicode Transformation Format">UTF</abbr>-8 content of <abbr title="JavaScript Object Notation">JSON</abbr> strings that come from a <strong>contiguous byte input</strong> (<code>std::string</code>, <code>std::vector&lt;char&gt;</code>/<code>&lt;std::uint8_t&gt;</code>, string literals, <code>const char*</code> ranges, …) using the <a href="https://github.com/simdutf/simdutf">simdutf</a> library instead of the built-in validator (which uses <abbr title="Supplemental Streaming SIMD Extensions 3">SSSE3</abbr> or <abbr title="Arm SIMD instruction set extension">NEON</abbr> where available, see <a href=../json_no_simd/ ><code>JSON_NO_SIMD</code></a>). On text with many non-<abbr title="American Standard Code for Information Interchange">ASCII</abbr> characters (e.g. CJK or emoji) this can validate faster, depending on the <abbr title="Central Processing Unit">CPU</abbr>.</p> <p>This is an <strong>opt-in external dependency</strong>. The library itself remains header-only and its behavior is unchanged: the same input is accepted or rejected either way, and every parse error is reported at the same position with the same message (simdutf is only used to fast-path <em>valid</em> runs; anything it flags falls back to the scalar path so the exact diagnostic is preserved). A <code>std::istream</code> uses simdutf for the characters its stream buffer holds (see <a href=../json_disable_stream_bulk_scan/ ><code>JSON_DISABLE_STREAM_BULK_SCAN</code></a>); other streaming inputs (<code>FILE*</code>, wide strings, user-defined adapters) always use the scalar path.</p> <p>When <code>JSON_USE_SIMDUTF</code> is defined you must make the <code>simdutf.h</code> header available on the include path and link the simdutf library. When it is not defined, no simdutf header is included and there is no dependency.</p> <div class="admonition note"> <p class=admonition-title>Requires C++17</p> <p>simdutf requires C++17 and its header rejects older standards with an <code class=highlight><span class=cp>#error</span></code>. The backend is therefore only compiled in from C++17 on. In C++11 and C++14 the macro has no effect and the scalar validator is used, which accepts and rejects exactly the same input -- only throughput differs. Setting the macro project-wide is therefore safe even when some translation units are built with an older standard.</p> </div> <div class="admonition warning"> <p class=admonition-title>Define consistently</p> <p>The macro selects between two definitions of the same inline validation function. It must therefore be defined identically for <strong>every</strong> translation unit that includes the library; mixing translation units that define it with ones that do not is an <abbr title="One Definition Rule">ODR</abbr> violation. Prefer setting it as a compile definition on the target rather than with <code class=highlight><span class=cp>#define</span></code> in individual source files.</p> </div> <h2 id=default-definition>Default definition<a class=headerlink href=#default-definition title="Permanent link">&para;</a></h2> <p>By default, <code class=highlight><span class=n>JSON_USE_SIMDUTF</span></code> is not defined and the portable C++11 scalar validator is used.</p> <div class=highlight><pre><span></span><code><span class=cp>#undef JSON_USE_SIMDUTF</span>
</code></pre></div> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The code below enables the simdutf backend for <abbr title="Unicode Transformation Format">UTF</abbr>-8 validation.</p> <div class=highlight><pre><span></span><code><span class=cp>#define JSON_USE_SIMDUTF 1</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
-52
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@@ -1,52 +0,0 @@
# JSON_VIEW_NO_SIMD
```cpp
#define JSON_VIEW_NO_SIMD
```
When defined, the parser of [`basic_json_document`](../basic_json_document/index.md) (`<nlohmann/json_view.hpp>`)
uses only portable C++ to scan strings. By default, it scans long runs of string bytes 16 at a time with NEON on
AArch64 (with GCC and Clang) and SSE2 on x86-64, which are part of the baseline instruction sets of these
architectures, and validates non-ASCII text with NEON (or SSSE3, see
[`JSON_VIEW_USE_SSSE3`](json_view_use_ssse3.md)).
The same input is accepted or rejected either way, with the same values, and errors are reported the same way; only
the speed differs. The macro exists for platforms whose compilers lack the intrinsics headers, and to test the portable
code.
!!! note "ABI compatibility"
The macro selects between two definitions of the same inline functions. Whether it is defined is encoded in the
[namespace](../../features/namespace.md) (tag `_vns`), resulting in distinct symbol names. Translation units
compiled with and without it can therefore be linked into the same program without One Definition Rule (ODR)
violations, but they cannot exchange instances of library types.
## Default definition
By default, `#!cpp JSON_VIEW_NO_SIMD` is not defined, and the vector code is used where available.
```cpp
#undef JSON_VIEW_NO_SIMD
```
## Examples
??? example
The code below uses the portable string scanning of the view.
```cpp
#define JSON_VIEW_NO_SIMD
#include <nlohmann/json_view.hpp>
...
```
## See also
- [JSON_VIEW_USE_SSSE3](json_view_use_ssse3.md) - validate non-ASCII strings with SSSE3 on x86-64
- [json_view](../../features/json_view.md) - the zero-copy view
## Version history
- Added in version 3.13.0.
-7
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<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/macros/json_view_no_simd/" rel="canonical"><link href=../json_use_simdutf/ rel=prev><link href=../json_view_use_ssse3/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>JSON_VIEW_NO_SIMD - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new URL("../../..",location),__md_hash=e=>[...e].reduce(((e,_)=>(e<<5)-e+_.charCodeAt(0)),0),__md_get=(e,_=localStorage,t=__md_scope)=>JSON.parse(_.getItem(t.pathname+"."+e)),__md_set=(e,_,t=localStorage,a=__md_scope)=>{try{t.setItem(a.pathname+"."+e,JSON.stringify(_))}catch(e){}}</script></head> <body dir=ltr data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo> <input class=md-toggle data-md-toggle=drawer type=checkbox id=__drawer autocomplete=off> <input class=md-toggle data-md-toggle=search type=checkbox id=__search autocomplete=off> <label class=md-overlay for=__drawer></label> <div data-md-component=skip> <a href=#json_view_no_simd class=md-skip> Skip to content </a> </div> <div data-md-component=announce> </div> <header class=md-header data-md-component=header> <nav class="md-header__inner md-grid" aria-label=Header> <a href=../../.. title="JSON for Modern C++" class="md-header__button md-logo" aria-label="JSON for Modern C++" data-md-component=logo> 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</code></pre></div> <p>When defined, the parser of <a href=../../basic_json_document/ ><code>basic_json_document</code></a> (<code>&lt;nlohmann/json_view.hpp&gt;</code>) uses only portable C++ to scan strings. By default, it scans long runs of string bytes 16 at a time with NEON on AArch64 (with <abbr title="GNU Compiler Collection">GCC</abbr> and Clang) and SSE2 on x86-64, which are part of the baseline instruction sets of these architectures, and validates non-<abbr title="American Standard Code for Information Interchange">ASCII</abbr> text with NEON (or SSSE3, see <a href=../json_view_use_ssse3/ ><code>JSON_VIEW_USE_SSSE3</code></a>).</p> <p>The same input is accepted or rejected either way, with the same values, and errors are reported the same way; only the speed differs. The macro exists for platforms whose compilers lack the intrinsics headers, and to test the portable code.</p> <div class="admonition note"> <p class=admonition-title>ABI compatibility</p> <p>The macro selects between two definitions of the same inline functions. Whether it is defined is encoded in the <a href=../../../features/namespace/ >namespace</a> (tag <code>_vns</code>), resulting in distinct symbol names. Translation units compiled with and without it can therefore be linked into the same program without One Definition Rule (ODR) violations, but they cannot exchange instances of library types.</p> </div> <h2 id=default-definition>Default definition<a class=headerlink href=#default-definition title="Permanent link">&para;</a></h2> <p>By default, <code class=highlight><span class=n>JSON_VIEW_NO_SIMD</span></code> is not defined, and the vector code is used where available.</p> <div class=highlight><pre><span></span><code><span class=cp>#undef JSON_VIEW_NO_SIMD</span>
</code></pre></div> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The code below uses the portable string scanning of the view.</p> <div class=highlight><pre><span></span><code><span class=cp>#define JSON_VIEW_NO_SIMD</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json_view.hpp&gt;</span>
<span class=p>...</span>
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../json_view_use_ssse3/ >JSON_VIEW_USE_SSSE3</a> - validate non-<abbr title="American Standard Code for Information Interchange">ASCII</abbr> strings with SSSE3 on x86-64</li> <li><a href=../../../features/json_view/ >json_view</a> - the zero-copy view</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ul> <li>Added in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 21, 2026 08:21:28 UTC">October 21, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 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-43
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@@ -1,43 +0,0 @@
# JSON_VIEW_NO_SIMD
```
#define JSON_VIEW_NO_SIMD
```
When defined, the parser of [`basic_json_document`](https://json.nlohmann.me/api/basic_json_document/index.md) (`<nlohmann/json_view.hpp>`) uses only portable C++ to scan strings. By default, it scans long runs of string bytes 16 at a time with NEON on AArch64 (with GCC and Clang) and SSE2 on x86-64, which are part of the baseline instruction sets of these architectures, and validates non-ASCII text with NEON (or SSSE3, see [`JSON_VIEW_USE_SSSE3`](https://json.nlohmann.me/api/macros/json_view_use_ssse3/index.md)).
The same input is accepted or rejected either way, with the same values, and errors are reported the same way; only the speed differs. The macro exists for platforms whose compilers lack the intrinsics headers, and to test the portable code.
ABI compatibility
The macro selects between two definitions of the same inline functions. Whether it is defined is encoded in the [namespace](https://json.nlohmann.me/features/namespace/index.md) (tag `_vns`), resulting in distinct symbol names. Translation units compiled with and without it can therefore be linked into the same program without One Definition Rule (ODR) violations, but they cannot exchange instances of library types.
## Default definition
By default, `JSON_VIEW_NO_SIMD` is not defined, and the vector code is used where available.
```
#undef JSON_VIEW_NO_SIMD
```
## Examples
Example
The code below uses the portable string scanning of the view.
```
#define JSON_VIEW_NO_SIMD
#include <nlohmann/json_view.hpp>
...
```
## See also
- [JSON_VIEW_USE_SSSE3](https://json.nlohmann.me/api/macros/json_view_use_ssse3/index.md) - validate non-ASCII strings with SSSE3 on x86-64
- [json_view](https://json.nlohmann.me/features/json_view/index.md) - the zero-copy view
## Version history
- Added in version 3.13.0 unreleased.
-53
View File
@@ -1,53 +0,0 @@
# JSON_VIEW_USE_SSSE3
```cpp
#define JSON_VIEW_USE_SSSE3
```
When defined on x86-64, the parser of [`basic_json_document`](../basic_json_document/index.md)
(`<nlohmann/json_view.hpp>`) validates non-ASCII text in strings with SSSE3 without asking the CPU first.
By default, the parser checks once at run time whether the CPU has SSSE3 (all x86-64 CPUs since about 2011 have it)
and then validates non-ASCII text 16 bytes at a time, using the "lookup4" algorithm of
[simdjson](https://github.com/simdjson/simdjson); on CPUs without SSSE3, it validates one UTF-8 sequence at a time.
The vector check is compiled for SSSE3 with a function attribute (GCC 4.9 and later, Clang), so this needs no compiler
option. With MSVC, the check uses `__cpuid`. On AArch64, the vector check uses NEON and is always on.
Define the macro only together with a compiler option that enables SSSE3 (e.g. `-mssse3`, or `-march=` with a CPU that
has it), and only for programs that run on such CPUs. It saves the check of the CPU, which costs little. The same
input is accepted or rejected either way; only the speed of non-ASCII text differs.
!!! note "ABI compatibility"
The macro selects between two definitions of the same inline functions. Whether it is defined is encoded in the
[namespace](../../features/namespace.md) (tag `_vssse3`, on every architecture), resulting in distinct symbol
names. Translation units compiled with and without it can therefore be linked into the same program without One
Definition Rule (ODR) violations, but they cannot exchange instances of library types.
## Default definition
By default, `#!cpp JSON_VIEW_USE_SSSE3` is not defined.
```cpp
#undef JSON_VIEW_USE_SSSE3
```
## Examples
??? example
With CMake, for a program that only runs on CPUs with SSSE3:
```cmake
target_compile_definitions(your_target PRIVATE JSON_VIEW_USE_SSSE3)
target_compile_options(your_target PRIVATE -mssse3)
```
## See also
- [JSON_VIEW_NO_SIMD](json_view_no_simd.md) - use only portable code in the view's parser
- [JSON_USE_SIMDUTF](json_use_simdutf.md) - validate UTF-8 with simdutf in `basic_json`'s parser
## Version history
- Added in version 3.13.0.
@@ -1,5 +0,0 @@
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</code></pre></div> <p>When defined on x86-64, the parser of <a href=../../basic_json_document/ ><code>basic_json_document</code></a> (<code>&lt;nlohmann/json_view.hpp&gt;</code>) validates non-<abbr title="American Standard Code for Information Interchange">ASCII</abbr> text in strings with SSSE3 without asking the CPU first.</p> <p>By default, the parser checks once at run time whether the CPU has SSSE3 (all x86-64 CPUs since about 2011 have it) and then validates non-<abbr title="American Standard Code for Information Interchange">ASCII</abbr> text 16 bytes at a time, using the "lookup4" algorithm of <a href="https://github.com/simdjson/simdjson">simdjson</a>; on CPUs without SSSE3, it validates one <abbr title="Unicode Transformation Format">UTF</abbr>-8 sequence at a time. The vector check is compiled for SSSE3 with a function attribute (<abbr title="GNU Compiler Collection">GCC</abbr> 4.9 and later, Clang), so this needs no compiler option. With <abbr title="Microsoft Visual C++">MSVC</abbr>, the check uses <code>__cpuid</code>. On AArch64, the vector check uses NEON and is always on.</p> <p>Define the macro only together with a compiler option that enables SSSE3 (e.g. <code>-mssse3</code>, or <code>-march=</code> with a CPU that has it), and only for programs that run on such CPUs. It saves the check of the CPU, which costs little. The same input is accepted or rejected either way; only the speed of non-<abbr title="American Standard Code for Information Interchange">ASCII</abbr> text differs.</p> <div class="admonition note"> <p class=admonition-title>ABI compatibility</p> <p>The macro selects between two definitions of the same inline functions. Whether it is defined is encoded in the <a href=../../../features/namespace/ >namespace</a> (tag <code>_vssse3</code>, on every architecture), resulting in distinct symbol names. Translation units compiled with and without it can therefore be linked into the same program without One Definition Rule (ODR) violations, but they cannot exchange instances of library types.</p> </div> <h2 id=default-definition>Default definition<a class=headerlink href=#default-definition title="Permanent link">&para;</a></h2> <p>By default, <code class=highlight><span class=n>JSON_VIEW_USE_SSSE3</span></code> is not defined.</p> <div class=highlight><pre><span></span><code><span class=cp>#undef JSON_VIEW_USE_SSSE3</span>
</code></pre></div> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>With CMake, for a program that only runs on CPUs with SSSE3:</p> <div class=highlight><pre><span></span><code><span class=nb>target_compile_definitions</span><span class=p>(</span><span class=s>your_target</span><span class=w> </span><span class=s>PRIVATE</span><span class=w> </span><span class=s>JSON_VIEW_USE_SSSE3</span><span class=p>)</span>
<span class=nb>target_compile_options</span><span class=p>(</span><span class=s>your_target</span><span class=w> </span><span class=s>PRIVATE</span><span class=w> </span><span class=s>-mssse3</span><span class=p>)</span>
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../json_view_no_simd/ >JSON_VIEW_NO_SIMD</a> - use only portable code in the view's parser</li> <li><a href=../json_use_simdutf/ >JSON_USE_SIMDUTF</a> - validate <abbr title="Unicode Transformation Format">UTF</abbr>-8 with simdutf in <code>basic_json</code>'s parser</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ul> <li>Added in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 21, 2026 08:21:28 UTC">October 21, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 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-43
View File
@@ -1,43 +0,0 @@
# JSON_VIEW_USE_SSSE3
```
#define JSON_VIEW_USE_SSSE3
```
When defined on x86-64, the parser of [`basic_json_document`](https://json.nlohmann.me/api/basic_json_document/index.md) (`<nlohmann/json_view.hpp>`) validates non-ASCII text in strings with SSSE3 without asking the CPU first.
By default, the parser checks once at run time whether the CPU has SSSE3 (all x86-64 CPUs since about 2011 have it) and then validates non-ASCII text 16 bytes at a time, using the "lookup4" algorithm of [simdjson](https://github.com/simdjson/simdjson); on CPUs without SSSE3, it validates one UTF-8 sequence at a time. The vector check is compiled for SSSE3 with a function attribute (GCC 4.9 and later, Clang), so this needs no compiler option. With MSVC, the check uses `__cpuid`. On AArch64, the vector check uses NEON and is always on.
Define the macro only together with a compiler option that enables SSSE3 (e.g. `-mssse3`, or `-march=` with a CPU that has it), and only for programs that run on such CPUs. It saves the check of the CPU, which costs little. The same input is accepted or rejected either way; only the speed of non-ASCII text differs.
ABI compatibility
The macro selects between two definitions of the same inline functions. Whether it is defined is encoded in the [namespace](https://json.nlohmann.me/features/namespace/index.md) (tag `_vssse3`, on every architecture), resulting in distinct symbol names. Translation units compiled with and without it can therefore be linked into the same program without One Definition Rule (ODR) violations, but they cannot exchange instances of library types.
## Default definition
By default, `JSON_VIEW_USE_SSSE3` is not defined.
```
#undef JSON_VIEW_USE_SSSE3
```
## Examples
Example
With CMake, for a program that only runs on CPUs with SSSE3:
```
target_compile_definitions(your_target PRIVATE JSON_VIEW_USE_SSSE3)
target_compile_options(your_target PRIVATE -mssse3)
```
## See also
- [JSON_VIEW_NO_SIMD](https://json.nlohmann.me/api/macros/json_view_no_simd/index.md) - use only portable code in the view's parser
- [JSON_USE_SIMDUTF](https://json.nlohmann.me/api/macros/json_use_simdutf/index.md) - validate UTF-8 with simdutf in `basic_json`'s parser
## Version history
- Added in version 3.13.0 unreleased.
+10 -1
View File
@@ -147,6 +147,13 @@ void to_json(BasicJsonType& j, const B& b) {
See Implementation limits for [NLOHMANN_DEFINE_TYPE_INTRUSIVE](nlohmann_define_type_intrusive.md) and
[NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE](nlohmann_define_type_non_intrusive.md), respectively.
!!! info "Views"
The generated `from_json()` also reads the views of [`json_document`](../json_document.md)s
(`<nlohmann/json_view.hpp>`): [`get<T>()`](../basic_json_view/get.md) on a view looks the members up in the
view, without building a `json` value first. The base part is read from the view as well if the base's
`from_json()` accepts views, and from [`materialize()`](../basic_json_view/materialize.md) otherwise.
## Examples
??? example "Example: (1) NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE"
@@ -189,7 +196,7 @@ void to_json(BasicJsonType& j, const B& b) {
B example(23, 42, 3.142, 1.777);
json example_json = example;
std::cout << std::setw(4) << example_json << std::endl;
std::cout << std::setw(4) << example_json << '\n';
}
```
@@ -234,3 +241,5 @@ void to_json(BasicJsonType& j, const B& b) {
6. Added in version 3.12.0.
All six macros were changed to allow an empty member list in version 3.13.0.
The generated `from_json()` reads the views of `json_document`s since version 3.13.0.
@@ -1,4 +1,4 @@
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NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_DEFAULT, NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_ONLY_SERIALIZE, NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE, NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_DEFAULT, NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark mode" type=radio name=__palette id=__palette_0> <label class="md-header__button md-icon" title="Switch to dark mode" for=__palette_1 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a4 4 0 0 0-4 4 4 4 0 0 0 4 4 4 4 0 0 0 4-4 4 4 0 0 0-4-4m0 10a6 6 0 0 1-6-6 6 6 0 0 1 6-6 6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> <input 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<span class=cp>#define NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE(type, base_type, member...)</span>
<span class=c1>// (2)</span>
<span class=cp>#define NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_DEFAULT(type, base_type, member...)</span>
@@ -47,7 +47,7 @@
<span class=p>{</span>
<span class=w> </span><span class=n>NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE</span><span class=p>(</span><span class=n>derived</span><span class=p>,</span><span class=w> </span><span class=n>base</span><span class=p>)</span>
<span class=p>};</span>
</code></pre></div> <p>The <code>WITH_NAMES</code> variants do not support this.</p> </div> <div class="admonition warning"> <p class=admonition-title>Implementation limits</p> <p>See Implementation limits for <a href=../nlohmann_define_type_intrusive/ >NLOHMANN_DEFINE_TYPE_INTRUSIVE</a> and <a href=../nlohmann_define_type_non_intrusive/ >NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE</a>, respectively.</p> </div> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example: (1) NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE</summary> <p>Consider the following complete example:</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
</code></pre></div> <p>The <code>WITH_NAMES</code> variants do not support this.</p> </div> <div class="admonition warning"> <p class=admonition-title>Implementation limits</p> <p>See Implementation limits for <a href=../nlohmann_define_type_intrusive/ >NLOHMANN_DEFINE_TYPE_INTRUSIVE</a> and <a href=../nlohmann_define_type_non_intrusive/ >NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE</a>, respectively.</p> </div> <div class="admonition info"> <p class=admonition-title>Views</p> <p>The generated <code>from_json()</code> also reads the views of <a href=../../json_document/ ><code>json_document</code></a>s (<code>&lt;nlohmann/json_view.hpp&gt;</code>): <a href=../../basic_json_view/get/ ><code>get&lt;T&gt;()</code></a> on a view looks the members up in the view, without building a <code>json</code> value first. The base part is read from the view as well if the base's <code>from_json()</code> accepts views, and from <a href=../../basic_json_view/materialize/ ><code>materialize()</code></a> otherwise.</p> </div> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example: (1) NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE</summary> <p>Consider the following complete example:</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iomanip&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
@@ -82,7 +82,7 @@
<span class=w> </span><span class=n>B</span><span class=w> </span><span class=n>example</span><span class=p>(</span><span class=mi>23</span><span class=p>,</span><span class=w> </span><span class=mi>42</span><span class=p>,</span><span class=w> </span><span class=mf>3.142</span><span class=p>,</span><span class=w> </span><span class=mf>1.777</span><span class=p>);</span>
<span class=w> </span><span class=n>json</span><span class=w> </span><span class=n>example_json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>example</span><span class=p>;</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>setw</span><span class=p>(</span><span class=mi>4</span><span class=p>)</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>example_json</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>endl</span><span class=p>;</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>setw</span><span class=p>(</span><span class=mi>4</span><span class=p>)</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>example_json</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=sc>'\n'</span><span class=p>;</span>
<span class=p>}</span>
</code></pre></div> <p>Output:</p> <div class=highlight><pre><span></span><code><span class=p>{</span>
<span class=w> </span><span class=nt>"Aa"</span><span class=p>:</span><span class=w> </span><span class=mf>3.142</span><span class=p>,</span>
@@ -90,4 +90,4 @@
<span class=w> </span><span class=nt>"Ba"</span><span class=p>:</span><span class=w> </span><span class=mi>23</span><span class=p>,</span>
<span class=w> </span><span class=nt>"Bb"</span><span class=p>:</span><span class=w> </span><span class=mi>42</span>
<span class=p>}</span>
</code></pre></div> <p>Notes:</p> <ul> <li><code>A</code> and <code>B</code> are default-constructible. This is a requirement for using the macro.</li> <li><code>A</code> has private members and is not a derived class. Hence, macro <code>NLOHMANN_DEFINE_TYPE_INTRUSIVE</code> is used.</li> <li>As <code>B</code> is a derived class, <code>NLOHMANN_DEFINE_TYPE_INTRUSIVE</code> is not applicable, but <code>NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE</code> must be used.</li> <li>The macro <code>NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE</code> is used <em>inside</em> the class use as <code>NLOHMANN_DEFINE_TYPE_INTRUSIVE</code>.</li> </ul> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../nlohmann_define_type_intrusive/ >NLOHMANN_DEFINE_TYPE_INTRUSIVE / NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT / NLOHMANN_DEFINE_TYPE_INTRUSIVE_ONLY_SERIALIZE</a> for similar macros that can be defined <em>inside</em> a non-derived type.</li> <li><a href=../nlohmann_define_type_non_intrusive/ >NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE / NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT / NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE</a> for similar macros that can be defined <em>outside</em> a non-derived type.</li> <li><a href=../../../features/arbitrary_types/ >Arbitrary Type Conversions</a> for an overview.</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ol> <li>Added in version 3.12.0.</li> <li>Added in version 3.12.0.</li> <li>Added in version 3.12.0.</li> <li>Added in version 3.12.0.</li> <li>Added in version 3.12.0.</li> <li>Added in version 3.12.0.</li> </ol> <p>All six macros were changed to allow an empty member list in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</p> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 11, 2026 06:21:51 UTC">October 11, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 2013-2026 Niels Lohmann </div> </div> <div class=md-social> <a href="https://github.com/nlohmann" target="_blank" rel="noopener" title="github.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 512 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M173.9 397.4c0 2-2.3 3.6-5.2 3.6-3.3.3-5.6-1.3-5.6-3.6 0-2 2.3-3.6 5.2-3.6 3-.3 5.6 1.3 5.6 3.6m-31.1-4.5c-.7 2 1.3 4.3 4.3 4.9 2.6 1 5.6 0 6.2-2s-1.3-4.3-4.3-5.2c-2.6-.7-5.5.3-6.2 2.3m44.2-1.7c-2.9.7-4.9 2.6-4.6 4.9.3 2 2.9 3.3 5.9 2.6 2.9-.7 4.9-2.6 4.6-4.6-.3-1.9-3-3.2-5.9-2.9M252.8 8C114.1 8 8 113.3 8 252c0 110.9 69.8 205.8 169.5 239.2 12.8 2.3 17.3-5.6 17.3-12.1 0-6.2-.3-40.4-.3-61.4 0 0-70 15-84.7-29.8 0 0-11.4-29.1-27.8-36.6 0 0-22.9-15.7 1.6-15.4 0 0 24.9 2 38.6 25.8 21.9 38.6 58.6 27.5 72.9 20.9 2.3-16 8.8-27.1 16-33.7-55.9-6.2-112.3-14.3-112.3-110.5 0-27.5 7.6-41.3 23.6-58.9-2.6-6.5-11.1-33.3 2.6-67.9 20.9-6.5 69 27 69 27 20-5.6 41.5-8.5 62.8-8.5s42.8 2.9 62.8 8.5c0 0 48.1-33.6 69-27 13.7 34.7 5.2 61.4 2.6 67.9 16 17.7 25.8 31.5 25.8 58.9 0 96.5-58.9 104.2-114.8 110.5 9.2 7.9 17 22.9 17 46.4 0 33.7-.3 75.4-.3 83.6 0 6.5 4.6 14.4 17.3 12.1C436.2 457.8 504 362.9 504 252 504 113.3 391.5 8 2Line truncated
</code></pre></div> <p>Notes:</p> <ul> <li><code>A</code> and <code>B</code> are default-constructible. This is a requirement for using the macro.</li> <li><code>A</code> has private members and is not a derived class. Hence, macro <code>NLOHMANN_DEFINE_TYPE_INTRUSIVE</code> is used.</li> <li>As <code>B</code> is a derived class, <code>NLOHMANN_DEFINE_TYPE_INTRUSIVE</code> is not applicable, but <code>NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE</code> must be used.</li> <li>The macro <code>NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE</code> is used <em>inside</em> the class use as <code>NLOHMANN_DEFINE_TYPE_INTRUSIVE</code>.</li> </ul> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../nlohmann_define_type_intrusive/ >NLOHMANN_DEFINE_TYPE_INTRUSIVE / NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT / NLOHMANN_DEFINE_TYPE_INTRUSIVE_ONLY_SERIALIZE</a> for similar macros that can be defined <em>inside</em> a non-derived type.</li> <li><a href=../nlohmann_define_type_non_intrusive/ >NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE / NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT / NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE</a> for similar macros that can be defined <em>outside</em> a non-derived type.</li> <li><a href=../../../features/arbitrary_types/ >Arbitrary Type Conversions</a> for an overview.</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ol> <li>Added in version 3.12.0.</li> <li>Added in version 3.12.0.</li> <li>Added in version 3.12.0.</li> <li>Added in version 3.12.0.</li> <li>Added in version 3.12.0.</li> <li>Added in version 3.12.0.</li> </ol> <p>All six macros were changed to allow an empty member list in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</p> <p>The generated <code>from_json()</code> reads the views of <code>json_document</code>s since version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</p> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 26, 2026 19:13:31 UTC">October 26, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 2013-2026 Niels Lohmann </div> </div> <div class=md-social> <a href="https://github.com/nlohmann" target="_blank" rel="noopener" title="github.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 512 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M173.9 397.4c0 2-2.3 3.6-5.2 3.6-3.3.3-5.6-1.3-5.6-3.6 0-2 2.3-3.6 5.2-3.6 3-.3 5.6 1.3 5.6 3.6m-31.1-4.5c-.7 2 1.3 4.3 4.3 4.9 2.6 1 5.6 0 6.2-2s-1.3-4.3-4.3-5.2c-2.6-.7-5.5.3-6.2 2.3m44.2-1.7c-2.9.7-4.9 2.6-4.6 4.9.3 2 2.9 3.3 5.9 2.6 2.9-.7 4.9-2.6 4.6-4.6-.3-1.9-3-3.2-5.9-2.9M252.8 8C114.1 8 8 113.3 8 252c0 110.9 69.8 205.8 169.5 239.2 12.8 2.3 17.3-5.6 17.3-12.1 0-6.2-.3-40.4-.3-61.4 0 0-70 15-84.7-29.8 0 0-11.4-29.1-27.8-36.6 0 0-22.9-15.7 1.6-15.4 0 0 24.9 2 38.6 25.8 21.9 38.6 58.6 27.5 72.9 20.9 2.3-16 8.8-27.1 16-33.7-55.9-6.2-112.3-14.3-112.3-110.5 0-27.5 7.6-41.3 23.6-58.9-2.6-6.5-11.1-33.3 2.6-67.9 20.9-6.5 69 27 69 27 20-5.6 41.5-8.5 62.8-8.5s42.8 2.9 62.8 8.Line truncated
@@ -129,6 +129,10 @@ Implementation limits
See Implementation limits for [NLOHMANN_DEFINE_TYPE_INTRUSIVE](https://json.nlohmann.me/api/macros/nlohmann_define_type_intrusive/index.md) and [NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE](https://json.nlohmann.me/api/macros/nlohmann_define_type_non_intrusive/index.md), respectively.
Views
The generated `from_json()` also reads the views of [`json_document`](https://json.nlohmann.me/api/json_document/index.md)s (`<nlohmann/json_view.hpp>`): [`get<T>()`](https://json.nlohmann.me/api/basic_json_view/get/index.md) on a view looks the members up in the view, without building a `json` value first. The base part is read from the view as well if the base's `from_json()` accepts views, and from [`materialize()`](https://json.nlohmann.me/api/basic_json_view/materialize/index.md) otherwise.
## Examples
Example: (1) NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE
@@ -171,7 +175,7 @@ int main()
B example(23, 42, 3.142, 1.777);
json example_json = example;
std::cout << std::setw(4) << example_json << std::endl;
std::cout << std::setw(4) << example_json << '\n';
}
```
@@ -209,3 +213,5 @@ Notes:
1. Added in version 3.12.0.
All six macros were changed to allow an empty member list in version 3.13.0 unreleased.
The generated `from_json()` reads the views of `json_document`s since version 3.13.0 unreleased.
+24 -16
View File
@@ -81,6 +81,12 @@ See the examples below for the concrete generated code.
that serializes a struct's members positionally into a JSON array; for that, write `to_json`/`from_json` by
hand, building/reading a `json::array()` of the members in order.
!!! info "Views"
The generated `from_json()` also reads the views of [`json_document`](../json_document.md)s
(`<nlohmann/json_view.hpp>`): [`get<T>()`](../basic_json_view/get.md) on a view looks the members up in the
view, without building a `json` value first.
## Examples
??? example "Example: (1) NLOHMANN_DEFINE_TYPE_INTRUSIVE"
@@ -91,7 +97,7 @@ See the examples below for the concrete generated code.
#include <iostream>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using nlohmann::json;
using namespace nlohmann::literals;
namespace ns
@@ -119,7 +125,7 @@ See the examples below for the concrete generated code.
// serialization: person -> json
json j = p;
std::cout << "serialization: " << j << std::endl;
std::cout << "serialization: " << j << '\n';
// deserialization: json -> person
json j2 = R"({"address": "742 Evergreen Terrace", "age": 40, "name": "Homer Simpson"})"_json;
@@ -133,7 +139,7 @@ See the examples below for the concrete generated code.
}
catch (const json::exception& e)
{
std::cout << "deserialization failed: " << e.what() << std::endl;
std::cout << "deserialization failed: " << e.what() << '\n';
}
}
@@ -162,7 +168,7 @@ See the examples below for the concrete generated code.
#include <iostream>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using nlohmann::json;
using namespace nlohmann::literals;
namespace ns
@@ -204,7 +210,7 @@ See the examples below for the concrete generated code.
// serialization: person -> json
json j = p;
std::cout << "serialization: " << j << std::endl;
std::cout << "serialization: " << j << '\n';
// deserialization: json -> person
json j2 = R"({"address": "742 Evergreen Terrace", "age": 40, "name": "Homer Simpson"})"_json;
@@ -218,7 +224,7 @@ See the examples below for the concrete generated code.
}
catch (const json::exception& e)
{
std::cout << "deserialization failed: " << e.what() << std::endl;
std::cout << "deserialization failed: " << e.what() << '\n';
}
}
@@ -232,7 +238,7 @@ See the examples below for the concrete generated code.
#include <iostream>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using nlohmann::json;
using namespace nlohmann::literals;
namespace ns
@@ -260,7 +266,7 @@ See the examples below for the concrete generated code.
// serialization: person -> json
json j = p;
std::cout << "serialization: " << j << std::endl;
std::cout << "serialization: " << j << '\n';
// deserialization: json -> person
json j2 = R"({"address": "742 Evergreen Terrace", "age": 40, "name": "Homer Simpson"})"_json;
@@ -269,7 +275,7 @@ See the examples below for the concrete generated code.
// incomplete deserialization:
json j3 = R"({"address": "742 Evergreen Terrace", "name": "Maggie Simpson"})"_json;
auto p3 = j3.get<ns::person>();
std::cout << "roundtrip: " << json(p3) << std::endl;
std::cout << "roundtrip: " << json(p3) << '\n';
}
```
@@ -296,7 +302,7 @@ See the examples below for the concrete generated code.
#include <iostream>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using nlohmann::json;
using namespace nlohmann::literals;
namespace ns
@@ -339,7 +345,7 @@ See the examples below for the concrete generated code.
// serialization: person -> json
json j = p;
std::cout << "serialization: " << j << std::endl;
std::cout << "serialization: " << j << '\n';
// deserialization: json -> person
json j2 = R"({"address": "742 Evergreen Terrace", "age": 40, "name": "Homer Simpson"})"_json;
@@ -348,7 +354,7 @@ See the examples below for the concrete generated code.
// incomplete deserialization:
json j3 = R"({"address": "742 Evergreen Terrace", "name": "Maggie Simpson"})"_json;
auto p3 = j3.get<ns::person>();
std::cout << "roundtrip: " << json(p3) << std::endl;
std::cout << "roundtrip: " << json(p3) << '\n';
}
```
@@ -362,7 +368,7 @@ See the examples below for the concrete generated code.
#include <iostream>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using nlohmann::json;
using namespace nlohmann::literals;
namespace ns
@@ -390,7 +396,7 @@ See the examples below for the concrete generated code.
// serialization: person -> json
json j = p;
std::cout << "serialization: " << j << std::endl;
std::cout << "serialization: " << j << '\n';
}
```
@@ -416,7 +422,7 @@ See the examples below for the concrete generated code.
#include <iostream>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using nlohmann::json;
using namespace nlohmann::literals;
namespace ns
@@ -450,7 +456,7 @@ See the examples below for the concrete generated code.
// serialization: person -> json
json j = p;
std::cout << "serialization: " << j << std::endl;
std::cout << "serialization: " << j << '\n';
}
```
@@ -475,3 +481,5 @@ See the examples below for the concrete generated code.
All three macros were changed to work with any `basic_json` specialization (not only `nlohmann::json`) in version 3.12.0,
and to allow an empty member list in version 3.13.0.
The generated `from_json()` reads the views of `json_document`s since version 3.13.0.
@@ -1,4 +1,4 @@
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/macros/nlohmann_define_type_intrusive/" rel="canonical"><link href=../nlohmann_define_derived_type/ rel=prev><link href=../nlohmann_define_type_non_intrusive/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>NLOHMANN_DEFINE_TYPE_INTRUSIVE, NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT, NLOHMANN_DEFINE_TYPE_INTRUSIVE_ONLY_SERIALIZE - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link 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<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/macros/nlohmann_define_type_intrusive/" rel="canonical"><link href=../nlohmann_define_derived_type/ rel=prev><link href=../nlohmann_define_type_non_intrusive/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>NLOHMANN_DEFINE_TYPE_INTRUSIVE, NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT, NLOHMANN_DEFINE_TYPE_INTRUSIVE_ONLY_SERIALIZE - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link 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<span class=cp>#define NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT(type, member...) </span><span class=c1>// (2)</span>
<span class=cp>#define NLOHMANN_DEFINE_TYPE_INTRUSIVE_ONLY_SERIALIZE(type, member...) </span><span class=c1>// (3)</span>
</code></pre></div> <p>These macros can be used to simplify the serialization/deserialization of types if you want to use a <abbr title="JavaScript Object Notation">JSON</abbr> object as serialization and want to use the member variable names as object keys in that object. The macro is to be defined <strong>inside</strong> the class/struct to create code for. Unlike <a href=../nlohmann_define_type_non_intrusive/ ><code>NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE</code></a>, it can access private members. The first parameter is the name of the class/struct, and all remaining parameters name the members.</p> <ol> <li>Will use <a href=../../basic_json/at/ ><code>at</code></a> during deserialization and will throw <a href=../../../home/exceptions/#jsonexceptionout_of_range403><code>out_of_range.403</code></a> if a key is missing in the <abbr title="JavaScript Object Notation">JSON</abbr> object.</li> <li>Will use <a href=../../basic_json/value/ ><code>value</code></a> during deserialization and fall back to the default value for the respective type of the member variable if a key in the <abbr title="JavaScript Object Notation">JSON</abbr> object is missing. The generated <code>from_json()</code> function default constructs an object and uses its values as the defaults when calling the <code>value</code> function.</li> <li>Only defines the serialization. Useful in cases when the type does not have a default constructor and only serialization is required.</li> </ol> <p>Summary:</p> <table> <thead> <tr> <th>Need access to private members</th> <th>Need only serialization</th> <th>Allow missing values when de-serializing</th> <th>macro</th> </tr> </thead> <tbody> <tr> <td><div style="color: green;"><span class=twemoji><svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M1 12C1 5.925 5.925 1 12 1s11 4.925 11 11-4.925 11-11 11S1 18.075 1 12m16.28-2.72a.75.75 0 0 0-.018-1.042.75.75 0 0 0-1.042-.018l-5.97 5.97-2.47-2.47a.75.75 0 0 0-1.042.018.75.75 0 0 0-.018 1.042l3 3a.75.75 0 0 0 1.06 0Z"/></svg></span></div></td> <td><div style="color: red;"><span class=twemoji><svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M1 12C1 5.925 5.925 1 12 1s11 4.925 11 11-4.925 11-11 11S1 18.075 1 12m8.036-4.024a.75.75 0 0 0-1.042.018.75.75 0 0 0-.018 1.042L10.939 12l-2.963 2.963a.749.749 0 0 0 .326 1.275.75.75 0 0 0 .734-.215L12 13.06l2.963 2.964a.75.75 0 0 0 1.061-1.06L13.061 12l2.963-2.964a.749.749 0 0 0-.326-1.275.75.75 0 0 0-.734.215L12 10.939Z"/></svg></span></div></td> <td><div style="color: red;"><span class=twemoji><svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M1 12C1 5.925 5.925 1 12 1s11 4.925 11 11-4.925 11-11 11S1 18.075 1 12m8.036-4.024a.75.75 0 0 0-1.042.018.75.75 0 0 0-.018 1.042L10.939 12l-2.963 2.963a.749.749 0 0 0 .326 1.275.75.75 0 0 0 .734-.215L12 13.06l2.963 2.964a.75.75 0 0 0 1.061-1.06L13.061 12l2.963-2.964a.749.749 0 0 0-.326-1.275.75.75 0 0 0-.734.215L12 10.939Z"/></svg></span></div></td> <td><strong>NLOHMANN_DEFINE_TYPE_INTRUSIVE</strong></td> </tr> <tr> <td><div style="color: green;"><span class=twemoji><svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M1 12C1 5.925 5.925 1 12 1s11 4.925 11 11-4.925 11-11 11S1 18.075 1 12m16.28-2.72a.75.75 0 0 0-.018-1.042.75.75 0 0 0-1.042-.018l-5.97 5.97-2.47-2.47a.75.75 0 0 0-1.042.018.75.75 0 0 0-.018 1.042l3 3a.75.75 0 0 0 1.06 0Z"/></svg></span></div></td> <td><div style="color: red;"><span class=twemoji><svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M1 12C1 5.925 5.925 1 12 1s11 4.925 11 11-4.925 11-11 11S1 18.075 1 12m8.036-4.024a.75.75 0 0 0-1.042.018.75.75 0 0 0-.018 1.042L10.939 12l-2.963 2.963a.749.749 0 0 0 .326 1.275.75.75 0 0 0 .734-.215L12 13.06l2.963 2.964a.75.75 0 0 0 1.061-1.06L13.061 12l2.963-2.964a.749.749 0 0 0-.326-1.275.75.75 0 0 0-.734.215L12 10.939Z"/></svg></span></div></td> <td><div style="color: green;"><span class=twemoji><svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M1 12C1 5.925 5.925 1 12 1s11 4.925 11 11-4.925 11-11 11S1 18.075 1 12m16.28-2.72a.75.75 0 0 0-.018-1.042.75.75 0 0 0-1.042-.018l-5.97 5.97-2.47-2.47a.75.75 0 0 0-1.042.018.75.75 0 0 0-.018 1.042l3 3a.75.75 0 0 0 1.06 0Z"/></svg></span></div></td> <td><strong>NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT</strong></td> </tr> <tr> <td><div style="color: green;"><span class=twemoji><svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M1 12C1 5.925 5.925 1 12 1s11 4.925 11 11-4.925 11-11 11S1 18.075 1 12m16.28-2.72a.75.75 0 0 0-.018-1.042.75.75 0 0 0-1.042-.018l-5.97 5.97-2.47-2.47a.75.75 0 0 0-1.042.018.75.75 0 0 0-.018 1.042l3 3a.75.75 0 0 0 1.06 0Z"/></svg></span></div></td> <td><div style="color: green;"><span class=twemoji><svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M1 12C1 5.925 5.925 1 12 1s11 4.925 11 11-4.925 11-11 11S1 18.075 1 12m16.28-2.72a.75.75 0 0 0-.018-1.042.75.75 0 0 0-1.042-.018l-5.97 5.97-2.47-2.47a.75.75 0 0 0-1.042.018.75.75 0 0 0-Line truncated
@@ -9,10 +9,10 @@
<span class=p>{</span>
<span class=w> </span><span class=n>NLOHMANN_DEFINE_TYPE_INTRUSIVE</span><span class=p>(</span><span class=n>marker</span><span class=p>)</span>
<span class=p>};</span>
</code></pre></div> <p>The <code>WITH_NAMES</code> variants do not support this.</p> </div> <div class="admonition warning"> <p class=admonition-title>Implementation limits</p> <ul> <li>The current implementation is limited to at most 63 member variables. If you want to serialize/deserialize types with more than 63 member variables, you need to define the <code>to_json</code>/<code>from_json</code> functions manually.</li> <li>These macros always produce object-style (named-key) <abbr title="JavaScript Object Notation">JSON</abbr>, one key per member. There is no macro variant that serializes a struct's members positionally into a <abbr title="JavaScript Object Notation">JSON</abbr> array; for that, write <code>to_json</code>/<code>from_json</code> by hand, building/reading a <code>json::array()</code> of the members in order.</li> </ul> </div> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example: (1) NLOHMANN_DEFINE_TYPE_INTRUSIVE</summary> <p>Consider the following complete example:</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
</code></pre></div> <p>The <code>WITH_NAMES</code> variants do not support this.</p> </div> <div class="admonition warning"> <p class=admonition-title>Implementation limits</p> <ul> <li>The current implementation is limited to at most 63 member variables. If you want to serialize/deserialize types with more than 63 member variables, you need to define the <code>to_json</code>/<code>from_json</code> functions manually.</li> <li>These macros always produce object-style (named-key) <abbr title="JavaScript Object Notation">JSON</abbr>, one key per member. There is no macro variant that serializes a struct's members positionally into a <abbr title="JavaScript Object Notation">JSON</abbr> array; for that, write <code>to_json</code>/<code>from_json</code> by hand, building/reading a <code>json::array()</code> of the members in order.</li> </ul> </div> <div class="admonition info"> <p class=admonition-title>Views</p> <p>The generated <code>from_json()</code> also reads the views of <a href=../../json_document/ ><code>json_document</code></a>s (<code>&lt;nlohmann/json_view.hpp&gt;</code>): <a href=../../basic_json_view/get/ ><code>get&lt;T&gt;()</code></a> on a view looks the members up in the view, without building a <code>json</code> value first.</p> </div> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example: (1) NLOHMANN_DEFINE_TYPE_INTRUSIVE</summary> <p>Consider the following complete example:</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=k>using</span><span class=w> </span><span class=k>namespace</span><span class=w> </span><span class=nn>nlohmann</span><span class=o>::</span><span class=nn>literals</span><span class=p>;</span>
<span class=k>namespace</span><span class=w> </span><span class=nn>ns</span>
@@ -40,7 +40,7 @@
<span class=w> </span><span class=c1>// serialization: person -&gt; json</span>
<span class=w> </span><span class=n>json</span><span class=w> </span><span class=n>j</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>p</span><span class=p>;</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>"serialization: "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>j</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>endl</span><span class=p>;</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>"serialization: "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>j</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=sc>'\n'</span><span class=p>;</span>
<span class=w> </span><span class=c1>// deserialization: json -&gt; person</span>
<span class=w> </span><span class=n>json</span><span class=w> </span><span class=n>j2</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=sa>R</span><span class=s>"</span><span class=dl>(</span><span class=s>{"address": "742 Evergreen Terrace", "age": 40, "name": "Homer Simpson"}</span><span class=dl>)</span><span class=s>"</span><span class=n>_json</span><span class=p>;</span>
@@ -54,7 +54,7 @@
<span class=w> </span><span class=p>}</span>
<span class=w> </span><span class=k>catch</span><span class=w> </span><span class=p>(</span><span class=k>const</span><span class=w> </span><span class=n>json</span><span class=o>::</span><span class=n>exception</span><span class=o>&amp;</span><span class=w> </span><span class=n>e</span><span class=p>)</span>
<span class=w> </span><span class=p>{</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>"deserialization failed: "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>e</span><span class=p>.</span><span class=n>what</span><span class=p>()</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>endl</span><span class=p>;</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>"deserialization failed: "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>e</span><span class=p>.</span><span class=n>what</span><span class=p>()</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=sc>'\n'</span><span class=p>;</span>
<span class=w> </span><span class=p>}</span>
<span class=p>}</span>
</code></pre></div> <p>Output:</p> <div class=highlight><pre><span></span><code><span class=err>serializa</span><span class=kc>t</span><span class=err>io</span><span class=kc>n</span><span class=p>:</span><span class=w> </span><span class=p>{</span><span class=nt>"address"</span><span class=p>:</span><span class=s2>"744 Evergreen Terrace"</span><span class=p>,</span><span class=nt>"age"</span><span class=p>:</span><span class=mi>60</span><span class=p>,</span><span class=nt>"name"</span><span class=p>:</span><span class=s2>"Ned Flanders"</span><span class=p>}</span>
@@ -62,7 +62,7 @@
</code></pre></div> <p>Notes:</p> <ul> <li><code>ns::person</code> is default-constructible. This is a requirement for using the macro.</li> <li><code>ns::person</code> has private member variables. This makes <code>NLOHMANN_DEFINE_TYPE_INTRUSIVE</code> applicable, but not <code>NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE</code>.</li> <li>The macro <code>NLOHMANN_DEFINE_TYPE_INTRUSIVE</code> is used <em>inside</em> the class.</li> <li>A missing key "age" in the deserialization yields an exception. To fall back to the default value, <code>NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT</code> can be used.</li> </ul> <p>The macro is equivalent to:</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=k>using</span><span class=w> </span><span class=k>namespace</span><span class=w> </span><span class=nn>nlohmann</span><span class=o>::</span><span class=nn>literals</span><span class=p>;</span>
<span class=k>namespace</span><span class=w> </span><span class=nn>ns</span>
@@ -104,7 +104,7 @@
<span class=w> </span><span class=c1>// serialization: person -&gt; json</span>
<span class=w> </span><span class=n>json</span><span class=w> </span><span class=n>j</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>p</span><span class=p>;</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>"serialization: "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>j</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>endl</span><span class=p>;</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>"serialization: "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>j</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=sc>'\n'</span><span class=p>;</span>
<span class=w> </span><span class=c1>// deserialization: json -&gt; person</span>
<span class=w> </span><span class=n>json</span><span class=w> </span><span class=n>j2</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=sa>R</span><span class=s>"</span><span class=dl>(</span><span class=s>{"address": "742 Evergreen Terrace", "age": 40, "name": "Homer Simpson"}</span><span class=dl>)</span><span class=s>"</span><span class=n>_json</span><span class=p>;</span>
@@ -118,13 +118,13 @@
<span class=w> </span><span class=p>}</span>
<span class=w> </span><span class=k>catch</span><span class=w> </span><span class=p>(</span><span class=k>const</span><span class=w> </span><span class=n>json</span><span class=o>::</span><span class=n>exception</span><span class=o>&amp;</span><span class=w> </span><span class=n>e</span><span class=p>)</span>
<span class=w> </span><span class=p>{</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>"deserialization failed: "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>e</span><span class=p>.</span><span class=n>what</span><span class=p>()</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>endl</span><span class=p>;</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>"deserialization failed: "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>e</span><span class=p>.</span><span class=n>what</span><span class=p>()</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=sc>'\n'</span><span class=p>;</span>
<span class=w> </span><span class=p>}</span>
<span class=p>}</span>
</code></pre></div> </details> <details class=example> <summary>Example: (2) NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT</summary> <p>Consider the following complete example:</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=k>using</span><span class=w> </span><span class=k>namespace</span><span class=w> </span><span class=nn>nlohmann</span><span class=o>::</span><span class=nn>literals</span><span class=p>;</span>
<span class=k>namespace</span><span class=w> </span><span class=nn>ns</span>
@@ -152,7 +152,7 @@
<span class=w> </span><span class=c1>// serialization: person -&gt; json</span>
<span class=w> </span><span class=n>json</span><span class=w> </span><span class=n>j</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>p</span><span class=p>;</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>"serialization: "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>j</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>endl</span><span class=p>;</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>"serialization: "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>j</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=sc>'\n'</span><span class=p>;</span>
<span class=w> </span><span class=c1>// deserialization: json -&gt; person</span>
<span class=w> </span><span class=n>json</span><span class=w> </span><span class=n>j2</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=sa>R</span><span class=s>"</span><span class=dl>(</span><span class=s>{"address": "742 Evergreen Terrace", "age": 40, "name": "Homer Simpson"}</span><span class=dl>)</span><span class=s>"</span><span class=n>_json</span><span class=p>;</span>
@@ -161,14 +161,14 @@
<span class=w> </span><span class=c1>// incomplete deserialization:</span>
<span class=w> </span><span class=n>json</span><span class=w> </span><span class=n>j3</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=sa>R</span><span class=s>"</span><span class=dl>(</span><span class=s>{"address": "742 Evergreen Terrace", "name": "Maggie Simpson"}</span><span class=dl>)</span><span class=s>"</span><span class=n>_json</span><span class=p>;</span>
<span class=w> </span><span class=k>auto</span><span class=w> </span><span class=n>p3</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>j3</span><span class=p>.</span><span class=n>get</span><span class=o>&lt;</span><span class=n>ns</span><span class=o>::</span><span class=n>person</span><span class=o>&gt;</span><span class=p>();</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>"roundtrip: "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>json</span><span class=p>(</span><span class=n>p3</span><span class=p>)</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>endl</span><span class=p>;</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>"roundtrip: "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>json</span><span class=p>(</span><span class=n>p3</span><span class=p>)</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=sc>'\n'</span><span class=p>;</span>
<span class=p>}</span>
</code></pre></div> <p>Output:</p> <div class=highlight><pre><span></span><code><span class=err>serializa</span><span class=kc>t</span><span class=err>io</span><span class=kc>n</span><span class=p>:</span><span class=w> </span><span class=p>{</span><span class=nt>"address"</span><span class=p>:</span><span class=s2>"744 Evergreen Terrace"</span><span class=p>,</span><span class=nt>"age"</span><span class=p>:</span><span class=mi>60</span><span class=p>,</span><span class=nt>"name"</span><span class=p>:</span><span class=s2>"Ned Flanders"</span><span class=p>}</span>
<span class=err>rou</span><span class=kc>n</span><span class=err>d</span><span class=kc>tr</span><span class=err>ip</span><span class=p>:</span><span class=w> </span><span class=p>{</span><span class=nt>"address"</span><span class=p>:</span><span class=s2>"742 Evergreen Terrace"</span><span class=p>,</span><span class=nt>"age"</span><span class=p>:</span><span class=mi>-1</span><span class=p>,</span><span class=nt>"name"</span><span class=p>:</span><span class=s2>"Maggie Simpson"</span><span class=p>}</span>
</code></pre></div> <p>Notes:</p> <ul> <li><code>ns::person</code> is default-constructible. This is a requirement for using the macro.</li> <li><code>ns::person</code> has private member variables. This makes <code>NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT</code> applicable, but not <code>NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT</code>.</li> <li>The macro <code>NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT</code> is used <em>inside</em> the class.</li> <li>A missing key "age" in the deserialization does not yield an exception. Instead, the default value <code>-1</code> is used.</li> </ul> <p>The macro is equivalent to:</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=k>using</span><span class=w> </span><span class=k>namespace</span><span class=w> </span><span class=nn>nlohmann</span><span class=o>::</span><span class=nn>literals</span><span class=p>;</span>
<span class=k>namespace</span><span class=w> </span><span class=nn>ns</span>
@@ -211,7 +211,7 @@
<span class=w> </span><span class=c1>// serialization: person -&gt; json</span>
<span class=w> </span><span class=n>json</span><span class=w> </span><span class=n>j</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>p</span><span class=p>;</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>"serialization: "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>j</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>endl</span><span class=p>;</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>"serialization: "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>j</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=sc>'\n'</span><span class=p>;</span>
<span class=w> </span><span class=c1>// deserialization: json -&gt; person</span>
<span class=w> </span><span class=n>json</span><span class=w> </span><span class=n>j2</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=sa>R</span><span class=s>"</span><span class=dl>(</span><span class=s>{"address": "742 Evergreen Terrace", "age": 40, "name": "Homer Simpson"}</span><span class=dl>)</span><span class=s>"</span><span class=n>_json</span><span class=p>;</span>
@@ -220,12 +220,12 @@
<span class=w> </span><span class=c1>// incomplete deserialization:</span>
<span class=w> </span><span class=n>json</span><span class=w> </span><span class=n>j3</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=sa>R</span><span class=s>"</span><span class=dl>(</span><span class=s>{"address": "742 Evergreen Terrace", "name": "Maggie Simpson"}</span><span class=dl>)</span><span class=s>"</span><span class=n>_json</span><span class=p>;</span>
<span class=w> </span><span class=k>auto</span><span class=w> </span><span class=n>p3</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>j3</span><span class=p>.</span><span class=n>get</span><span class=o>&lt;</span><span class=n>ns</span><span class=o>::</span><span class=n>person</span><span class=o>&gt;</span><span class=p>();</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>"roundtrip: "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>json</span><span class=p>(</span><span class=n>p3</span><span class=p>)</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>endl</span><span class=p>;</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>"roundtrip: "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>json</span><span class=p>(</span><span class=n>p3</span><span class=p>)</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=sc>'\n'</span><span class=p>;</span>
<span class=p>}</span>
</code></pre></div> <p>Note how a default-initialized <code>person</code> object is used in the <code>from_json</code> to fill missing values.</p> </details> <details class=example> <summary>Example: (3) NLOHMANN_DEFINE_TYPE_INTRUSIVE_ONLY_SERIALIZE</summary> <p>Consider the following complete example:</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=k>using</span><span class=w> </span><span class=k>namespace</span><span class=w> </span><span class=nn>nlohmann</span><span class=o>::</span><span class=nn>literals</span><span class=p>;</span>
<span class=k>namespace</span><span class=w> </span><span class=nn>ns</span>
@@ -253,13 +253,13 @@
<span class=w> </span><span class=c1>// serialization: person -&gt; json</span>
<span class=w> </span><span class=n>json</span><span class=w> </span><span class=n>j</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>p</span><span class=p>;</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>"serialization: "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>j</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>endl</span><span class=p>;</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>"serialization: "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>j</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=sc>'\n'</span><span class=p>;</span>
<span class=p>}</span>
</code></pre></div> <p>Output:</p> <div class=highlight><pre><span></span><code><span class=err>serializa</span><span class=kc>t</span><span class=err>io</span><span class=kc>n</span><span class=p>:</span><span class=w> </span><span class=p>{</span><span class=nt>"address"</span><span class=p>:</span><span class=s2>"744 Evergreen Terrace"</span><span class=p>,</span><span class=nt>"age"</span><span class=p>:</span><span class=mi>60</span><span class=p>,</span><span class=nt>"name"</span><span class=p>:</span><span class=s2>"Ned Flanders"</span><span class=p>}</span>
</code></pre></div> <p>Notes:</p> <ul> <li><code>ns::person</code> is non-default-constructible. This allows this macro to be used instead of <code>NLOHMANN_DEFINE_TYPE_INTRUSIVE</code> and <code>NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT</code>.</li> <li><code>ns::person</code> has private member variables. This makes <code>NLOHMANN_DEFINE_TYPE_INTRUSIVE_ONLY_SERIALIZE</code> applicable, but not <code>NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE</code>.</li> <li>The macro <code>NLOHMANN_DEFINE_TYPE_INTRUSIVE_ONLY_SERIALIZE</code> is used <em>inside</em> the class.</li> </ul> <p>The macro is equivalent to:</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=k>using</span><span class=w> </span><span class=k>namespace</span><span class=w> </span><span class=nn>nlohmann</span><span class=o>::</span><span class=nn>literals</span><span class=p>;</span>
<span class=k>namespace</span><span class=w> </span><span class=nn>ns</span>
@@ -293,6 +293,6 @@
<span class=w> </span><span class=c1>// serialization: person -&gt; json</span>
<span class=w> </span><span class=n>json</span><span class=w> </span><span class=n>j</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>p</span><span class=p>;</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>"serialization: "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>j</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>endl</span><span class=p>;</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>"serialization: "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>j</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=sc>'\n'</span><span class=p>;</span>
<span class=p>}</span>
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../nlohmann_define_type_non_intrusive/ >NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE, NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT, NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE</a> for a similar macro that can be defined <em>outside</em> the type.</li> <li><a href=../nlohmann_define_derived_type/ >NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE, NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_DEFAULT, NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_ONLY_SERIALIZE, NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE, NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_DEFAULT, NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE</a> for similar macros for derived types</li> <li><a href=../../../features/arbitrary_types/ >Arbitrary Type Conversions</a> for an overview.</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ol> <li>Added in version 3.9.0.</li> <li>Added in version 3.11.0.</li> <li>Added in version 3.11.3.</li> </ol> <p>All three macros were changed to work with any <code>basic_json</code> specialization (not only <code>nlohmann::json</code>) in version 3.12.0, and to allow an empty member list in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</p> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 11, 2026 06:21:51 UTC">October 11, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 2013-2026 Niels Lohmann </div> </div> <div class=md-social> <a href="https://github.com/nlohmann" target="_blank" rel="noopener" title="github.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 512 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M173.9 397.4c0 2-2.3 3.6-5.2 3.6-3.3.3-5.6-1.3-5.6-3.6 0-2 2.3-3.6 5.2-3.6 3-.3 5.6 1.3 5.6 3.6m-31.1-4.5c-.7 2 1.3 4.3 4.3 4.9 2.6 1 5.6 0 6.2-2s-1.3-4.3-4.3-5.2c-2.6-.7-5.5.3-6.2 2.3m44.2-1.7c-2.9.7-4.9 2.6-4.6 4.9.3 2 2.9 3.3 5.9 2.6 2.9-.7 4.9-2.6 4.6-4.6-.3-1.9-3-3.2-5.9-2.9M252.8 8C114.1 8 8 113.3 8 252c0 110.9 69.8 205.8 169.5 239.2 12.8 2.3 17.3-5.6 17.3-12.1 0-6.2-.3-40.4-.3-61.4 0 0-70 15-84.7-29.8 0 0-11.4-29.1-27.8-36.6 0 0-22.9-15.7 1.6-15.4 0 0 24.9 2 38.6 25.8 21.9 38.6 58.6 27.5 72.9 20.9 2.3-16 8.8-27.1 16-33.7-55.9-6.2-112.3-14.3-112.3-110.5 0-27.5 7.6-41.3 23.6-58.9-2.6-6.5-11.1-33.3 2.6-67.9 20.9-6.5 69 27 69 27 20-5.6 41.5-8.5 62.8-8.5s42.8 2.9 62.8 8.5c0 0 48.1-33.6 69-27 13.7 34.7 5.2 61.4 2.6 67.9 16 17.7 25.8 31.5 25.8 58.9 0 96.5-58.9 104.2-114.8 110.5 9.2 7.9 17 22.9 17 46.4 0 33.7-.3 75.4-.3 83.6 0 6.5 4.6 14.4 17.3 12.1C436.2 457.8 504 362.9 504 252 504 113.3 391.5 8 252.8 8M105.2 352.9c-1.3 1-1 3.3.7 5.2 1.6 1.6 3.9 2.3 5.2 1 1.3-1 1-3.3-.7-5.2-1.6-1.6-3.9-2.3-5.2-1m-10.8-8.1c-.7 1.3.3 2.9 2.3 3.9 1.6 1 3.6.7 4.3-.7.7-1.3-.3-2.9-2.3-3.9-2-.6-3.6-.3-4.3.7m32.4 35.6c-1.6 1.3-1 4.3 1.3 6.2 2.3 2.3 5.2 2.6 6.5 1 1.3-1.3.7-4.3-1.3-6.2-2.2-2.3-5.2-2.6-6.5-1m-11.4-14.7c-1.6 1-1.6 3.6 0 5.9s4.3 3.3 5.6 2.3c1.6-1.3 1.6-3.9 0-6.2-1.4-2.3-4-3.3-5.6-2"/></svg> </a> <a href="https://www.linkedin.com/in/nielslohmann/" target="_blank" relLine truncated
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../nlohmann_define_type_non_intrusive/ >NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE, NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT, NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE</a> for a similar macro that can be defined <em>outside</em> the type.</li> <li><a href=../nlohmann_define_derived_type/ >NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE, NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_DEFAULT, NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_ONLY_SERIALIZE, NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE, NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_DEFAULT, NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE</a> for similar macros for derived types</li> <li><a href=../../../features/arbitrary_types/ >Arbitrary Type Conversions</a> for an overview.</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ol> <li>Added in version 3.9.0.</li> <li>Added in version 3.11.0.</li> <li>Added in version 3.11.3.</li> </ol> <p>All three macros were changed to work with any <code>basic_json</code> specialization (not only <code>nlohmann::json</code>) in version 3.12.0, and to allow an empty member list in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</p> <p>The generated <code>from_json()</code> reads the views of <code>json_document</code>s since version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</p> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 26, 2026 19:13:31 UTC">October 26, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 2013-2026 Niels Lohmann </div> </div> <div class=md-social> <a href="https://github.com/nlohmann" target="_blank" rel="noopener" title="github.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 512 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M173.9 397.4c0 2-2.3 3.6-5.2 3.6-3.3.3-5.6-1.3-5.6-3.6 0-2 2.3-3.6 5.2-3.6 3-.3 5.6 1.3 5.6 3.6m-31.1-4.5c-.7 2 1.3 4.3 4.3 4.9 2.6 1 5.6 0 6.2-2s-1.3-4.3-4.3-5.2c-2.6-.7-5.5.3-6.2 2.3m44.2-1.7c-2.9.7-4.9 2.6-4.6 4.9.3 2 2.9 3.3 5.9 2.6 2.9-.7 4.9-2.6 4.6-4.6-.3-1.9-3-3.2-5.9-2.9M252.8 8C114.1 8 8 113.3 8 252c0 110.9 69.8 205.8 169.5 239.2 12.8 2.3 17.3-5.6 17.3-12.1 0-6.2-.3-40.4-.3-61.4 0 0-70 15-84.7-29.8 0 0-11.4-29.1-27.8-36.6 0 0-22.9-15.7 1.6-15.4 0 0 24.9 2 38.6 25.8 21.9 38.6 58.6 27.5 72.9 20.9 2.3-16 8.8-27.1 16-33.7-55.9-6.2-112.3-14.3-112.3-110.5 0-27.5 7.6-41.3 23.6-58.9-2.6-6.5-11.1-33.3 2.6-67.9 20.9-6.5 69 27 69 27 20-5.6 41.5-8.5 62.8-8.5s42.8 2.9 62.8 8.5c0 0 48.1-33.6 69-27 13.7 34.7 5.2 61.4 2.6 67.9 16 17.7 25.8 31.5 25.8 58.9 0 96.5-58.9 104.2-114.8 110.5 9.2 7.9 17 22.9 17 46.4 0 33.7-.3 75.4-.3 83.6 0 6.5 4.6 14.4 17.3 12.1C436.2 457.8 504 362.9 504 252 504 113.3 391.5 8 252.8 8M105.2 352.9c-1.3 1-1 3.3.7 5.2 1.6 1.6 3.9 2.3 5.2 1 1.3-1 1-3.3-.7-5.2-1.6-1.6-3.9-2.3-5.2-1m-10.8-8.1c-.7 1.3.3 2.9 2.3 3.9 1.6 1 3.6.7 4.3-.7.7-1.3-.3-2.9-2.3-3.9-2-.6-3.6-.3-4.3.7m32.4 35.6c-1.6 1.3-1 4.3 1.3 6.2 2.3 2.3 5.2 Line truncated
@@ -64,6 +64,10 @@ Implementation limits
- The current implementation is limited to at most 63 member variables. If you want to serialize/deserialize types with more than 63 member variables, you need to define the `to_json`/`from_json` functions manually.
- These macros always produce object-style (named-key) JSON, one key per member. There is no macro variant that serializes a struct's members positionally into a JSON array; for that, write `to_json`/`from_json` by hand, building/reading a `json::array()` of the members in order.
Views
The generated `from_json()` also reads the views of [`json_document`](https://json.nlohmann.me/api/json_document/index.md)s (`<nlohmann/json_view.hpp>`): [`get<T>()`](https://json.nlohmann.me/api/basic_json_view/get/index.md) on a view looks the members up in the view, without building a `json` value first.
## Examples
Example: (1) NLOHMANN_DEFINE_TYPE_INTRUSIVE
@@ -74,7 +78,7 @@ Consider the following complete example:
#include <iostream>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using nlohmann::json;
using namespace nlohmann::literals;
namespace ns
@@ -102,7 +106,7 @@ int main()
// serialization: person -> json
json j = p;
std::cout << "serialization: " << j << std::endl;
std::cout << "serialization: " << j << '\n';
// deserialization: json -> person
json j2 = R"({"address": "742 Evergreen Terrace", "age": 40, "name": "Homer Simpson"})"_json;
@@ -116,7 +120,7 @@ int main()
}
catch (const json::exception& e)
{
std::cout << "deserialization failed: " << e.what() << std::endl;
std::cout << "deserialization failed: " << e.what() << '\n';
}
}
```
@@ -141,7 +145,7 @@ The macro is equivalent to:
#include <iostream>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using nlohmann::json;
using namespace nlohmann::literals;
namespace ns
@@ -183,7 +187,7 @@ int main()
// serialization: person -> json
json j = p;
std::cout << "serialization: " << j << std::endl;
std::cout << "serialization: " << j << '\n';
// deserialization: json -> person
json j2 = R"({"address": "742 Evergreen Terrace", "age": 40, "name": "Homer Simpson"})"_json;
@@ -197,7 +201,7 @@ int main()
}
catch (const json::exception& e)
{
std::cout << "deserialization failed: " << e.what() << std::endl;
std::cout << "deserialization failed: " << e.what() << '\n';
}
}
```
@@ -210,7 +214,7 @@ Consider the following complete example:
#include <iostream>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using nlohmann::json;
using namespace nlohmann::literals;
namespace ns
@@ -238,7 +242,7 @@ int main()
// serialization: person -> json
json j = p;
std::cout << "serialization: " << j << std::endl;
std::cout << "serialization: " << j << '\n';
// deserialization: json -> person
json j2 = R"({"address": "742 Evergreen Terrace", "age": 40, "name": "Homer Simpson"})"_json;
@@ -247,7 +251,7 @@ int main()
// incomplete deserialization:
json j3 = R"({"address": "742 Evergreen Terrace", "name": "Maggie Simpson"})"_json;
auto p3 = j3.get<ns::person>();
std::cout << "roundtrip: " << json(p3) << std::endl;
std::cout << "roundtrip: " << json(p3) << '\n';
}
```
@@ -271,7 +275,7 @@ The macro is equivalent to:
#include <iostream>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using nlohmann::json;
using namespace nlohmann::literals;
namespace ns
@@ -314,7 +318,7 @@ int main()
// serialization: person -> json
json j = p;
std::cout << "serialization: " << j << std::endl;
std::cout << "serialization: " << j << '\n';
// deserialization: json -> person
json j2 = R"({"address": "742 Evergreen Terrace", "age": 40, "name": "Homer Simpson"})"_json;
@@ -323,7 +327,7 @@ int main()
// incomplete deserialization:
json j3 = R"({"address": "742 Evergreen Terrace", "name": "Maggie Simpson"})"_json;
auto p3 = j3.get<ns::person>();
std::cout << "roundtrip: " << json(p3) << std::endl;
std::cout << "roundtrip: " << json(p3) << '\n';
}
```
@@ -337,7 +341,7 @@ Consider the following complete example:
#include <iostream>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using nlohmann::json;
using namespace nlohmann::literals;
namespace ns
@@ -365,7 +369,7 @@ int main()
// serialization: person -> json
json j = p;
std::cout << "serialization: " << j << std::endl;
std::cout << "serialization: " << j << '\n';
}
```
@@ -387,7 +391,7 @@ The macro is equivalent to:
#include <iostream>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using nlohmann::json;
using namespace nlohmann::literals;
namespace ns
@@ -421,7 +425,7 @@ int main()
// serialization: person -> json
json j = p;
std::cout << "serialization: " << j << std::endl;
std::cout << "serialization: " << j << '\n';
}
```
@@ -438,3 +442,5 @@ int main()
1. Added in version 3.11.3.
All three macros were changed to work with any `basic_json` specialization (not only `nlohmann::json`) in version 3.12.0, and to allow an empty member list in version 3.13.0 unreleased.
The generated `from_json()` reads the views of `json_document`s since version 3.13.0 unreleased.
@@ -80,6 +80,12 @@ See the examples below for the concrete generated code.
that serializes a struct's members positionally into a JSON array; for that, write `to_json`/`from_json` by
hand, building/reading a `json::array()` of the members in order.
!!! info "Views"
The generated `from_json()` also reads the views of [`json_document`](../json_document.md)s
(`<nlohmann/json_view.hpp>`): [`get<T>()`](../basic_json_view/get.md) on a view looks the members up in the
view, without building a `json` value first.
## Examples
??? example "Example: (1) NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE"
@@ -90,7 +96,7 @@ See the examples below for the concrete generated code.
#include <iostream>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using nlohmann::json;
using namespace nlohmann::literals;
namespace ns
@@ -111,7 +117,7 @@ See the examples below for the concrete generated code.
// serialization: person -> json
json j = p;
std::cout << "serialization: " << j << std::endl;
std::cout << "serialization: " << j << '\n';
// deserialization: json -> person
json j2 = R"({"address": "742 Evergreen Terrace", "age": 40, "name": "Homer Simpson"})"_json;
@@ -125,7 +131,7 @@ See the examples below for the concrete generated code.
}
catch (const json::exception& e)
{
std::cout << "deserialization failed: " << e.what() << std::endl;
std::cout << "deserialization failed: " << e.what() << '\n';
}
}
@@ -153,7 +159,7 @@ See the examples below for the concrete generated code.
#include <iostream>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using nlohmann::json;
using namespace nlohmann::literals;
namespace ns
@@ -188,7 +194,7 @@ See the examples below for the concrete generated code.
// serialization: person -> json
json j = p;
std::cout << "serialization: " << j << std::endl;
std::cout << "serialization: " << j << '\n';
// deserialization: json -> person
json j2 = R"({"address": "742 Evergreen Terrace", "age": 40, "name": "Homer Simpson"})"_json;
@@ -202,7 +208,7 @@ See the examples below for the concrete generated code.
}
catch (const json::exception& e)
{
std::cout << "deserialization failed: " << e.what() << std::endl;
std::cout << "deserialization failed: " << e.what() << '\n';
}
}
@@ -216,7 +222,7 @@ See the examples below for the concrete generated code.
#include <iostream>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using nlohmann::json;
using namespace nlohmann::literals;
namespace ns
@@ -242,7 +248,7 @@ See the examples below for the concrete generated code.
// serialization: person -> json
json j = p;
std::cout << "serialization: " << j << std::endl;
std::cout << "serialization: " << j << '\n';
// deserialization: json -> person
json j2 = R"({"address": "742 Evergreen Terrace", "age": 40, "name": "Homer Simpson"})"_json;
@@ -251,7 +257,7 @@ See the examples below for the concrete generated code.
// incomplete deserialization:
json j3 = R"({"address": "742 Evergreen Terrace", "name": "Maggie Simpson"})"_json;
auto p3 = j3.get<ns::person>();
std::cout << "roundtrip: " << json(p3) << std::endl;
std::cout << "roundtrip: " << json(p3) << '\n';
}
```
@@ -279,7 +285,7 @@ See the examples below for the concrete generated code.
#include <iostream>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using nlohmann::json;
using namespace nlohmann::literals;
namespace ns
@@ -320,7 +326,7 @@ See the examples below for the concrete generated code.
// serialization: person -> json
json j = p;
std::cout << "serialization: " << j << std::endl;
std::cout << "serialization: " << j << '\n';
// deserialization: json -> person
json j2 = R"({"address": "742 Evergreen Terrace", "age": 40, "name": "Homer Simpson"})"_json;
@@ -329,7 +335,7 @@ See the examples below for the concrete generated code.
// incomplete deserialization:
json j3 = R"({"address": "742 Evergreen Terrace", "name": "Maggie Simpson"})"_json;
auto p3 = j3.get<ns::person>();
std::cout << "roundtrip: " << json(p3) << std::endl;
std::cout << "roundtrip: " << json(p3) << '\n';
}
```
@@ -344,7 +350,7 @@ See the examples below for the concrete generated code.
#include <iostream>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using nlohmann::json;
using namespace nlohmann::literals;
namespace ns
@@ -365,7 +371,7 @@ See the examples below for the concrete generated code.
// serialization: person -> json
json j = p;
std::cout << "serialization: " << j << std::endl;
std::cout << "serialization: " << j << '\n';
}
```
@@ -390,7 +396,7 @@ See the examples below for the concrete generated code.
#include <iostream>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using nlohmann::json;
using namespace nlohmann::literals;
namespace ns
@@ -417,7 +423,7 @@ See the examples below for the concrete generated code.
// serialization: person -> json
json j = p;
std::cout << "serialization: " << j << std::endl;
std::cout << "serialization: " << j << '\n';
}
```
@@ -442,3 +448,5 @@ See the examples below for the concrete generated code.
All three macros were changed to work with any `basic_json` specialization (not only `nlohmann::json`) in version 3.12.0,
and to allow an empty member list in version 3.13.0.
The generated `from_json()` reads the views of `json_document`s since version 3.13.0.
@@ -1,4 +1,4 @@
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/macros/nlohmann_define_type_non_intrusive/" rel="canonical"><link href=../nlohmann_define_type_intrusive/ rel=prev><link href=../nlohmann_define_type_with_names/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE, NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT, NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains 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<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/macros/nlohmann_define_type_non_intrusive/" rel="canonical"><link href=../nlohmann_define_type_intrusive/ rel=prev><link href=../nlohmann_define_type_with_names/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE, NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT, NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains 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NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark mode" type=radio name=__palette id=__palette_0> <label class="md-header__button md-icon" title="Switch to dark mode" for=__palette_1 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a4 4 0 0 0-4 4 4 4 0 0 0 4 4 4 4 0 0 0 4-4 4 4 0 0 0-4-4m0 10a6 6 0 0 1-6-6 6 6 0 0 1 6-6 6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> <input class=md-option data-md-color-media="(prefers-color-scheme: dark)" data-md-color-scheme=slate data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to light mode" type=radio name=__palette 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<span class=cp>#define NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT(type, member...) </span><span class=c1>// (2)</span>
<span class=cp>#define NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE(type, member...) </span><span class=c1>// (3)</span>
</code></pre></div> <p>These macros can be used to simplify the serialization/deserialization of types if you want to use a <abbr title="JavaScript Object Notation">JSON</abbr> object as serialization and want to use the member variable names as object keys in that object. The macro is to be defined <strong>outside</strong> the class/struct to create code for, but <strong>inside</strong> its namespace. Unlike <a href=../nlohmann_define_type_intrusive/ ><code>NLOHMANN_DEFINE_TYPE_INTRUSIVE</code></a>, it <strong>cannot</strong> access private members. The first parameter is the name of the class/struct, and all remaining parameters name the members.</p> <ol> <li>Will use <a href=../../basic_json/at/ ><code>at</code></a> during deserialization and will throw <a href=../../../home/exceptions/#jsonexceptionout_of_range403><code>out_of_range.403</code></a> if a key is missing in the <abbr title="JavaScript Object Notation">JSON</abbr> object.</li> <li>Will use <a href=../../basic_json/value/ ><code>value</code></a> during deserialization and fall back to the default value for the respective type of the member variable if a key in the <abbr title="JavaScript Object Notation">JSON</abbr> object is missing. The generated <code>from_json()</code> function default constructs an object and uses its values as the defaults when calling the <code>value</code> function.</li> <li>Only defines the serialization. Useful in cases when the type does not have a default constructor and only serialization is required.</li> </ol> <p>Summary:</p> <table> <thead> <tr> <th>Need access to private members</th> <th>Need only serialization</th> <th>Allow missing values when de-serializing</th> <th>macro</th> </tr> </thead> <tbody> <tr> <td><div style="color: red;"><span class=twemoji><svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M1 12C1 5.925 5.925 1 12 1s11 4.925 11 11-4.925 11-11 11S1 18.075 1 12m8.036-4.024a.75.75 0 0 0-1.042.018.75.75 0 0 0-.018 1.042L10.939 12l-2.963 2.963a.749.749 0 0 0 .326 1.275.75.75 0 0 0 .734-.215L12 13.06l2.963 2.964a.75.75 0 0 0 1.061-1.06L13.061 12l2.963-2.964a.749.749 0 0 0-.326-1.275.75.75 0 0 0-.734.215L12 10.939Z"/></svg></span></div></td> <td><div style="color: red;"><span class=twemoji><svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M1 12C1 5.925 5.925 1 12 1s11 4.925 11 11-4.925 11-11 11S1 18.075 1 12m8.036-4.024a.75.75 0 0 0-1.042.018.75.75 0 0 0-.018 1.042L10.939 12l-2.963 2.963a.749.749 0 0 0 .326 1.275.75.75 0 0 0 .734-.215L12 13.06l2.963 2.964a.75.75 0 0 0 1.061-1.06L13.061 12l2.963-2.964a.749.749 0 0 0-.326-1.275.75.75 0 0 0-.734.215L12 10.939Z"/></svg></span></div></td> <td><div style="color: red;"><span class=twemoji><svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M1 12C1 5.925 5.925 1 12 1s11 4.925 11 11-4.925 11-11 11S1 18.075 1 12m8.036-4.024a.75.75 0 0 0-1.042.018.75.75 0 0 0-.018 1.042L10.939 12l-2.963 2.963a.749.749 0 0 0 .326 1.275.75.75 0 0 0 .734-.215L12 13.06l2.963 2.964a.75.75 0 0 0 1.061-1.06L13.061 12l2.963-2.964a.749.749 0 0 0-.326-1.275.75.75 0 0 0-.734.215L12 10.939Z"/></svg></span></div></td> <td><strong>NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE</strong></td> </tr> <tr> <td><div style="color: red;"><span class=twemoji><svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M1 12C1 5.925 5.925 1 12 1s11 4.925 11 11-4.925 11-11 11S1 18.075 1 12m8.036-4.024a.75.75 0 0 0-1.042.018.75.75 0 0 0-.018 1.042L10.939 12l-2.963 2.963a.749.749 0 0 0 .326 1.275.75.75 0 0 0 .734-.215L12 13.06l2.963 2.964a.75.75 0 0 0 1.061-1.06L13.061 12l2.963-2.964a.749.749 0 0 0-.326-1.275.75.75 0 0 0-.734.215L12 10.939Z"/></svg></span></div></td> <td><div style="color: red;"><span class=twemoji><svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M1 12C1 5.925 5.925 1 12 1s11 4.925 11 11-4.925 11-11 11S1 18.075 1 12m8.036-4.024a.75.75 0 0 0-1.042.018.75.75 0 0 0-.018 1.042L10.939 12l-2.963 2.963a.749.749 0 0 0 .326 1.275.75.75 0 0 0 .734-.215L12 13.06l2.963 2.964a.75.75 0 0 0 1.061-1.06L13.061 12l2.963-2.964a.749.749 0 0 0-.326-1.275.75.75 0 0 0-.734.215L12 10.939Z"/></svg></span></div></td> <td><div style="color: green;"><span class=twemoji><svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M1 12C1 5.925 5.925 1 12 1s11 4.925 11 11-4.925 11-11 11S1 18.075 1 12m16.28-2.72a.75.75 0 0 0-.018-1.042.75.75 0 0 0-1.042-.018l-5.97 5.97-2.47-2.47a.75.75 0 0 0-1.042.018.75.75 0 0 0-.018 1.042l3 3a.75.75 0 0 0 1.06 0Z"/></svg></span></div></td> <td><strong>NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT</strong></td> </tr> <tr> <td><div style="color: red;"><span class=twemoji><svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M1 12C1 5.925 5.925 1 12 1s11 4.925 11 11-4.925 11-11 11S1 18.075 1 12m8.036-4.024a.75.75 0 0 0-1.042.018.75.75 0 0 0-.018 1.042L10.939 12l-2.963 2.963a.749.749 0 0 0 .326 1.275.75.75 0 0 0 .734-.215L12 13.06l2.963 2.964a.75.75 0 0 0 1.061-1.06L13.061 12l2.963-2.964a.749.749 0 0 0-.32Line truncated
@@ -7,10 +7,10 @@
<span class=kt>void</span><span class=w> </span><span class=n>from_json</span><span class=p>(</span><span class=k>const</span><span class=w> </span><span class=n>BasicJsonType</span><span class=o>&amp;</span><span class=p>,</span><span class=w> </span><span class=n>type</span><span class=o>&amp;</span><span class=p>);</span><span class=w> </span><span class=c1>// except (3)</span>
</code></pre></div> <p>See the examples below for the concrete generated code.</p> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <div class="admonition info"> <p class=admonition-title>Prerequisites</p> <ol> <li>The type <code>type</code> must be default constructible (except (3). See <a href=../../../features/arbitrary_types/#how-can-i-use-get-for-non-default-constructiblenon-copyable-types>How can I use <code>get()</code> for non-default constructible/non-copyable types?</a> for how to overcome this limitation.</li> <li>The macro must be used outside the type (class/struct).</li> <li>The passed members must be public.</li> </ol> </div> <div class="admonition info"> <p class=admonition-title>Types without members</p> <p>The member list may be empty. The macro then generates a <code>to_json</code> that produces an empty <abbr title="JavaScript Object Notation">JSON</abbr> object <code class=highlight><span class=p>{}</span></code>, and a <code>from_json</code> that reads no members:</p> <div class=highlight><pre><span></span><code><span class=k>struct</span><span class=w> </span><span class=nc>marker</span><span class=w> </span><span class=p>{};</span>
<span class=n>NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE</span><span class=p>(</span><span class=n>marker</span><span class=p>)</span>
</code></pre></div> <p>The <code>WITH_NAMES</code> variants do not support this.</p> </div> <div class="admonition warning"> <p class=admonition-title>Implementation limits</p> <ul> <li>The current implementation is limited to at most 63 member variables. If you want to serialize/deserialize types with more than 63 member variables, you need to define the <code>to_json</code>/<code>from_json</code> functions manually.</li> <li>These macros always produce object-style (named-key) <abbr title="JavaScript Object Notation">JSON</abbr>, one key per member. There is no macro variant that serializes a struct's members positionally into a <abbr title="JavaScript Object Notation">JSON</abbr> array; for that, write <code>to_json</code>/<code>from_json</code> by hand, building/reading a <code>json::array()</code> of the members in order.</li> </ul> </div> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example: (1) NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE</summary> <p>Consider the following complete example:</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
</code></pre></div> <p>The <code>WITH_NAMES</code> variants do not support this.</p> </div> <div class="admonition warning"> <p class=admonition-title>Implementation limits</p> <ul> <li>The current implementation is limited to at most 63 member variables. If you want to serialize/deserialize types with more than 63 member variables, you need to define the <code>to_json</code>/<code>from_json</code> functions manually.</li> <li>These macros always produce object-style (named-key) <abbr title="JavaScript Object Notation">JSON</abbr>, one key per member. There is no macro variant that serializes a struct's members positionally into a <abbr title="JavaScript Object Notation">JSON</abbr> array; for that, write <code>to_json</code>/<code>from_json</code> by hand, building/reading a <code>json::array()</code> of the members in order.</li> </ul> </div> <div class="admonition info"> <p class=admonition-title>Views</p> <p>The generated <code>from_json()</code> also reads the views of <a href=../../json_document/ ><code>json_document</code></a>s (<code>&lt;nlohmann/json_view.hpp&gt;</code>): <a href=../../basic_json_view/get/ ><code>get&lt;T&gt;()</code></a> on a view looks the members up in the view, without building a <code>json</code> value first.</p> </div> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example: (1) NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE</summary> <p>Consider the following complete example:</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=k>using</span><span class=w> </span><span class=k>namespace</span><span class=w> </span><span class=nn>nlohmann</span><span class=o>::</span><span class=nn>literals</span><span class=p>;</span>
<span class=k>namespace</span><span class=w> </span><span class=nn>ns</span>
@@ -31,7 +31,7 @@
<span class=w> </span><span class=c1>// serialization: person -&gt; json</span>
<span class=w> </span><span class=n>json</span><span class=w> </span><span class=n>j</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>p</span><span class=p>;</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>"serialization: "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>j</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>endl</span><span class=p>;</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>"serialization: "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>j</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=sc>'\n'</span><span class=p>;</span>
<span class=w> </span><span class=c1>// deserialization: json -&gt; person</span>
<span class=w> </span><span class=n>json</span><span class=w> </span><span class=n>j2</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=sa>R</span><span class=s>"</span><span class=dl>(</span><span class=s>{"address": "742 Evergreen Terrace", "age": 40, "name": "Homer Simpson"}</span><span class=dl>)</span><span class=s>"</span><span class=n>_json</span><span class=p>;</span>
@@ -45,7 +45,7 @@
<span class=w> </span><span class=p>}</span>
<span class=w> </span><span class=k>catch</span><span class=w> </span><span class=p>(</span><span class=k>const</span><span class=w> </span><span class=n>json</span><span class=o>::</span><span class=n>exception</span><span class=o>&amp;</span><span class=w> </span><span class=n>e</span><span class=p>)</span>
<span class=w> </span><span class=p>{</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>"deserialization failed: "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>e</span><span class=p>.</span><span class=n>what</span><span class=p>()</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>endl</span><span class=p>;</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>"deserialization failed: "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>e</span><span class=p>.</span><span class=n>what</span><span class=p>()</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=sc>'\n'</span><span class=p>;</span>
<span class=w> </span><span class=p>}</span>
<span class=p>}</span>
</code></pre></div> <p>Output:</p> <div class=highlight><pre><span></span><code><span class=err>serializa</span><span class=kc>t</span><span class=err>io</span><span class=kc>n</span><span class=p>:</span><span class=w> </span><span class=p>{</span><span class=nt>"address"</span><span class=p>:</span><span class=s2>"744 Evergreen Terrace"</span><span class=p>,</span><span class=nt>"age"</span><span class=p>:</span><span class=mi>60</span><span class=p>,</span><span class=nt>"name"</span><span class=p>:</span><span class=s2>"Ned Flanders"</span><span class=p>}</span>
@@ -53,7 +53,7 @@
</code></pre></div> <p>Notes:</p> <ul> <li><code>ns::person</code> is default-constructible. This is a requirement for using the macro.</li> <li><code>ns::person</code> has only public member variables. This makes <code>NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE</code> applicable.</li> <li>The macro <code>NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE</code> is used <em>outside</em> the class, but <em>inside</em> its namespace <code>ns</code>.</li> <li>A missing key "age" in the deserialization yields an exception. To fall back to the default value, <code>NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT</code> can be used.</li> </ul> <p>The macro is equivalent to:</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=k>using</span><span class=w> </span><span class=k>namespace</span><span class=w> </span><span class=nn>nlohmann</span><span class=o>::</span><span class=nn>literals</span><span class=p>;</span>
<span class=k>namespace</span><span class=w> </span><span class=nn>ns</span>
@@ -88,7 +88,7 @@
<span class=w> </span><span class=c1>// serialization: person -&gt; json</span>
<span class=w> </span><span class=n>json</span><span class=w> </span><span class=n>j</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>p</span><span class=p>;</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>"serialization: "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>j</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>endl</span><span class=p>;</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>"serialization: "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>j</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=sc>'\n'</span><span class=p>;</span>
<span class=w> </span><span class=c1>// deserialization: json -&gt; person</span>
<span class=w> </span><span class=n>json</span><span class=w> </span><span class=n>j2</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=sa>R</span><span class=s>"</span><span class=dl>(</span><span class=s>{"address": "742 Evergreen Terrace", "age": 40, "name": "Homer Simpson"}</span><span class=dl>)</span><span class=s>"</span><span class=n>_json</span><span class=p>;</span>
@@ -102,13 +102,13 @@
<span class=w> </span><span class=p>}</span>
<span class=w> </span><span class=k>catch</span><span class=w> </span><span class=p>(</span><span class=k>const</span><span class=w> </span><span class=n>json</span><span class=o>::</span><span class=n>exception</span><span class=o>&amp;</span><span class=w> </span><span class=n>e</span><span class=p>)</span>
<span class=w> </span><span class=p>{</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>"deserialization failed: "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>e</span><span class=p>.</span><span class=n>what</span><span class=p>()</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>endl</span><span class=p>;</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>"deserialization failed: "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>e</span><span class=p>.</span><span class=n>what</span><span class=p>()</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=sc>'\n'</span><span class=p>;</span>
<span class=w> </span><span class=p>}</span>
<span class=p>}</span>
</code></pre></div> </details> <details class=example> <summary>Example: (2) NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT</summary> <p>Consider the following complete example:</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=k>using</span><span class=w> </span><span class=k>namespace</span><span class=w> </span><span class=nn>nlohmann</span><span class=o>::</span><span class=nn>literals</span><span class=p>;</span>
<span class=k>namespace</span><span class=w> </span><span class=nn>ns</span>
@@ -134,7 +134,7 @@
<span class=w> </span><span class=c1>// serialization: person -&gt; json</span>
<span class=w> </span><span class=n>json</span><span class=w> </span><span class=n>j</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>p</span><span class=p>;</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>"serialization: "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>j</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>endl</span><span class=p>;</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>"serialization: "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>j</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=sc>'\n'</span><span class=p>;</span>
<span class=w> </span><span class=c1>// deserialization: json -&gt; person</span>
<span class=w> </span><span class=n>json</span><span class=w> </span><span class=n>j2</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=sa>R</span><span class=s>"</span><span class=dl>(</span><span class=s>{"address": "742 Evergreen Terrace", "age": 40, "name": "Homer Simpson"}</span><span class=dl>)</span><span class=s>"</span><span class=n>_json</span><span class=p>;</span>
@@ -143,14 +143,14 @@
<span class=w> </span><span class=c1>// incomplete deserialization:</span>
<span class=w> </span><span class=n>json</span><span class=w> </span><span class=n>j3</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=sa>R</span><span class=s>"</span><span class=dl>(</span><span class=s>{"address": "742 Evergreen Terrace", "name": "Maggie Simpson"}</span><span class=dl>)</span><span class=s>"</span><span class=n>_json</span><span class=p>;</span>
<span class=w> </span><span class=k>auto</span><span class=w> </span><span class=n>p3</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>j3</span><span class=p>.</span><span class=n>get</span><span class=o>&lt;</span><span class=n>ns</span><span class=o>::</span><span class=n>person</span><span class=o>&gt;</span><span class=p>();</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>"roundtrip: "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>json</span><span class=p>(</span><span class=n>p3</span><span class=p>)</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>endl</span><span class=p>;</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>"roundtrip: "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>json</span><span class=p>(</span><span class=n>p3</span><span class=p>)</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=sc>'\n'</span><span class=p>;</span>
<span class=p>}</span>
</code></pre></div> <p>Output:</p> <div class=highlight><pre><span></span><code><span class=err>serializa</span><span class=kc>t</span><span class=err>io</span><span class=kc>n</span><span class=p>:</span><span class=w> </span><span class=p>{</span><span class=nt>"address"</span><span class=p>:</span><span class=s2>"744 Evergreen Terrace"</span><span class=p>,</span><span class=nt>"age"</span><span class=p>:</span><span class=mi>60</span><span class=p>,</span><span class=nt>"name"</span><span class=p>:</span><span class=s2>"Ned Flanders"</span><span class=p>}</span>
<span class=err>rou</span><span class=kc>n</span><span class=err>d</span><span class=kc>tr</span><span class=err>ip</span><span class=p>:</span><span class=w> </span><span class=p>{</span><span class=nt>"address"</span><span class=p>:</span><span class=s2>"742 Evergreen Terrace"</span><span class=p>,</span><span class=nt>"age"</span><span class=p>:</span><span class=mi>-1</span><span class=p>,</span><span class=nt>"name"</span><span class=p>:</span><span class=s2>"Maggie Simpson"</span><span class=p>}</span>
</code></pre></div> <p>Notes:</p> <ul> <li><code>ns::person</code> is default-constructible. This is a requirement for using the macro.</li> <li><code>ns::person</code> has only public member variables. This makes <code>NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT</code> applicable.</li> <li>The macro <code>NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT</code> is used <em>outside</em> the class, but <em>inside</em> its namespace <code>ns</code>.</li> <li>A missing key "age" in the deserialization does not yield an exception. Instead, the default value <code>-1</code> is used.</li> </ul> <p>The macro is equivalent to:</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=k>using</span><span class=w> </span><span class=k>namespace</span><span class=w> </span><span class=nn>nlohmann</span><span class=o>::</span><span class=nn>literals</span><span class=p>;</span>
<span class=k>namespace</span><span class=w> </span><span class=nn>ns</span>
@@ -191,7 +191,7 @@
<span class=w> </span><span class=c1>// serialization: person -&gt; json</span>
<span class=w> </span><span class=n>json</span><span class=w> </span><span class=n>j</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>p</span><span class=p>;</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>"serialization: "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>j</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>endl</span><span class=p>;</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>"serialization: "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>j</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=sc>'\n'</span><span class=p>;</span>
<span class=w> </span><span class=c1>// deserialization: json -&gt; person</span>
<span class=w> </span><span class=n>json</span><span class=w> </span><span class=n>j2</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=sa>R</span><span class=s>"</span><span class=dl>(</span><span class=s>{"address": "742 Evergreen Terrace", "age": 40, "name": "Homer Simpson"}</span><span class=dl>)</span><span class=s>"</span><span class=n>_json</span><span class=p>;</span>
@@ -200,12 +200,12 @@
<span class=w> </span><span class=c1>// incomplete deserialization:</span>
<span class=w> </span><span class=n>json</span><span class=w> </span><span class=n>j3</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=sa>R</span><span class=s>"</span><span class=dl>(</span><span class=s>{"address": "742 Evergreen Terrace", "name": "Maggie Simpson"}</span><span class=dl>)</span><span class=s>"</span><span class=n>_json</span><span class=p>;</span>
<span class=w> </span><span class=k>auto</span><span class=w> </span><span class=n>p3</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>j3</span><span class=p>.</span><span class=n>get</span><span class=o>&lt;</span><span class=n>ns</span><span class=o>::</span><span class=n>person</span><span class=o>&gt;</span><span class=p>();</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>"roundtrip: "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>json</span><span class=p>(</span><span class=n>p3</span><span class=p>)</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>endl</span><span class=p>;</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>"roundtrip: "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>json</span><span class=p>(</span><span class=n>p3</span><span class=p>)</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=sc>'\n'</span><span class=p>;</span>
<span class=p>}</span>
</code></pre></div> <p>Note how a default-initialized <code>person</code> object is used in the <code>from_json</code> to fill missing values.</p> </details> <details class=example> <summary>Example: (3) NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE</summary> <p>Consider the following complete example:</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=k>using</span><span class=w> </span><span class=k>namespace</span><span class=w> </span><span class=nn>nlohmann</span><span class=o>::</span><span class=nn>literals</span><span class=p>;</span>
<span class=k>namespace</span><span class=w> </span><span class=nn>ns</span>
@@ -226,13 +226,13 @@
<span class=w> </span><span class=c1>// serialization: person -&gt; json</span>
<span class=w> </span><span class=n>json</span><span class=w> </span><span class=n>j</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>p</span><span class=p>;</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>"serialization: "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>j</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>endl</span><span class=p>;</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>"serialization: "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>j</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=sc>'\n'</span><span class=p>;</span>
<span class=p>}</span>
</code></pre></div> <p>Output:</p> <div class=highlight><pre><span></span><code><span class=err>serializa</span><span class=kc>t</span><span class=err>io</span><span class=kc>n</span><span class=p>:</span><span class=w> </span><span class=p>{</span><span class=nt>"address"</span><span class=p>:</span><span class=s2>"744 Evergreen Terrace"</span><span class=p>,</span><span class=nt>"age"</span><span class=p>:</span><span class=mi>60</span><span class=p>,</span><span class=nt>"name"</span><span class=p>:</span><span class=s2>"Ned Flanders"</span><span class=p>}</span>
</code></pre></div> <p>Notes:</p> <ul> <li><code>ns::person</code> is non-default-constructible. This allows this macro to be used instead of <code>NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE</code> and <code>NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT</code>.</li> <li><code>ns::person</code> has only public member variables. This makes <code>NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE</code> applicable.</li> <li>The macro <code>NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE</code> is used <em>outside</em> the class, but <em>inside</em> its namespace <code>ns</code>.</li> </ul> <p>The macro is equivalent to:</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=k>using</span><span class=w> </span><span class=k>namespace</span><span class=w> </span><span class=nn>nlohmann</span><span class=o>::</span><span class=nn>literals</span><span class=p>;</span>
<span class=k>namespace</span><span class=w> </span><span class=nn>ns</span>
@@ -259,6 +259,6 @@
<span class=w> </span><span class=c1>// serialization: person -&gt; json</span>
<span class=w> </span><span class=n>json</span><span class=w> </span><span class=n>j</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>p</span><span class=p>;</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>"serialization: "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>j</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>endl</span><span class=p>;</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>"serialization: "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>j</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=sc>'\n'</span><span class=p>;</span>
<span class=p>}</span>
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../nlohmann_define_type_intrusive/ >NLOHMANN_DEFINE_TYPE_INTRUSIVE, NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT, NLOHMANN_DEFINE_TYPE_INTRUSIVE_ONLY_SERIALIZE</a> for a similar macro that can be defined <em>inside</em> the type.</li> <li><a href=../nlohmann_define_derived_type/ >NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE, NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_DEFAULT, NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_ONLY_SERIALIZE, NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE, NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_DEFAULT, NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE</a> for similar macros for derived types</li> <li><a href=../../../features/arbitrary_types/ >Arbitrary Type Conversions</a> for an overview.</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ol> <li>Added in version 3.9.0.</li> <li>Added in version 3.11.0.</li> <li>Added in version 3.11.3.</li> </ol> <p>All three macros were changed to work with any <code>basic_json</code> specialization (not only <code>nlohmann::json</code>) in version 3.12.0, and to allow an empty member list in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</p> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 11, 2026 06:21:51 UTC">October 11, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 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</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../nlohmann_define_type_intrusive/ >NLOHMANN_DEFINE_TYPE_INTRUSIVE, NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT, NLOHMANN_DEFINE_TYPE_INTRUSIVE_ONLY_SERIALIZE</a> for a similar macro that can be defined <em>inside</em> the type.</li> <li><a href=../nlohmann_define_derived_type/ >NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE, NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_DEFAULT, NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_ONLY_SERIALIZE, NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE, NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_DEFAULT, NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE</a> for similar macros for derived types</li> <li><a href=../../../features/arbitrary_types/ >Arbitrary Type Conversions</a> for an overview.</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ol> <li>Added in version 3.9.0.</li> <li>Added in version 3.11.0.</li> <li>Added in version 3.11.3.</li> </ol> <p>All three macros were changed to work with any <code>basic_json</code> specialization (not only <code>nlohmann::json</code>) in version 3.12.0, and to allow an empty member list in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</p> <p>The generated <code>from_json()</code> reads the views of <code>json_document</code>s since version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</p> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 26, 2026 19:13:31 UTC">October 26, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 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@@ -63,6 +63,10 @@ Implementation limits
- The current implementation is limited to at most 63 member variables. If you want to serialize/deserialize types with more than 63 member variables, you need to define the `to_json`/`from_json` functions manually.
- These macros always produce object-style (named-key) JSON, one key per member. There is no macro variant that serializes a struct's members positionally into a JSON array; for that, write `to_json`/`from_json` by hand, building/reading a `json::array()` of the members in order.
Views
The generated `from_json()` also reads the views of [`json_document`](https://json.nlohmann.me/api/json_document/index.md)s (`<nlohmann/json_view.hpp>`): [`get<T>()`](https://json.nlohmann.me/api/basic_json_view/get/index.md) on a view looks the members up in the view, without building a `json` value first.
## Examples
Example: (1) NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE
@@ -73,7 +77,7 @@ Consider the following complete example:
#include <iostream>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using nlohmann::json;
using namespace nlohmann::literals;
namespace ns
@@ -94,7 +98,7 @@ int main()
// serialization: person -> json
json j = p;
std::cout << "serialization: " << j << std::endl;
std::cout << "serialization: " << j << '\n';
// deserialization: json -> person
json j2 = R"({"address": "742 Evergreen Terrace", "age": 40, "name": "Homer Simpson"})"_json;
@@ -108,7 +112,7 @@ int main()
}
catch (const json::exception& e)
{
std::cout << "deserialization failed: " << e.what() << std::endl;
std::cout << "deserialization failed: " << e.what() << '\n';
}
}
```
@@ -133,7 +137,7 @@ The macro is equivalent to:
#include <iostream>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using nlohmann::json;
using namespace nlohmann::literals;
namespace ns
@@ -168,7 +172,7 @@ int main()
// serialization: person -> json
json j = p;
std::cout << "serialization: " << j << std::endl;
std::cout << "serialization: " << j << '\n';
// deserialization: json -> person
json j2 = R"({"address": "742 Evergreen Terrace", "age": 40, "name": "Homer Simpson"})"_json;
@@ -182,7 +186,7 @@ int main()
}
catch (const json::exception& e)
{
std::cout << "deserialization failed: " << e.what() << std::endl;
std::cout << "deserialization failed: " << e.what() << '\n';
}
}
```
@@ -195,7 +199,7 @@ Consider the following complete example:
#include <iostream>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using nlohmann::json;
using namespace nlohmann::literals;
namespace ns
@@ -221,7 +225,7 @@ int main()
// serialization: person -> json
json j = p;
std::cout << "serialization: " << j << std::endl;
std::cout << "serialization: " << j << '\n';
// deserialization: json -> person
json j2 = R"({"address": "742 Evergreen Terrace", "age": 40, "name": "Homer Simpson"})"_json;
@@ -230,7 +234,7 @@ int main()
// incomplete deserialization:
json j3 = R"({"address": "742 Evergreen Terrace", "name": "Maggie Simpson"})"_json;
auto p3 = j3.get<ns::person>();
std::cout << "roundtrip: " << json(p3) << std::endl;
std::cout << "roundtrip: " << json(p3) << '\n';
}
```
@@ -254,7 +258,7 @@ The macro is equivalent to:
#include <iostream>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using nlohmann::json;
using namespace nlohmann::literals;
namespace ns
@@ -295,7 +299,7 @@ int main()
// serialization: person -> json
json j = p;
std::cout << "serialization: " << j << std::endl;
std::cout << "serialization: " << j << '\n';
// deserialization: json -> person
json j2 = R"({"address": "742 Evergreen Terrace", "age": 40, "name": "Homer Simpson"})"_json;
@@ -304,7 +308,7 @@ int main()
// incomplete deserialization:
json j3 = R"({"address": "742 Evergreen Terrace", "name": "Maggie Simpson"})"_json;
auto p3 = j3.get<ns::person>();
std::cout << "roundtrip: " << json(p3) << std::endl;
std::cout << "roundtrip: " << json(p3) << '\n';
}
```
@@ -318,7 +322,7 @@ Consider the following complete example:
#include <iostream>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using nlohmann::json;
using namespace nlohmann::literals;
namespace ns
@@ -339,7 +343,7 @@ int main()
// serialization: person -> json
json j = p;
std::cout << "serialization: " << j << std::endl;
std::cout << "serialization: " << j << '\n';
}
```
@@ -361,7 +365,7 @@ The macro is equivalent to:
#include <iostream>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using nlohmann::json;
using namespace nlohmann::literals;
namespace ns
@@ -388,7 +392,7 @@ int main()
// serialization: person -> json
json j = p;
std::cout << "serialization: " << j << std::endl;
std::cout << "serialization: " << j << '\n';
}
```
@@ -405,3 +409,5 @@ int main()
1. Added in version 3.11.3.
All three macros were changed to work with any `basic_json` specialization (not only `nlohmann::json`) in version 3.12.0, and to allow an empty member list in version 3.13.0 unreleased.
The generated `from_json()` reads the views of `json_document`s since version 3.13.0 unreleased.
@@ -53,7 +53,7 @@ For further information please refer to the corresponding macros without `WITH_N
#include <iostream>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using nlohmann::json;
using namespace nlohmann::literals;
namespace ns
@@ -74,7 +74,7 @@ For further information please refer to the corresponding macros without `WITH_N
// serialization: person -> json
json j = p;
std::cout << "serialization: " << j << std::endl;
std::cout << "serialization: " << j << '\n';
// deserialization: json -> person
json j2 = R"({"json_address": "742 Evergreen Terrace", "json_age": 40, "json_name": "Homer Simpson"})"_json;
@@ -88,7 +88,7 @@ For further information please refer to the corresponding macros without `WITH_N
}
catch (const json::exception& e)
{
std::cout << "deserialization failed: " << e.what() << std::endl;
std::cout << "deserialization failed: " << e.what() << '\n';
}
}
@@ -116,7 +116,7 @@ For further information please refer to the corresponding macros without `WITH_N
#include <iostream>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using nlohmann::json;
using namespace nlohmann::literals;
namespace ns
@@ -151,7 +151,7 @@ For further information please refer to the corresponding macros without `WITH_N
// serialization: person -> json
json j = p;
std::cout << "serialization: " << j << std::endl;
std::cout << "serialization: " << j << '\n';
// deserialization: json -> person
json j2 = R"({"json_address": "742 Evergreen Terrace", "json_age": 40, "json_name": "Homer Simpson"})"_json;
@@ -165,7 +165,7 @@ For further information please refer to the corresponding macros without `WITH_N
}
catch (const json::exception& e)
{
std::cout << "deserialization failed: " << e.what() << std::endl;
std::cout << "deserialization failed: " << e.what() << '\n';
}
}
@@ -1,4 +1,4 @@
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/macros/nlohmann_define_type_with_names/" rel="canonical"><link href=../nlohmann_define_type_non_intrusive/ rel=prev><link href=../nlohmann_json_namespace/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_NAMES, NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT_WITH_NAMES, NLOHMANN_DEFINE_TYPE_INTRUSIVE_ONLY_SERIALIZE_WITH_NAMES, NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_NAMES, NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT_WITH_NAMES, NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE_WITH_NAMES, NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_NAMES, NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_DEFAULT_WITH_NAMES, NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_ONLY_SERIALIZE_WITH_NAMES, NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_NAMES, NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_DEFAULT_WITH_NAMES, NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE_WITH_NAMES - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new URL("../../..",location),__md_hash=e=>[...e].reduce(((e,_)=>(e<<5)-e+_.charCodeAt(0)),0),__md_get=(e,_=localStorage,t=__md_scope)=>JSON.parse(_.getItem(t.pathname+"."+e)),__md_set=(e,_,t=localStorage,a=__md_scope)=>{try{t.setItem(a.pathname+"."+e,JSON.stringify(_))}catch(e){}}</script></head> <body dir=ltr data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo> <input class=md-toggle data-md-toggle=drawer type=checkbox id=__drawer autocomplete=off> <input class=md-toggle data-md-toggle=search type=checkbox id=__search autocomplete=off> <label class=md-overlay for=__drawer></label> <div data-md-component=skip> <a href=#parameters class=md-skip> Skip to content </a> </div> <div data-md-component=announce> </div> <header class=md-header data-md-component=header> <nav class="md-header__inner md-grid" aria-label=Header> <a href=../../.. title="JSON for Modern C++" class="md-header__button md-logo" aria-label="JSON for Modern C++" data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_NAMES, NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT_WITH_NAMES, NLOHMANN_DEFINE_TYPE_INTRUSIVE_ONLY_SERIALIZE_WITH_NAMES, NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_NAMES, NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT_WITH_NAMES, NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE_WITH_NAMES, NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_NAMES, NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_DEFAULT_WITH_NAMES, NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_ONLY_SERIALIZE_WITH_NAMES, NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_NAMES, NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_DEFAULT_WITH_NAMES, NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE_WITH_NAMES </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark mode" type=radio name=__palette id=__palette_0> <label class="md-header__button md-icon" title="Switch to dark mode" for=__palette_1 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a4 4 0 0 0-4 4 4 4 0 0 0 4 4 4 4 0 0 0 4-4 4 4 0 0 0-4-4m0 10a6 6 0 0 1-6-6 6 6 0 0 1 6-6 6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> <input class=md-option data-md-color-media="(prefers-color-scheme: dark)" data-md-color-scheme=slate data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to light mode" type=radio name=__palette id=__palette_1> <label class="md-header__buLine truncated
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/macros/nlohmann_define_type_with_names/" rel="canonical"><link href=../nlohmann_define_type_non_intrusive/ rel=prev><link href=../nlohmann_json_namespace/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_NAMES, NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT_WITH_NAMES, NLOHMANN_DEFINE_TYPE_INTRUSIVE_ONLY_SERIALIZE_WITH_NAMES, NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_NAMES, NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT_WITH_NAMES, NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE_WITH_NAMES, NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_NAMES, NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_DEFAULT_WITH_NAMES, NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_ONLY_SERIALIZE_WITH_NAMES, NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_NAMES, NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_DEFAULT_WITH_NAMES, NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE_WITH_NAMES - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new URL("../../..",location),__md_hash=e=>[...e].reduce(((e,_)=>(e<<5)-e+_.charCodeAt(0)),0),__md_get=(e,_=localStorage,t=__md_scope)=>JSON.parse(_.getItem(t.pathname+"."+e)),__md_set=(e,_,t=localStorage,a=__md_scope)=>{try{t.setItem(a.pathname+"."+e,JSON.stringify(_))}catch(e){}}</script></head> <body dir=ltr data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo> <input class=md-toggle data-md-toggle=drawer type=checkbox id=__drawer autocomplete=off> <input class=md-toggle data-md-toggle=search type=checkbox id=__search autocomplete=off> <label class=md-overlay for=__drawer></label> <div data-md-component=skip> <a href=#parameters class=md-skip> Skip to content </a> </div> <div data-md-component=announce> </div> <header class=md-header data-md-component=header> <nav class="md-header__inner md-grid" aria-label=Header> <a href=../../.. title="JSON for Modern C++" class="md-header__button md-logo" aria-label="JSON for Modern C++" data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_NAMES, NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT_WITH_NAMES, NLOHMANN_DEFINE_TYPE_INTRUSIVE_ONLY_SERIALIZE_WITH_NAMES, NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_NAMES, NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT_WITH_NAMES, NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE_WITH_NAMES, NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_NAMES, NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_DEFAULT_WITH_NAMES, NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_ONLY_SERIALIZE_WITH_NAMES, NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_NAMES, NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_DEFAULT_WITH_NAMES, NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE_WITH_NAMES </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark mode" type=radio name=__palette id=__palette_0> <label class="md-header__button md-icon" title="Switch to dark mode" for=__palette_1 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a4 4 0 0 0-4 4 4 4 0 0 0 4 4 4 4 0 0 0 4-4 4 4 0 0 0-4-4m0 10a6 6 0 0 1-6-6 6 6 0 0 1 6-6 6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> <input class=md-option data-md-color-media="(prefers-color-scheme: dark)" data-md-color-scheme=slate data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to light mode" type=radio name=__palette id=__palette_1> <label class="md-header__buLine truncated
<span class=cp>#define NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT_WITH_NAMES(type, "json_member_name", member...)</span>
<span class=cp>#define NLOHMANN_DEFINE_TYPE_INTRUSIVE_ONLY_SERIALIZE_WITH_NAMES(type, "json_member_name", member...)</span>
<span class=cp>#define NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_NAMES(type, "json_member_name", member...)</span>
@@ -13,7 +13,7 @@
</code></pre></div> <p>These macros can be used in case you want to use the custom names for the member variables in the resulting <abbr title="JavaScript Object Notation">JSON</abbr>. They behave exactly as their non-<code>WITH_NAMES</code> counterparts, but require an additional parameter for each member variable which will be used in <abbr title="JavaScript Object Notation">JSON</abbr>. Both serialization and deserialization will only use the custom names for <abbr title="JavaScript Object Notation">JSON</abbr>, the names of the member variables themselves will be ignored.</p> <p>Using the named conversion macros will halve the maximum number of member variables from 63 to 31.</p> <p>For further information please refer to the corresponding macros without <code>WITH_NAMES</code>.</p> <h2 id=parameters>Parameters<a class=headerlink href=#parameters title="Permanent link">&para;</a></h2> <dl> <dt><code>type</code> (in)</dt> <dd>name of the type (class, struct) to serialize/deserialize</dd> <dt><code>base_type</code> (in)</dt> <dd>name of the base type (class, struct) <code>type</code> is derived from (used only in <code>DEFINE_DERIVED_TYPE</code> macros)</dd> <dt><code>json_member_name</code> (in)</dt> <dd>the string that will be used as the name for the next value</dd> <dt><code>member</code> (in)</dt> <dd>name of the member variable to serialize/deserialize</dd> </dl> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example: NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_NAMES</summary> <p>Consider the following complete example:</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=k>using</span><span class=w> </span><span class=k>namespace</span><span class=w> </span><span class=nn>nlohmann</span><span class=o>::</span><span class=nn>literals</span><span class=p>;</span>
<span class=k>namespace</span><span class=w> </span><span class=nn>ns</span>
@@ -34,7 +34,7 @@
<span class=w> </span><span class=c1>// serialization: person -&gt; json</span>
<span class=w> </span><span class=n>json</span><span class=w> </span><span class=n>j</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>p</span><span class=p>;</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>"serialization: "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>j</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>endl</span><span class=p>;</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>"serialization: "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>j</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=sc>'\n'</span><span class=p>;</span>
<span class=w> </span><span class=c1>// deserialization: json -&gt; person</span>
<span class=w> </span><span class=n>json</span><span class=w> </span><span class=n>j2</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=sa>R</span><span class=s>"</span><span class=dl>(</span><span class=s>{"json_address": "742 Evergreen Terrace", "json_age": 40, "json_name": "Homer Simpson"}</span><span class=dl>)</span><span class=s>"</span><span class=n>_json</span><span class=p>;</span>
@@ -48,7 +48,7 @@
<span class=w> </span><span class=p>}</span>
<span class=w> </span><span class=k>catch</span><span class=w> </span><span class=p>(</span><span class=k>const</span><span class=w> </span><span class=n>json</span><span class=o>::</span><span class=n>exception</span><span class=o>&amp;</span><span class=w> </span><span class=n>e</span><span class=p>)</span>
<span class=w> </span><span class=p>{</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>"deserialization failed: "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>e</span><span class=p>.</span><span class=n>what</span><span class=p>()</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>endl</span><span class=p>;</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>"deserialization failed: "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>e</span><span class=p>.</span><span class=n>what</span><span class=p>()</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=sc>'\n'</span><span class=p>;</span>
<span class=w> </span><span class=p>}</span>
<span class=p>}</span>
</code></pre></div> <p>Output:</p> <div class=highlight><pre><span></span><code><span class=err>serializa</span><span class=kc>t</span><span class=err>io</span><span class=kc>n</span><span class=p>:</span><span class=w> </span><span class=p>{</span><span class=nt>"json_address"</span><span class=p>:</span><span class=s2>"744 Evergreen Terrace"</span><span class=p>,</span><span class=nt>"json_age"</span><span class=p>:</span><span class=mi>60</span><span class=p>,</span><span class=nt>"json_name"</span><span class=p>:</span><span class=s2>"Ned Flanders"</span><span class=p>}</span>
@@ -56,7 +56,7 @@
</code></pre></div> <p>Notes:</p> <ul> <li><code>ns::person</code> is default-constructible. This is a requirement for using the macro.</li> <li><code>ns::person</code> has only public member variables. This makes <code>NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_NAMES</code> applicable.</li> <li>The macro <code>NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_NAMES</code> is used <em>outside</em> the class, but <em>inside</em> its namespace <code>ns</code>.</li> <li>A missing key "age" in the deserialization yields an exception. To fall back to the default value, <code>NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT_WITH_NAMES</code> can be used.</li> </ul> <p>The macro is equivalent to:</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=k>using</span><span class=w> </span><span class=k>namespace</span><span class=w> </span><span class=nn>nlohmann</span><span class=o>::</span><span class=nn>literals</span><span class=p>;</span>
<span class=k>namespace</span><span class=w> </span><span class=nn>ns</span>
@@ -91,7 +91,7 @@
<span class=w> </span><span class=c1>// serialization: person -&gt; json</span>
<span class=w> </span><span class=n>json</span><span class=w> </span><span class=n>j</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>p</span><span class=p>;</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>"serialization: "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>j</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>endl</span><span class=p>;</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>"serialization: "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>j</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=sc>'\n'</span><span class=p>;</span>
<span class=w> </span><span class=c1>// deserialization: json -&gt; person</span>
<span class=w> </span><span class=n>json</span><span class=w> </span><span class=n>j2</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=sa>R</span><span class=s>"</span><span class=dl>(</span><span class=s>{"json_address": "742 Evergreen Terrace", "json_age": 40, "json_name": "Homer Simpson"}</span><span class=dl>)</span><span class=s>"</span><span class=n>_json</span><span class=p>;</span>
@@ -105,7 +105,7 @@
<span class=w> </span><span class=p>}</span>
<span class=w> </span><span class=k>catch</span><span class=w> </span><span class=p>(</span><span class=k>const</span><span class=w> </span><span class=n>json</span><span class=o>::</span><span class=n>exception</span><span class=o>&amp;</span><span class=w> </span><span class=n>e</span><span class=p>)</span>
<span class=w> </span><span class=p>{</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>"deserialization failed: "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>e</span><span class=p>.</span><span class=n>what</span><span class=p>()</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>endl</span><span class=p>;</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>"deserialization failed: "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>e</span><span class=p>.</span><span class=n>what</span><span class=p>()</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=sc>'\n'</span><span class=p>;</span>
<span class=w> </span><span class=p>}</span>
<span class=p>}</span>
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../nlohmann_define_type_intrusive/ >NLOHMANN_DEFINE_TYPE_INTRUSIVE, NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT, NLOHMANN_DEFINE_TYPE_INTRUSIVE_ONLY_SERIALIZE</a> - the macros these variants add custom <abbr title="JavaScript Object Notation">JSON</abbr> key names to</li> <li><a href=../nlohmann_define_type_non_intrusive/ >NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE, NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT, NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE</a> - the macros these variants add custom <abbr title="JavaScript Object Notation">JSON</abbr> key names to</li> <li><a href=../nlohmann_define_derived_type/ >NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE, NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_DEFAULT, NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_ONLY_SERIALIZE, NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE, NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_DEFAULT, NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE</a> - similar macros for derived types, also available with custom names</li> <li><a href=../../../features/arbitrary_types/ >Arbitrary Type Conversions</a> - overview of type conversion mechanisms</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ul> <li>Added in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 2, 2026 09:32:15 UTC">October 2, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 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@@ -41,7 +41,7 @@ Consider the following complete example:
#include <iostream>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using nlohmann::json;
using namespace nlohmann::literals;
namespace ns
@@ -62,7 +62,7 @@ int main()
// serialization: person -> json
json j = p;
std::cout << "serialization: " << j << std::endl;
std::cout << "serialization: " << j << '\n';
// deserialization: json -> person
json j2 = R"({"json_address": "742 Evergreen Terrace", "json_age": 40, "json_name": "Homer Simpson"})"_json;
@@ -76,7 +76,7 @@ int main()
}
catch (const json::exception& e)
{
std::cout << "deserialization failed: " << e.what() << std::endl;
std::cout << "deserialization failed: " << e.what() << '\n';
}
}
```
@@ -101,7 +101,7 @@ The macro is equivalent to:
#include <iostream>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using nlohmann::json;
using namespace nlohmann::literals;
namespace ns
@@ -136,7 +136,7 @@ int main()
// serialization: person -> json
json j = p;
std::cout << "serialization: " << j << std::endl;
std::cout << "serialization: " << j << '\n';
// deserialization: json -> person
json j2 = R"({"json_address": "742 Evergreen Terrace", "json_age": 40, "json_name": "Homer Simpson"})"_json;
@@ -150,7 +150,7 @@ int main()
}
catch (const json::exception& e)
{
std::cout << "deserialization failed: " << e.what() << std::endl;
std::cout << "deserialization failed: " << e.what() << '\n';
}
}
```
+4 -4
View File
@@ -26,7 +26,7 @@ the library.
#include <nlohmann/json.hpp>
// possible use case: use NLOHMANN_JSON_NAMESPACE instead of nlohmann
using json = NLOHMANN_JSON_NAMESPACE::json;
using NLOHMANN_JSON_NAMESPACE::json;
// macro needed to output the NLOHMANN_JSON_NAMESPACE as string literal
#define Q(x) #x
@@ -34,7 +34,7 @@ the library.
int main()
{
std::cout << QUOTE(NLOHMANN_JSON_NAMESPACE) << std::endl;
std::cout << QUOTE(NLOHMANN_JSON_NAMESPACE) << '\n';
}
```
@@ -54,6 +54,6 @@ the library.
## Version history
- Added in version 3.11.0. Changed inline namespace name in version 3.11.2. Added the ABI tag `_dp` in
version 3.12.0, and the ABI tags `_bics`, `_psp`, `_snul`, `_sbu8`, `_ekmo`, `_dsbs`, `_dufio`, `_ns`, `_vns`,
and `_vssse3` in version 3.13.0; see
version 3.12.0, and the ABI tags `_bics`, `_psp`, `_snul`, `_sbu8`, `_ekmo`, `_dsbs`, `_dufio`, and `_ns` in
version 3.13.0; see
[`nlohmann` Namespace](../../features/namespace.md#structure).
@@ -1,9 +1,9 @@
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/macros/nlohmann_json_namespace/" rel="canonical"><link href=../nlohmann_define_type_with_names/ rel=prev><link href=../nlohmann_json_namespace_begin/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>NLOHMANN_JSON_NAMESPACE - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new 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</code></pre></div> <p>This macro evaluates to the full name of the <code>nlohmann</code> namespace.</p> <h2 id=default-definition>Default definition<a class=headerlink href=#default-definition title="Permanent link">&para;</a></h2> <p>The default value consists of the root namespace (<code>nlohmann</code>) and an inline ABI namespace. See <a href=../../../features/namespace/#structure><code>nlohmann</code> Namespace</a> for details.</p> <p>When the macro is not defined, the library will define it to its default value. Overriding this value has no effect on the library.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The example shows how to use <code>NLOHMANN_JSON_NAMESPACE</code> instead of just <code>nlohmann</code>, as well as how to output the value of <code>NLOHMANN_JSON_NAMESPACE</code>.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/macros/nlohmann_json_namespace/" rel="canonical"><link href=../nlohmann_define_type_with_names/ rel=prev><link href=../nlohmann_json_namespace_begin/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>NLOHMANN_JSON_NAMESPACE - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new URL("../../..",location),__md_hash=e=>[...e].reduce(((e,_)=>(e<<5)-e+_.charCodeAt(0)),0),__md_get=(e,_=localStorage,t=__md_scope)=>JSON.parse(_.getItem(t.pathname+"."+e)),__md_set=(e,_,t=localStorage,a=__md_scope)=>{try{t.setItem(a.pathname+"."+e,JSON.stringify(_))}catch(e){}}</script></head> <body dir=ltr data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo> <input class=md-toggle data-md-toggle=drawer type=checkbox id=__drawer autocomplete=off> <input class=md-toggle data-md-toggle=search type=checkbox id=__search autocomplete=off> <label class=md-overlay for=__drawer></label> <div data-md-component=skip> <a href=#nlohmann_json_namespace class=md-skip> Skip to content </a> </div> <div data-md-component=announce> </div> <header class=md-header data-md-component=header> <nav class="md-header__inner md-grid" aria-label=Header> <a href=../../.. title="JSON for Modern C++" class="md-header__button md-logo" aria-label="JSON for Modern C++" data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> NLOHMANN_JSON_NAMESPACE </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo 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6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.52 6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5Line truncated
</code></pre></div> <p>This macro evaluates to the full name of the <code>nlohmann</code> namespace.</p> <h2 id=default-definition>Default definition<a class=headerlink href=#default-definition title="Permanent link">&para;</a></h2> <p>The default value consists of the root namespace (<code>nlohmann</code>) and an inline <abbr title="Application Binary Interface">ABI</abbr> namespace. See <a href=../../../features/namespace/#structure><code>nlohmann</code> Namespace</a> for details.</p> <p>When the macro is not defined, the library will define it to its default value. Overriding this value has no effect on the library.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The example shows how to use <code>NLOHMANN_JSON_NAMESPACE</code> instead of just <code>nlohmann</code>, as well as how to output the value of <code>NLOHMANN_JSON_NAMESPACE</code>.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=c1>// possible use case: use NLOHMANN_JSON_NAMESPACE instead of nlohmann</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>NLOHMANN_JSON_NAMESPACE</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=k>using</span><span class=w> </span><span class=n>NLOHMANN_JSON_NAMESPACE</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=c1>// macro needed to output the NLOHMANN_JSON_NAMESPACE as string literal</span>
<span class=cp>#define Q(x) #x</span>
@@ -11,7 +11,7 @@
<span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span>
<span class=p>{</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>QUOTE</span><span class=p>(</span><span class=n>NLOHMANN_JSON_NAMESPACE</span><span class=p>)</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>endl</span><span class=p>;</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>QUOTE</span><span class=p>(</span><span class=n>NLOHMANN_JSON_NAMESPACE</span><span class=p>)</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=sc>'\n'</span><span class=p>;</span>
<span class=p>}</span>
</code></pre></div> <p>Output:</p> <div class=highlight><pre><span></span><code><span class=kc>nl</span><span class=err>ohma</span><span class=kc>nn</span><span class=p>::</span><span class=err>jso</span><span class=kc>n</span><span class=err>_abi_v</span><span class=mi>3</span><span class=err>_</span><span class=mi>12</span><span class=err>_</span><span class=mi>0</span>
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../nlohmann_json_namespace_begin/ ><code>NLOHMANN_JSON_NAMESPACE_BEGIN, NLOHMANN_JSON_NAMESPACE_END</code></a></li> <li><a href=../nlohmann_json_namespace_no_version/ ><code>NLOHMANN_JSON_NAMESPACE_NO_VERSION</code></a></li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ul> <li>Added in version 3.11.0. Changed inline namespace name in version 3.11.2. Added the ABI tag <code>_dp</code> in version 3.12.0, and the ABI tags <code>_bics</code>, <code>_psp</code>, <code>_snul</code>, <code>_sbu8</code>, <code>_ekmo</code>, <code>_dsbs</code>, <code>_dufio</code>, <code>_ns</code>, <code>_vns</code>, and <code>_vssse3</code> in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>; see <a href=../../../features/namespace/#structure><code>nlohmann</code> Namespace</a>.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 21, 2026 18:00:50 UTC">October 21, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 2013-2026 Niels Lohmann </div> </div> <div class=md-social> <a href="https://github.com/nlohmann" target="_blank" rel="noopener" title="github.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 512 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M173.9 397.4c0 2-2.3 3.6-5.2 3.6-3.3.3-5.6-1.3-5.6-3.6 0-2 2.3-3.6 5.2-3.6 3-.3 5.6 1.3 5.6 3.6m-31.1-4.5c-.7 2 1.3 4.3 4.3 4.9 2.6 1 5.6 0 6.2-2s-1.3-4.3-4.3-5.2c-2.6-.7-5.5.3-6.2 2.3m44.2-1.7c-2.9.7-4.9 2.6-4.6 4.9.3 2 2.9 3.3 5.9 2.6 2.9-.7 4.9-2.6 4.6-4.6-.3-1.9-3-3.2-5.9-2.9M252.8 8C114.1 8 8 113.3 8 252c0 110.9 69.8 205.8 169.5 239.2 12.8 2.3 17.3-5.6 17.3-12.1 0-6.2-.3-40.4-.3-61.4 0 0-70 15-84.7-29.8 0 0-11.4-29.1-27.8-36.6 0 0-22.9-15.7 1.6-15.4 0 0 24.9 2 38.6 25.8 21.9 38.6 58.6 27.5 72.9 20.9 2.3-16 8.8-27.1 16-33.7-55.9-6.2-112.3-14.3-112.3-110.5 0-27.5 7.6-41.3 23.6-58.9-2.6-6.5-11.1-33.3 2.6-67.9 20.9-6.5 69 27 69 27 20-5.6 41.5-8.5 62.8-8.5s42.8 2.9 62.8 8.5c0 0 48.1-33.6 69-27 13.7 34.7 5.2 61.4 2.6 67.9 16 17.7 25.8 31.5 25.8 58.9 0 96.5-58.9 104.2-114.8 110.5 9.2 7.9 17 22.9 17 46.4 0 33.7-.3 75.4-.3 83.6 0 6.5 4.6 14.4 17.3 12.1C436.2 457.8 504 362.9 504 252 504 113.3 391.5 8 252.8 8M105.2 352.9c-1.3 1-1 3.3.7 5.2 1.6 1.6 3.9 2.3 5.2 1 1.3-1 1-3.3-.7-5.2-1.6-1.6-3.9-2.3-5.2-1m-10.8-8.1c-.7 1.3.3 2.9 2.3 3.9 1.6 1 3.6.7 4.3-.7.7-1.3-.3-2.9-2.3-3.9-2-.6-3.6-.3-4.3.7m32.4 35.6c-1.6 1.3-1 4.3 1.3 6.2 2.3 2.3 5.2 2.6 6.5 1 1.3-1.3.7-4.3-1.3-6.2-2.2-2.3-5.2-2.6-6.5-1m-11.4-14.7c-1.6 1-1.6 3.6 0 5.9s4.3 3.3 5.6 2.3c1.6-1.3 1.6-3.9 0-6.2-1.4-2.3-4-3.3-5.6-2"/></svg> </a> <a href="https://www.linkedin.com/in/nielslohmann/" target="_blank" rel="noopener" title="www.linkedin.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 448 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M416 32H31.9C14.3 32 0 46.5 Line truncated
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../nlohmann_json_namespace_begin/ ><code>NLOHMANN_JSON_NAMESPACE_BEGIN, NLOHMANN_JSON_NAMESPACE_END</code></a></li> <li><a href=../nlohmann_json_namespace_no_version/ ><code>NLOHMANN_JSON_NAMESPACE_NO_VERSION</code></a></li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ul> <li>Added in version 3.11.0. Changed inline namespace name in version 3.11.2. Added the <abbr title="Application Binary Interface">ABI</abbr> tag <code>_dp</code> in version 3.12.0, and the <abbr title="Application Binary Interface">ABI</abbr> tags <code>_bics</code>, <code>_psp</code>, <code>_snul</code>, <code>_sbu8</code>, <code>_ekmo</code>, <code>_dsbs</code>, <code>_dufio</code>, and <code>_ns</code> in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>; see <a href=../../../features/namespace/#structure><code>nlohmann</code> Namespace</a>.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 26, 2026 19:13:31 UTC">October 26, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 2013-2026 Niels Lohmann </div> </div> <div class=md-social> <a href="https://github.com/nlohmann" target="_blank" rel="noopener" title="github.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 512 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M173.9 397.4c0 2-2.3 3.6-5.2 3.6-3.3.3-5.6-1.3-5.6-3.6 0-2 2.3-3.6 5.2-3.6 3-.3 5.6 1.3 5.6 3.6m-31.1-4.5c-.7 2 1.3 4.3 4.3 4.9 2.6 1 5.6 0 6.2-2s-1.3-4.3-4.3-5.2c-2.6-.7-5.5.3-6.2 2.3m44.2-1.7c-2.9.7-4.9 2.6-4.6 4.9.3 2 2.9 3.3 5.9 2.6 2.9-.7 4.9-2.6 4.6-4.6-.3-1.9-3-3.2-5.9-2.9M252.8 8C114.1 8 8 113.3 8 252c0 110.9 69.8 205.8 169.5 239.2 12.8 2.3 17.3-5.6 17.3-12.1 0-6.2-.3-40.4-.3-61.4 0 0-70 15-84.7-29.8 0 0-11.4-29.1-27.8-36.6 0 0-22.9-15.7 1.6-15.4 0 0 24.9 2 38.6 25.8 21.9 38.6 58.6 27.5 72.9 20.9 2.3-16 8.8-27.1 16-33.7-55.9-6.2-112.3-14.3-112.3-110.5 0-27.5 7.6-41.3 23.6-58.9-2.6-6.5-11.1-33.3 2.6-67.9 20.9-6.5 69 27 69 27 20-5.6 41.5-8.5 62.8-8.5s42.8 2.9 62.8 8.5c0 0 48.1-33.6 69-27 13.7 34.7 5.2 61.4 2.6 67.9 16 17.7 25.8 31.5 25.8 58.9 0 96.5-58.9 104.2-114.8 110.5 9.2 7.9 17 22.9 17 46.4 0 33.7-.3 75.4-.3 83.6 0 6.5 4.6 14.4 17.3 12.1C436.2 457.8 504 362.9 504 252 504 113.3 391.5 8 252.8 8M105.2 352.9c-1.3 1-1 3.3.7 5.2 1.6 1.6 3.9 2.3 5.2 1 1.3-1 1-3.3-.7-5.2-1.6-1.6-3.9-2.3-5.2-1m-10.8-8.1c-.7 1.3.3 2.9 2.3 3.9 1.6 1 3.6.7 4.3-.7.7-1.3-.3-2.9-2.3-3.9-2-.6-3.6-.3-4.3.7m32.4 35.6c-1.6 1.3-1 4.3 1.3 6.2 2.3 2.3 5.2 2.6 6.5 1 1.3-1.3.7-4.3-1.3-6.2-2.2-2.3-5.2-2.6-6.5-1m-11.4-14.7c-1.6 1-1.6 3.6 0 5.9s4.3 3.3 5.6 2.3c1.6-1.3 1.6-3.9 0-6.2-1.4-2.3-4-3.3-5.6-2"/></svg> </a> <a href="https://www.linkedin.com/in/nielslohmann/" target="_blank" rel="noopener" title="www.linkedin.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 448 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2Line truncated
+3 -3
View File
@@ -23,7 +23,7 @@ The example shows how to use `NLOHMANN_JSON_NAMESPACE` instead of just `nlohmann
#include <nlohmann/json.hpp>
// possible use case: use NLOHMANN_JSON_NAMESPACE instead of nlohmann
using json = NLOHMANN_JSON_NAMESPACE::json;
using NLOHMANN_JSON_NAMESPACE::json;
// macro needed to output the NLOHMANN_JSON_NAMESPACE as string literal
#define Q(x) #x
@@ -31,7 +31,7 @@ using json = NLOHMANN_JSON_NAMESPACE::json;
int main()
{
std::cout << QUOTE(NLOHMANN_JSON_NAMESPACE) << std::endl;
std::cout << QUOTE(NLOHMANN_JSON_NAMESPACE) << '\n';
}
```
@@ -48,4 +48,4 @@ nlohmann::json_abi_v3_12_0
## Version history
- Added in version 3.11.0. Changed inline namespace name in version 3.11.2. Added the ABI tag `_dp` in version 3.12.0, and the ABI tags `_bics`, `_psp`, `_snul`, `_sbu8`, `_ekmo`, `_dsbs`, `_dufio`, `_ns`, `_vns`, and `_vssse3` in version 3.13.0 unreleased; see [`nlohmann` Namespace](https://json.nlohmann.me/features/namespace/#structure).
- Added in version 3.11.0. Changed inline namespace name in version 3.11.2. Added the ABI tag `_dp` in version 3.12.0, and the ABI tags `_bics`, `_psp`, `_snul`, `_sbu8`, `_ekmo`, `_dsbs`, `_dufio`, and `_ns` in version 3.13.0 unreleased; see [`nlohmann` Namespace](https://json.nlohmann.me/features/namespace/#structure).
+1 -1
View File
@@ -72,7 +72,7 @@ When these macros are not defined, the library will define them to their default
NLOHMANN_JSON_NAMESPACE::json j;
j.push_back(o1);
j.push_back(o2);
std::cout << j << std::endl;
std::cout << j << '\n';
}
```
@@ -1,4 +1,4 @@
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/macros/nlohmann_json_namespace_begin/" rel="canonical"><link href=../nlohmann_json_namespace/ rel=prev><link href=../nlohmann_json_namespace_no_version/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>NLOHMANN_JSON_NAMESPACE_BEGIN, NLOHMANN_JSON_NAMESPACE_END - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new 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0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 Line truncated
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for Modern C++" data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> NLOHMANN_JSON_NAMESPACE_BEGIN, NLOHMANN_JSON_NAMESPACE_END </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default 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0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 Line truncated
<span class=cp>#define NLOHMANN_JSON_NAMESPACE_END </span><span class=cm>/* value */</span><span class=cp> </span><span class=c1>// (2)</span>
</code></pre></div> <p>These macros can be used to open and close the <code>nlohmann</code> namespace. See <a href=../../../features/namespace/#structure><code>nlohmann</code> Namespace</a> for details.</p> <ol> <li>Opens the namespace.</li> <li>Closes the namespace.</li> </ol> <h2 id=default-definition>Default definition<a class=headerlink href=#default-definition title="Permanent link">&para;</a></h2> <p>The default definitions open and close the <code>nlohmann</code> namespace. The precise definition of <code>NLOHMANN_JSON_NAMESPACE_BEGIN</code> varies as described <a href=../../../features/namespace/#structure>here</a>.</p> <ol> <li> <p>Default definition of <code>NLOHMANN_JSON_NAMESPACE_BEGIN</code>:</p> <div class=highlight><pre><span></span><code><span class=k>namespace</span><span class=w> </span><span class=nn>nlohmann</span>
<span class=p>{</span>
@@ -37,7 +37,7 @@
<span class=w> </span><span class=n>NLOHMANN_JSON_NAMESPACE</span><span class=o>::</span><span class=n>json</span><span class=w> </span><span class=n>j</span><span class=p>;</span>
<span class=w> </span><span class=n>j</span><span class=p>.</span><span class=n>push_back</span><span class=p>(</span><span class=n>o1</span><span class=p>);</span>
<span class=w> </span><span class=n>j</span><span class=p>.</span><span class=n>push_back</span><span class=p>(</span><span class=n>o2</span><span class=p>);</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>j</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>endl</span><span class=p>;</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>j</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=sc>'\n'</span><span class=p>;</span>
<span class=p>}</span>
</code></pre></div> <p>Output:</p> <div class=highlight><pre><span></span><code><span class=p>[</span><span class=mi>1</span><span class=p>,</span><span class=kc>null</span><span class=p>]</span>
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../../../features/namespace/ ><code>nlohmann</code> Namespace</a></li> <li><a href=../nlohmann_json_namespace/ >NLOHMANN_JSON_NAMESPACE</a></li> <li><a href=../nlohmann_json_namespace_no_version/ ><code>NLOHMANN_JSON_NAMESPACE_NO_VERSION</code></a></li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ul> <li>Added in version 3.11.0. Changed inline namespace name in version 3.11.2.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 11, 2026 06:21:51 UTC">October 11, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 2013-2026 Niels Lohmann </div> </div> <div class=md-social> <a href="https://github.com/nlohmann" target="_blank" rel="noopener" title="github.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 512 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M173.9 397.4c0 2-2.3 3.6-5.2 3.6-3.3.3-5.6-1.3-5.6-3.6 0-2 2.3-3.6 5.2-3.6 3-.3 5.6 1.3 5.6 3.6m-31.1-4.5c-.7 2 1.3 4.3 4.3 4.9 2.6 1 5.6 0 6.2-2s-1.3-4.3-4.3-5.2c-2.6-.7-5.5.3-6.2 2.3m44.2-1.7c-2.9.7-4.9 2.6-4.6 4.9.3 2 2.9 3.3 5.9 2.6 2.9-.7 4.9-2.6 4.6-4.6-.3-1.9-3-3.2-5.9-2.9M252.8 8C114.1 8 8 113.3 8 252c0 110.9 69.8 205.8 169.5 239.2 12.8 2.3 17.3-5.6 17.3-12.1 0-6.2-.3-40.4-.3-61.4 0 0-70 15-84.7-29.8 0 0-11.4-29.1-27.8-36.6 0 0-22.9-15.7 1.6-15.4 0 0 24.9 2 38.6 25.8 21.9 38.6 58.6 27.5 72.9 20.9 2.3-16 8.8-27.1 16-33.7-55.9-6.2-112.3-14.3-112.3-110.5 0-27.5 7.6-41.3 23.6-58.9-2.6-6.5-11.1-33.3 2.6-67.9 20.9-6.5 69 27 69 27 20-5.6 41.5-8.5 62.8-8.5s42.8 2.9 62.8 8.5c0 0 48.1-33.6 69-27 13.7 34.7 5.2 61.4 2.6 67.9 16 17.7 25.8 31.5 25.8 58.9 0 96.5-58.9 104.2-114.8 110.5 9.2 7.9 17 22.9 17 46.4 0 33.7-.3 75.4-.3 83.6 0 6.5 4.6 14.4 17.3 12.1C436.2 457.8 504 362.9 504 252 504 113.3 391.5 8 252.8 8M105.2 352.9c-1.3 1-1 3.3.7 5.2 1.6 1.6 3.9 2.3 5.2 1 1.3-1 1-3.3-.7-5.2-1.6-1.6-3.9-2.3-5.2-1m-10.8-8.1c-.7 1.3.3 2.9 2.3 3.9 1.6 1 3.6.7 4.3-.7.7-1.3-.3-2.9-2.3-3.9-2-.6-3.6-.3-4.3.7m32.4 35.6c-1.6 1.3-1 4.3 1.3 6.2 2.3 2.3 5.2 2.6 6.5 1 1.3-1.3.7-4.3-1.3-6.2-2.2-2.3-5.2-2.6-6.5-1m-11.4-14.7c-1.6 1-1.6 3.6 0 5.9s4.3 3.3 5.6 2.3c1.6-1.3 1.6-3.9 0-6.2-1.4-2.3-4-3.3-5.6-2"/></svg> </a> <a href="https://www.linkedin.com/in/nielslohmann/" target="_blank" rel="noopener" title="www.linkedin.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 448 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M416 32H31.9C14.3 32 0 46.5 0 64.3v383.4C0 465.5 14.3 480 31.9 480H416c17.6 0 32-14.5 32-32.3V64.3c0-17.8-14.4-32.3-32-32.3M135.4 416H69V202.2h66.5V416zM102.2 96a38.5 38.5 0 1 1 0 77 38.5 38.5 0 1 1 0-77m282.1 320h-66.4V312c0-24.8-.5-56.7-34.5-56.7-34.6 0-39.9 27-39.9 54.9V416h-66.4V202.2h63.7v29.2h.9c8.9-16.8 30.6-34.5 62.9-34.5 67.2 0 79.7 44.3 79.7 101.9z"/></svg> </a> <a href="https://www.xing.com/profile/Niels_Lohmann" target="_blank" rel="noopener" title="www.xing.com" class="md-socLine truncated
@@ -70,7 +70,7 @@ int main()
NLOHMANN_JSON_NAMESPACE::json j;
j.push_back(o1);
j.push_back(o2);
std::cout << j << std::endl;
std::cout << j << '\n';
}
```
@@ -36,7 +36,7 @@ When the macro is not defined, the library will define it to its default value.
int main()
{
std::cout << QUOTE(NLOHMANN_JSON_NAMESPACE) << std::endl;
std::cout << QUOTE(NLOHMANN_JSON_NAMESPACE) << '\n';
}
```
@@ -1,4 +1,4 @@
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/macros/nlohmann_json_namespace_no_version/" rel="canonical"><link href=../nlohmann_json_namespace_begin/ rel=prev><link href=../nlohmann_json_serialize_enum/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>NLOHMANN_JSON_NAMESPACE_NO_VERSION - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new 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data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> NLOHMANN_JSON_NAMESPACE_NO_VERSION </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo 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6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 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<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/macros/nlohmann_json_namespace_no_version/" rel="canonical"><link href=../nlohmann_json_namespace_begin/ rel=prev><link href=../nlohmann_json_serialize_enum/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>NLOHMANN_JSON_NAMESPACE_NO_VERSION - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new URL("../../..",location),__md_hash=e=>[...e].reduce(((e,_)=>(e<<5)-e+_.charCodeAt(0)),0),__md_get=(e,_=localStorage,t=__md_scope)=>JSON.parse(_.getItem(t.pathname+"."+e)),__md_set=(e,_,t=localStorage,a=__md_scope)=>{try{t.setItem(a.pathname+"."+e,JSON.stringify(_))}catch(e){}}</script></head> <body dir=ltr data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo> <input class=md-toggle data-md-toggle=drawer type=checkbox id=__drawer autocomplete=off> <input class=md-toggle data-md-toggle=search type=checkbox id=__search autocomplete=off> <label class=md-overlay for=__drawer></label> <div data-md-component=skip> <a href=#nlohmann_json_namespace_no_version class=md-skip> Skip to content </a> </div> <div data-md-component=announce> </div> <header class=md-header data-md-component=header> <nav class="md-header__inner md-grid" aria-label=Header> <a href=../../.. title="JSON for Modern C++" class="md-header__button md-logo" aria-label="JSON for Modern C++" data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> NLOHMANN_JSON_NAMESPACE_NO_VERSION </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo 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6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6Line truncated
</code></pre></div> <p>If defined to <code>1</code>, the version component is omitted from the inline namespace. See <a href=../../../features/namespace/#structure><code>nlohmann</code> Namespace</a> for details.</p> <h2 id=default-definition>Default definition<a class=headerlink href=#default-definition title="Permanent link">&para;</a></h2> <p>The default value is <code>0</code>.</p> <div class=highlight><pre><span></span><code><span class=cp>#define NLOHMANN_JSON_NAMESPACE_NO_VERSION 0</span>
</code></pre></div> <p>When the macro is not defined, the library will define it to its default value.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The example shows how to use <code>NLOHMANN_JSON_NAMESPACE_NO_VERSION</code> to disable the version component of the inline namespace.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
@@ -11,7 +11,7 @@
<span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span>
<span class=p>{</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>QUOTE</span><span class=p>(</span><span class=n>NLOHMANN_JSON_NAMESPACE</span><span class=p>)</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>endl</span><span class=p>;</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>QUOTE</span><span class=p>(</span><span class=n>NLOHMANN_JSON_NAMESPACE</span><span class=p>)</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=sc>'\n'</span><span class=p>;</span>
<span class=p>}</span>
</code></pre></div> <p>Output:</p> <div class=highlight><pre><span></span><code><span class=kc>nl</span><span class=err>ohma</span><span class=kc>nn</span><span class=p>::</span><span class=err>jso</span><span class=kc>n</span><span class=err>_abi</span>
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../../../features/namespace/ ><code>nlohmann</code> Namespace</a></li> <li><a href=../nlohmann_json_namespace/ ><code>NLOHMANN_JSON_NAMESPACE</code></a></li> <li><a href=../nlohmann_json_namespace_begin/ ><code>NLOHMANN_JSON_NAMESPACE_BEGIN, NLOHMANN_JSON_NAMESPACE_END</code></a></li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ul> <li>Added in version 3.11.2.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="August 10, 2022 18:24:16 UTC">August 10, 2022</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 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@@ -34,7 +34,7 @@ The example shows how to use `NLOHMANN_JSON_NAMESPACE_NO_VERSION` to disable the
int main()
{
std::cout << QUOTE(NLOHMANN_JSON_NAMESPACE) << std::endl;
std::cout << QUOTE(NLOHMANN_JSON_NAMESPACE) << '\n';
}
```
+16 -8
View File
@@ -45,6 +45,12 @@ inline void from_json(const BasicJsonType& j, type& e);
Define [`JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS`](json_use_objects_for_enum_keyed_maps.md) to store them as objects
with the converted keys. Such maps can be read from both forms.
!!! info "Views"
The generated `from_json()` also reads the views of [`json_document`](../json_document.md)s
(`<nlohmann/json_view.hpp>`), comparing the view with the entries of the mapping, without building a `json` value
first.
## Examples
??? example "Example: Basic usage"
@@ -56,7 +62,7 @@ inline void from_json(const BasicJsonType& j, type& e);
#include <iostream>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using nlohmann::json;
namespace ns
{
@@ -94,7 +100,7 @@ inline void from_json(const BasicJsonType& j, type& e);
json j_stopped = ns::TS_STOPPED;
json j_red = ns::Color::red;
std::cout << "ns::TS_STOPPED -> " << j_stopped
<< ", ns::Color::red -> " << j_red << std::endl;
<< ", ns::Color::red -> " << j_red << '\n';
// deserialization
json j_running = "running";
@@ -102,7 +108,7 @@ inline void from_json(const BasicJsonType& j, type& e);
auto running = j_running.get<ns::TaskState>();
auto blue = j_blue.get<ns::Color>();
std::cout << j_running << " -> " << running
<< ", " << j_blue << " -> " << static_cast<int>(blue) << std::endl;
<< ", " << j_blue << " -> " << static_cast<int>(blue) << '\n';
// deserializing undefined JSON value to enum
// (where the first map entry above is the default)
@@ -110,7 +116,7 @@ inline void from_json(const BasicJsonType& j, type& e);
auto invalid = j_pi.get<ns::TaskState>();
auto unknown = j_pi.get<ns::Color>();
std::cout << j_pi << " -> " << invalid << ", "
<< j_pi << " -> " << static_cast<int>(unknown) << std::endl;
<< j_pi << " -> " << static_cast<int>(unknown) << '\n';
}
```
@@ -134,7 +140,7 @@ inline void from_json(const BasicJsonType& j, type& e);
#include <iostream>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using nlohmann::json;
namespace ns
{
@@ -155,14 +161,14 @@ inline void from_json(const BasicJsonType& j, type& e);
{
// serialization
json j_red = ns::Color::red;
std::cout << static_cast<int>(ns::Color::red) << " -> " << j_red << std::endl;
std::cout << static_cast<int>(ns::Color::red) << " -> " << j_red << '\n';
// deserialization
json j_rot = "rot";
auto rot = j_rot.get<ns::Color>();
auto red = j_red.get<ns::Color>();
std::cout << j_rot << " -> " << static_cast<int>(rot) << std::endl;
std::cout << j_red << " -> " << static_cast<int>(red) << std::endl;
std::cout << j_rot << " -> " << static_cast<int>(rot) << '\n';
std::cout << j_red << " -> " << static_cast<int>(red) << '\n';
}
```
@@ -186,3 +192,5 @@ inline void from_json(const BasicJsonType& j, type& e);
## Version history
Added in version 3.4.0.
The generated `from_json()` reads the views of `json_document`s since version 3.13.0.
@@ -1,12 +1,12 @@
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/macros/nlohmann_json_serialize_enum/" rel="canonical"><link href=../nlohmann_json_namespace_no_version/ rel=prev><link href=../nlohmann_json_serialize_enum_strict/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>NLOHMANN_JSON_SERIALIZE_ENUM - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new 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<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/macros/nlohmann_json_serialize_enum/" rel="canonical"><link href=../nlohmann_json_namespace_no_version/ rel=prev><link href=../nlohmann_json_serialize_enum_strict/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>NLOHMANN_JSON_SERIALIZE_ENUM - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new 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6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 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</code></pre></div> <p>By default, enum values are serialized to <abbr title="JavaScript Object Notation">JSON</abbr> as integers. In some cases, this could result in undesired behavior. If an enum is modified or re-ordered after data has been serialized to <abbr title="JavaScript Object Notation">JSON</abbr>, the later deserialized <abbr title="JavaScript Object Notation">JSON</abbr> data may be undefined or a different enum value than was originally intended.</p> <p>The <code>NLOHMANN_JSON_SERIALIZE_ENUM</code> allows to define a user-defined serialization for every enumerator.</p> <h2 id=parameters>Parameters<a class=headerlink href=#parameters title="Permanent link">&para;</a></h2> <dl> <dt><code>type</code> (in)</dt> <dd>name of the enum to serialize/deserialize</dd> <dt><code>conversion</code> (in)</dt> <dd>a pair of an enumerator and a <abbr title="JavaScript Object Notation">JSON</abbr> serialization; arbitrary pairs can be given as a comma-separated list</dd> </dl> <h2 id=default-definition>Default definition<a class=headerlink href=#default-definition title="Permanent link">&para;</a></h2> <p>The macro adds two functions to the namespace which take care of the serialization and deserialization:</p> <div class=highlight><pre><span></span><code><span class=k>template</span><span class=o>&lt;</span><span class=k>typename</span><span class=w> </span><span class=nc>BasicJsonType</span><span class=o>&gt;</span>
<span class=kr>inline</span><span class=w> </span><span class=kt>void</span><span class=w> </span><span class=n>to_json</span><span class=p>(</span><span class=n>BasicJsonType</span><span class=o>&amp;</span><span class=w> </span><span class=n>j</span><span class=p>,</span><span class=w> </span><span class=k>const</span><span class=w> </span><span class=n>type</span><span class=o>&amp;</span><span class=w> </span><span class=n>e</span><span class=p>);</span>
<span class=k>template</span><span class=o>&lt;</span><span class=k>typename</span><span class=w> </span><span class=nc>BasicJsonType</span><span class=o>&gt;</span>
<span class=kr>inline</span><span class=w> </span><span class=kt>void</span><span class=w> </span><span class=n>from_json</span><span class=p>(</span><span class=k>const</span><span class=w> </span><span class=n>BasicJsonType</span><span class=o>&amp;</span><span class=w> </span><span class=n>j</span><span class=p>,</span><span class=w> </span><span class=n>type</span><span class=o>&amp;</span><span class=w> </span><span class=n>e</span><span class=p>);</span>
</code></pre></div> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <div class="admonition info"> <p class=admonition-title>Prerequisites</p> <p>The macro must be used inside the namespace of the enum.</p> </div> <div class="admonition important"> <p class=admonition-title>Important notes</p> <ul> <li>When using <a href=../../basic_json/get/ ><code>get&lt;ENUM_TYPE&gt;()</code></a>, undefined <abbr title="JavaScript Object Notation">JSON</abbr> values will default to the first specified conversion. Select this default pair carefully. See example 1 below.</li> <li>If an enum or <abbr title="JavaScript Object Notation">JSON</abbr> value is specified in multiple conversions, the first matching conversion from the top of the list will be returned when converting to or from <abbr title="JavaScript Object Notation">JSON</abbr>. See example 2 below.</li> <li>Maps with enum keys (e.g., <code>std::map&lt;ENUM_TYPE, T&gt;</code>) are stored as arrays of <code>[key, value]</code> pairs by default. Define <a href=../json_use_objects_for_enum_keyed_maps/ ><code>JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS</code></a> to store them as objects with the converted keys. Such maps can be read from both forms.</li> </ul> </div> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example: Basic usage</summary> <p>The example shows how <code>NLOHMANN_JSON_SERIALIZE_ENUM</code> can be used to serialize/deserialize both classical enums and C++11 enum classes:</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
</code></pre></div> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <div class="admonition info"> <p class=admonition-title>Prerequisites</p> <p>The macro must be used inside the namespace of the enum.</p> </div> <div class="admonition important"> <p class=admonition-title>Important notes</p> <ul> <li>When using <a href=../../basic_json/get/ ><code>get&lt;ENUM_TYPE&gt;()</code></a>, undefined <abbr title="JavaScript Object Notation">JSON</abbr> values will default to the first specified conversion. Select this default pair carefully. See example 1 below.</li> <li>If an enum or <abbr title="JavaScript Object Notation">JSON</abbr> value is specified in multiple conversions, the first matching conversion from the top of the list will be returned when converting to or from <abbr title="JavaScript Object Notation">JSON</abbr>. See example 2 below.</li> <li>Maps with enum keys (e.g., <code>std::map&lt;ENUM_TYPE, T&gt;</code>) are stored as arrays of <code>[key, value]</code> pairs by default. Define <a href=../json_use_objects_for_enum_keyed_maps/ ><code>JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS</code></a> to store them as objects with the converted keys. Such maps can be read from both forms.</li> </ul> </div> <div class="admonition info"> <p class=admonition-title>Views</p> <p>The generated <code>from_json()</code> also reads the views of <a href=../../json_document/ ><code>json_document</code></a>s (<code>&lt;nlohmann/json_view.hpp&gt;</code>), comparing the view with the entries of the mapping, without building a <code>json</code> value first.</p> </div> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example: Basic usage</summary> <p>The example shows how <code>NLOHMANN_JSON_SERIALIZE_ENUM</code> can be used to serialize/deserialize both classical enums and C++11 enum classes:</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=k>namespace</span><span class=w> </span><span class=nn>ns</span>
<span class=p>{</span>
@@ -44,7 +44,7 @@
<span class=w> </span><span class=n>json</span><span class=w> </span><span class=n>j_stopped</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>ns</span><span class=o>::</span><span class=n>TS_STOPPED</span><span class=p>;</span>
<span class=w> </span><span class=n>json</span><span class=w> </span><span class=n>j_red</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>ns</span><span class=o>::</span><span class=n>Color</span><span class=o>::</span><span class=n>red</span><span class=p>;</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>"ns::TS_STOPPED -&gt; "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>j_stopped</span>
<span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>", ns::Color::red -&gt; "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>j_red</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>endl</span><span class=p>;</span>
<span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>", ns::Color::red -&gt; "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>j_red</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=sc>'\n'</span><span class=p>;</span>
<span class=w> </span><span class=c1>// deserialization</span>
<span class=w> </span><span class=n>json</span><span class=w> </span><span class=n>j_running</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=s>"running"</span><span class=p>;</span>
@@ -52,7 +52,7 @@
<span class=w> </span><span class=k>auto</span><span class=w> </span><span class=n>running</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>j_running</span><span class=p>.</span><span class=n>get</span><span class=o>&lt;</span><span class=n>ns</span><span class=o>::</span><span class=n>TaskState</span><span class=o>&gt;</span><span class=p>();</span>
<span class=w> </span><span class=k>auto</span><span class=w> </span><span class=n>blue</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>j_blue</span><span class=p>.</span><span class=n>get</span><span class=o>&lt;</span><span class=n>ns</span><span class=o>::</span><span class=n>Color</span><span class=o>&gt;</span><span class=p>();</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>j_running</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>" -&gt; "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>running</span>
<span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>", "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>j_blue</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>" -&gt; "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=k>static_cast</span><span class=o>&lt;</span><span class=kt>int</span><span class=o>&gt;</span><span class=p>(</span><span class=n>blue</span><span class=p>)</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>endl</span><span class=p>;</span>
<span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>", "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>j_blue</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>" -&gt; "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=k>static_cast</span><span class=o>&lt;</span><span class=kt>int</span><span class=o>&gt;</span><span class=p>(</span><span class=n>blue</span><span class=p>)</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=sc>'\n'</span><span class=p>;</span>
<span class=w> </span><span class=c1>// deserializing undefined JSON value to enum</span>
<span class=w> </span><span class=c1>// (where the first map entry above is the default)</span>
@@ -60,7 +60,7 @@
<span class=w> </span><span class=k>auto</span><span class=w> </span><span class=n>invalid</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>j_pi</span><span class=p>.</span><span class=n>get</span><span class=o>&lt;</span><span class=n>ns</span><span class=o>::</span><span class=n>TaskState</span><span class=o>&gt;</span><span class=p>();</span>
<span class=w> </span><span class=k>auto</span><span class=w> </span><span class=n>unknown</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>j_pi</span><span class=p>.</span><span class=n>get</span><span class=o>&lt;</span><span class=n>ns</span><span class=o>::</span><span class=n>Color</span><span class=o>&gt;</span><span class=p>();</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>j_pi</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>" -&gt; "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>invalid</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>", "</span>
<span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>j_pi</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>" -&gt; "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=k>static_cast</span><span class=o>&lt;</span><span class=kt>int</span><span class=o>&gt;</span><span class=p>(</span><span class=n>unknown</span><span class=p>)</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>endl</span><span class=p>;</span>
<span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>j_pi</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>" -&gt; "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=k>static_cast</span><span class=o>&lt;</span><span class=kt>int</span><span class=o>&gt;</span><span class=p>(</span><span class=n>unknown</span><span class=p>)</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=sc>'\n'</span><span class=p>;</span>
<span class=p>}</span>
</code></pre></div> <p>Output:</p> <div class=highlight><pre><span></span><code><span class=kc>ns</span><span class=p>::</span><span class=err>TS_STOPPED</span><span class=w> </span><span class=mi>-</span><span class=err>&gt;</span><span class=w> </span><span class=s2>"stopped"</span><span class=p>,</span><span class=w> </span><span class=kc>ns</span><span class=p>::</span><span class=err>Color</span><span class=p>::</span><span class=err>red</span><span class=w> </span><span class=mi>-</span><span class=err>&gt;</span><span class=w> </span><span class=s2>"red"</span>
<span class=s2>"running"</span><span class=w> </span><span class=mi>-</span><span class=err>&gt;</span><span class=w> </span><span class=mi>1</span><span class=p>,</span><span class=w> </span><span class=s2>"blue"</span><span class=w> </span><span class=mi>-</span><span class=err>&gt;</span><span class=w> </span><span class=mi>2</span>
@@ -68,7 +68,7 @@
</code></pre></div> </details> <details class=example> <summary>Example: Multiple conversions for one enumerator</summary> <p>The example shows how to use multiple conversions for a single enumerator. In the example, <code>Color::red</code> will always be <em>serialized</em> to <code>"red"</code>, because the first occurring conversion. The second conversion, however, offers an alternative <em>deserialization</em> from <code>"rot"</code> to <code>Color::red</code>.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=k>namespace</span><span class=w> </span><span class=nn>ns</span>
<span class=p>{</span>
@@ -89,16 +89,16 @@
<span class=p>{</span>
<span class=w> </span><span class=c1>// serialization</span>
<span class=w> </span><span class=n>json</span><span class=w> </span><span class=n>j_red</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>ns</span><span class=o>::</span><span class=n>Color</span><span class=o>::</span><span class=n>red</span><span class=p>;</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=k>static_cast</span><span class=o>&lt;</span><span class=kt>int</span><span class=o>&gt;</span><span class=p>(</span><span class=n>ns</span><span class=o>::</span><span class=n>Color</span><span class=o>::</span><span class=n>red</span><span class=p>)</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>" -&gt; "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>j_red</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>endl</span><span class=p>;</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=k>static_cast</span><span class=o>&lt;</span><span class=kt>int</span><span class=o>&gt;</span><span class=p>(</span><span class=n>ns</span><span class=o>::</span><span class=n>Color</span><span class=o>::</span><span class=n>red</span><span class=p>)</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>" -&gt; "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>j_red</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=sc>'\n'</span><span class=p>;</span>
<span class=w> </span><span class=c1>// deserialization</span>
<span class=w> </span><span class=n>json</span><span class=w> </span><span class=n>j_rot</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=s>"rot"</span><span class=p>;</span>
<span class=w> </span><span class=k>auto</span><span class=w> </span><span class=n>rot</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>j_rot</span><span class=p>.</span><span class=n>get</span><span class=o>&lt;</span><span class=n>ns</span><span class=o>::</span><span class=n>Color</span><span class=o>&gt;</span><span class=p>();</span>
<span class=w> </span><span class=k>auto</span><span class=w> </span><span class=n>red</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>j_red</span><span class=p>.</span><span class=n>get</span><span class=o>&lt;</span><span class=n>ns</span><span class=o>::</span><span class=n>Color</span><span class=o>&gt;</span><span class=p>();</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>j_rot</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>" -&gt; "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=k>static_cast</span><span class=o>&lt;</span><span class=kt>int</span><span class=o>&gt;</span><span class=p>(</span><span class=n>rot</span><span class=p>)</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>endl</span><span class=p>;</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>j_red</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>" -&gt; "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=k>static_cast</span><span class=o>&lt;</span><span class=kt>int</span><span class=o>&gt;</span><span class=p>(</span><span class=n>red</span><span class=p>)</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>endl</span><span class=p>;</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>j_rot</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>" -&gt; "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=k>static_cast</span><span class=o>&lt;</span><span class=kt>int</span><span class=o>&gt;</span><span class=p>(</span><span class=n>rot</span><span class=p>)</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=sc>'\n'</span><span class=p>;</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>j_red</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>" -&gt; "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=k>static_cast</span><span class=o>&lt;</span><span class=kt>int</span><span class=o>&gt;</span><span class=p>(</span><span class=n>red</span><span class=p>)</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=sc>'\n'</span><span class=p>;</span>
<span class=p>}</span>
</code></pre></div> <p>Output:</p> <div class=highlight><pre><span></span><code><span class=mi>0</span><span class=w> </span><span class=mi>-</span><span class=err>&gt;</span><span class=w> </span><span class=s2>"red"</span>
<span class=s2>"rot"</span><span class=w> </span><span class=mi>-</span><span class=err>&gt;</span><span class=w> </span><span class=mi>0</span>
<span class=s2>"red"</span><span class=w> </span><span class=mi>-</span><span class=err>&gt;</span><span class=w> </span><span class=mi>0</span>
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../../../features/enum_conversion/ >Specializing enum conversion</a></li> <li><a href=../nlohmann_json_serialize_enum_strict/ ><code>NLOHMANN_JSON_SERIALIZE_ENUM_STRICT</code></a></li> <li><a href=../json_disable_enum_serialization/ ><code>JSON_DISABLE_ENUM_SERIALIZATION</code></a></li> <li><a href=../json_use_objects_for_enum_keyed_maps/ ><code>JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS</code></a></li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <p>Added in version 3.4.0.</p> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 4, 2026 15:54:05 UTC">October 4, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 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</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../../../features/enum_conversion/ >Specializing enum conversion</a></li> <li><a href=../nlohmann_json_serialize_enum_strict/ ><code>NLOHMANN_JSON_SERIALIZE_ENUM_STRICT</code></a></li> <li><a href=../json_disable_enum_serialization/ ><code>JSON_DISABLE_ENUM_SERIALIZATION</code></a></li> <li><a href=../json_use_objects_for_enum_keyed_maps/ ><code>JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS</code></a></li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <p>Added in version 3.4.0.</p> <p>The generated <code>from_json()</code> reads the views of <code>json_document</code>s since version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</p> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 26, 2026 19:13:31 UTC">October 26, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 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@@ -37,6 +37,10 @@ Important notes
- If an enum or JSON value is specified in multiple conversions, the first matching conversion from the top of the list will be returned when converting to or from JSON. See example 2 below.
- Maps with enum keys (e.g., `std::map<ENUM_TYPE, T>`) are stored as arrays of `[key, value]` pairs by default. Define [`JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS`](https://json.nlohmann.me/api/macros/json_use_objects_for_enum_keyed_maps/index.md) to store them as objects with the converted keys. Such maps can be read from both forms.
Views
The generated `from_json()` also reads the views of [`json_document`](https://json.nlohmann.me/api/json_document/index.md)s (`<nlohmann/json_view.hpp>`), comparing the view with the entries of the mapping, without building a `json` value first.
## Examples
Example: Basic usage
@@ -47,7 +51,7 @@ The example shows how `NLOHMANN_JSON_SERIALIZE_ENUM` can be used to serialize/de
#include <iostream>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using nlohmann::json;
namespace ns
{
@@ -85,7 +89,7 @@ int main()
json j_stopped = ns::TS_STOPPED;
json j_red = ns::Color::red;
std::cout << "ns::TS_STOPPED -> " << j_stopped
<< ", ns::Color::red -> " << j_red << std::endl;
<< ", ns::Color::red -> " << j_red << '\n';
// deserialization
json j_running = "running";
@@ -93,7 +97,7 @@ int main()
auto running = j_running.get<ns::TaskState>();
auto blue = j_blue.get<ns::Color>();
std::cout << j_running << " -> " << running
<< ", " << j_blue << " -> " << static_cast<int>(blue) << std::endl;
<< ", " << j_blue << " -> " << static_cast<int>(blue) << '\n';
// deserializing undefined JSON value to enum
// (where the first map entry above is the default)
@@ -101,7 +105,7 @@ int main()
auto invalid = j_pi.get<ns::TaskState>();
auto unknown = j_pi.get<ns::Color>();
std::cout << j_pi << " -> " << invalid << ", "
<< j_pi << " -> " << static_cast<int>(unknown) << std::endl;
<< j_pi << " -> " << static_cast<int>(unknown) << '\n';
}
```
@@ -121,7 +125,7 @@ The example shows how to use multiple conversions for a single enumerator. In th
#include <iostream>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using nlohmann::json;
namespace ns
{
@@ -142,14 +146,14 @@ int main()
{
// serialization
json j_red = ns::Color::red;
std::cout << static_cast<int>(ns::Color::red) << " -> " << j_red << std::endl;
std::cout << static_cast<int>(ns::Color::red) << " -> " << j_red << '\n';
// deserialization
json j_rot = "rot";
auto rot = j_rot.get<ns::Color>();
auto red = j_red.get<ns::Color>();
std::cout << j_rot << " -> " << static_cast<int>(rot) << std::endl;
std::cout << j_red << " -> " << static_cast<int>(red) << std::endl;
std::cout << j_rot << " -> " << static_cast<int>(rot) << '\n';
std::cout << j_red << " -> " << static_cast<int>(red) << '\n';
}
```
@@ -171,3 +175,5 @@ Output:
## Version history
Added in version 3.4.0.
The generated `from_json()` reads the views of `json_document`s since version 3.13.0 unreleased.
@@ -48,6 +48,12 @@ inline void from_json(const BasicJsonType& j, type& e);
Define [`JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS`](json_use_objects_for_enum_keyed_maps.md) to store them as objects
with the converted keys. Such maps can be read from both forms.
!!! info "Views"
The generated `from_json()` also reads the views of [`json_document`](../json_document.md)s
(`<nlohmann/json_view.hpp>`), comparing the view with the entries of the mapping, without building a `json` value
first.
## Examples
??? example "Example: Basic usage"
@@ -59,7 +65,7 @@ inline void from_json(const BasicJsonType& j, type& e);
#include <iostream>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using nlohmann::json;
namespace ns
{
@@ -97,7 +103,7 @@ inline void from_json(const BasicJsonType& j, type& e);
json j_stopped = ns::TS_STOPPED;
json j_red = ns::Color::red;
std::cout << "ns::TS_STOPPED -> " << j_stopped
<< ", ns::Color::red -> " << j_red << std::endl;
<< ", ns::Color::red -> " << j_red << '\n';
// deserialization
json j_running = "running";
@@ -105,7 +111,7 @@ inline void from_json(const BasicJsonType& j, type& e);
auto running = j_running.get<ns::TaskState>();
auto blue = j_blue.get<ns::Color>();
std::cout << j_running << " -> " << running
<< ", " << j_blue << " -> " << static_cast<int>(blue) << std::endl;
<< ", " << j_blue << " -> " << static_cast<int>(blue) << '\n';
}
@@ -129,7 +135,7 @@ inline void from_json(const BasicJsonType& j, type& e);
#include <iostream>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using nlohmann::json;
namespace ns
{
@@ -150,14 +156,14 @@ inline void from_json(const BasicJsonType& j, type& e);
{
// serialization
json j_red = ns::Color::red;
std::cout << static_cast<int>(ns::Color::red) << " -> " << j_red << std::endl;
std::cout << static_cast<int>(ns::Color::red) << " -> " << j_red << '\n';
// deserialization
json j_rot = "rot";
auto rot = j_rot.get<ns::Color>();
auto red = j_red.get<ns::Color>();
std::cout << j_rot << " -> " << static_cast<int>(rot) << std::endl;
std::cout << j_red << " -> " << static_cast<int>(red) << std::endl;
std::cout << j_rot << " -> " << static_cast<int>(rot) << '\n';
std::cout << j_red << " -> " << static_cast<int>(red) << '\n';
}
```
@@ -182,7 +188,7 @@ inline void from_json(const BasicJsonType& j, type& e);
#include <iostream>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using nlohmann::json;
namespace ns
{
@@ -215,7 +221,7 @@ inline void from_json(const BasicJsonType& j, type& e);
}
catch (const json::exception e)
{
std::cout << "deserialization failed: " << e.what() << std::endl;
std::cout << "deserialization failed: " << e.what() << '\n';
}
// invalid deserialization
@@ -227,7 +233,7 @@ inline void from_json(const BasicJsonType& j, type& e);
}
catch (const json::exception e)
{
std::cout << "deserialization failed: " << e.what() << std::endl;
std::cout << "deserialization failed: " << e.what() << '\n';
}
return 0;
@@ -1,12 +1,12 @@
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</code></pre></div> <p>By default, enum values are serialized to <abbr title="JavaScript Object Notation">JSON</abbr> as integers. In some cases, this could result in undesired behavior. If an enum is modified or re-ordered after data has been serialized to <abbr title="JavaScript Object Notation">JSON</abbr>, the later deserialized <abbr title="JavaScript Object Notation">JSON</abbr> data may be undefined or a different enum value than was originally intended.</p> <p><code>NLOHMANN_JSON_SERIALIZE_ENUM_STRICT</code> allows to define a user-defined serialization for every enumerator that throws an exception on undefined input.</p> <h2 id=parameters>Parameters<a class=headerlink href=#parameters title="Permanent link">&para;</a></h2> <dl> <dt><code>type</code> (in)</dt> <dd>name of the enum to serialize/deserialize</dd> <dt><code>conversion</code> (in)</dt> <dd>a pair of an enumerator and a <abbr title="JavaScript Object Notation">JSON</abbr> serialization; arbitrary pairs can be given as a comma-separated list</dd> </dl> <h2 id=default-definition>Default definition<a class=headerlink href=#default-definition title="Permanent link">&para;</a></h2> <p>The macro adds two functions to the namespace which take care of the serialization and deserialization:</p> <div class=highlight><pre><span></span><code><span class=k>template</span><span class=o>&lt;</span><span class=k>typename</span><span class=w> </span><span class=nc>BasicJsonType</span><span class=o>&gt;</span>
<span class=kr>inline</span><span class=w> </span><span class=kt>void</span><span class=w> </span><span class=n>to_json</span><span class=p>(</span><span class=n>BasicJsonType</span><span class=o>&amp;</span><span class=w> </span><span class=n>j</span><span class=p>,</span><span class=w> </span><span class=k>const</span><span class=w> </span><span class=n>type</span><span class=o>&amp;</span><span class=w> </span><span class=n>e</span><span class=p>);</span>
<span class=k>template</span><span class=o>&lt;</span><span class=k>typename</span><span class=w> </span><span class=nc>BasicJsonType</span><span class=o>&gt;</span>
<span class=kr>inline</span><span class=w> </span><span class=kt>void</span><span class=w> </span><span class=n>from_json</span><span class=p>(</span><span class=k>const</span><span class=w> </span><span class=n>BasicJsonType</span><span class=o>&amp;</span><span class=w> </span><span class=n>j</span><span class=p>,</span><span class=w> </span><span class=n>type</span><span class=o>&amp;</span><span class=w> </span><span class=n>e</span><span class=p>);</span>
</code></pre></div> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <div class="admonition info"> <p class=admonition-title>Prerequisites</p> <p>The macro must be used inside the namespace of the enum.</p> </div> <div class="admonition important"> <p class=admonition-title>Important notes</p> <ul> <li>Undefined input throws <a href=../../../home/exceptions/#jsonexceptionout_of_range410><code>out_of_range.410</code></a> in both directions: when serializing an enum value not listed in the conversions, and when deserializing (e.g., via <a href=../../basic_json/get/ ><code>get&lt;ENUM_TYPE&gt;()</code></a>) a <abbr title="JavaScript Object Notation">JSON</abbr> value that matches no conversion; example: <code>"enum value out of range for &lt;type&gt;"</code>.</li> <li>If an enum or <abbr title="JavaScript Object Notation">JSON</abbr> value is specified in multiple conversions, the first matching conversion from the top of the list will be returned when converting to or from <abbr title="JavaScript Object Notation">JSON</abbr>. See example 2 below.</li> <li>Maps with enum keys (e.g., <code>std::map&lt;ENUM_TYPE, T&gt;</code>) are stored as arrays of <code>[key, value]</code> pairs by default. Define <a href=../json_use_objects_for_enum_keyed_maps/ ><code>JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS</code></a> to store them as objects with the converted keys. Such maps can be read from both forms.</li> </ul> </div> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example: Basic usage</summary> <p>The example shows how <code>NLOHMANN_JSON_SERIALIZE_ENUM_STRICT</code> can be used to serialize/deserialize both classical enums and C++11 enum classes:</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
</code></pre></div> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <div class="admonition info"> <p class=admonition-title>Prerequisites</p> <p>The macro must be used inside the namespace of the enum.</p> </div> <div class="admonition important"> <p class=admonition-title>Important notes</p> <ul> <li>Undefined input throws <a href=../../../home/exceptions/#jsonexceptionout_of_range410><code>out_of_range.410</code></a> in both directions: when serializing an enum value not listed in the conversions, and when deserializing (e.g., via <a href=../../basic_json/get/ ><code>get&lt;ENUM_TYPE&gt;()</code></a>) a <abbr title="JavaScript Object Notation">JSON</abbr> value that matches no conversion; example: <code>"enum value out of range for &lt;type&gt;"</code>.</li> <li>If an enum or <abbr title="JavaScript Object Notation">JSON</abbr> value is specified in multiple conversions, the first matching conversion from the top of the list will be returned when converting to or from <abbr title="JavaScript Object Notation">JSON</abbr>. See example 2 below.</li> <li>Maps with enum keys (e.g., <code>std::map&lt;ENUM_TYPE, T&gt;</code>) are stored as arrays of <code>[key, value]</code> pairs by default. Define <a href=../json_use_objects_for_enum_keyed_maps/ ><code>JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS</code></a> to store them as objects with the converted keys. Such maps can be read from both forms.</li> </ul> </div> <div class="admonition info"> <p class=admonition-title>Views</p> <p>The generated <code>from_json()</code> also reads the views of <a href=../../json_document/ ><code>json_document</code></a>s (<code>&lt;nlohmann/json_view.hpp&gt;</code>), comparing the view with the entries of the mapping, without building a <code>json</code> value first.</p> </div> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example: Basic usage</summary> <p>The example shows how <code>NLOHMANN_JSON_SERIALIZE_ENUM_STRICT</code> can be used to serialize/deserialize both classical enums and C++11 enum classes:</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=k>namespace</span><span class=w> </span><span class=nn>ns</span>
<span class=p>{</span>
@@ -44,7 +44,7 @@
<span class=w> </span><span class=n>json</span><span class=w> </span><span class=n>j_stopped</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>ns</span><span class=o>::</span><span class=n>TS_STOPPED</span><span class=p>;</span>
<span class=w> </span><span class=n>json</span><span class=w> </span><span class=n>j_red</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>ns</span><span class=o>::</span><span class=n>Color</span><span class=o>::</span><span class=n>red</span><span class=p>;</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>"ns::TS_STOPPED -&gt; "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>j_stopped</span>
<span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>", ns::Color::red -&gt; "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>j_red</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>endl</span><span class=p>;</span>
<span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>", ns::Color::red -&gt; "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>j_red</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=sc>'\n'</span><span class=p>;</span>
<span class=w> </span><span class=c1>// deserialization</span>
<span class=w> </span><span class=n>json</span><span class=w> </span><span class=n>j_running</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=s>"running"</span><span class=p>;</span>
@@ -52,7 +52,7 @@
<span class=w> </span><span class=k>auto</span><span class=w> </span><span class=n>running</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>j_running</span><span class=p>.</span><span class=n>get</span><span class=o>&lt;</span><span class=n>ns</span><span class=o>::</span><span class=n>TaskState</span><span class=o>&gt;</span><span class=p>();</span>
<span class=w> </span><span class=k>auto</span><span class=w> </span><span class=n>blue</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>j_blue</span><span class=p>.</span><span class=n>get</span><span class=o>&lt;</span><span class=n>ns</span><span class=o>::</span><span class=n>Color</span><span class=o>&gt;</span><span class=p>();</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>j_running</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>" -&gt; "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>running</span>
<span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>", "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>j_blue</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>" -&gt; "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=k>static_cast</span><span class=o>&lt;</span><span class=kt>int</span><span class=o>&gt;</span><span class=p>(</span><span class=n>blue</span><span class=p>)</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>endl</span><span class=p>;</span>
<span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>", "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>j_blue</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>" -&gt; "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=k>static_cast</span><span class=o>&lt;</span><span class=kt>int</span><span class=o>&gt;</span><span class=p>(</span><span class=n>blue</span><span class=p>)</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=sc>'\n'</span><span class=p>;</span>
<span class=p>}</span>
</code></pre></div> <p>Output:</p> <div class=highlight><pre><span></span><code><span class=kc>ns</span><span class=p>::</span><span class=err>TS_STOPPED</span><span class=w> </span><span class=mi>-</span><span class=err>&gt;</span><span class=w> </span><span class=s2>"stopped"</span><span class=p>,</span><span class=w> </span><span class=kc>ns</span><span class=p>::</span><span class=err>Color</span><span class=p>::</span><span class=err>red</span><span class=w> </span><span class=mi>-</span><span class=err>&gt;</span><span class=w> </span><span class=s2>"red"</span>
@@ -60,7 +60,7 @@
</code></pre></div> </details> <details class=example> <summary>Example: Multiple conversions for one enumerator</summary> <p>The example shows how to use multiple conversions for a single enumerator. In the example, <code>Color::red</code> will always be <em>serialized</em> to <code>"red"</code>, because the first occurring conversion. The second conversion, however, offers an alternative <em>deserialization</em> from <code>"rot"</code> to <code>Color::red</code>.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=k>namespace</span><span class=w> </span><span class=nn>ns</span>
<span class=p>{</span>
@@ -81,14 +81,14 @@
<span class=p>{</span>
<span class=w> </span><span class=c1>// serialization</span>
<span class=w> </span><span class=n>json</span><span class=w> </span><span class=n>j_red</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>ns</span><span class=o>::</span><span class=n>Color</span><span class=o>::</span><span class=n>red</span><span class=p>;</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=k>static_cast</span><span class=o>&lt;</span><span class=kt>int</span><span class=o>&gt;</span><span class=p>(</span><span class=n>ns</span><span class=o>::</span><span class=n>Color</span><span class=o>::</span><span class=n>red</span><span class=p>)</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>" -&gt; "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>j_red</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>endl</span><span class=p>;</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=k>static_cast</span><span class=o>&lt;</span><span class=kt>int</span><span class=o>&gt;</span><span class=p>(</span><span class=n>ns</span><span class=o>::</span><span class=n>Color</span><span class=o>::</span><span class=n>red</span><span class=p>)</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>" -&gt; "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>j_red</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=sc>'\n'</span><span class=p>;</span>
<span class=w> </span><span class=c1>// deserialization</span>
<span class=w> </span><span class=n>json</span><span class=w> </span><span class=n>j_rot</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=s>"rot"</span><span class=p>;</span>
<span class=w> </span><span class=k>auto</span><span class=w> </span><span class=n>rot</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>j_rot</span><span class=p>.</span><span class=n>get</span><span class=o>&lt;</span><span class=n>ns</span><span class=o>::</span><span class=n>Color</span><span class=o>&gt;</span><span class=p>();</span>
<span class=w> </span><span class=k>auto</span><span class=w> </span><span class=n>red</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>j_red</span><span class=p>.</span><span class=n>get</span><span class=o>&lt;</span><span class=n>ns</span><span class=o>::</span><span class=n>Color</span><span class=o>&gt;</span><span class=p>();</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>j_rot</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>" -&gt; "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=k>static_cast</span><span class=o>&lt;</span><span class=kt>int</span><span class=o>&gt;</span><span class=p>(</span><span class=n>rot</span><span class=p>)</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>endl</span><span class=p>;</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>j_red</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>" -&gt; "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=k>static_cast</span><span class=o>&lt;</span><span class=kt>int</span><span class=o>&gt;</span><span class=p>(</span><span class=n>red</span><span class=p>)</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>endl</span><span class=p>;</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>j_rot</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>" -&gt; "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=k>static_cast</span><span class=o>&lt;</span><span class=kt>int</span><span class=o>&gt;</span><span class=p>(</span><span class=n>rot</span><span class=p>)</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=sc>'\n'</span><span class=p>;</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>j_red</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>" -&gt; "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=k>static_cast</span><span class=o>&lt;</span><span class=kt>int</span><span class=o>&gt;</span><span class=p>(</span><span class=n>red</span><span class=p>)</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=sc>'\n'</span><span class=p>;</span>
<span class=p>}</span>
</code></pre></div> <p>Output:</p> <div class=highlight><pre><span></span><code><span class=mi>0</span><span class=w> </span><span class=mi>-</span><span class=err>&gt;</span><span class=w> </span><span class=s2>"red"</span>
<span class=s2>"rot"</span><span class=w> </span><span class=mi>-</span><span class=err>&gt;</span><span class=w> </span><span class=mi>0</span>
@@ -96,7 +96,7 @@
</code></pre></div> </details> <details class=example> <summary>Example: exceptions on invalid serialization</summary> <p>The example shows how an invalid serialization causes an exception to be thrown. In the example, Color::unknown is not defined in the mapping used to call <code>NLOHMANN_JSON_SERIALIZE_ENUM_STRICT</code> so causes an exception when used to serialize. Similarly, "what" does not refer to an enum value so also causes an exception when deserialization is attempted.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=k>namespace</span><span class=w> </span><span class=nn>ns</span>
<span class=p>{</span>
@@ -129,7 +129,7 @@
</span><span class=w> </span><span class=p>}</span>
<span class=w> </span><span class=k>catch</span><span class=w> </span><span class=p>(</span><span class=k>const</span><span class=w> </span><span class=n>json</span><span class=o>::</span><span class=n>exception</span><span class=w> </span><span class=n>e</span><span class=p>)</span>
<span class=w> </span><span class=p>{</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>"deserialization failed: "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>e</span><span class=p>.</span><span class=n>what</span><span class=p>()</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>endl</span><span class=p>;</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>"deserialization failed: "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>e</span><span class=p>.</span><span class=n>what</span><span class=p>()</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=sc>'\n'</span><span class=p>;</span>
<span class=w> </span><span class=p>}</span>
<span class=w> </span><span class=c1>// invalid deserialization</span>
@@ -141,11 +141,11 @@
</span><span class=w> </span><span class=p>}</span>
<span class=w> </span><span class=k>catch</span><span class=w> </span><span class=p>(</span><span class=k>const</span><span class=w> </span><span class=n>json</span><span class=o>::</span><span class=n>exception</span><span class=w> </span><span class=n>e</span><span class=p>)</span>
<span class=w> </span><span class=p>{</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>"deserialization failed: "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>e</span><span class=p>.</span><span class=n>what</span><span class=p>()</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>endl</span><span class=p>;</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>"deserialization failed: "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>e</span><span class=p>.</span><span class=n>what</span><span class=p>()</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=sc>'\n'</span><span class=p>;</span>
<span class=w> </span><span class=p>}</span>
<span class=w> </span><span class=k>return</span><span class=w> </span><span class=mi>0</span><span class=p>;</span>
<span class=p>}</span>
</code></pre></div> <p>Output: <div class=highlight><pre><span></span><code><span class=err>deserializa</span><span class=kc>t</span><span class=err>io</span><span class=kc>n</span><span class=w> </span><span class=kc>fa</span><span class=err>iled</span><span class=p>:</span><span class=w> </span><span class=p>[</span><span class=err>jso</span><span class=kc>n</span><span class=err>.excep</span><span class=kc>t</span><span class=err>io</span><span class=kc>n</span><span class=err>.ou</span><span class=kc>t</span><span class=err>_o</span><span class=kc>f</span><span class=err>_ra</span><span class=kc>n</span><span class=err>ge.</span><span class=mi>410</span><span class=p>]</span><span class=w> </span><span class=err>e</span><span class=kc>nu</span><span class=err>m</span><span class=w> </span><span class=err>value</span><span class=w> </span><span class=err>ou</span><span class=kc>t</span><span class=w> </span><span class=err>o</span><span class=kc>f</span><span class=w> </span><span class=err>ra</span><span class=kc>n</span><span class=err>ge</span><span class=w> </span><span class=kc>f</span><span class=err>or</span><span class=w> </span><span class=err>Color</span>
<span class=err>deserializa</span><span class=kc>t</span><span class=err>io</span><span class=kc>n</span><span class=w> </span><span class=kc>fa</span><span class=err>iled</span><span class=p>:</span><span class=w> </span><span class=p>[</span><span class=err>jso</span><span class=kc>n</span><span class=err>.excep</span><span class=kc>t</span><span class=err>io</span><span class=kc>n</span><span class=err>.ou</span><span class=kc>t</span><span class=err>_o</span><span class=kc>f</span><span class=err>_ra</span><span class=kc>n</span><span class=err>ge.</span><span class=mi>410</span><span class=p>]</span><span class=w> </span><span class=err>e</span><span class=kc>nu</span><span class=err>m</span><span class=w> </span><span class=err>value</span><span class=w> </span><span class=err>ou</span><span class=kc>t</span><span class=w> </span><span class=err>o</span><span class=kc>f</span><span class=w> </span><span class=err>ra</span><span class=kc>n</span><span class=err>ge</span><span class=w> </span><span class=kc>f</span><span class=err>or</span><span class=w> </span><span class=err>Color</span><span class=p>:</span><span class=w> </span><span class=s2>"what"</span>
</code></pre></div></p> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../../../features/enum_conversion/ >Specializing enum conversion</a></li> <li><a href=../nlohmann_json_serialize_enum/ ><code>NLOHMANN_JSON_SERIALIZE_ENUM</code></a></li> <li><a href=../json_disable_enum_serialization/ ><code>JSON_DISABLE_ENUM_SERIALIZATION</code></a></li> <li><a href=../json_use_objects_for_enum_keyed_maps/ ><code>JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS</code></a></li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <p>Added in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</p> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 4, 2026 15:54:05 UTC">October 4, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 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</code></pre></div></p> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../../../features/enum_conversion/ >Specializing enum conversion</a></li> <li><a href=../nlohmann_json_serialize_enum/ ><code>NLOHMANN_JSON_SERIALIZE_ENUM</code></a></li> <li><a href=../json_disable_enum_serialization/ ><code>JSON_DISABLE_ENUM_SERIALIZATION</code></a></li> <li><a href=../json_use_objects_for_enum_keyed_maps/ ><code>JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS</code></a></li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <p>Added in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</p> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 26, 2026 19:13:31 UTC">October 26, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 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@@ -37,6 +37,10 @@ Important notes
- If an enum or JSON value is specified in multiple conversions, the first matching conversion from the top of the list will be returned when converting to or from JSON. See example 2 below.
- Maps with enum keys (e.g., `std::map<ENUM_TYPE, T>`) are stored as arrays of `[key, value]` pairs by default. Define [`JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS`](https://json.nlohmann.me/api/macros/json_use_objects_for_enum_keyed_maps/index.md) to store them as objects with the converted keys. Such maps can be read from both forms.
Views
The generated `from_json()` also reads the views of [`json_document`](https://json.nlohmann.me/api/json_document/index.md)s (`<nlohmann/json_view.hpp>`), comparing the view with the entries of the mapping, without building a `json` value first.
## Examples
Example: Basic usage
@@ -47,7 +51,7 @@ The example shows how `NLOHMANN_JSON_SERIALIZE_ENUM_STRICT` can be used to seria
#include <iostream>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using nlohmann::json;
namespace ns
{
@@ -85,7 +89,7 @@ int main()
json j_stopped = ns::TS_STOPPED;
json j_red = ns::Color::red;
std::cout << "ns::TS_STOPPED -> " << j_stopped
<< ", ns::Color::red -> " << j_red << std::endl;
<< ", ns::Color::red -> " << j_red << '\n';
// deserialization
json j_running = "running";
@@ -93,7 +97,7 @@ int main()
auto running = j_running.get<ns::TaskState>();
auto blue = j_blue.get<ns::Color>();
std::cout << j_running << " -> " << running
<< ", " << j_blue << " -> " << static_cast<int>(blue) << std::endl;
<< ", " << j_blue << " -> " << static_cast<int>(blue) << '\n';
}
```
@@ -113,7 +117,7 @@ The example shows how to use multiple conversions for a single enumerator. In th
#include <iostream>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using nlohmann::json;
namespace ns
{
@@ -134,14 +138,14 @@ int main()
{
// serialization
json j_red = ns::Color::red;
std::cout << static_cast<int>(ns::Color::red) << " -> " << j_red << std::endl;
std::cout << static_cast<int>(ns::Color::red) << " -> " << j_red << '\n';
// deserialization
json j_rot = "rot";
auto rot = j_rot.get<ns::Color>();
auto red = j_red.get<ns::Color>();
std::cout << j_rot << " -> " << static_cast<int>(rot) << std::endl;
std::cout << j_red << " -> " << static_cast<int>(red) << std::endl;
std::cout << j_rot << " -> " << static_cast<int>(rot) << '\n';
std::cout << j_red << " -> " << static_cast<int>(red) << '\n';
}
```
@@ -161,7 +165,7 @@ The example shows how an invalid serialization causes an exception to be thrown.
#include <iostream>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using nlohmann::json;
namespace ns
{
@@ -194,7 +198,7 @@ int main()
}
catch (const json::exception e)
{
std::cout << "deserialization failed: " << e.what() << std::endl;
std::cout << "deserialization failed: " << e.what() << '\n';
}
// invalid deserialization
@@ -206,7 +210,7 @@ int main()
}
catch (const json::exception e)
{
std::cout << "deserialization failed: " << e.what() << std::endl;
std::cout << "deserialization failed: " << e.what() << '\n';
}
return 0;
+2 -2
View File
@@ -24,14 +24,14 @@ The macros are defined according to the current library version.
#include <iostream>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using nlohmann::json;
int main()
{
std::cout << "JSON for Modern C++ version "
<< NLOHMANN_JSON_VERSION_MAJOR << "."
<< NLOHMANN_JSON_VERSION_MINOR << "."
<< NLOHMANN_JSON_VERSION_PATCH << std::endl;
<< NLOHMANN_JSON_VERSION_PATCH << '\n';
}
```
@@ -1,17 +1,17 @@
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/macros/nlohmann_json_version_major/" rel="canonical"><link href=../nlohmann_json_serialize_enum_strict/ rel=prev><link href=../../../community/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>NLOHMANN_JSON_VERSION_MAJOR, NLOHMANN_JSON_VERSION_MINOR, NLOHMANN_JSON_VERSION_PATCH - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new URL("../../..",location),__md_hash=e=>[...e].reduce(((e,_)=>(e<<5)-e+_.charCodeAt(0)),0),__md_get=(e,_=localStorage,t=__md_scope)=>JSON.parse(_.getItem(t.pathname+"."+e)),__md_set=(e,_,t=localStorage,a=__md_scope)=>{try{t.setItem(a.pathname+"."+e,JSON.stringify(_))}catch(e){}}</script></head> <body dir=ltr data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo> <input class=md-toggle data-md-toggle=drawer type=checkbox id=__drawer autocomplete=off> <input class=md-toggle data-md-toggle=search type=checkbox id=__search autocomplete=off> <label class=md-overlay for=__drawer></label> <div data-md-component=skip> <a href=#nlohmann_json_version_major-nlohmann_json_version_minor-nlohmann_json_version_patch class=md-skip> Skip to content </a> </div> <div data-md-component=announce> </div> <header class=md-header data-md-component=header> <nav class="md-header__inner md-grid" aria-label=Header> <a href=../../.. 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<span class=cp>#define NLOHMANN_JSON_VERSION_MINOR </span><span class=cm>/* value */</span>
<span class=cp>#define NLOHMANN_JSON_VERSION_PATCH </span><span class=cm>/* value */</span>
</code></pre></div> <p>These macros are defined by the library and contain the version numbers according to <a href="https://semver.org/spec/v2.0.0.html">Semantic Versioning 2.0.0</a>.</p> <h2 id=default-definition>Default definition<a class=headerlink href=#default-definition title="Permanent link">&para;</a></h2> <p>The macros are defined according to the current library version.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The example below shows how <code>NLOHMANN_JSON_VERSION_MAJOR</code>, <code>NLOHMANN_JSON_VERSION_MINOR</code>, and <code>NLOHMANN_JSON_VERSION_PATCH</code> are defined by the library.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span>
<span class=p>{</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>"JSON for Modern C++ version "</span>
<span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>NLOHMANN_JSON_VERSION_MAJOR</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>"."</span>
<span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>NLOHMANN_JSON_VERSION_MINOR</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>"."</span>
<span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>NLOHMANN_JSON_VERSION_PATCH</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>endl</span><span class=p>;</span>
<span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>NLOHMANN_JSON_VERSION_PATCH</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=sc>'\n'</span><span class=p>;</span>
<span class=p>}</span>
</code></pre></div> <p>Output:</p> <div class=highlight><pre><span></span><code><span class=err>JSON</span><span class=w> </span><span class=kc>f</span><span class=err>or</span><span class=w> </span><span class=err>Moder</span><span class=kc>n</span><span class=w> </span><span class=err>C++</span><span class=w> </span><span class=err>versio</span><span class=kc>n</span><span class=w> </span><span class=mf>3.12.0</span>
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../../basic_json/meta/ >meta</a> - returns version information on the library</li> <li><a href=../json_skip_library_version_check/ >JSON_SKIP_LIBRARY_VERSION_CHECK</a> - skip library version check</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ul> <li>Added in version 3.1.0.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="May 17, 2022 11:08:56 UTC">May 17, 2022</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 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@@ -22,14 +22,14 @@ The example below shows how `NLOHMANN_JSON_VERSION_MAJOR`, `NLOHMANN_JSON_VERSIO
#include <iostream>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using nlohmann::json;
int main()
{
std::cout << "JSON for Modern C++ version "
<< NLOHMANN_JSON_VERSION_MAJOR << "."
<< NLOHMANN_JSON_VERSION_MINOR << "."
<< NLOHMANN_JSON_VERSION_PATCH << std::endl;
<< NLOHMANN_JSON_VERSION_PATCH << '\n';
}
```