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@@ -33,10 +33,10 @@ struct adl_serializer {
## See also
- [Arbitrary type conversions](../../features/arbitrary_types.md) - how to make your types convertible
- [**get**](../basic_json/get.md) / [**get_to**](../basic_json/get_to.md) - convert a JSON value to a C++ type
- [**basic_json**](../basic_json/basic_json.md) - construct a JSON value from a C++ value
- [**NLOHMANN_DEFINE_TYPE_INTRUSIVE**](../macros/nlohmann_define_type_intrusive.md) - generate the conversion functions for a type
- [Specializing enum conversion](../../features/enum_conversion.md)
- [`get`](../basic_json/get.md) - / [`get_to`](../basic_json/get_to.md) - convert a JSON value to a C++ type
- [`basic_json`](../basic_json/basic_json.md) - construct a JSON value from a C++ value
- [`NLOHMANN_DEFINE_TYPE_INTRUSIVE`](../macros/nlohmann_define_type_intrusive.md) - generate the conversion functions for a type
- [Specializing enum conversion](../../features/enum_conversion.md) - serializing enums as JSON strings
## Version history
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@@ -30,7 +30,7 @@ class (either explicitly or via the conversion operators).
## Return value
1. (none) -- the converted value is written to the output parameter `val`.
1. (none) — the converted value is written to the output parameter `val`.
2. the JSON value `j` converted to `TargetType`
## Examples
@@ -159,7 +159,9 @@ class (either explicitly or via the conversion operators).
## See also
- [to_json](to_json.md)
- [`to_json`](to_json.md) - convert a C++ value to JSON
- [Arbitrary Type Conversions](../../features/arbitrary_types.md) - write your own `from_json` and `to_json` functions
- [Converting values](../../features/conversions.md) - overview of `get`, `get_to` and implicit conversions
## Version history
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@@ -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/adl_serializer/from_json/" rel="canonical"><link href=../ rel=prev><link href=../to_json/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>from_json - 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=description content="JSON for Modern C++ is a header-only C++11 library that makes JSON a first-class data type."><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/adl_serializer/from_json/" rel="canonical"><link href=../ rel=prev><link href=../to_json/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>from_json - 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=../../../css/custom.css><link rel=stylesheet href=../../../css/brand.css><link rel=stylesheet href=../../../css/fig-sax.css><link rel=stylesheet href=../../../css/fig-jsonview.css><link rel=stylesheet 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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> <img src=../../../images/wordmark-header.svg alt=logo> </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> from_json </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)" 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<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=p>,</span><span class=w> </span><span class=k>typename</span><span class=w> </span><span class=nc>TargetType</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>ValueType</span><span class=o>&gt;</span>
<span class=k>static</span><span class=w> </span><span class=k>auto</span><span class=w> </span><span class=n>from_json</span><span class=p>(</span><span class=n>BasicJsonType</span><span class=w> </span><span class=o>&amp;&amp;</span><span class=w> </span><span class=n>j</span><span class=p>,</span><span class=w> </span><span class=n>TargetType</span><span class=o>&amp;</span><span class=w> </span><span class=n>val</span><span class=p>)</span><span class=w> </span><span class=k>noexcept</span><span class=p>(</span>
<span class=w> </span><span class=k>noexcept</span><span class=p>(</span><span class=o>::</span><span class=n>nlohmann</span><span class=o>::</span><span class=n>from_json</span><span class=p>(</span><span class=n>std</span><span class=o>::</span><span class=n>forward</span><span class=o>&lt;</span><span class=n>BasicJsonType</span><span class=o>&gt;</span><span class=p>(</span><span class=n>j</span><span class=p>),</span><span class=w> </span><span class=n>val</span><span class=p>)))</span>
@@ -9,7 +9,7 @@
<span class=k>static</span><span class=w> </span><span class=k>auto</span><span class=w> </span><span class=n>from_json</span><span class=p>(</span><span class=n>BasicJsonType</span><span class=w> </span><span class=o>&amp;&amp;</span><span class=w> </span><span class=n>j</span><span class=p>)</span><span class=w> </span><span class=k>noexcept</span><span class=p>(</span>
<span class=k>noexcept</span><span class=p>(</span><span class=o>::</span><span class=n>nlohmann</span><span class=o>::</span><span class=n>from_json</span><span class=p>(</span><span class=n>std</span><span class=o>::</span><span class=n>forward</span><span class=o>&lt;</span><span class=n>BasicJsonType</span><span class=o>&gt;</span><span class=p>(</span><span class=n>j</span><span class=p>),</span><span class=w> </span><span class=n>detail</span><span class=o>::</span><span class=n>identity_tag</span><span class=o>&lt;</span><span class=n>TargetType</span><span class=o>&gt;</span><span class=w> </span><span class=p>{})))</span>
<span class=o>-&gt;</span><span class=w> </span><span class=k>decltype</span><span class=p>(</span><span class=o>::</span><span class=n>nlohmann</span><span class=o>::</span><span class=n>from_json</span><span class=p>(</span><span class=n>std</span><span class=o>::</span><span class=n>forward</span><span class=o>&lt;</span><span class=n>BasicJsonType</span><span class=o>&gt;</span><span class=p>(</span><span class=n>j</span><span class=p>),</span><span class=w> </span><span class=n>detail</span><span class=o>::</span><span class=n>identity_tag</span><span class=o>&lt;</span><span class=n>TargetType</span><span class=o>&gt;</span><span class=w> </span><span class=p>{}))</span>
</code></pre></div> <p>This function is usually called by the <a href=../../basic_json/get/ ><code>get()</code></a> function of the <a href=../../basic_json/ >basic_json</a> class (either explicitly or via the conversion operators).</p> <ol> <li>This function is chosen for default-constructible value types.</li> <li>This function is chosen for value types which are not default-constructible.</li> </ol> <h2 id=parameters>Parameters<a class=headerlink href=#parameters title="Permanent link">&para;</a></h2> <dl> <dt><code>j</code> (in)</dt> <dd><abbr title="JavaScript Object Notation">JSON</abbr> value to read from</dd> <dt><code>val</code> (out)</dt> <dd>value to write to</dd> </dl> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <ol> <li>(none) -- the converted value is written to the output parameter <code>val</code>.</li> <li>the <abbr title="JavaScript Object Notation">JSON</abbr> value <code>j</code> converted to <code>TargetType</code></li> </ol> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example: (1) Default-constructible type</summary> <p>The example below shows how a <code>from_json</code> function can be implemented for a user-defined type. This function is called by the <code>adl_serializer</code> when <code>get&lt;ns::person&gt;()</code> is called.</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>This function is usually called by the <a href=../../basic_json/get/ ><code>get()</code></a> function of the <a href=../../basic_json/ >basic_json</a> class (either explicitly or via the conversion operators).</p> <ol> <li>This function is chosen for default-constructible value types.</li> <li>This function is chosen for value types which are not default-constructible.</li> </ol> <h2 id=parameters>Parameters<a class=headerlink href=#parameters title="Permanent link">&para;</a></h2> <dl> <dt><code>j</code> (in)</dt> <dd><abbr title="JavaScript Object Notation">JSON</abbr> value to read from</dd> <dt><code>val</code> (out)</dt> <dd>value to write to</dd> </dl> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <ol> <li>(none) — the converted value is written to the output parameter <code>val</code>.</li> <li>the <abbr title="JavaScript Object Notation">JSON</abbr> value <code>j</code> converted to <code>TargetType</code></li> </ol> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example: (1) Default-constructible type</summary> <p>The example below shows how a <code>from_json</code> function can be implemented for a user-defined type. This function is called by the <code>adl_serializer</code> when <code>get&lt;ns::person&gt;()</code> is called.</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>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
@@ -101,4 +101,4 @@
<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>p</span><span class=p>.</span><span class=n>name</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>p</span><span class=p>.</span><span class=n>age</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>") lives in "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>p</span><span class=p>.</span><span class=n>address</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>Ned</span><span class=w> </span><span class=err>Fla</span><span class=kc>n</span><span class=err>ders</span><span class=w> </span><span class=err>(</span><span class=mi>60</span><span class=err>)</span><span class=w> </span><span class=err>lives</span><span class=w> </span><span class=err>i</span><span class=kc>n</span><span class=w> </span><span class=mi>744</span><span class=w> </span><span class=err>Evergree</span><span class=kc>n</span><span class=w> </span><span class=err>Terrace</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=../to_json/ >to_json</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 2.1.0.</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="June 29, 2026 20:15:18 UTC">June 29, 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=../to_json/ ><code>to_json</code></a> - convert a C++ value to <abbr title="JavaScript Object Notation">JSON</abbr></li> <li><a href=../../../features/arbitrary_types/ >Arbitrary Type Conversions</a> - write your own <code>from_json</code> and <code>to_json</code> functions</li> <li><a href=../../../features/conversions/ >Converting values</a> - overview of <code>get</code>, <code>get_to</code> and implicit conversions</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 2.1.0.</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="October 27, 2026 06:41:42 UTC">October 27, 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> <nav class="md-footer__inner md-grid" aria-label=Footer> <a href=../ class="md-footer__link md-footer__link--prev" aria-label="Previous: Overview"> <div class="md-footer__button md-icon"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M20 11v2H8l5.5 5.5-1.42 1.42L4.16 12l7.92-7.92L13.5 5.5 8 11z"/></svg> </div> <div class=md-footer__title> <span class=md-footer__direction> Previous </span> <div class=md-ellipsis> Overview </div> </div> </a> <a href=../to_json/ class="md-footer__link md-footer__link--next" aria-label="Next: to_json"> <div class=md-footer__title> <span class=md-footer__direction> Next </span> <div class=md-ellipsis> to_json </div> </div> <div class="md-footer__button md-icon"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M4 11v2h12l-5.5 5.5 1.42 1.42L19.84 12l-7.92-7.92L10.5 5.5 16 11z"/></svg> </div> </a> </nav> <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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+4 -2
View File
@@ -27,7 +27,7 @@ This function is usually called by the [`get()`](https://json.nlohmann.me/api/ba
## Return value
1. (none) -- the converted value is written to the output parameter `val`.
1. (none) — the converted value is written to the output parameter `val`.
1. the JSON value `j` converted to `TargetType`
## Examples
@@ -150,7 +150,9 @@ Ned Flanders (60) lives in 744 Evergreen Terrace
## See also
- [to_json](https://json.nlohmann.me/api/adl_serializer/to_json/index.md)
- [`to_json`](https://json.nlohmann.me/api/adl_serializer/to_json/index.md) - convert a C++ value to JSON
- [Arbitrary Type Conversions](https://json.nlohmann.me/features/arbitrary_types/index.md) - write your own `from_json` and `to_json` functions
- [Converting values](https://json.nlohmann.me/features/conversions/index.md) - overview of `get`, `get_to` and implicit conversions
## Version history
+2 -2
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@@ -1,4 +1,4 @@
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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=description content="JSON for Modern C++ is a header-only C++11 library that makes JSON a first-class data type."><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/adl_serializer/" rel="canonical"><link href=../byte_container_with_subtype/subtype/ rel=prev><link href=from_json/ rel=next><link rel=icon href=../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>Overview - 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=../../css/custom.css><link rel=stylesheet href=../../css/brand.css><link rel=stylesheet href=../../css/fig-sax.css><link rel=stylesheet href=../../css/fig-jsonview.css><link rel=stylesheet 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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> <img src=../../images/wordmark-header.svg alt=logo> </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> Overview </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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<span class=k>struct</span><span class=w> </span><span class=nc>adl_serializer</span><span class=p>;</span>
</code></pre></div> <p>Serializer that uses <abbr title="Argument-dependent lookup">ADL</abbr> (<a href="https://en.cppreference.com/w/cpp/language/adl">Argument-Dependent Lookup</a>) to choose <code>to_json</code>/<code>from_json</code> functions from the types' namespaces.</p> <p>It is implemented similarly to</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>ValueType</span><span class=o>&gt;</span>
<span class=k>struct</span><span class=w> </span><span class=nc>adl_serializer</span><span class=w> </span><span class=p>{</span>
@@ -12,4 +12,4 @@
<span class=w> </span><span class=c1>// same thing, but with the "from_json" method</span>
<span class=w> </span><span class=p>}</span>
<span class=p>};</span>
</code></pre></div> <h2 id=member-functions>Member functions<a class=headerlink href=#member-functions title="Permanent link">&para;</a></h2> <ul> <li><a href=from_json/ ><strong>from_json</strong></a> - convert a <abbr title="JavaScript Object Notation">JSON</abbr> value to any value type</li> <li><a href=to_json/ ><strong>to_json</strong></a> - convert any value type to a <abbr title="JavaScript Object Notation">JSON</abbr> value</li> </ul> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../../features/arbitrary_types/ >Arbitrary type conversions</a> - how to make your types convertible</li> <li><a href=../basic_json/get/ ><strong>get</strong></a> / <a href=../basic_json/get_to/ ><strong>get_to</strong></a> - convert a <abbr title="JavaScript Object Notation">JSON</abbr> value to a C++ type</li> <li><a href=../basic_json/basic_json/ ><strong>basic_json</strong></a> - construct a <abbr title="JavaScript Object Notation">JSON</abbr> value from a C++ value</li> <li><a href=../macros/nlohmann_define_type_intrusive/ ><strong>NLOHMANN_DEFINE_TYPE_INTRUSIVE</strong></a> - generate the conversion functions for a type</li> <li><a href=../../features/enum_conversion/ >Specializing enum conversion</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 2.1.0.</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="October 24, 2026 15:57:44 UTC">October 24, 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> <h2 id=member-functions>Member functions<a class=headerlink href=#member-functions title="Permanent link">&para;</a></h2> <ul> <li><a href=from_json/ ><strong>from_json</strong></a> - convert a <abbr title="JavaScript Object Notation">JSON</abbr> value to any value type</li> <li><a href=to_json/ ><strong>to_json</strong></a> - convert any value type to a <abbr title="JavaScript Object Notation">JSON</abbr> value</li> </ul> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../../features/arbitrary_types/ >Arbitrary type conversions</a> - how to make your types convertible</li> <li><a href=../basic_json/get/ ><code>get</code></a> - / <a href=../basic_json/get_to/ ><code>get_to</code></a> - convert a <abbr title="JavaScript Object Notation">JSON</abbr> value to a C++ type</li> <li><a href=../basic_json/basic_json/ ><code>basic_json</code></a> - construct a <abbr title="JavaScript Object Notation">JSON</abbr> value from a C++ value</li> <li><a href=../macros/nlohmann_define_type_intrusive/ ><code>NLOHMANN_DEFINE_TYPE_INTRUSIVE</code></a> - generate the conversion functions for a type</li> <li><a href=../../features/enum_conversion/ >Specializing enum conversion</a> - serializing enums as <abbr title="JavaScript Object Notation">JSON</abbr> strings</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 2.1.0.</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="October 27, 2026 06:41:42 UTC">October 27, 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> <nav class="md-footer__inner md-grid" aria-label=Footer> <a href=../byte_container_with_subtype/subtype/ class="md-footer__link md-footer__link--prev" aria-label="Previous: subtype"> <div class="md-footer__button md-icon"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M20 11v2H8l5.5 5.5-1.42 1.42L4.16 12l7.92-7.92L13.5 5.5 8 11z"/></svg> </div> <div class=md-footer__title> <span class=md-footer__direction> Previous </span> <div class=md-ellipsis> subtype </div> </div> </a> <a href=from_json/ class="md-footer__link md-footer__link--next" aria-label="Next: from_json"> <div class=md-footer__title> <span class=md-footer__direction> Next </span> <div class=md-ellipsis> from_json </div> </div> <div class="md-footer__button md-icon"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M4 11v2h12l-5.5 5.5 1.42 1.42L19.84 12l-7.92-7.92L10.5 5.5 16 11z"/></svg> </div> </a> </nav> <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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+4 -4
View File
@@ -32,10 +32,10 @@ struct adl_serializer {
## See also
- [Arbitrary type conversions](https://json.nlohmann.me/features/arbitrary_types/index.md) - how to make your types convertible
- [**get**](https://json.nlohmann.me/api/basic_json/get/index.md) / [**get_to**](https://json.nlohmann.me/api/basic_json/get_to/index.md) - convert a JSON value to a C++ type
- [**basic_json**](https://json.nlohmann.me/api/basic_json/basic_json/index.md) - construct a JSON value from a C++ value
- [**NLOHMANN_DEFINE_TYPE_INTRUSIVE**](https://json.nlohmann.me/api/macros/nlohmann_define_type_intrusive/index.md) - generate the conversion functions for a type
- [Specializing enum conversion](https://json.nlohmann.me/features/enum_conversion/index.md)
- [`get`](https://json.nlohmann.me/api/basic_json/get/index.md) - / [`get_to`](https://json.nlohmann.me/api/basic_json/get_to/index.md) - convert a JSON value to a C++ type
- [`basic_json`](https://json.nlohmann.me/api/basic_json/basic_json/index.md) - construct a JSON value from a C++ value
- [`NLOHMANN_DEFINE_TYPE_INTRUSIVE`](https://json.nlohmann.me/api/macros/nlohmann_define_type_intrusive/index.md) - generate the conversion functions for a type
- [Specializing enum conversion](https://json.nlohmann.me/features/enum_conversion/index.md) - serializing enums as JSON strings
## Version history
+3 -1
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@@ -69,7 +69,9 @@ This function is usually called by the constructors of the [basic_json](../basic
## See also
- [from_json](from_json.md)
- [`from_json`](from_json.md) - convert JSON to a C++ value
- [Arbitrary Type Conversions](../../features/arbitrary_types.md) - write your own `from_json` and `to_json` functions
- [Converting values](../../features/conversions.md) - overview of `get`, `get_to` and implicit conversions
## Version history
+2 -2
View File
@@ -1,4 +1,4 @@
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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=description content="JSON for Modern C++ is a header-only C++11 library that makes JSON a first-class data type."><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/adl_serializer/to_json/" rel="canonical"><link href=../from_json/ rel=prev><link href=../../is_json_view/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>to_json - 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=../../../css/custom.css><link rel=stylesheet href=../../../css/brand.css><link rel=stylesheet href=../../../css/fig-sax.css><link rel=stylesheet href=../../../css/fig-jsonview.css><link 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<span class=k>static</span><span class=w> </span><span class=k>auto</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=n>TargetType</span><span class=w> </span><span class=o>&amp;&amp;</span><span class=w> </span><span class=n>val</span><span class=p>)</span><span class=w> </span><span class=k>noexcept</span><span class=p>(</span>
<span class=w> </span><span class=k>noexcept</span><span class=p>(</span><span class=o>::</span><span class=n>nlohmann</span><span class=o>::</span><span class=n>to_json</span><span class=p>(</span><span class=n>j</span><span class=p>,</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>forward</span><span class=o>&lt;</span><span class=n>TargetType</span><span class=o>&gt;</span><span class=p>(</span><span class=n>val</span><span class=p>))))</span>
<span class=o>-&gt;</span><span class=w> </span><span class=k>decltype</span><span class=p>(</span><span class=o>::</span><span class=n>nlohmann</span><span class=o>::</span><span class=n>to_json</span><span class=p>(</span><span class=n>j</span><span class=p>,</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>forward</span><span class=o>&lt;</span><span class=n>TargetType</span><span class=o>&gt;</span><span class=p>(</span><span class=n>val</span><span class=p>)),</span><span class=w> </span><span class=kt>void</span><span class=p>())</span>
@@ -35,4 +35,4 @@
<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=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> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../from_json/ >from_json</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 2.1.0.</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="November 1, 2023 20:23:55 UTC">November 1, 2023</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=../from_json/ ><code>from_json</code></a> - convert <abbr title="JavaScript Object Notation">JSON</abbr> to a C++ value</li> <li><a href=../../../features/arbitrary_types/ >Arbitrary Type Conversions</a> - write your own <code>from_json</code> and <code>to_json</code> functions</li> <li><a href=../../../features/conversions/ >Converting values</a> - overview of <code>get</code>, <code>get_to</code> and implicit conversions</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 2.1.0.</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="October 27, 2026 06:41:42 UTC">October 27, 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> <nav class="md-footer__inner md-grid" aria-label=Footer> <a href=../from_json/ class="md-footer__link md-footer__link--prev" aria-label="Previous: from_json"> <div class="md-footer__button md-icon"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M20 11v2H8l5.5 5.5-1.42 1.42L4.16 12l7.92-7.92L13.5 5.5 8 11z"/></svg> </div> <div class=md-footer__title> <span class=md-footer__direction> Previous </span> <div class=md-ellipsis> from_json </div> </div> </a> <a href=../../is_json_view/ class="md-footer__link md-footer__link--next" aria-label="Next: is_json_view"> <div class=md-footer__title> <span class=md-footer__direction> Next </span> <div class=md-ellipsis> is_json_view </div> </div> <div class="md-footer__button md-icon"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M4 11v2h12l-5.5 5.5 1.42 1.42L19.84 12l-7.92-7.92L10.5 5.5 16 11z"/></svg> </div> </a> </nav> <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 -1
View File
@@ -64,7 +64,9 @@ Output:
## See also
- [from_json](https://json.nlohmann.me/api/adl_serializer/from_json/index.md)
- [`from_json`](https://json.nlohmann.me/api/adl_serializer/from_json/index.md) - convert JSON to a C++ value
- [Arbitrary Type Conversions](https://json.nlohmann.me/features/arbitrary_types/index.md) - write your own `from_json` and `to_json` functions
- [Converting values](https://json.nlohmann.me/features/conversions/index.md) - overview of `get`, `get_to` and implicit conversions
## Version history
+9 -4
View File
@@ -189,7 +189,7 @@ The class satisfies the following concept requirements:
Functions to inspect the type of a JSON value.
- [**type**](type.md) - return the type of the JSON value
- [**operator value_t**](operator_value_t.md) - return the type of the JSON value
- [`operator value_t`](operator_value_t.md) - return the type of the JSON value
- [**type_name**](type_name.md) - return the type as string
- [**is_primitive**](is_primitive.md) - return whether the type is primitive
- [**is_structured**](is_structured.md) - return whether the type is structured
@@ -218,7 +218,7 @@ Direct access to the stored value of a JSON value.
- [**get_to**](get_to.md) - get a value and write it to a destination
- [**get_ptr**](get_ptr.md) - get a pointer value
- [**get_ref**](get_ref.md) - get a reference value
- [**operator ValueType**](operator_ValueType.md) - get a value
- [`operator ValueType`](operator_ValueType.md) - get a value
- [**get_binary**](get_binary.md) - get a binary value
- [**as_base_class**](as_base_class.md) - access the custom base class
@@ -425,10 +425,15 @@ Access to the JSON value
## See also
- [RFC 8259: The JavaScript Object Notation (JSON) Data Interchange Format](https://tools.ietf.org/html/rfc8259)
- [basic_json_document](../basic_json_document/index.md) / [basic_json_view](../basic_json_view/index.md) - parse a JSON
- [RFC 8259: The JavaScript Object Notation (JSON) Data Interchange Format](https://tools.ietf.org/html/rfc8259) -
specification of the JSON data interchange format
- [`basic_json_document`](../basic_json_document/index.md) - / [`basic_json_view`](../basic_json_view/index.md) - parse a JSON
text into a flat index and read it through a view
- [Zero-copy JSON views](../../features/json_view.md) - when to use a document and a view instead of a `basic_json`
- [Types](../../features/types/index.md) - how JSON values are stored and which types exist
- [Converting values](../../features/conversions.md) - get values out of a JSON value and put values in
- [Creating JSON values](../../features/creating_values.md) - all the ways to build a JSON value
- [Arbitrary Type Conversions](../../features/arbitrary_types.md) - convert your own types to and from JSON
## Version history
+8 -3
View File
@@ -210,15 +210,20 @@ outside of a string, invalid) byte; see the [FAQ entry](../../home/faq.md#nul-by
## See also
- [parse](parse.md) - deserialize from a compatible input
- [sax_parse](sax_parse.md) - parse input using the SAX interface
- [operator>>](../operator_gtgt.md) - deserialize from stream
- [`parse`](parse.md) - deserialize from a compatible input
- [`sax_parse`](sax_parse.md) - parse input using the SAX interface
- [`operator>>`](../operator_gtgt.md) - deserialize from stream
- [`JSON_STRICT_NUL_HANDLING`](../macros/json_strict_nul_handling.md) - opt in to rejecting a NUL byte in the input
instead of treating it as end of input
- [`JSON_DISABLE_STREAM_BULK_SCAN`](../macros/json_disable_stream_bulk_scan.md) - read a `std::istream` one character
at a time
- [`JSON_DISABLE_UNLOCKED_FILE_IO`](../macros/json_disable_unlocked_file_io.md) - read a `FILE*` with the locking stdio
functions
- [Parsing](../../features/parsing/index.md) - overview of the parsing functions
- [Comments](../../features/comments.md) - ignore `//` and `/* */` comments while parsing
- [Trailing Commas](../../features/trailing_commas.md) - accept trailing commas in arrays and objects
- [Parsing and Exceptions](../../features/parsing/parse_exceptions.md) - handling parse errors and locating them in the input
- [Parsing Untrusted Input](../../features/parsing/untrusted_input.md) - limits and checks for input you do not control
## Version history
+2 -2
View File
@@ -1,4 +1,4 @@
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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=description content="JSON for Modern C++ is a header-only C++11 library that makes JSON a first-class data type."><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/accept/" rel="canonical"><link href=../~basic_json/ rel=prev><link href=../array/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>accept - 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=../../../css/custom.css><link rel=stylesheet href=../../../css/brand.css><link rel=stylesheet href=../../../css/fig-sax.css><link rel=stylesheet href=../../../css/fig-jsonview.css><link rel=stylesheet 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</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> <img src=../../../images/wordmark-header.svg alt=logo> </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> accept </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 Line truncated
<span class=k>template</span><span class=o>&lt;</span><span class=k>typename</span><span class=w> </span><span class=nc>InputType</span><span class=o>&gt;</span>
<span class=k>static</span><span class=w> </span><span class=kt>bool</span><span class=w> </span><span class=n>accept</span><span class=p>(</span><span class=n>InputType</span><span class=o>&amp;&amp;</span><span class=w> </span><span class=n>i</span><span class=p>,</span>
<span class=w> </span><span class=k>const</span><span class=w> </span><span class=kt>bool</span><span class=w> </span><span class=n>ignore_comments</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=nb>false</span><span class=p>,</span>
@@ -71,4 +71,4 @@
<span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>json</span><span class=o>::</span><span class=n>accept</span><span class=p>(</span><span class=n>invalid_text</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>true</span><span class=w> </span><span class=kc>false</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=../parse/ >parse</a> - deserialize from a compatible input</li> <li><a href=../sax_parse/ >sax_parse</a> - parse input using the <abbr title="Simple API for XML">SAX</abbr> interface</li> <li><a href=../../operator_gtgt/ >operator&gt;&gt;</a> - deserialize from stream</li> <li><a href=../../macros/json_strict_nul_handling/ ><code>JSON_STRICT_NUL_HANDLING</code></a> - opt in to rejecting a <abbr title="Null character (U+0000, byte value 0)">NUL</abbr> byte in the input instead of treating it as end of input</li> <li><a href=../../macros/json_disable_stream_bulk_scan/ ><code>JSON_DISABLE_STREAM_BULK_SCAN</code></a> - read a <code>std::istream</code> one character at a time</li> <li><a href=../../macros/json_disable_unlocked_file_io/ ><code>JSON_DISABLE_UNLOCKED_FILE_IO</code></a> - read a <code>FILE*</code> with the locking stdio functions</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 3.0.0.</li> <li>Ignoring comments via <code>ignore_comments</code> added in version 3.9.0.</li> <li>Changed <a href=../../../features/assertions/ >runtime assertion</a> in case of <code>FILE*</code> null pointers to exception in version 3.12.0.</li> <li>Added <code>ignore_trailing_commas</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>.</li> <li>Extended container support (1) to include types with lvalue-only <abbr title="Argument-dependent lookup">ADL</abbr> <code>begin</code>/<code>end</code> (matching <code>std::begin</code>/<code>std::end</code> semantics) 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>Extended overload (2) to accept heterogeneous iterator+sentinel pairs (C++20 ranges support) 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><code>JSON_STRICT_NUL_HANDLING</code> 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> to optionally reject a <abbr title="Null character (U+0000, byte value 0)">NUL</abbr> byte in the input instead of treating it as end of input; planned to become the default in version 4.0.0.</li> <li>Parsing from an <code>std::istream</code> scans the characters in its stream buffer in bulk 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> (<a href=../../macros/json_disable_stream_bulk_scan/ ><code>JSON_DISABLE_STREAM_BULK_SCAN</code></a>).</li> <li>Parsing from a <code>FILE*</code> locks the file once instead of once per character 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> (<a href=../../macros/json_disable_unlocked_file_io/ ><code>JSON_DISABLE_UNLOCKED_FILE_IO</code></a>).</li> <li>Ill-formed <abbr title="Unicode Transformation Format">UTF</abbr>-16 and <abbr title="Unicode Transformation Format">UTF</abbr>-32 input (a lone surrogate, a high surrogate that is not followed by its low surrogate, or a code point above <code>U+10FFFF</code>) is rejected 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>; before that, some such sequences were accepted or ended the input silently.</li> </ul> <div class="admonition warning"> <p class=admonition-title>Deprecation</p> <p>Overload (2) replaces calls to <code>accept</code> with a pair of iterators as their first parameter which has been deprecated in version 3.8.0. This overload will be removed in version 4.0.0. Please replace all calls like <code class=highlight><span class=n>accept</span><span class=p>({</span><span class=n>ptr</span><span class=p>,</span><span class=w> </span><span class=n>ptr</span><span class=o>+</span><span class=n>len</span><span class=p>},</span><span class=w> </span><span class=p>...);</span></code> with <code class=highlight><span class=n>accept</span><span class=p>(</span><span class=n>ptr</span><span class=p>,</span><span class=w> </span><span class=n>ptr</span><span class=o>+</span><span class=n>len</span><span class=p>,</span><span class=w> </span><span class=p>...);</span></code>.</p> <p>You should be warned by your compiler with a <code>-Wdeprecated-declarations</code> warning if you are using a deprecated function.</p> <p>See the <a href=../../../integration/migration_guide/#parsing>migration guide</a> for how to update existing code.</p> </div> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <spaLine 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=../parse/ ><code>parse</code></a> - deserialize from a compatible input</li> <li><a href=../sax_parse/ ><code>sax_parse</code></a> - parse input using the <abbr title="Simple API for XML">SAX</abbr> interface</li> <li><a href=../../operator_gtgt/ ><code>operator&gt;&gt;</code></a> - deserialize from stream</li> <li><a href=../../macros/json_strict_nul_handling/ ><code>JSON_STRICT_NUL_HANDLING</code></a> - opt in to rejecting a <abbr title="Null character (U+0000, byte value 0)">NUL</abbr> byte in the input instead of treating it as end of input</li> <li><a href=../../macros/json_disable_stream_bulk_scan/ ><code>JSON_DISABLE_STREAM_BULK_SCAN</code></a> - read a <code>std::istream</code> one character at a time</li> <li><a href=../../macros/json_disable_unlocked_file_io/ ><code>JSON_DISABLE_UNLOCKED_FILE_IO</code></a> - read a <code>FILE*</code> with the locking stdio functions</li> <li><a href=../../../features/parsing/ >Parsing</a> - overview of the parsing functions</li> <li><a href=../../../features/comments/ >Comments</a> - ignore <code>//</code> and <code>/* */</code> comments while parsing</li> <li><a href=../../../features/trailing_commas/ >Trailing Commas</a> - accept trailing commas in arrays and objects</li> <li><a href=../../../features/parsing/parse_exceptions/ >Parsing and Exceptions</a> - handling parse errors and locating them in the input</li> <li><a href=../../../features/parsing/untrusted_input/ >Parsing Untrusted Input</a> - limits and checks for input you do not control</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 3.0.0.</li> <li>Ignoring comments via <code>ignore_comments</code> added in version 3.9.0.</li> <li>Changed <a href=../../../features/assertions/ >runtime assertion</a> in case of <code>FILE*</code> null pointers to exception in version 3.12.0.</li> <li>Added <code>ignore_trailing_commas</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>.</li> <li>Extended container support (1) to include types with lvalue-only <abbr title="Argument-dependent lookup">ADL</abbr> <code>begin</code>/<code>end</code> (matching <code>std::begin</code>/<code>std::end</code> semantics) 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>Extended overload (2) to accept heterogeneous iterator+sentinel pairs (C++20 ranges support) 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><code>JSON_STRICT_NUL_HANDLING</code> 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> to optionally reject a <abbr title="Null character (U+0000, byte value 0)">NUL</abbr> byte in the input instead of treating it as end of input; planned to become the default in version 4.0.0.</li> <li>Parsing from an <code>std::istream</code> scans the characters in its stream buffer in bulk 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> (<a href=../../macros/json_disable_stream_bulk_scan/ ><code>JSON_DISABLE_STREAM_BULK_SCAN</code></a>).</li> <li>Parsing from a <code>FILE*</code> locks the file once instead of once per character 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> (<a href=../../macros/json_disable_unlocked_file_io/ ><code>JSON_DISABLE_UNLOCKED_FILE_IO</code></a>).</li> <li>Ill-formed <abbr title="Unicode Transformation Format">UTF</abbr>-16 and <abbr title="Unicode Transformation Format">UTF</abbr>-32 input (a lone surrogate, a high surrogate that is not followed by its low surrogate, or a code point above <code>U+10FFFF</code>) is rejected 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>; before that, some such sequences were accepted or ended the input silently.</li> </ul> <div class="admonition warning"> <p class=admonition-title>Deprecation</p> <p>Overload (2) replaces calls to <code>accept</code> with a pair of iterators as their first parameter which has been deprecated in version 3.8.0. This overload will be removed in version 4.0.0. Please replace all calls like <code class=highlight><span class=n>accept</span><span class=p>({</span><span class=n>ptr</span><span class=p>,</span><span class=w> </span><span class=n>ptr</span><span class=o>+</span><span class=n>len</span><span class=p>},</span><span class=w> </span><span class=p>...);</span></code> with <code class=highlighLine truncated
+8 -3
View File
@@ -193,12 +193,17 @@ true false
## See also
- [parse](https://json.nlohmann.me/api/basic_json/parse/index.md) - deserialize from a compatible input
- [sax_parse](https://json.nlohmann.me/api/basic_json/sax_parse/index.md) - parse input using the SAX interface
- [operator>>](https://json.nlohmann.me/api/operator_gtgt/index.md) - deserialize from stream
- [`parse`](https://json.nlohmann.me/api/basic_json/parse/index.md) - deserialize from a compatible input
- [`sax_parse`](https://json.nlohmann.me/api/basic_json/sax_parse/index.md) - parse input using the SAX interface
- [`operator>>`](https://json.nlohmann.me/api/operator_gtgt/index.md) - deserialize from stream
- [`JSON_STRICT_NUL_HANDLING`](https://json.nlohmann.me/api/macros/json_strict_nul_handling/index.md) - opt in to rejecting a NUL byte in the input instead of treating it as end of input
- [`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
- [`JSON_DISABLE_UNLOCKED_FILE_IO`](https://json.nlohmann.me/api/macros/json_disable_unlocked_file_io/index.md) - read a `FILE*` with the locking stdio functions
- [Parsing](https://json.nlohmann.me/features/parsing/index.md) - overview of the parsing functions
- [Comments](https://json.nlohmann.me/features/comments/index.md) - ignore `//` and `/* */` comments while parsing
- [Trailing Commas](https://json.nlohmann.me/features/trailing_commas/index.md) - accept trailing commas in arrays and objects
- [Parsing and Exceptions](https://json.nlohmann.me/features/parsing/parse_exceptions/index.md) - handling parse errors and locating them in the input
- [Parsing Untrusted Input](https://json.nlohmann.me/features/parsing/untrusted_input/index.md) - limits and checks for input you do not control
## Version history
+2 -2
View File
@@ -29,9 +29,9 @@ Linear in the size of `init`.
This function is only needed to express two edge cases that cannot be realized with the initializer list constructor
([`basic_json(initializer_list_t, bool, value_t)`](basic_json.md)). These cases are:
1. creating an array whose elements are all pairs whose first element is a string -- in this case, the initializer list
1. creating an array whose elements are all pairs whose first element is a string — in this case, the initializer list
constructor would create an object, taking the first elements as keys
2. creating an empty array -- passing the empty initializer list to the initializer list constructor yields an empty
2. creating an empty array — passing the empty initializer list to the initializer list constructor yields an empty
object
## Examples
+3 -3
View File
@@ -1,5 +1,5 @@
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</code></pre></div> <p>Creates a <abbr title="JavaScript Object Notation">JSON</abbr> array value from a given initializer list. That is, given a list of values <code>a, b, c</code>, creates the <abbr title="JavaScript Object Notation">JSON</abbr> value <code class=highlight><span class=p>[</span><span class=err>a</span><span class=p>,</span><span class=w> </span><span class=err>b</span><span class=p>,</span><span class=w> </span><span class=err>c</span><span class=p>]</span></code>. If the initializer list is empty, the empty array <code class=highlight><span class=p>[]</span></code> is created.</p> <h2 id=parameters>Parameters<a class=headerlink href=#parameters title="Permanent link">&para;</a></h2> <dl> <dt><code>init</code> (in)</dt> <dd>initializer list with <abbr title="JavaScript Object Notation">JSON</abbr> values to create an array from (optional)</dd> </dl> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <p><abbr title="JavaScript Object Notation">JSON</abbr> array value</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">&para;</a></h2> <p>Strong guarantee: if an exception is thrown, there are no changes in the <abbr title="JavaScript Object Notation">JSON</abbr> value.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">&para;</a></h2> <p>Linear in the size of <code>init</code>.</p> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <p>This function is only needed to express two edge cases that cannot be realized with the initializer list constructor (<a href=../basic_json/ ><code>basic_json(initializer_list_t, bool, value_t)</code></a>). These cases are:</p> <ol> <li>creating an array whose elements are all pairs whose first element is a string -- in this case, the initializer list constructor would create an object, taking the first elements as keys</li> <li>creating an empty array -- passing the empty initializer list to the initializer list constructor yields an empty object</li> </ol> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The following code shows an example for the <code>array</code> function.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
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</code></pre></div> <p>Creates a <abbr title="JavaScript Object Notation">JSON</abbr> array value from a given initializer list. That is, given a list of values <code>a, b, c</code>, creates the <abbr title="JavaScript Object Notation">JSON</abbr> value <code class=highlight><span class=p>[</span><span class=err>a</span><span class=p>,</span><span class=w> </span><span class=err>b</span><span class=p>,</span><span class=w> </span><span class=err>c</span><span class=p>]</span></code>. If the initializer list is empty, the empty array <code class=highlight><span class=p>[]</span></code> is created.</p> <h2 id=parameters>Parameters<a class=headerlink href=#parameters title="Permanent link">&para;</a></h2> <dl> <dt><code>init</code> (in)</dt> <dd>initializer list with <abbr title="JavaScript Object Notation">JSON</abbr> values to create an array from (optional)</dd> </dl> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <p><abbr title="JavaScript Object Notation">JSON</abbr> array value</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">&para;</a></h2> <p>Strong guarantee: if an exception is thrown, there are no changes in the <abbr title="JavaScript Object Notation">JSON</abbr> value.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">&para;</a></h2> <p>Linear in the size of <code>init</code>.</p> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <p>This function is only needed to express two edge cases that cannot be realized with the initializer list constructor (<a href=../basic_json/ ><code>basic_json(initializer_list_t, bool, value_t)</code></a>). These cases are:</p> <ol> <li>creating an array whose elements are all pairs whose first element is a string — in this case, the initializer list constructor would create an object, taking the first elements as keys</li> <li>creating an empty array — passing the empty initializer list to the initializer list constructor yields an empty object</li> </ol> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The following code shows an example for the <code>array</code> function.</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>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
@@ -22,4 +22,4 @@
<span class=p>[]</span>
<span class=p>[</span><span class=mi>1</span><span class=p>,</span><span class=mi>2</span><span class=p>,</span><span class=mi>3</span><span class=p>,</span><span class=mi>4</span><span class=p>]</span>
<span class=p>[[</span><span class=s2>"one"</span><span class=p>,</span><span class=mi>1</span><span class=p>],[</span><span class=s2>"two"</span><span class=p>,</span><span class=mi>2</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/ ><code>basic_json(initializer_list_t)</code></a> - create a <abbr title="JavaScript Object Notation">JSON</abbr> value from an initializer list</li> <li><a href=../object/ ><code>object</code></a> - create a <abbr title="JavaScript Object Notation">JSON</abbr> object value from an initializer list</li> <li><a href=../../../features/creating_values/ >Creating <abbr title="JavaScript Object Notation">JSON</abbr> values</a> - the article on creating <abbr title="JavaScript Object Notation">JSON</abbr> values</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 1.0.0.</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="July 4, 2026 09:13:25 UTC">July 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/ ><code>basic_json(initializer_list_t)</code></a> - create a <abbr title="JavaScript Object Notation">JSON</abbr> value from an initializer list</li> <li><a href=../object/ ><code>object</code></a> - create a <abbr title="JavaScript Object Notation">JSON</abbr> object value from an initializer list</li> <li><a href=../../../features/creating_values/ >Creating <abbr title="JavaScript Object Notation">JSON</abbr> values</a> - the article on creating <abbr title="JavaScript Object Notation">JSON</abbr> values</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 1.0.0.</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 27, 2026 06:41:42 UTC">October 27, 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> <nav class="md-footer__inner md-grid" aria-label=Footer> <a href=../accept/ class="md-footer__link md-footer__link--prev" aria-label="Previous: accept"> <div class="md-footer__button md-icon"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M20 11v2H8l5.5 5.5-1.42 1.42L4.16 12l7.92-7.92L13.5 5.5 8 11z"/></svg> </div> <div class=md-footer__title> <span class=md-footer__direction> Previous </span> <div class=md-ellipsis> accept </div> </div> </a> <a href=../array_t/ class="md-footer__link md-footer__link--next" aria-label="Next: array_t"> <div class=md-footer__title> <span class=md-footer__direction> Next </span> <div class=md-ellipsis> array_t </div> </div> <div class="md-footer__button md-icon"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M4 11v2h12l-5.5 5.5 1.42 1.42L19.84 12l-7.92-7.92L10.5 5.5 16 11z"/></svg> </div> </a> </nav> <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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@@ -26,8 +26,8 @@ Linear in the size of `init`.
This function is only needed to express two edge cases that cannot be realized with the initializer list constructor ([`basic_json(initializer_list_t, bool, value_t)`](https://json.nlohmann.me/api/basic_json/basic_json/index.md)). These cases are:
1. creating an array whose elements are all pairs whose first element is a string -- in this case, the initializer list constructor would create an object, taking the first elements as keys
1. creating an empty array -- passing the empty initializer list to the initializer list constructor yields an empty object
1. creating an array whose elements are all pairs whose first element is a string — in this case, the initializer list constructor would create an object, taking the first elements as keys
1. creating an empty array — passing the empty initializer list to the initializer list constructor yields an empty object
## Examples
+6 -4
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@@ -80,10 +80,12 @@ Arrays are stored as pointers in a `basic_json` type. That is, for any access to
## See also
- [object_t](object_t.md) the type used to store JSON objects
- [binary_t](binary_t.md) the type used to store binary values
- [is_array](is_array.md) checks whether the JSON value is an array
- [max_size](max_size.md) returns the maximum possible number of elements
- [`object_t`](object_t.md) - the type used to store JSON objects
- [`binary_t`](binary_t.md) - the type used to store binary values
- [`is_array`](is_array.md) - checks whether the JSON value is an array
- [`max_size`](max_size.md) - returns the maximum possible number of elements
- [Types](../../features/types/index.md) - how arrays are stored
- [Template Parameter Requirements](../../features/types/template_parameters.md) - requirements on the `ArrayType` template parameter
## Version history
+2 -2
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@@ -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/basic_json/array_t/" rel="canonical"><link href=../array/ rel=prev><link href=../as_base_class/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>array_t - 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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</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> <img src=../../../images/wordmark-header.svg alt=logo> </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> array_t </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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</code></pre></div> <p>The type used to store <abbr title="JavaScript Object Notation">JSON</abbr> arrays.</p> <p><a href="https://tools.ietf.org/html/rfc8259"><abbr title="Request for Comments">RFC</abbr> 8259</a> describes <abbr title="JavaScript Object Notation">JSON</abbr> arrays as follows:</p> <blockquote> <p>An array is an ordered sequence of zero or more values.</p> </blockquote> <p>To store objects in C++, a type is defined by the template parameters explained below.</p> <h2 id=template-parameters>Template parameters<a class=headerlink href=#template-parameters title="Permanent link">&para;</a></h2> <dl> <dt><code>ArrayType</code></dt> <dd>container type to store arrays. It must be a vector-like container: the library uses <code>operator[]</code>, <code>at()</code>, and <code>resize()</code>, and requires random-access iterators. <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>vector</span></code> and <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>deque</span></code> qualify; <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>list</span></code> does not. See <a href=../../../features/types/template_parameters/#arraytype>Template Parameter Requirements</a> for the full list of requirements.</dd> <dt><code>AllocatorType</code></dt> <dd>the allocator to use for objects (e.g., <code>std::allocator</code>)</dd> </dl> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <h3 id=default-type>Default type<a class=headerlink href=#default-type title="Permanent link">&para;</a></h3> <p>With the default values for <code>ArrayType</code> (<code>std::vector</code>) and <code>AllocatorType</code> (<code>std::allocator</code>), the default type for <code>array_t</code> is:</p> <div class=highlight><pre><span></span><code><span class=n>std</span><span class=o>::</span><span class=n>vector</span><span class=o>&lt;</span>
<span class=w> </span><span class=n>basic_json</span><span class=p>,</span><span class=w> </span><span class=c1>// value_type</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>allocator</span><span class=o>&lt;</span><span class=n>basic_json</span><span class=o>&gt;</span><span class=w> </span><span class=c1>// allocator_type</span>
@@ -14,4 +14,4 @@
<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>boolalpha</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>is_same</span><span class=o>&lt;</span><span class=n>std</span><span class=o>::</span><span class=n>vector</span><span class=o>&lt;</span><span class=n>json</span><span class=o>&gt;</span><span class=p>,</span><span class=w> </span><span class=n>json</span><span class=o>::</span><span class=n>array_t</span><span class=o>&gt;::</span><span class=n>value</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>true</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=../object_t/ >object_t</a> the type used to store <abbr title="JavaScript Object Notation">JSON</abbr> objects</li> <li><a href=../binary_t/ >binary_t</a> the type used to store binary values</li> <li><a href=../is_array/ >is_array</a> checks whether the <abbr title="JavaScript Object Notation">JSON</abbr> value is an array</li> <li><a href=../max_size/ >max_size</a> returns the maximum possible number of elements</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 1.0.0.</li> <li>Made <code>capacity()</code> optional, so that array types such as <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>deque</span></code> can be used, in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; 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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=../object_t/ ><code>object_t</code></a> - the type used to store <abbr title="JavaScript Object Notation">JSON</abbr> objects</li> <li><a href=../binary_t/ ><code>binary_t</code></a> - the type used to store binary values</li> <li><a href=../is_array/ ><code>is_array</code></a> - checks whether the <abbr title="JavaScript Object Notation">JSON</abbr> value is an array</li> <li><a href=../max_size/ ><code>max_size</code></a> - returns the maximum possible number of elements</li> <li><a href=../../../features/types/ >Types</a> - how arrays are stored</li> <li><a href=../../../features/types/template_parameters/ >Template Parameter Requirements</a> - requirements on the <code>ArrayType</code> template parameter</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 1.0.0.</li> <li>Made <code>capacity()</code> optional, so that array types such as <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>deque</span></code> can be used, in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; 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+6 -4
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@@ -70,10 +70,12 @@ true
## See also
- [object_t](https://json.nlohmann.me/api/basic_json/object_t/index.md) the type used to store JSON objects
- [binary_t](https://json.nlohmann.me/api/basic_json/binary_t/index.md) the type used to store binary values
- [is_array](https://json.nlohmann.me/api/basic_json/is_array/index.md) checks whether the JSON value is an array
- [max_size](https://json.nlohmann.me/api/basic_json/max_size/index.md) returns the maximum possible number of elements
- [`object_t`](https://json.nlohmann.me/api/basic_json/object_t/index.md) - the type used to store JSON objects
- [`binary_t`](https://json.nlohmann.me/api/basic_json/binary_t/index.md) - the type used to store binary values
- [`is_array`](https://json.nlohmann.me/api/basic_json/is_array/index.md) - checks whether the JSON value is an array
- [`max_size`](https://json.nlohmann.me/api/basic_json/max_size/index.md) - returns the maximum possible number of elements
- [Types](https://json.nlohmann.me/features/types/index.md) - how arrays are stored
- [Template Parameter Requirements](https://json.nlohmann.me/features/types/template_parameters/index.md) - requirements on the `ArrayType` template parameter
## Version history
+2 -1
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@@ -77,7 +77,8 @@ The function is equivalent to `static_cast<json_base_class_t&>(j)` (or `static_c
## See also
- [json_base_class_t](json_base_class_t.md) - type of the custom base class
- [`json_base_class_t`](json_base_class_t.md) - type of the custom base class
- [Template Parameter Requirements](../../features/types/template_parameters.md) - requirements on the `CustomBaseClass` template parameter
## Version history
+2 -2
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@@ -1,4 +1,4 @@
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<span class=k>const</span><span class=w> </span><span class=n>json_base_class_t</span><span class=o>&amp;</span><span class=w> </span><span class=nf>as_base_class</span><span class=p>()</span><span class=w> </span><span class=k>const</span><span class=w> </span><span class=k>noexcept</span><span class=p>;</span>
</code></pre></div> <p>Returns a reference to this object as its custom base class <a href=../json_base_class_t/ ><code>json_base_class_t</code></a>. No copy is made.</p> <p>Since <code>basic_json</code> derives from <code>json_base_class_t</code>, a member of <code>basic_json</code> hides any member of the custom base class with the same name. This function makes such hidden members accessible again.</p> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <p>reference to this object as <a href=../json_base_class_t/ ><code>json_base_class_t</code></a></p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">&para;</a></h2> <p>No-throw guarantee: this function never throws exceptions.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">&para;</a></h2> <p>Constant.</p> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <p>The function is equivalent to <code>static_cast&lt;json_base_class_t&amp;&gt;(j)</code> (or <code>static_cast&lt;const json_base_class_t&amp;&gt;(j)</code>).</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>as_base_class</code> to access members of the custom base class that are hidden by members of <code>basic_json</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>
@@ -31,4 +31,4 @@
<span class=p>}</span>
</code></pre></div> <p>Output:</p> <div class=highlight><pre><span></span><code><span class=err>array</span><span class=w> </span><span class=mi>3</span>
<span class=err>my_</span><span class=kc>t</span><span class=err>ype_</span><span class=kc>na</span><span class=err>me</span><span class=w> </span><span class=mi>42</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_base_class_t/ >json_base_class_t</a> - type of the custom base class</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 10:00:31 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=../json_base_class_t/ ><code>json_base_class_t</code></a> - type of the custom base class</li> <li><a href=../../../features/types/template_parameters/ >Template Parameter Requirements</a> - requirements on the <code>CustomBaseClass</code> template parameter</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 27, 2026 06:41:42 UTC">October 27, 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> <nav class="md-footer__inner md-grid" aria-label=Footer> <a href=../array_t/ class="md-footer__link md-footer__link--prev" aria-label="Previous: array_t"> <div class="md-footer__button md-icon"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M20 11v2H8l5.5 5.5-1.42 1.42L4.16 12l7.92-7.92L13.5 5.5 8 11z"/></svg> </div> <div class=md-footer__title> <span class=md-footer__direction> Previous </span> <div class=md-ellipsis> array_t </div> </div> </a> <a href=../at/ class="md-footer__link md-footer__link--next" aria-label="Next: at"> <div class=md-footer__title> <span class=md-footer__direction> Next </span> <div class=md-ellipsis> at </div> </div> <div class="md-footer__button md-icon"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M4 11v2h12l-5.5 5.5 1.42 1.42L19.84 12l-7.92-7.92L10.5 5.5 16 11z"/></svg> </div> </a> </nav> <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 -1
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@@ -72,7 +72,8 @@ my_type_name 42
## See also
- [json_base_class_t](https://json.nlohmann.me/api/basic_json/json_base_class_t/index.md) - type of the custom base class
- [`json_base_class_t`](https://json.nlohmann.me/api/basic_json/json_base_class_t/index.md) - type of the custom base class
- [Template Parameter Requirements](https://json.nlohmann.me/features/types/template_parameters/index.md) - requirements on the `CustomBaseClass` template parameter
## Version history
+6 -4
View File
@@ -713,10 +713,12 @@ Strong exception safety: if an exception occurs, the original value stays intact
## See also
- documentation on [checked access](../../features/element_access/checked_access.md)
- [`operator[]`](operator%5B%5D.md) for unchecked access by reference
- [`value`](value.md) for access with default value
- [basic_json_view::at](../basic_json_view/at.md) - the same access on a zero-copy view
- [Checked access](../../features/element_access/checked_access.md) - element access with range checking
- [`operator[]`](operator%5B%5D.md) - unchecked access by reference
- [`value`](value.md) - access with default value
- [`basic_json_view::at`](../basic_json_view/at.md) - the same access on a zero-copy view
- [Element Access](../../features/element_access/index.md) - overview of all ways to access elements
- [JSON Pointer](../../features/json_pointer.md) - access nested values with a pointer
## Version history
+2 -2
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@@ -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/basic_json/at/" rel="canonical"><link href=../as_base_class/ rel=prev><link href=../back/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>at - 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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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 Line truncated
<span class=n>reference</span><span class=w> </span><span class=nf>at</span><span class=p>(</span><span class=n>size_type</span><span class=w> </span><span class=n>idx</span><span class=p>);</span>
<span class=n>const_reference</span><span class=w> </span><span class=nf>at</span><span class=p>(</span><span class=n>size_type</span><span class=w> </span><span class=n>idx</span><span class=p>)</span><span class=w> </span><span class=k>const</span><span class=p>;</span>
@@ -498,4 +498,4 @@
<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>402</span><span class=p>]</span><span class=w> </span><span class=err>array</span><span class=w> </span><span class=err>i</span><span class=kc>n</span><span class=err>dex</span><span class=w> </span><span class=err>'</span><span class=mi>-</span><span class=err>'</span><span class=w> </span><span class=err>(</span><span class=mi>2</span><span class=err>)</span><span class=w> </span><span class=err>is</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=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>403</span><span class=p>]</span><span class=w> </span><span class=err>key</span><span class=w> </span><span class=err>'</span><span class=kc>f</span><span class=err>oo'</span><span class=w> </span><span class=kc>n</span><span class=err>o</span><span class=kc>t</span><span class=w> </span><span class=kc>f</span><span class=err>ou</span><span class=kc>n</span><span class=err>d</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>404</span><span class=p>]</span><span class=w> </span><span class=err>u</span><span class=kc>nres</span><span class=err>olved</span><span class=w> </span><span class=err>re</span><span class=kc>feren</span><span class=err>ce</span><span class=w> </span><span class=kc>t</span><span class=err>oke</span><span class=kc>n</span><span class=w> </span><span class=err>'</span><span class=kc>f</span><span class=err>oo'</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>documentation on <a href=../../../features/element_access/checked_access/ >checked access</a></li> <li><a href=../operator%5B%5D/ ><code>operator[]</code></a> for unchecked access by reference</li> <li><a href=../value/ ><code>value</code></a> for access with default value</li> <li><a href=../../basic_json_view/at/ >basic_json_view::at</a> - the same access on a zero-copy view</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 1.0.0.</li> <li>Added in version 1.0.0.</li> <li>Added in version 3.11.0. Support for keys convertible to <code>std::string_view</code> 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>, consistently across the lookup functions.</li> <li>Added in version 2.0.0. Throws <a href=../../../home/exceptions/#jsonexceptionparse_error109><code>parse_error.109</code></a> instead of <a href=../../../home/exceptions/#jsonexceptionout_of_range404><code>out_of_range.404</code></a> for a one-character array index that is not a digit (e.g., <code>/x</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>, as it already did for longer ones.</li> </ol> <!-- 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 24, 2026 15:57:44 UTC">October 24, 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/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=../../../features/element_access/checked_access/ >Checked access</a> - element access with range checking</li> <li><a href=../operator%5B%5D/ ><code>operator[]</code></a> - unchecked access by reference</li> <li><a href=../value/ ><code>value</code></a> - access with default value</li> <li><a href=../../basic_json_view/at/ ><code>basic_json_view::at</code></a> - the same access on a zero-copy view</li> <li><a href=../../../features/element_access/ >Element Access</a> - overview of all ways to access elements</li> <li><a href=../../../features/json_pointer/ ><abbr title="JavaScript Object Notation">JSON</abbr> Pointer</a> - access nested values with a pointer</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 1.0.0.</li> <li>Added in version 1.0.0.</li> <li>Added in version 3.11.0. Support for keys convertible to <code>std::string_view</code> 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>, consistently across the lookup functions.</li> <li>Added in version 2.0.0. Throws <a href=../../../home/exceptions/#jsonexceptionparse_error109><code>parse_error.109</code></a> instead of <a href=../../../home/exceptions/#jsonexceptionout_of_range404><code>out_of_range.404</code></a> for a one-character array index that is not a digit (e.g., <code>/x</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>, as it already did for longer ones.</li> </ol> <!-- 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 27, 2026 06:41:42 UTC">October 27, 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> <nav class="md-footer__inner md-grid" aria-label=Footer> <a href=../as_base_class/ class="md-footer__link md-footer__link--prev" aria-label="Previous: as_base_class"> <div class="md-footer__button md-icon"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M20 11v2H8l5.5 5.5-1.42 1.42L4.16 12l7.92-7.92L13.5 5.5 8 11z"/></svg> </div> <div class=md-footer__title> <span class=md-footer__direction> Previous </span> <div class=md-ellipsis> as_base_class </div> </div> </a> <a href=../back/ class="md-footer__link md-footer__link--next" aria-label="Next: back"> <div class=md-footer__title> <span class=md-footer__direction> Next </span> <div class=md-ellipsis> back </div> </div> <div class="md-footer__button md-icon"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M4 11v2h12l-5.5 5.5 1.42 1.42L19.84 12l-7.92-7.92L10.5 5.5 16 11z"/></svg> </div> </a> </nav> <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 6.2-2sLine truncated
+6 -4
View File
@@ -666,10 +666,12 @@ Output:
## See also
- documentation on [checked access](https://json.nlohmann.me/features/element_access/checked_access/index.md)
- [`operator[]`](https://json.nlohmann.me/api/basic_json/operator%5B%5D/index.md) for unchecked access by reference
- [`value`](https://json.nlohmann.me/api/basic_json/value/index.md) for access with default value
- [basic_json_view::at](https://json.nlohmann.me/api/basic_json_view/at/index.md) - the same access on a zero-copy view
- [Checked access](https://json.nlohmann.me/features/element_access/checked_access/index.md) - element access with range checking
- [`operator[]`](https://json.nlohmann.me/api/basic_json/operator%5B%5D/index.md) - unchecked access by reference
- [`value`](https://json.nlohmann.me/api/basic_json/value/index.md) - access with default value
- [`basic_json_view::at`](https://json.nlohmann.me/api/basic_json_view/at/index.md) - the same access on a zero-copy view
- [Element Access](https://json.nlohmann.me/features/element_access/index.md) - overview of all ways to access elements
- [JSON Pointer](https://json.nlohmann.me/features/json_pointer/index.md) - access nested values with a pointer
## Version history
+3 -2
View File
@@ -102,8 +102,9 @@ Constant.
## See also
- [front](front.md) to access the first element
- [basic_json_view::back](../basic_json_view/back.md) - the same access on a zero-copy view
- [`front`](front.md) - to access the first element
- [`basic_json_view::back`](../basic_json_view/back.md) - the same access on a zero-copy view
- [Element Access](../../features/element_access/index.md) - overview of all ways to access elements
## Version history
+2 -2
View File
@@ -1,4 +1,4 @@
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<span class=n>const_reference</span><span class=w> </span><span class=nf>back</span><span class=p>()</span><span class=w> </span><span class=k>const</span><span class=p>;</span>
</code></pre></div> <p>Returns a reference to the last element in the container. For a <abbr title="JavaScript Object Notation">JSON</abbr> container <code>c</code>, the expression <code>c.back()</code> is equivalent to</p> <div class=highlight><pre><span></span><code><span class=k>auto</span><span class=w> </span><span class=n>tmp</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>c</span><span class=p>.</span><span class=n>end</span><span class=p>();</span>
@@ -49,4 +49,4 @@
<span class=mi>16</span>
<span class=s2>"Hello, world"</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>.i</span><span class=kc>n</span><span class=err>valid_i</span><span class=kc>terat</span><span class=err>or.</span><span class=mi>214</span><span class=p>]</span><span class=w> </span><span class=err>ca</span><span class=kc>nn</span><span class=err>o</span><span class=kc>t</span><span class=w> </span><span class=err>ge</span><span class=kc>t</span><span class=w> </span><span class=err>value</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=../front/ >front</a> to access the first element</li> <li><a href=../../basic_json_view/back/ >basic_json_view::back</a> - the same access on a 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 1.0.0.</li> <li>Binary values are supported since version 3.8.0.</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 24, 2026 15:57:44 UTC">October 24, 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=../front/ ><code>front</code></a> - to access the first element</li> <li><a href=../../basic_json_view/back/ ><code>basic_json_view::back</code></a> - the same access on a zero-copy view</li> <li><a href=../../../features/element_access/ >Element Access</a> - overview of all ways to access elements</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 1.0.0.</li> <li>Binary values are supported since version 3.8.0.</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 27, 2026 06:41:42 UTC">October 27, 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> <nav class="md-footer__inner md-grid" aria-label=Footer> <a href=../at/ class="md-footer__link md-footer__link--prev" aria-label="Previous: at"> <div class="md-footer__button md-icon"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M20 11v2H8l5.5 5.5-1.42 1.42L4.16 12l7.92-7.92L13.5 5.5 8 11z"/></svg> </div> <div class=md-footer__title> <span class=md-footer__direction> Previous </span> <div class=md-ellipsis> at </div> </div> </a> <a href=../begin/ class="md-footer__link md-footer__link--next" aria-label="Next: begin"> <div class=md-footer__title> <span class=md-footer__direction> Next </span> <div class=md-ellipsis> begin </div> </div> <div class="md-footer__button md-icon"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M4 11v2h12l-5.5 5.5 1.42 1.42L19.84 12l-7.92-7.92L10.5 5.5 16 11z"/></svg> </div> </a> </nav> <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.Line truncated
+3 -2
View File
@@ -97,8 +97,9 @@ true
## See also
- [front](https://json.nlohmann.me/api/basic_json/front/index.md) to access the first element
- [basic_json_view::back](https://json.nlohmann.me/api/basic_json_view/back/index.md) - the same access on a zero-copy view
- [`front`](https://json.nlohmann.me/api/basic_json/front/index.md) - to access the first element
- [`basic_json_view::back`](https://json.nlohmann.me/api/basic_json_view/back/index.md) - the same access on a zero-copy view
- [Element Access](https://json.nlohmann.me/features/element_access/index.md) - overview of all ways to access elements
## Version history
+14 -10
View File
@@ -52,7 +52,7 @@ basic_json(basic_json&& other) noexcept;
The postcondition of this constructor can be restored by calling [`clear()`](clear.md).
2. Create a `#!json null` JSON value. It either takes a null pointer as parameter (explicitly creating `#!json null`)
or no parameter (implicitly creating `#!json null`). The passed null pointer itself is not read -- it is only used to
or no parameter (implicitly creating `#!json null`). The passed null pointer itself is not read — it is only used to
choose the right constructor.
3. This is a "catch all" constructor for all compatible JSON types; that is, types for which a `to_json()` method
@@ -113,19 +113,22 @@ basic_json(basic_json&& other) noexcept;
```mermaid
flowchart TD
A(["initializer_list init"]) --> B{"empty, or every element is a 2-element<br/>array whose first element is a string?"}
B -->|"yes"| C{"type_deduction"}
B -->|"no"| D{"type_deduction"}
A(["initializer_list init"]) --> B{{"empty, or every element is a 2-element<br/>array whose first element is a string?"}}
B -->|"yes"| C{{"type_deduction"}}
B -->|"no"| D{{"type_deduction"}}
C -->|"true"| OBJ["create object"]
C -->|"false"| E{"manual_type"}
C -->|"false"| E{{"manual_type"}}
E -->|"object"| OBJ
E -->|"array"| ARR["create array"]
D -->|"true"| ARR
D -->|"false"| F{"manual_type"}
D -->|"false"| F{{"manual_type"}}
F -->|"array"| ARR
F -->|"object"| ERR["throw type_error.301"]
```
<p class="nj-caption" markdown>Decision flow for an initializer list: hexagons are checks, edge labels are their
outcomes, and rectangles are the resulting value or exception.</p>
The rules aim to create the best fit between a C++ initializer list and JSON values. The rationale is as follows:
1. The empty initializer list is written as `#!cpp {}` which is exactly an empty JSON object.
@@ -922,12 +925,13 @@ basic_json(basic_json&& other) noexcept;
## See also
- [array](array.md) create a JSON array value, forcing array creation from an initializer list even when it looks like
- [`array`](array.md) - create a JSON array value, forcing array creation from an initializer list even when it looks like
an object
- [object](object.md) create a JSON object value, forcing object creation from an initializer list
- [binary](binary.md) create a JSON binary array value
- [operator=](operator=.md) copy assignment operator
- [`object`](object.md) - create a JSON object value, forcing object creation from an initializer list
- [`binary`](binary.md) - create a JSON binary array value
- [`operator=`](operator=.md) - copy assignment operator
- [Creating JSON values](../../features/creating_values.md) - the article on creating JSON values
- [Converting values](../../features/conversions.md) - which C++ types can be converted
## Version history
+9 -9
View File
@@ -1,4 +1,4 @@
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viewbox="0 0 24 24"><path d="M9.5 3A6Line truncated
<span class=n>basic_json</span><span class=p>(</span><span class=k>const</span><span class=w> </span><span class=n>value_t</span><span class=w> </span><span class=n>v</span><span class=p>);</span>
<span class=c1>// (2)</span>
@@ -31,18 +31,18 @@
<span class=c1>// (9)</span>
<span class=n>basic_json</span><span class=p>(</span><span class=n>basic_json</span><span class=o>&amp;&amp;</span><span class=w> </span><span class=n>other</span><span class=p>)</span><span class=w> </span><span class=k>noexcept</span><span class=p>;</span>
</code></pre></div> <ol> <li> <p>Create an empty <abbr title="JavaScript Object Notation">JSON</abbr> value with a given type. The value will be default initialized with an empty value which depends on the type:</p> <table> <thead> <tr> <th>Value type</th> <th>initial value</th> </tr> </thead> <tbody> <tr> <td>null</td> <td><code class=highlight><span class=kc>null</span></code></td> </tr> <tr> <td>boolean</td> <td><code class=highlight><span class=kc>false</span></code></td> </tr> <tr> <td>string</td> <td><code class=highlight><span class=s2>""</span></code></td> </tr> <tr> <td>number</td> <td><code class=highlight><span class=mi>0</span></code></td> </tr> <tr> <td>object</td> <td><code class=highlight><span class=p>{}</span></code></td> </tr> <tr> <td>array</td> <td><code class=highlight><span class=p>[]</span></code></td> </tr> <tr> <td>binary</td> <td>empty array</td> </tr> </tbody> </table> <p>The postcondition of this constructor can be restored by calling <a href=../clear/ ><code>clear()</code></a>.</p> </li> <li> <p>Create a <code class=highlight><span class=kc>null</span></code> <abbr title="JavaScript Object Notation">JSON</abbr> value. It either takes a null pointer as parameter (explicitly creating <code class=highlight><span class=kc>null</span></code>) or no parameter (implicitly creating <code class=highlight><span class=kc>null</span></code>). The passed null pointer itself is not read -- it is only used to choose the right constructor.</p> </li> <li> <p>This is a "catch all" constructor for all compatible <abbr title="JavaScript Object Notation">JSON</abbr> types; that is, types for which a <code>to_json()</code> method exists. The constructor forwards the parameter <code>val</code> to that method (to <code>json_serializer&lt;U&gt;::to_json</code> method with <code>U = uncvref_t&lt;CompatibleType&gt;</code>, to be exact).</p> <p>Template type <code>CompatibleType</code> includes, but is not limited to, the following types:</p> <ul> <li><strong>arrays</strong>: <a href=../array_t/ ><code>array_t</code></a> and all kinds of compatible containers such as <code>std::vector</code>, <code>std::deque</code>, <code>std::list</code>, <code>std::forward_list</code>, <code>std::array</code>, <code>std::valarray</code>, <code>std::set</code>, <code>std::unordered_set</code>, <code>std::multiset</code>, and <code>std::unordered_multiset</code> with a <code>value_type</code> from which a <code>basic_json</code> value can be constructed.</li> <li><strong>objects</strong>: <a href=../object_t/ ><code>object_t</code></a> and all kinds of compatible associative containers such as <code>std::map</code>, <code>std::unordered_map</code>, <code>std::multimap</code>, and <code>std::unordered_multimap</code> with a <code>key_type</code> compatible to <code>string_t</code> and a <code>value_type</code> from which a <code>basic_json</code> value can be constructed.</li> <li><strong>strings</strong>: <code>string_t</code>, string literals, and all compatible string containers can be used.</li> </ul> <div class="admonition note"> <p class=admonition-title>Rvalue containers are moved from</p> <p>If <code>val</code> is an rvalue of a compatible array-like or object-like container other than <code>array_t</code>/<code>object_t</code> (e.g., <code>json j = std::move(vec);</code> or <code>json j(std::vector&lt;std::string&gt;{...});</code>), the elements are moved into the <abbr title="JavaScript Object Notation">JSON</abbr> value instead of copied. Afterwards, the elements of the source container are in a valid but unspecified state (<strong>moved-from</strong>). Keys of associative containers are <code>const</code> and therefore still copied. Lvalues and <code>const</code> rvalues are copied, and the source is left unchanged.</p> </div> <ul> <li><strong>numbers</strong>: <a href=../number_integer_t/ ><code>number_integer_t</code></a>, <a href=../number_unsigned_t/ ><code>number_unsigned_t</code></a>, <a href=../number_float_t/ ><code>number_float_t</code></a>, and all convertible number types such as <code>int</code>, <code>size_t</code>, <code>int64_t</code>, <code>float</code> or <code>double</code> can be used.</li> <li><strong>boolean</strong>: <code>boolean_t</code> / <code>bool</code> can be used.</li> <li><strong>binary</strong>: <code>binary_t</code> / <code>std::vector&lt;uint8_t&gt;</code> may be used; unfortunately because string literals cannot be distinguished from binary character arrays by the C++ type system, all types compatible with <code>const char*</code> will be directed to the string constructor instead. This is both for backwards compatibility and due to the fact that a binary type is not a standard <abbr title="JavaScript Object Notation">JSON</abbr> type.</li> </ul> <p>See the examples below.</p> </li> <li> <p>This is a constructor for existing <code>basic_json</code> types. It does not hijack copy/move constructors, since the parameter has different template arguments than the current ones.</p>Line truncated
A(["initializer_list init"]) --&gt; B{"empty, or every element is a 2-element&lt;br/&gt;array whose first element is a string?"}
B --&gt;|"yes"| C{"type_deduction"}
B --&gt;|"no"| D{"type_deduction"}
</code></pre></div> <ol> <li> <p>Create an empty <abbr title="JavaScript Object Notation">JSON</abbr> value with a given type. The value will be default initialized with an empty value which depends on the type:</p> <table> <thead> <tr> <th>Value type</th> <th>initial value</th> </tr> </thead> <tbody> <tr> <td>null</td> <td><code class=highlight><span class=kc>null</span></code></td> </tr> <tr> <td>boolean</td> <td><code class=highlight><span class=kc>false</span></code></td> </tr> <tr> <td>string</td> <td><code class=highlight><span class=s2>""</span></code></td> </tr> <tr> <td>number</td> <td><code class=highlight><span class=mi>0</span></code></td> </tr> <tr> <td>object</td> <td><code class=highlight><span class=p>{}</span></code></td> </tr> <tr> <td>array</td> <td><code class=highlight><span class=p>[]</span></code></td> </tr> <tr> <td>binary</td> <td>empty array</td> </tr> </tbody> </table> <p>The postcondition of this constructor can be restored by calling <a href=../clear/ ><code>clear()</code></a>.</p> </li> <li> <p>Create a <code class=highlight><span class=kc>null</span></code> <abbr title="JavaScript Object Notation">JSON</abbr> value. It either takes a null pointer as parameter (explicitly creating <code class=highlight><span class=kc>null</span></code>) or no parameter (implicitly creating <code class=highlight><span class=kc>null</span></code>). The passed null pointer itself is not read — it is only used to choose the right constructor.</p> </li> <li> <p>This is a "catch all" constructor for all compatible <abbr title="JavaScript Object Notation">JSON</abbr> types; that is, types for which a <code>to_json()</code> method exists. The constructor forwards the parameter <code>val</code> to that method (to <code>json_serializer&lt;U&gt;::to_json</code> method with <code>U = uncvref_t&lt;CompatibleType&gt;</code>, to be exact).</p> <p>Template type <code>CompatibleType</code> includes, but is not limited to, the following types:</p> <ul> <li><strong>arrays</strong>: <a href=../array_t/ ><code>array_t</code></a> and all kinds of compatible containers such as <code>std::vector</code>, <code>std::deque</code>, <code>std::list</code>, <code>std::forward_list</code>, <code>std::array</code>, <code>std::valarray</code>, <code>std::set</code>, <code>std::unordered_set</code>, <code>std::multiset</code>, and <code>std::unordered_multiset</code> with a <code>value_type</code> from which a <code>basic_json</code> value can be constructed.</li> <li><strong>objects</strong>: <a href=../object_t/ ><code>object_t</code></a> and all kinds of compatible associative containers such as <code>std::map</code>, <code>std::unordered_map</code>, <code>std::multimap</code>, and <code>std::unordered_multimap</code> with a <code>key_type</code> compatible to <code>string_t</code> and a <code>value_type</code> from which a <code>basic_json</code> value can be constructed.</li> <li><strong>strings</strong>: <code>string_t</code>, string literals, and all compatible string containers can be used.</li> </ul> <div class="admonition note"> <p class=admonition-title>Rvalue containers are moved from</p> <p>If <code>val</code> is an rvalue of a compatible array-like or object-like container other than <code>array_t</code>/<code>object_t</code> (e.g., <code>json j = std::move(vec);</code> or <code>json j(std::vector&lt;std::string&gt;{...});</code>), the elements are moved into the <abbr title="JavaScript Object Notation">JSON</abbr> value instead of copied. Afterwards, the elements of the source container are in a valid but unspecified state (<strong>moved-from</strong>). Keys of associative containers are <code>const</code> and therefore still copied. Lvalues and <code>const</code> rvalues are copied, and the source is left unchanged.</p> </div> <ul> <li><strong>numbers</strong>: <a href=../number_integer_t/ ><code>number_integer_t</code></a>, <a href=../number_unsigned_t/ ><code>number_unsigned_t</code></a>, <a href=../number_float_t/ ><code>number_float_t</code></a>, and all convertible number types such as <code>int</code>, <code>size_t</code>, <code>int64_t</code>, <code>float</code> or <code>double</code> can be used.</li> <li><strong>boolean</strong>: <code>boolean_t</code> / <code>bool</code> can be used.</li> <li><strong>binary</strong>: <code>binary_t</code> / <code>std::vector&lt;uint8_t&gt;</code> may be used; unfortunately because string literals cannot be distinguished from binary character arrays by the C++ type system, all types compatible with <code>const char*</code> will be directed to the string constructor instead. This is both for backwards compatibility and due to the fact that a binary type is not a standard <abbr title="JavaScript Object Notation">JSON</abbr> type.</li> </ul> <p>See the examples below.</p> </li> <li> <p>This is a constructor for existing <code>basic_json</code> types. It does not hijack copy/move constructors, since the parameter has different template arguments than the current ones.</pLine truncated
A(["initializer_list init"]) --&gt; B{{"empty, or every element is a 2-element&lt;br/&gt;array whose first element is a string?"}}
B --&gt;|"yes"| C{{"type_deduction"}}
B --&gt;|"no"| D{{"type_deduction"}}
C --&gt;|"true"| OBJ["create object"]
C --&gt;|"false"| E{"manual_type"}
C --&gt;|"false"| E{{"manual_type"}}
E --&gt;|"object"| OBJ
E --&gt;|"array"| ARR["create array"]
D --&gt;|"true"| ARR
D --&gt;|"false"| F{"manual_type"}
D --&gt;|"false"| F{{"manual_type"}}
F --&gt;|"array"| ARR
F --&gt;|"object"| ERR["throw type_error.301"]</code></pre> <p>The rules aim to create the best fit between a C++ initializer list and <abbr title="JavaScript Object Notation">JSON</abbr> values. The rationale is as follows:</p> <ol> <li>The empty initializer list is written as <code class=highlight><span class=p>{}</span></code> which is exactly an empty <abbr title="JavaScript Object Notation">JSON</abbr> object.</li> <li>C++ has no way of describing mapped types other than to list a list of pairs. As <abbr title="JavaScript Object Notation">JSON</abbr> requires that keys must be of type string, rule 2 is the weakest constraint one can pose on initializer lists to interpret them as an object.</li> <li>In all other cases, the initializer list could not be interpreted as a <abbr title="JavaScript Object Notation">JSON</abbr> object type, so interpreting it as a <abbr title="JavaScript Object Notation">JSON</abbr> array type is safe.</li> </ol> <p>With the rules described above, the following <abbr title="JavaScript Object Notation">JSON</abbr> values cannot be expressed by an initializer list:</p> <ul> <li>the empty array (<code class=highlight><span class=p>[]</span></code>): use <code>array(initializer_list_t)</code> with an empty initializer list in this case</li> <li>arrays whose elements satisfy rule 2: use <code>array(initializer_list_t)</code> with the same initializer list in this case</li> </ul> <p>Function <a href=../array/ ><code>array()</code></a> and <a href=../object/ ><code>object()</code></a> force array and object creation from initializer lists, respectively.</p> <div class="admonition warning"> <p class=admonition-title>Brace initialization yields arrays</p> <p>Because this constructor takes an <code>initializer_list_t</code>, brace-initializing a <code>json</code>/<code>ordered_json</code> from another <code>json</code> value wraps it in a single-element array rather than copying it:</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=s>"hello"</span><span class=p>;</span>
F --&gt;|"object"| ERR["throw type_error.301"]</code></pre> <p><p class=nj-caption markdown>Decision flow for an initializer list: hexagons are checks, edge labels are their outcomes, and rectangles are the resulting value or exception.</p></p> <p>The rules aim to create the best fit between a C++ initializer list and <abbr title="JavaScript Object Notation">JSON</abbr> values. The rationale is as follows:</p> <ol> <li>The empty initializer list is written as <code class=highlight><span class=p>{}</span></code> which is exactly an empty <abbr title="JavaScript Object Notation">JSON</abbr> object.</li> <li>C++ has no way of describing mapped types other than to list a list of pairs. As <abbr title="JavaScript Object Notation">JSON</abbr> requires that keys must be of type string, rule 2 is the weakest constraint one can pose on initializer lists to interpret them as an object.</li> <li>In all other cases, the initializer list could not be interpreted as a <abbr title="JavaScript Object Notation">JSON</abbr> object type, so interpreting it as a <abbr title="JavaScript Object Notation">JSON</abbr> array type is safe.</li> </ol> <p>With the rules described above, the following <abbr title="JavaScript Object Notation">JSON</abbr> values cannot be expressed by an initializer list:</p> <ul> <li>the empty array (<code class=highlight><span class=p>[]</span></code>): use <code>array(initializer_list_t)</code> with an empty initializer list in this case</li> <li>arrays whose elements satisfy rule 2: use <code>array(initializer_list_t)</code> with the same initializer list in this case</li> </ul> <p>Function <a href=../array/ ><code>array()</code></a> and <a href=../object/ ><code>object()</code></a> force array and object creation from initializer lists, respectively.</p> <div class="admonition warning"> <p class=admonition-title>Brace initialization yields arrays</p> <p>Because this constructor takes an <code>initializer_list_t</code>, brace-initializing a <code>json</code>/<code>ordered_json</code> from another <code>json</code> value wraps it in a single-element array rather than copying it:</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=s>"hello"</span><span class=p>;</span>
<span class=n>json</span><span class=w> </span><span class=n>j2</span><span class=p>{</span><span class=n>j1</span><span class=p>};</span><span class=w> </span><span class=c1>// [!] j2 is ["hello"], NOT a copy of j1</span>
<span class=n>json</span><span class=w> </span><span class=nf>j3</span><span class=p>(</span><span class=n>j1</span><span class=p>);</span><span class=w> </span><span class=c1>// j3 is "hello" -- parentheses copy as expected</span>
</code></pre></div> <p>See the <abbr title="Frequently Asked Questions">FAQ</abbr> entry on <a href=../../../home/faq/#brace-initialization-yields-arrays>brace initialization</a> for the full explanation, an opt-in macro to change this behavior, and how to explicitly create a single-element array (<code>json::array({value})</code>) if that is what you want.</p> </div> </li> <li> <p>Constructs a <abbr title="JavaScript Object Notation">JSON</abbr> array value by creating <code>cnt</code> copies of a passed value. In case <code>cnt</code> is <code>0</code>, an empty array is created.</p> </li> <li> <p>Constructs the <abbr title="JavaScript Object Notation">JSON</abbr> value with the contents of the range <code>[first, last)</code>. The semantics depend on the different types a <abbr title="JavaScript Object Notation">JSON</abbr> value can have:</p> <ul> <li>In case of a <code class=highlight><span class=kc>null</span></code> type, <a href=../../../home/exceptions/#jsonexceptioninvalid_iterator206>invalid_iterator.206</a> is thrown.</li> <li>In case of other primitive types (number, boolean, string, or binary), <code>first</code> must be <code>begin()</code> and <code>last</code> must be <code>end()</code>. In this case, the value is copied. Otherwise, <a href=../../../home/exceptions/#jsonexceptioninvalid_iterator204><code>invalid_iterator.204</code></a> is thrown.</li> <li>In case of structured types (array, object), the constructor behaves as similar versions for <code>std::vector</code> or <code>std::map</code>; that is, a <abbr title="JavaScript Object Notation">JSON</abbr> array or object is constructed from the values in the range.</li> </ul> </li> <li> <p>Creates a copy of a given <abbr title="JavaScript Object Notation">JSON</abbr> value.</p> </li> <li> <p>Move constructor. Constructs a <abbr title="JavaScript Object Notation">JSON</abbr> value with the contents of the given value <code>other</code> using move semantics. It "steals" the resources from <code>other</code> and leaves it as <abbr title="JavaScript Object Notation">JSON</abbr> <code class=highlight><span class=kc>null</span></code> value.</p> </li> </ol> <h2 id=template-parameters>Template parameters<a class=headerlink href=#template-parameters title="Permanent link">&para;</a></h2> <dl> <dt><code>CompatibleType</code></dt> <dd> <p>a type such that:</p> <ul> <li><code>CompatibleType</code> is not derived from <code>std::istream</code>,</li> <li><code>CompatibleType</code> is not <code>basic_json</code> (to avoid hijacking copy/move constructors),</li> <li><code>CompatibleType</code> is not a different <code>basic_json</code> type (i.e. with different template arguments)</li> <li><code>CompatibleType</code> is not a <code>basic_json</code> nested type (e.g., <code>json_pointer</code>, <code>iterator</code>, etc.)</li> <li>if <a href=../../macros/json_disable_tuple_reference_conversion/ ><code>JSON_DISABLE_TUPLE_REFERENCE_CONVERSION</code></a> is defined to <code>1</code>: <code>CompatibleType</code> is not a one-element <code>std::tuple</code> holding a reference to <code>basic_json</code></li> <li><code>json_serializer&lt;U&gt;</code> (with <code>U = uncvref_t&lt;CompatibleType&gt;</code>) has a <code>to_json(basic_json_t&amp;, CompatibleType&amp;&amp;)</code> method</li> </ul> </dd> <dt><code>BasicJsonType</code>:</dt> <dd> <p>a type such that:</p> <ul> <li><code>BasicJsonType</code> is a <code>basic_json</code> type.</li> <li><code>BasicJsonType</code> has different template arguments than <code>basic_json_t</code>.</li> </ul> <p><strong>Note:</strong> For cross-<code>basic_json</code> conversions to produce correct results, the target <code>basic_json</code>'s <a href=../object_t/ ><code>object_t</code></a><code>::key_type</code> and <a href=../string_t/ ><code>string_t</code></a> must be directly constructible from the source <code>basic_json</code>'s corresponding types. See the description of overload (4) above for details on what happens when this requirement is not met.</p> </dd> <dt><code>U</code>:</dt> <dd><code>uncvref_t&lt;CompatibleType&gt;</code></dd> </dl> <h2 id=parameters>Parameters<a class=headerlink href=#parameters title="Permanent link">&para;</a></h2> <dl> <dt><code>v</code> (in)</dt> <dd>the type of the value to create</dd> <dt><code>val</code> (in)</dt> <dd>the value to be forwarded to the respective constructor</dd> <dt><code>init</code> (in)</dt> <dd>initializer list with <abbr title="JavaScript Object Notation">JSON</abbr> values</dd> <dt><code>type_deduction</code> (in)</dt> <dd>internal parameter; when set to <code class=highlight><span class=nb>true</span></code>, the type of the <abbr title="JavaScript Object Notation">JSON</abbr> value is deducted from the initializer list <code>init</code>; when set to <code class=highlight><span class=nb>false</span></code>, the type provided via <code>manual_type</code> is forced. This mode is used by the functions <code>array(initializer_list_t)</code> and <code>object(Line truncated
@@ -494,4 +494,4 @@
<span class=p>}</span>
</code></pre></div> <p>Output:</p> <div class=highlight><pre><span></span><code><span class=kc>null</span>
<span class=mi>23</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=../array/ >array</a> create a <abbr title="JavaScript Object Notation">JSON</abbr> array value, forcing array creation from an initializer list even when it looks like an object</li> <li><a href=../object/ >object</a> create a <abbr title="JavaScript Object Notation">JSON</abbr> object value, forcing object creation from an initializer list</li> <li><a href=../binary/ >binary</a> create a <abbr title="JavaScript Object Notation">JSON</abbr> binary array value</li> <li><a href=../operator%3D/ >operator=</a> copy assignment operator</li> <li><a href=../../../features/creating_values/ >Creating <abbr title="JavaScript Object Notation">JSON</abbr> values</a> - the article on creating <abbr title="JavaScript Object Notation">JSON</abbr> values</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 1.0.0.</li> <li>Added in version 1.0.0.</li> <li>Added in version 2.1.0.</li> <li>Added in version 3.1.2. Explicit for different string types if <code>JSON_USE_IMPLICIT_CONVERSIONS</code> is <code>0</code> 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>.</li> <li>Added in version 1.0.0.</li> <li>Added in version 1.0.0.</li> <li>Added in version 1.0.0. Fixed 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> to also check the iterator range for binary values; before, a range that did not cover the whole value (such as <code>(end(), end())</code>) was accepted and the whole binary value was copied, unlike the other primitive types.</li> <li>Added in version 1.0.0.</li> <li>Added in version 1.0.0.</li> </ol> <!-- 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 24, 2026 15:57:44 UTC">October 24, 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 50Line 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=../array/ ><code>array</code></a> - create a <abbr title="JavaScript Object Notation">JSON</abbr> array value, forcing array creation from an initializer list even when it looks like an object</li> <li><a href=../object/ ><code>object</code></a> - create a <abbr title="JavaScript Object Notation">JSON</abbr> object value, forcing object creation from an initializer list</li> <li><a href=../binary/ ><code>binary</code></a> - create a <abbr title="JavaScript Object Notation">JSON</abbr> binary array value</li> <li><a href=../operator%3D/ ><code>operator=</code></a> - copy assignment operator</li> <li><a href=../../../features/creating_values/ >Creating <abbr title="JavaScript Object Notation">JSON</abbr> values</a> - the article on creating <abbr title="JavaScript Object Notation">JSON</abbr> values</li> <li><a href=../../../features/conversions/ >Converting values</a> - which C++ types can be converted</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 1.0.0.</li> <li>Added in version 1.0.0.</li> <li>Added in version 2.1.0.</li> <li>Added in version 3.1.2. Explicit for different string types if <code>JSON_USE_IMPLICIT_CONVERSIONS</code> is <code>0</code> 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>.</li> <li>Added in version 1.0.0.</li> <li>Added in version 1.0.0.</li> <li>Added in version 1.0.0. Fixed 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> to also check the iterator range for binary values; before, a range that did not cover the whole value (such as <code>(end(), end())</code>) was accepted and the whole binary value was copied, unlike the other primitive types.</li> <li>Added in version 1.0.0.</li> <li>Added in version 1.0.0.</li> </ol> <!-- 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 27, 2026 06:41:42 UTC">October 27, 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> <nav class="md-footer__inner md-grid" aria-label=Footer> <a href=../ class="md-footer__link md-footer__link--prev" aria-label="Previous: Overview"> <div class="md-footer__button md-icon"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M20 11v2H8l5.5 5.5-1.42 1.42L4.16 12l7.92-7.92L13.5 5.5 8 11z"/></svg> </div> <div class=md-footer__title> <span class=md-footer__direction> Previous </span> <div class=md-ellipsis> Overview </div> </div> </a> <a href=../~basic_json/ class="md-footer__link md-footer__link--next" aria-label="Next: (Destructor)"> <div class=md-footer__title> <span class=md-footer__direction> Next </span> <div class=md-ellipsis> (Destructor) </div> </div> <div class="md-footer__button md-icon"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M4 11v2h12l-5.5 5.5 1.42 1.42L19.84 12l-7.92-7.92L10.5 5.5 16 11z"/></svg> </div> </a> </nav> <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 - htLine truncated
+13 -10
View File
@@ -50,7 +50,7 @@ basic_json(basic_json&& other) noexcept;
The postcondition of this constructor can be restored by calling [`clear()`](https://json.nlohmann.me/api/basic_json/clear/index.md).
1. Create a `null` JSON value. It either takes a null pointer as parameter (explicitly creating `null`) or no parameter (implicitly creating `null`). The passed null pointer itself is not read -- it is only used to choose the right constructor.
1. Create a `null` JSON value. It either takes a null pointer as parameter (explicitly creating `null`) or no parameter (implicitly creating `null`). The passed null pointer itself is not read — it is only used to choose the right constructor.
1. This is a "catch all" constructor for all compatible JSON types; that is, types for which a `to_json()` method exists. The constructor forwards the parameter `val` to that method (to `json_serializer<U>::to_json` method with `U = uncvref_t<CompatibleType>`, to be exact).
@@ -84,19 +84,21 @@ basic_json(basic_json&& other) noexcept;
```
flowchart TD
A(["initializer_list init"]) --> B{"empty, or every element is a 2-element<br/>array whose first element is a string?"}
B -->|"yes"| C{"type_deduction"}
B -->|"no"| D{"type_deduction"}
A(["initializer_list init"]) --> B{{"empty, or every element is a 2-element<br/>array whose first element is a string?"}}
B -->|"yes"| C{{"type_deduction"}}
B -->|"no"| D{{"type_deduction"}}
C -->|"true"| OBJ["create object"]
C -->|"false"| E{"manual_type"}
C -->|"false"| E{{"manual_type"}}
E -->|"object"| OBJ
E -->|"array"| ARR["create array"]
D -->|"true"| ARR
D -->|"false"| F{"manual_type"}
D -->|"false"| F{{"manual_type"}}
F -->|"array"| ARR
F -->|"object"| ERR["throw type_error.301"]
```
Decision flow for an initializer list: hexagons are checks, edge labels are their outcomes, and rectangles are the resulting value or exception.
The rules aim to create the best fit between a C++ initializer list and JSON values. The rationale is as follows:
1. The empty initializer list is written as `{}` which is exactly an empty JSON object.
@@ -824,11 +826,12 @@ null
## See also
- [array](https://json.nlohmann.me/api/basic_json/array/index.md) create a JSON array value, forcing array creation from an initializer list even when it looks like an object
- [object](https://json.nlohmann.me/api/basic_json/object/index.md) create a JSON object value, forcing object creation from an initializer list
- [binary](https://json.nlohmann.me/api/basic_json/binary/index.md) create a JSON binary array value
- [operator=](https://json.nlohmann.me/api/basic_json/operator%3D/index.md) copy assignment operator
- [`array`](https://json.nlohmann.me/api/basic_json/array/index.md) - create a JSON array value, forcing array creation from an initializer list even when it looks like an object
- [`object`](https://json.nlohmann.me/api/basic_json/object/index.md) - create a JSON object value, forcing object creation from an initializer list
- [`binary`](https://json.nlohmann.me/api/basic_json/binary/index.md) - create a JSON binary array value
- [`operator=`](https://json.nlohmann.me/api/basic_json/operator%3D/index.md) - copy assignment operator
- [Creating JSON values](https://json.nlohmann.me/features/creating_values/index.md) - the article on creating JSON values
- [Converting values](https://json.nlohmann.me/features/conversions/index.md) - which C++ types can be converted
## Version history
+39 -6
View File
@@ -7,7 +7,40 @@ const_iterator begin() const noexcept;
Returns an iterator to the first element.
![Illustration from cppreference.com](../../images/range-begin-end.svg)
<div class="nj-fig-wrap" markdown>
<svg class="nj-fig nj-fig--range" viewBox="0 0 600 150" role="img" aria-labelledby="fig-be-title" xmlns="http://www.w3.org/2000/svg">
<title id="fig-be-title">A row of fifteen elements followed by a dashed past-the-last position. begin() points to the first element and end() points to the past-the-last position.</title>
<defs><marker id="fig-be-arrow" viewBox="0 0 10 10" refX="9" refY="5" markerWidth="7" markerHeight="7" orient="auto"><path class="fg-head" d="M0 1 L10 5 L0 9 z"/></marker></defs>
<rect class="fg-cell" x="30" y="62" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="64" y="62" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="98" y="62" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="132" y="62" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="166" y="62" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="200" y="62" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="234" y="62" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="268" y="62" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="302" y="62" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="336" y="62" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="370" y="62" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="404" y="62" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="438" y="62" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="472" y="62" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="506" y="62" width="30" height="30" rx="5"/>
<rect class="fg-cell fg-cell--end" x="540" y="62" width="30" height="30" rx="5"/>
<rect class="fg-pill" x="15" y="8" width="60" height="24" rx="6"/>
<text class="fg-pilltext" x="45" y="24">begin</text>
<line class="fg-arrow" x1="45" y1="32" x2="45" y2="60" marker-end="url(#fig-be-arrow)"/>
<rect class="fg-pill" x="531" y="8" width="48" height="24" rx="6"/>
<text class="fg-pilltext" x="555" y="24">end</text>
<line class="fg-arrow" x1="555" y1="32" x2="555" y2="60" marker-end="url(#fig-be-arrow)"/>
<text class="fg-note fg-note--r" x="537" y="132">Past-the-last element</text>
<line class="fg-arrow" x1="555" y1="124" x2="555" y2="96" marker-end="url(#fig-be-arrow)"/>
</svg>
</div>
<p class="nj-caption" markdown>`begin()` points to the first element and `end()` to the position after the last element;
the dashed cell is the past-the-last position, which must not be dereferenced.</p>
## Return value
@@ -56,12 +89,12 @@ Constant.
## See also
- [end](end.md) returns an iterator to one past the last element
- [cbegin](cbegin.md) returns a const iterator to the first element
- [rbegin](rbegin.md) returns a reverse iterator to the last element
- [items](items.md) returns an iteration proxy to access keys and values during range-based for loops
- [`end`](end.md) - returns an iterator to one past the last element
- [`cbegin`](cbegin.md) - returns a const iterator to the first element
- [`rbegin`](rbegin.md) - returns a reverse iterator to the last element
- [`items`](items.md) - returns an iteration proxy to access keys and values during range-based for loops
- [Iterators](../../features/iterators.md) - the article on iterators
- [basic_json_view::begin](../basic_json_view/begin.md) - the same iteration on a zero-copy view (in document order,
- [`basic_json_view::begin`](../basic_json_view/begin.md) - the same iteration on a zero-copy view (in document order,
not sorted by key)
## Version history
+3 -3
View File
@@ -1,6 +1,6 @@
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<span class=n>const_iterator</span><span class=w> </span><span class=nf>begin</span><span class=p>()</span><span class=w> </span><span class=k>const</span><span class=w> </span><span class=k>noexcept</span><span class=p>;</span>
</code></pre></div> <p>Returns an iterator to the first element.</p> <p><img alt="Illustration from cppreference.com" src=../../../images/range-begin-end.svg></p> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <p>iterator to the first element</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">&para;</a></h2> <p>No-throw guarantee: this member function never throws exceptions.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">&para;</a></h2> <p>Constant.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The following code shows an example for <code>begin()</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>
</code></pre></div> <p>Returns an iterator to the first element.</p> <div class=nj-fig-wrap> <p><svg class="nj-fig nj-fig--range" viewbox="0 0 600 150" role=img aria-labelledby=fig-be-title xmlns=http://www.w3.org/2000/svg> <title id=fig-be-title>A row of fifteen elements followed by a dashed past-the-last position. begin() points to the first element and end() points to the past-the-last position.</title> <defs><marker id=fig-be-arrow viewbox="0 0 10 10" refx=9 refy=5 markerwidth=7 markerheight=7 orient=auto><path class=fg-head d="M0 1 L10 5 L0 9 z"/></marker></defs> <rect class=fg-cell x=30 y=62 width=30 height=30 rx=5 /> <rect class=fg-cell x=64 y=62 width=30 height=30 rx=5 /> <rect class=fg-cell x=98 y=62 width=30 height=30 rx=5 /> <rect class=fg-cell x=132 y=62 width=30 height=30 rx=5 /> <rect class=fg-cell x=166 y=62 width=30 height=30 rx=5 /> <rect class=fg-cell x=200 y=62 width=30 height=30 rx=5 /> <rect class=fg-cell x=234 y=62 width=30 height=30 rx=5 /> <rect class=fg-cell x=268 y=62 width=30 height=30 rx=5 /> <rect class=fg-cell x=302 y=62 width=30 height=30 rx=5 /> <rect class=fg-cell x=336 y=62 width=30 height=30 rx=5 /> <rect class=fg-cell x=370 y=62 width=30 height=30 rx=5 /> <rect class=fg-cell x=404 y=62 width=30 height=30 rx=5 /> <rect class=fg-cell x=438 y=62 width=30 height=30 rx=5 /> <rect class=fg-cell x=472 y=62 width=30 height=30 rx=5 /> <rect class=fg-cell x=506 y=62 width=30 height=30 rx=5 /> <rect x=540 y=62 width=30 height=30 rx=5 class="fg-cell fg-cell--end"/> <rect class=fg-pill x=15 y=8 width=60 height=24 rx=6 /> <text class=fg-pilltext x=45 y=24>begin</text> <line class=fg-arrow x1=45 y1=32 x2=45 y2=60 marker-end=url(#fig-be-arrow) /> <rect class=fg-pill x=531 y=8 width=48 height=24 rx=6 /> <text class=fg-pilltext x=555 y=24>end</text> <line class=fg-arrow x1=555 y1=32 x2=555 y2=60 marker-end=url(#fig-be-arrow) /> <text class="fg-note fg-note--r" x=537 y=132>Past-the-last element</text> <line class=fg-arrow x1=555 y1=124 x2=555 y2=96 marker-end=url(#fig-be-arrow) /> </svg></p> </div> <p class=nj-caption><code>begin()</code> points to the first element and <code>end()</code> to the position after the last element; the dashed cell is the past-the-last position, which must not be dereferenced.</p> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <p>iterator to the first element</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">&para;</a></h2> <p>No-throw guarantee: this member function never throws exceptions.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">&para;</a></h2> <p>Constant.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The following code shows an example for <code>begin()</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>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
@@ -17,4 +17,4 @@
<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=o>*</span><span class=n>it</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>1</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=../end/ >end</a> returns an iterator to one past the last element</li> <li><a href=../cbegin/ >cbegin</a> returns a const iterator to the first element</li> <li><a href=../rbegin/ >rbegin</a> returns a reverse iterator to the last element</li> <li><a href=../items/ >items</a> returns an iteration proxy to access keys and values during range-based for loops</li> <li><a href=../../../features/iterators/ >Iterators</a> - the article on iterators</li> <li><a href=../../basic_json_view/begin/ >basic_json_view::begin</a> - the same iteration on a zero-copy view (in document order, not sorted by key)</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 1.0.0.</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 21, 2026 08:21:27 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=../end/ ><code>end</code></a> - returns an iterator to one past the last element</li> <li><a href=../cbegin/ ><code>cbegin</code></a> - returns a const iterator to the first element</li> <li><a href=../rbegin/ ><code>rbegin</code></a> - returns a reverse iterator to the last element</li> <li><a href=../items/ ><code>items</code></a> - returns an iteration proxy to access keys and values during range-based for loops</li> <li><a href=../../../features/iterators/ >Iterators</a> - the article on iterators</li> <li><a href=../../basic_json_view/begin/ ><code>basic_json_view::begin</code></a> - the same iteration on a zero-copy view (in document order, not sorted by key)</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 1.0.0.</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 27, 2026 06:41:42 UTC">October 27, 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> <nav class="md-footer__inner md-grid" aria-label=Footer> <a href=../back/ class="md-footer__link md-footer__link--prev" aria-label="Previous: back"> <div class="md-footer__button md-icon"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M20 11v2H8l5.5 5.5-1.42 1.42L4.16 12l7.92-7.92L13.5 5.5 8 11z"/></svg> </div> <div class=md-footer__title> <span class=md-footer__direction> Previous </span> <div class=md-ellipsis> back </div> </div> </a> <a href=../binary/ class="md-footer__link md-footer__link--next" aria-label="Next: binary"> <div class=md-footer__title> <span class=md-footer__direction> Next </span> <div class=md-ellipsis> binary </div> </div> <div class="md-footer__button md-icon"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M4 11v2h12l-5.5 5.5 1.42 1.42L19.84 12l-7.92-7.92L10.5 5.5 16 11z"/></svg> </div> </a> </nav> <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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+7 -5
View File
@@ -7,6 +7,8 @@ const_iterator begin() const noexcept;
Returns an iterator to the first element.
`begin()` points to the first element and `end()` to the position after the last element; the dashed cell is the past-the-last position, which must not be dereferenced.
## Return value
iterator to the first element
@@ -52,12 +54,12 @@ Output:
## See also
- [end](https://json.nlohmann.me/api/basic_json/end/index.md) returns an iterator to one past the last element
- [cbegin](https://json.nlohmann.me/api/basic_json/cbegin/index.md) returns a const iterator to the first element
- [rbegin](https://json.nlohmann.me/api/basic_json/rbegin/index.md) returns a reverse iterator to the last element
- [items](https://json.nlohmann.me/api/basic_json/items/index.md) returns an iteration proxy to access keys and values during range-based for loops
- [`end`](https://json.nlohmann.me/api/basic_json/end/index.md) - returns an iterator to one past the last element
- [`cbegin`](https://json.nlohmann.me/api/basic_json/cbegin/index.md) - returns a const iterator to the first element
- [`rbegin`](https://json.nlohmann.me/api/basic_json/rbegin/index.md) - returns a reverse iterator to the last element
- [`items`](https://json.nlohmann.me/api/basic_json/items/index.md) - returns an iteration proxy to access keys and values during range-based for loops
- [Iterators](https://json.nlohmann.me/features/iterators/index.md) - the article on iterators
- [basic_json_view::begin](https://json.nlohmann.me/api/basic_json_view/begin/index.md) - the same iteration on a zero-copy view (in document order, not sorted by key)
- [`basic_json_view::begin`](https://json.nlohmann.me/api/basic_json_view/begin/index.md) - the same iteration on a zero-copy view (in document order, not sorted by key)
## Version history
+5 -4
View File
@@ -80,10 +80,11 @@ initialization of a binary array type, for backwards compatibility and so it doe
## See also
- [binary_t](binary_t.md) type for binary values
- [get_binary](get_binary.md) get a reference to the stored binary value
- [is_binary](is_binary.md) return whether the value is binary
- [byte_container_with_subtype](../byte_container_with_subtype/index.md) container for binary values with subtype
- [Binary formats](../../features/binary_formats/index.md) - formats that can store binary values
- [`binary_t`](binary_t.md) - type for binary values
- [`get_binary`](get_binary.md) - get a reference to the stored binary value
- [`is_binary`](is_binary.md) - return whether the value is binary
- [`byte_container_with_subtype`](../byte_container_with_subtype/index.md) - container for binary values with subtype
- [Binary Values](../../features/binary_values.md) - the article on binary values
## Version history
+2 -2
View File
@@ -1,4 +1,4 @@
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</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> <img src=../../../images/wordmark-header.svg alt=logo> </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> binary </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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<span class=k>static</span><span class=w> </span><span class=n>basic_json</span><span class=w> </span><span class=nf>binary</span><span class=p>(</span><span class=k>const</span><span class=w> </span><span class=k>typename</span><span class=w> </span><span class=nc>binary_t</span><span class=o>::</span><span class=n>container_type</span><span class=o>&amp;</span><span class=w> </span><span class=n>init</span><span class=p>);</span>
<span class=k>static</span><span class=w> </span><span class=n>basic_json</span><span class=w> </span><span class=nf>binary</span><span class=p>(</span><span class=k>typename</span><span class=w> </span><span class=nc>binary_t</span><span class=o>::</span><span class=n>container_type</span><span class=o>&amp;&amp;</span><span class=w> </span><span class=n>init</span><span class=p>);</span>
@@ -24,4 +24,4 @@
<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>"type: "</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>type_name</span><span class=p>()</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>", subtype: "</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>get_binary</span><span class=p>().</span><span class=n>subtype</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>t</span><span class=err>ype</span><span class=p>:</span><span class=w> </span><span class=err>bi</span><span class=kc>nar</span><span class=err>y</span><span class=p>,</span><span class=w> </span><span class=err>sub</span><span class=kc>t</span><span class=err>ype</span><span class=p>:</span><span class=w> </span><span class=mi>42</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=../binary_t/ >binary_t</a> type for binary values</li> <li><a href=../get_binary/ >get_binary</a> get a reference to the stored binary value</li> <li><a href=../is_binary/ >is_binary</a> return whether the value is binary</li> <li><a href=../../byte_container_with_subtype/ >byte_container_with_subtype</a> container for binary values with subtype</li> <li><a href=../../../features/binary_values/ >Binary Values</a> - the article on binary values</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 3.8.0.</li> <li>Changed the type of <code>subtype</code> from <code>std::uint8_t</code> to <code>binary_t::subtype_type</code> (<code>std::uint64_t</code>) in version 3.10.0.</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/binary_formats/ >Binary formats</a> - formats that can store binary values</li> <li><a href=../binary_t/ ><code>binary_t</code></a> - type for binary values</li> <li><a href=../get_binary/ ><code>get_binary</code></a> - get a reference to the stored binary value</li> <li><a href=../is_binary/ ><code>is_binary</code></a> - return whether the value is binary</li> <li><a href=../../byte_container_with_subtype/ ><code>byte_container_with_subtype</code></a> - container for binary values with subtype</li> <li><a href=../../../features/binary_values/ >Binary Values</a> - the article on binary values</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 3.8.0.</li> <li>Changed the type of <code>subtype</code> from <code>std::uint8_t</code> to <code>binary_t::subtype_type</code> (<code>std::uint64_t</code>) in version 3.10.0.</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 27, 2026 06:41:42 UTC">October 27, 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> <nav class="md-footer__inner md-grid" aria-label=Footer> <a href=../begin/ class="md-footer__link md-footer__link--prev" aria-label="Previous: begin"> <div class="md-footer__button md-icon"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M20 11v2H8l5.5 5.5-1.42 1.42L4.16 12l7.92-7.92L13.5 5.5 8 11z"/></svg> </div> <div class=md-footer__title> <span class=md-footer__direction> Previous </span> <div class=md-ellipsis> begin </div> </div> </a> <a href=../binary_t/ class="md-footer__link md-footer__link--next" aria-label="Next: binary_t"> <div class=md-footer__title> <span class=md-footer__direction> Next </span> <div class=md-ellipsis> binary_t </div> </div> <div class="md-footer__button md-icon"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M4 11v2h12l-5.5 5.5 1.42 1.42L19.84 12l-7.92-7.92L10.5 5.5 16 11z"/></svg> </div> </a> </nav> <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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+5 -4
View File
@@ -72,10 +72,11 @@ type: binary, subtype: 42
## See also
- [binary_t](https://json.nlohmann.me/api/basic_json/binary_t/index.md) type for binary values
- [get_binary](https://json.nlohmann.me/api/basic_json/get_binary/index.md) get a reference to the stored binary value
- [is_binary](https://json.nlohmann.me/api/basic_json/is_binary/index.md) return whether the value is binary
- [byte_container_with_subtype](https://json.nlohmann.me/api/byte_container_with_subtype/index.md) container for binary values with subtype
- [Binary formats](https://json.nlohmann.me/features/binary_formats/index.md) - formats that can store binary values
- [`binary_t`](https://json.nlohmann.me/api/basic_json/binary_t/index.md) - type for binary values
- [`get_binary`](https://json.nlohmann.me/api/basic_json/get_binary/index.md) - get a reference to the stored binary value
- [`is_binary`](https://json.nlohmann.me/api/basic_json/is_binary/index.md) - return whether the value is binary
- [`byte_container_with_subtype`](https://json.nlohmann.me/api/byte_container_with_subtype/index.md) - container for binary values with subtype
- [Binary Values](https://json.nlohmann.me/features/binary_values/index.md) - the article on binary values
## Version history
+4 -2
View File
@@ -41,7 +41,7 @@ represent a byte array in modern C++.
[`byte_container_with_subtype`](../byte_container_with_subtype/index.md) derives directly from it. Its
`value_type` must additionally be exactly one byte wide (e.g., `std::uint8_t`/`char`/`std::byte`): the binary
serializers (CBOR, MessagePack, BSON, UBJSON) read and write the container's raw bytes via
`reinterpret_cast`, which is only correct for byte-sized elements -- a container like
`reinterpret_cast`, which is only correct for byte-sized elements — a container like
`#!cpp std::vector<std::intptr_t>` will not work as `BinaryType`. The elements must be stored contiguously, and
the binary readers additionally require `resize()` and `operator[]`. See
[Template Parameter Requirements](../../features/types/template_parameters.md#binarytype) for the full list.
@@ -129,7 +129,9 @@ type `#!cpp binary_t*` must be dereferenced.
## See also
- [byte_container_with_subtype](../byte_container_with_subtype/index.md)
- [Binary values](../../features/binary_values.md) - how binary values and subtypes are handled
- [Binary formats](../../features/binary_formats/index.md) - formats that can store binary values
- [`byte_container_with_subtype`](../byte_container_with_subtype/index.md) - container type used by binary values
## Version history
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@@ -1,5 +1,5 @@
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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> binary_t </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 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</code></pre></div> <p>This type is a type designed to carry binary data that appears in various serialized formats, such as <abbr title="Concise Binary Object Representation">CBOR</abbr>'s Major Type 2, MessagePack's bin, and <abbr title="Binary JSON">BSON</abbr>'s generic binary subtype. This type is NOT a part of standard <abbr title="JavaScript Object Notation">JSON</abbr> and exists solely for compatibility with these binary types. As such, it is simply defined as an ordered sequence of zero or more byte values.</p> <p>Additionally, as an implementation detail, the subtype of the binary data is carried around as a <code>std::uint64_t</code>, which is compatible with both of the binary data formats that use binary subtyping, (though the specific numbering is incompatible with each other, and it is up to the user to translate between them). The subtype is added to <code>BinaryType</code> via the helper type <a href=../../byte_container_with_subtype/ >byte_container_with_subtype</a>.</p> <p><a href="https://www.rfc-editor.org/rfc/rfc8949.html#section-3.1"><abbr title="Concise Binary Object Representation">CBOR</abbr>'s <abbr title="Request for Comments">RFC</abbr> 8949</a> describes this type as:</p> <blockquote> <p>Major type 2: A byte string. The number of bytes in the string is equal to the argument.</p> </blockquote> <p><a href="https://github.com/msgpack/msgpack/blob/master/spec.md#bin-format-family">MessagePack's documentation on the bin type family</a> describes this type as:</p> <blockquote> <p>Bin format family stores a byte array in 2, 3, or 5 bytes of extra bytes in addition to the size of the byte array.</p> </blockquote> <p><a href="http://bsonspec.org/spec.html"><abbr title="Binary JSON">BSON</abbr>'s specifications</a> describe several binary types; however, this type is intended to represent the generic binary type which has the description:</p> <blockquote> <p>Generic binary subtype - This is the most commonly used binary subtype and should be the 'default' for drivers and tools.</p> </blockquote> <p>None of these impose any limitations on the internal representation other than the basic unit of storage be some type of array whose parts are decomposable into bytes.</p> <p>The default representation of this binary format is a <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>vector</span><span class=o>&lt;</span><span class=n>std</span><span class=o>::</span><span class=kt>uint8_t</span><span class=o>&gt;</span></code>, which is a very common way to represent a byte array in modern C++.</p> <h2 id=template-parameters>Template parameters<a class=headerlink href=#template-parameters title="Permanent link">&para;</a></h2> <dl> <dt><code>BinaryType</code></dt> <dd> <p>container type to store arrays</p> <p>Although not formally expressed as a C++ concept, <code>BinaryType</code> must be default-constructible, copy/move-constructible, and support <code>push_back()</code>, <code>.data()</code>, and <code>.size()</code>, because <a href=../../byte_container_with_subtype/ ><code>byte_container_with_subtype</code></a> derives directly from it. Its <code>value_type</code> must additionally be exactly one byte wide (e.g., <code>std::uint8_t</code>/<code>char</code>/<code>std::byte</code>): the binary serializers (<abbr title="Concise Binary Object Representation">CBOR</abbr>, MessagePack, <abbr title="Binary JSON">BSON</abbr>, <abbr title="Universal Binary JSON">UBJSON</abbr>) read and write the container's raw bytes via <code>reinterpret_cast</code>, which is only correct for byte-sized elements -- a container like <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>vector</span><span class=o>&lt;</span><span class=n>std</span><span class=o>::</span><span class=kt>intptr_t</span><span class=o>&gt;</span></code> will not work as <code>BinaryType</code>. The elements must be stored contiguously, and the binary readers additionally require <code>resize()</code> and <code>operator[]</code>. See <a href=../../../features/types/template_parameters/#binarytype>Template Parameter Requirements</a> for the full list.</p> </dd> </dl> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <h3 id=default-type>Default type<a class=headerlink href=#default-type title="Permanent link">&para;</a></h3> <p>The default values for <code>BinaryType</code> is <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>vector</span><span class=o>&lt;</span><span class=n>std</span><span class=o>::</span><span class=kt>uint8_t</span><span class=o>&gt;</span></code>.</p> <h3 id=supported-byte-types>Supported byte types<a class=headerlink href=#supported-byte-types title="Permanent link">&para;</a></h3> <p><code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>vector</span><span class=o>&lt;</span><span class=n>std</span><span class=o>::</span><span class=kt>uint8_t</span><span clLine truncated
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0 24 24"><path d="M9.5 3A6.5Line truncated
</code></pre></div> <p>This type is a type designed to carry binary data that appears in various serialized formats, such as <abbr title="Concise Binary Object Representation">CBOR</abbr>'s Major Type 2, MessagePack's bin, and <abbr title="Binary JSON">BSON</abbr>'s generic binary subtype. This type is NOT a part of standard <abbr title="JavaScript Object Notation">JSON</abbr> and exists solely for compatibility with these binary types. As such, it is simply defined as an ordered sequence of zero or more byte values.</p> <p>Additionally, as an implementation detail, the subtype of the binary data is carried around as a <code>std::uint64_t</code>, which is compatible with both of the binary data formats that use binary subtyping, (though the specific numbering is incompatible with each other, and it is up to the user to translate between them). The subtype is added to <code>BinaryType</code> via the helper type <a href=../../byte_container_with_subtype/ >byte_container_with_subtype</a>.</p> <p><a href="https://www.rfc-editor.org/rfc/rfc8949.html#section-3.1"><abbr title="Concise Binary Object Representation">CBOR</abbr>'s <abbr title="Request for Comments">RFC</abbr> 8949</a> describes this type as:</p> <blockquote> <p>Major type 2: A byte string. The number of bytes in the string is equal to the argument.</p> </blockquote> <p><a href="https://github.com/msgpack/msgpack/blob/master/spec.md#bin-format-family">MessagePack's documentation on the bin type family</a> describes this type as:</p> <blockquote> <p>Bin format family stores a byte array in 2, 3, or 5 bytes of extra bytes in addition to the size of the byte array.</p> </blockquote> <p><a href="http://bsonspec.org/spec.html"><abbr title="Binary JSON">BSON</abbr>'s specifications</a> describe several binary types; however, this type is intended to represent the generic binary type which has the description:</p> <blockquote> <p>Generic binary subtype - This is the most commonly used binary subtype and should be the 'default' for drivers and tools.</p> </blockquote> <p>None of these impose any limitations on the internal representation other than the basic unit of storage be some type of array whose parts are decomposable into bytes.</p> <p>The default representation of this binary format is a <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>vector</span><span class=o>&lt;</span><span class=n>std</span><span class=o>::</span><span class=kt>uint8_t</span><span class=o>&gt;</span></code>, which is a very common way to represent a byte array in modern C++.</p> <h2 id=template-parameters>Template parameters<a class=headerlink href=#template-parameters title="Permanent link">&para;</a></h2> <dl> <dt><code>BinaryType</code></dt> <dd> <p>container type to store arrays</p> <p>Although not formally expressed as a C++ concept, <code>BinaryType</code> must be default-constructible, copy/move-constructible, and support <code>push_back()</code>, <code>.data()</code>, and <code>.size()</code>, because <a href=../../byte_container_with_subtype/ ><code>byte_container_with_subtype</code></a> derives directly from it. Its <code>value_type</code> must additionally be exactly one byte wide (e.g., <code>std::uint8_t</code>/<code>char</code>/<code>std::byte</code>): the binary serializers (<abbr title="Concise Binary Object Representation">CBOR</abbr>, MessagePack, <abbr title="Binary JSON">BSON</abbr>, <abbr title="Universal Binary JSON">UBJSON</abbr>) read and write the container's raw bytes via <code>reinterpret_cast</code>, which is only correct for byte-sized elements — a container like <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>vector</span><span class=o>&lt;</span><span class=n>std</span><span class=o>::</span><span class=kt>intptr_t</span><span class=o>&gt;</span></code> will not work as <code>BinaryType</code>. The elements must be stored contiguously, and the binary readers additionally require <code>resize()</code> and <code>operator[]</code>. See <a href=../../../features/types/template_parameters/#binarytype>Template Parameter Requirements</a> for the full list.</p> </dd> </dl> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <h3 id=default-type>Default type<a class=headerlink href=#default-type title="Permanent link">&para;</a></h3> <p>The default values for <code>BinaryType</code> is <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>vector</span><span class=o>&lt;</span><span class=n>std</span><span class=o>::</span><span class=kt>uint8_t</span><span class=o>&gt;</span></code>.</p> <h3 id=supported-byte-types>Supported byte types<a class=headerlink href=#supported-byte-types title="Permanent link">&para;</a></h3> <p><code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>vector</span><span class=o>&lt;</span><span class=n>std</span><span class=o>::</span><span class=kt>uint8_t</span><span cLine truncated
<span class=n>std</span><span class=o>::</span><span class=n>vector</span><span class=o>&lt;</span><span class=n>std</span><span class=o>::</span><span class=kt>byte</span><span class=o>&gt;</span><span class=w> </span><span class=n>data</span><span class=p>{</span><span class=n>std</span><span class=o>::</span><span class=kt>byte</span><span class=p>{</span><span class=mi>1</span><span class=p>},</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=kt>byte</span><span class=p>{</span><span class=mi>2</span><span class=p>},</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=kt>byte</span><span class=p>{</span><span class=mi>3</span><span class=p>}};</span>
<span class=n>custom_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>data</span><span class=p>;</span><span class=w> </span><span class=c1>// Creates a binary value, not an array</span>
@@ -19,4 +19,4 @@
<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>boolalpha</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>is_same</span><span class=o>&lt;</span><span class=n>nlohmann</span><span class=o>::</span><span class=n>byte_container_with_subtype</span><span class=o>&lt;</span><span class=n>std</span><span class=o>::</span><span class=n>vector</span><span class=o>&lt;</span><span class=n>std</span><span class=o>::</span><span class=kt>uint8_t</span><span class=o>&gt;&gt;</span><span class=p>,</span><span class=w> </span><span class=n>json</span><span class=o>::</span><span class=n>binary_t</span><span class=o>&gt;::</span><span class=n>value</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>true</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=../../byte_container_with_subtype/ >byte_container_with_subtype</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 3.8.0. Changed the type of subtype to <code>std::uint64_t</code> in version 3.10.0.</li> <li>Fixed <a href=../dump/ ><code>dump</code></a>, <a href=../std_hash/ ><code>std::hash</code></a>, and <a href=../to_ubjson/ ><code>to_ubjson</code></a> for byte types that are not integers (e.g., <code class=highlight><span class=n>std</span><span class=o>::</span><span class=kt>byte</span></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>. <code>dump</code> now writes the bytes of a signed byte type (e.g., <code class=highlight><span class=kt>char</span></code>) as 0..255 rather than as negative numbers.</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 17:25:44 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 2025 Fonticons, Inc.--><path d="M416 32H31.9C14.3 32 0 46.5 0 64.3v383Line 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=../../../features/binary_values/ >Binary values</a> - how binary values and subtypes are handled</li> <li><a href=../../../features/binary_formats/ >Binary formats</a> - formats that can store binary values</li> <li><a href=../../byte_container_with_subtype/ ><code>byte_container_with_subtype</code></a> - container type used by binary values</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 3.8.0. Changed the type of subtype to <code>std::uint64_t</code> in version 3.10.0.</li> <li>Fixed <a href=../dump/ ><code>dump</code></a>, <a href=../std_hash/ ><code>std::hash</code></a>, and <a href=../to_ubjson/ ><code>to_ubjson</code></a> for byte types that are not integers (e.g., <code class=highlight><span class=n>std</span><span class=o>::</span><span class=kt>byte</span></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>. <code>dump</code> now writes the bytes of a signed byte type (e.g., <code class=highlight><span class=kt>char</span></code>) as 0..255 rather than as negative numbers.</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 27, 2026 06:41:42 UTC">October 27, 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> <nav class="md-footer__inner md-grid" aria-label=Footer> <a href=../binary/ class="md-footer__link md-footer__link--prev" aria-label="Previous: binary"> <div class="md-footer__button md-icon"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M20 11v2H8l5.5 5.5-1.42 1.42L4.16 12l7.92-7.92L13.5 5.5 8 11z"/></svg> </div> <div class=md-footer__title> <span class=md-footer__direction> Previous </span> <div class=md-ellipsis> binary </div> </div> </a> <a href=../bjdata_version_t/ class="md-footer__link md-footer__link--next" aria-label="Next: bjdata_version_t"> <div class=md-footer__title> <span class=md-footer__direction> Next </span> <div class=md-ellipsis> bjdata_version_t </div> </div> <div class="md-footer__button md-icon"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M4 11v2h12l-5.5 5.5 1.42 1.42L19.84 12l-7.92-7.92L10.5 5.5 16 11z"/></svg> </div> </a> </nav> <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 16-33.7-55.9-6.2-112.3-14.3-112.3-110.5Line truncated
+4 -2
View File
@@ -34,7 +34,7 @@ copy/move-constructible, and support `push_back()`, `.data()`, and `.size()`, be
[`byte_container_with_subtype`](https://json.nlohmann.me/api/byte_container_with_subtype/index.md) derives directly from it. Its
`value_type` must additionally be exactly one byte wide (e.g., `std::uint8_t`/`char`/`std::byte`): the binary
serializers (CBOR, MessagePack, BSON, UBJSON) read and write the container's raw bytes via
`reinterpret_cast`, which is only correct for byte-sized elements -- a container like
`reinterpret_cast`, which is only correct for byte-sized elements — a container like
`std::vector<std::intptr_t>` will not work as `BinaryType`. The elements must be stored contiguously, and
the binary readers additionally require `resize()` and `operator[]`. See
[Template Parameter Requirements](https://json.nlohmann.me/features/types/template_parameters/#binarytype) for the full list.
@@ -115,7 +115,9 @@ true
## See also
- [byte_container_with_subtype](https://json.nlohmann.me/api/byte_container_with_subtype/index.md)
- [Binary values](https://json.nlohmann.me/features/binary_values/index.md) - how binary values and subtypes are handled
- [Binary formats](https://json.nlohmann.me/features/binary_formats/index.md) - formats that can store binary values
- [`byte_container_with_subtype`](https://json.nlohmann.me/api/byte_container_with_subtype/index.md) - container type used by binary values
## Version history
+2 -2
View File
@@ -1,4 +1,4 @@
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xmlns=http://www.w3.org/2000/svg viewbox="0 0Line truncated
<span class=p>{</span>
<span class=w> </span><span class=n>draft2</span><span class=p>,</span>
<span class=w> </span><span class=n>draft3</span>
@@ -40,4 +40,4 @@
<span class=err>dra</span><span class=kc>ft</span><span class=mi>3</span><span class=p>:</span><span class=w> </span><span class=mi>5</span><span class=err>b</span><span class=w> </span><span class=mi>24</span><span class=w> </span><span class=mi>42</span><span class=w> </span><span class=mi>23</span><span class=w> </span><span class=mi>69</span><span class=w> </span><span class=mi>04</span><span class=w> </span><span class=err>ca</span><span class=w> </span><span class=kc>fe</span><span class=w> </span><span class=err>ba</span><span class=w> </span><span class=err>be</span>
<span class=p>[</span><span class=mi>202</span><span class=p>,</span><span class=mi>254</span><span class=p>,</span><span class=mi>186</span><span class=p>,</span><span class=mi>190</span><span class=p>]</span>
<span class=p>{</span><span class=nt>"bytes"</span><span class=p>:[</span><span class=mi>202</span><span class=p>,</span><span class=mi>254</span><span class=p>,</span><span class=mi>186</span><span class=p>,</span><span class=mi>190</span><span class=p>],</span><span class=nt>"subtype"</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=../to_bjdata/ >to_bjdata</a> serializes a <abbr title="JavaScript Object Notation">JSON</abbr> value to <abbr title="Binary JData">BJData</abbr></li> <li><a href=../../../features/binary_formats/bjdata/ ><abbr title="Binary JData">BJData</abbr></a> - the article on the <abbr title="Binary JData">BJData</abbr> format</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 3.12.0.</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 26, 2026 17:25:46 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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</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=../to_bjdata/ >to_bjdata</a> serializes a <abbr title="JavaScript Object Notation">JSON</abbr> value to <abbr title="Binary JData">BJData</abbr></li> <li><a href=../../../features/binary_formats/bjdata/ ><abbr title="Binary JData">BJData</abbr></a> - the article on the <abbr title="Binary JData">BJData</abbr> format</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 3.12.0.</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 26, 2026 17:25:46 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> <nav class="md-footer__inner md-grid" aria-label=Footer> <a href=../binary_t/ class="md-footer__link md-footer__link--prev" aria-label="Previous: binary_t"> <div class="md-footer__button md-icon"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M20 11v2H8l5.5 5.5-1.42 1.42L4.16 12l7.92-7.92L13.5 5.5 8 11z"/></svg> </div> <div class=md-footer__title> <span class=md-footer__direction> Previous </span> <div class=md-ellipsis> binary_t </div> </div> </a> <a href=../boolean_t/ class="md-footer__link md-footer__link--next" aria-label="Next: boolean_t"> <div class=md-footer__title> <span class=md-footer__direction> Next </span> <div class=md-ellipsis> boolean_t </div> </div> <div class="md-footer__button md-icon"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M4 11v2h12l-5.5 5.5 1.42 1.42L19.84 12l-7.92-7.92L10.5 5.5 16 11z"/></svg> </div> </a> </nav> <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 -1
View File
@@ -58,7 +58,9 @@ Boolean values are stored directly inside a `basic_json` type.
## See also
- [is_boolean](is_boolean.md) checks whether the JSON value is a boolean
- [`is_boolean`](is_boolean.md) - checks whether the JSON value is a boolean
- [Types](../../features/types/index.md) - how booleans are stored
- [Template Parameter Requirements](../../features/types/template_parameters.md) - requirements on the `BooleanType` template parameter
## Version history
+2 -2
View File
@@ -1,4 +1,4 @@
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</code></pre></div> <p>The type used to store <abbr title="JavaScript Object Notation">JSON</abbr> booleans.</p> <p><a href="https://tools.ietf.org/html/rfc8259"><abbr title="Request for Comments">RFC</abbr> 8259</a> implicitly describes a boolean as a type which differentiates the two literals <code class=highlight><span class=kc>true</span></code> and <code class=highlight><span class=kc>false</span></code>.</p> <p>To store boolean values in C++, a type is defined by the template parameter <code>BooleanType</code> which chooses the type to use.</p> <h2 id=template-parameters>Template parameters<a class=headerlink href=#template-parameters title="Permanent link">&para;</a></h2> <dl> <dt><code>BooleanType</code></dt> <dd>the type to store booleans. As it is stored directly inside a <code>basic_json</code> value (in a union), it must be a trivially default-constructible, trivially copyable, and trivially destructible type that is convertible to and from <code class=highlight><span class=kt>bool</span></code>. See <a href=../../../features/types/template_parameters/#booleantype>Template Parameter Requirements</a>.</dd> </dl> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <h3 id=default-type>Default type<a class=headerlink href=#default-type title="Permanent link">&para;</a></h3> <p>With the default values for <code>BooleanType</code> (<code class=highlight><span class=kt>bool</span></code>), the default type for <code>boolean_t</code> is <code class=highlight><span class=kt>bool</span></code>.</p> <h3 id=storage>Storage<a class=headerlink href=#storage title="Permanent link">&para;</a></h3> <p>Boolean values are stored directly inside a <code>basic_json</code> type.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The following code shows that <code>boolean_t</code> is by default, a typedef to <code class=highlight><span class=kt>bool</span></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;iomanip&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
@@ -10,4 +10,4 @@
<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>boolalpha</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>is_same</span><span class=o>&lt;</span><span class=kt>bool</span><span class=p>,</span><span class=w> </span><span class=n>json</span><span class=o>::</span><span class=n>boolean_t</span><span class=o>&gt;::</span><span class=n>value</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>true</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=../is_boolean/ >is_boolean</a> checks whether the <abbr title="JavaScript Object Notation">JSON</abbr> value is a boolean</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 1.0.0.</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 14, 2026 16:28:49 UTC">October 14, 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=../is_boolean/ ><code>is_boolean</code></a> - checks whether the <abbr title="JavaScript Object Notation">JSON</abbr> value is a boolean</li> <li><a href=../../../features/types/ >Types</a> - how booleans are stored</li> <li><a href=../../../features/types/template_parameters/ >Template Parameter Requirements</a> - requirements on the <code>BooleanType</code> template parameter</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 1.0.0.</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 27, 2026 06:41:42 UTC">October 27, 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> <nav class="md-footer__inner md-grid" aria-label=Footer> <a href=../bjdata_version_t/ class="md-footer__link md-footer__link--prev" aria-label="Previous: bjdata_version_t"> <div class="md-footer__button md-icon"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M20 11v2H8l5.5 5.5-1.42 1.42L4.16 12l7.92-7.92L13.5 5.5 8 11z"/></svg> </div> <div class=md-footer__title> <span class=md-footer__direction> Previous </span> <div class=md-ellipsis> bjdata_version_t </div> </div> </a> <a href=../cbegin/ class="md-footer__link md-footer__link--next" aria-label="Next: cbegin"> <div class=md-footer__title> <span class=md-footer__direction> Next </span> <div class=md-ellipsis> cbegin </div> </div> <div class="md-footer__button md-icon"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M4 11v2h12l-5.5 5.5 1.42 1.42L19.84 12l-7.92-7.92L10.5 5.5 16 11z"/></svg> </div> </a> </nav> <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 -1
View File
@@ -51,7 +51,9 @@ true
## See also
- [is_boolean](https://json.nlohmann.me/api/basic_json/is_boolean/index.md) checks whether the JSON value is a boolean
- [`is_boolean`](https://json.nlohmann.me/api/basic_json/is_boolean/index.md) - checks whether the JSON value is a boolean
- [Types](https://json.nlohmann.me/features/types/index.md) - how booleans are stored
- [Template Parameter Requirements](https://json.nlohmann.me/features/types/template_parameters/index.md) - requirements on the `BooleanType` template parameter
## Version history
+38 -5
View File
@@ -6,7 +6,40 @@ const_iterator cbegin() const noexcept;
Returns an iterator to the first element.
![Illustration from cppreference.com](../../images/range-begin-end.svg)
<div class="nj-fig-wrap" markdown>
<svg class="nj-fig nj-fig--range" viewBox="0 0 600 150" role="img" aria-labelledby="fig-be-title" xmlns="http://www.w3.org/2000/svg">
<title id="fig-be-title">A row of fifteen elements followed by a dashed past-the-last position. begin() points to the first element and end() points to the past-the-last position.</title>
<defs><marker id="fig-be-arrow" viewBox="0 0 10 10" refX="9" refY="5" markerWidth="7" markerHeight="7" orient="auto"><path class="fg-head" d="M0 1 L10 5 L0 9 z"/></marker></defs>
<rect class="fg-cell" x="30" y="62" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="64" y="62" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="98" y="62" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="132" y="62" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="166" y="62" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="200" y="62" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="234" y="62" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="268" y="62" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="302" y="62" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="336" y="62" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="370" y="62" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="404" y="62" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="438" y="62" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="472" y="62" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="506" y="62" width="30" height="30" rx="5"/>
<rect class="fg-cell fg-cell--end" x="540" y="62" width="30" height="30" rx="5"/>
<rect class="fg-pill" x="15" y="8" width="60" height="24" rx="6"/>
<text class="fg-pilltext" x="45" y="24">begin</text>
<line class="fg-arrow" x1="45" y1="32" x2="45" y2="60" marker-end="url(#fig-be-arrow)"/>
<rect class="fg-pill" x="531" y="8" width="48" height="24" rx="6"/>
<text class="fg-pilltext" x="555" y="24">end</text>
<line class="fg-arrow" x1="555" y1="32" x2="555" y2="60" marker-end="url(#fig-be-arrow)"/>
<text class="fg-note fg-note--r" x="537" y="132">Past-the-last element</text>
<line class="fg-arrow" x1="555" y1="124" x2="555" y2="96" marker-end="url(#fig-be-arrow)"/>
</svg>
</div>
<p class="nj-caption" markdown>`cbegin()` points to the first element, like `begin()`, and `end()` to the position after
the last element; the dashed cell is the past-the-last position, which must not be dereferenced.</p>
## Return value
@@ -55,11 +88,11 @@ Constant.
## See also
- [begin](begin.md) returns an iterator to the first element
- [cend](cend.md) returns a const iterator to one past the last element
- [crbegin](crbegin.md) returns a const reverse iterator to the last element
- [`begin`](begin.md) - returns an iterator to the first element
- [`cend`](cend.md) - returns a const iterator to one past the last element
- [`crbegin`](crbegin.md) - returns a const reverse iterator to the last element
- [Iterators](../../features/iterators.md) - the article on iterators
- [basic_json_view::cbegin](../basic_json_view/cbegin.md) - the same iteration on a zero-copy view
- [`basic_json_view::cbegin`](../basic_json_view/cbegin.md) - the same iteration on a zero-copy view
## Version history
+3 -3
View File
@@ -1,5 +1,5 @@
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</code></pre></div> <p>Returns an iterator to the first element.</p> <p><img alt="Illustration from cppreference.com" src=../../../images/range-begin-end.svg></p> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <p>iterator to the first element</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">&para;</a></h2> <p>No-throw guarantee: this member function never throws exceptions.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">&para;</a></h2> <p>Constant.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The following code shows an example for <code>cbegin()</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>
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</code></pre></div> <p>Returns an iterator to the first element.</p> <div class=nj-fig-wrap> <p><svg class="nj-fig nj-fig--range" viewbox="0 0 600 150" role=img aria-labelledby=fig-be-title xmlns=http://www.w3.org/2000/svg> <title id=fig-be-title>A row of fifteen elements followed by a dashed past-the-last position. begin() points to the first element and end() points to the past-the-last position.</title> <defs><marker id=fig-be-arrow viewbox="0 0 10 10" refx=9 refy=5 markerwidth=7 markerheight=7 orient=auto><path class=fg-head d="M0 1 L10 5 L0 9 z"/></marker></defs> <rect class=fg-cell x=30 y=62 width=30 height=30 rx=5 /> <rect class=fg-cell x=64 y=62 width=30 height=30 rx=5 /> <rect class=fg-cell x=98 y=62 width=30 height=30 rx=5 /> <rect class=fg-cell x=132 y=62 width=30 height=30 rx=5 /> <rect class=fg-cell x=166 y=62 width=30 height=30 rx=5 /> <rect class=fg-cell x=200 y=62 width=30 height=30 rx=5 /> <rect class=fg-cell x=234 y=62 width=30 height=30 rx=5 /> <rect class=fg-cell x=268 y=62 width=30 height=30 rx=5 /> <rect class=fg-cell x=302 y=62 width=30 height=30 rx=5 /> <rect class=fg-cell x=336 y=62 width=30 height=30 rx=5 /> <rect class=fg-cell x=370 y=62 width=30 height=30 rx=5 /> <rect class=fg-cell x=404 y=62 width=30 height=30 rx=5 /> <rect class=fg-cell x=438 y=62 width=30 height=30 rx=5 /> <rect class=fg-cell x=472 y=62 width=30 height=30 rx=5 /> <rect class=fg-cell x=506 y=62 width=30 height=30 rx=5 /> <rect x=540 y=62 width=30 height=30 rx=5 class="fg-cell fg-cell--end"/> <rect class=fg-pill x=15 y=8 width=60 height=24 rx=6 /> <text class=fg-pilltext x=45 y=24>begin</text> <line class=fg-arrow x1=45 y1=32 x2=45 y2=60 marker-end=url(#fig-be-arrow) /> <rect class=fg-pill x=531 y=8 width=48 height=24 rx=6 /> <text class=fg-pilltext x=555 y=24>end</text> <line class=fg-arrow x1=555 y1=32 x2=555 y2=60 marker-end=url(#fig-be-arrow) /> <text class="fg-note fg-note--r" x=537 y=132>Past-the-last element</text> <line class=fg-arrow x1=555 y1=124 x2=555 y2=96 marker-end=url(#fig-be-arrow) /> </svg></p> </div> <p class=nj-caption><code>cbegin()</code> points to the first element, like <code>begin()</code>, and <code>end()</code> to the position after the last element; the dashed cell is the past-the-last position, which must not be dereferenced.</p> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <p>iterator to the first element</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">&para;</a></h2> <p>No-throw guarantee: this member function never throws exceptions.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">&para;</a></h2> <p>Constant.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The following code shows an example for <code>cbegin()</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>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
@@ -16,4 +16,4 @@
<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=o>*</span><span class=n>it</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>1</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=../begin/ >begin</a> returns an iterator to the first element</li> <li><a href=../cend/ >cend</a> returns a const iterator to one past the last element</li> <li><a href=../crbegin/ >crbegin</a> returns a const reverse iterator to the last element</li> <li><a href=../../../features/iterators/ >Iterators</a> - the article on iterators</li> <li><a href=../../basic_json_view/cbegin/ >basic_json_view::cbegin</a> - the same iteration on a 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 1.0.0.</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 21, 2026 08:21:27 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=../begin/ ><code>begin</code></a> - returns an iterator to the first element</li> <li><a href=../cend/ ><code>cend</code></a> - returns a const iterator to one past the last element</li> <li><a href=../crbegin/ ><code>crbegin</code></a> - returns a const reverse iterator to the last element</li> <li><a href=../../../features/iterators/ >Iterators</a> - the article on iterators</li> <li><a href=../../basic_json_view/cbegin/ ><code>basic_json_view::cbegin</code></a> - the same iteration on a 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 1.0.0.</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 27, 2026 06:41:42 UTC">October 27, 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> <nav class="md-footer__inner md-grid" aria-label=Footer> <a href=../boolean_t/ class="md-footer__link md-footer__link--prev" aria-label="Previous: boolean_t"> <div class="md-footer__button md-icon"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M20 11v2H8l5.5 5.5-1.42 1.42L4.16 12l7.92-7.92L13.5 5.5 8 11z"/></svg> </div> <div class=md-footer__title> <span class=md-footer__direction> Previous </span> <div class=md-ellipsis> boolean_t </div> </div> </a> <a href=../cbor_tag_handler_t/ class="md-footer__link md-footer__link--next" aria-label="Next: cbor_tag_handler_t"> <div class=md-footer__title> <span class=md-footer__direction> Next </span> <div class=md-ellipsis> cbor_tag_handler_t </div> </div> <div class="md-footer__button md-icon"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M4 11v2h12l-5.5 5.5 1.42 1.42L19.84 12l-7.92-7.92L10.5 5.5 16 11z"/></svg> </div> </a> </nav> <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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+6 -4
View File
@@ -6,6 +6,8 @@ const_iterator cbegin() const noexcept;
Returns an iterator to the first element.
`cbegin()` points to the first element, like `begin()`, and `end()` to the position after the last element; the dashed cell is the past-the-last position, which must not be dereferenced.
## Return value
iterator to the first element
@@ -51,11 +53,11 @@ Output:
## See also
- [begin](https://json.nlohmann.me/api/basic_json/begin/index.md) returns an iterator to the first element
- [cend](https://json.nlohmann.me/api/basic_json/cend/index.md) returns a const iterator to one past the last element
- [crbegin](https://json.nlohmann.me/api/basic_json/crbegin/index.md) returns a const reverse iterator to the last element
- [`begin`](https://json.nlohmann.me/api/basic_json/begin/index.md) - returns an iterator to the first element
- [`cend`](https://json.nlohmann.me/api/basic_json/cend/index.md) - returns a const iterator to one past the last element
- [`crbegin`](https://json.nlohmann.me/api/basic_json/crbegin/index.md) - returns a const reverse iterator to the last element
- [Iterators](https://json.nlohmann.me/features/iterators/index.md) - the article on iterators
- [basic_json_view::cbegin](https://json.nlohmann.me/api/basic_json_view/cbegin/index.md) - the same iteration on a zero-copy view
- [`basic_json_view::cbegin`](https://json.nlohmann.me/api/basic_json_view/cbegin/index.md) - the same iteration on a zero-copy view
## Version history
+3 -2
View File
@@ -73,8 +73,9 @@ store
## See also
- [from_cbor](from_cbor.md) deserializes a JSON value from CBOR
- [input_format_t](input_format_t.md) the enumeration of supported input formats
- [Binary values](../../features/binary_values.md) - how binary values and subtypes are handled
- [`from_cbor`](from_cbor.md) - deserializes a JSON value from CBOR
- [`input_format_t`](input_format_t.md) - the enumeration of supported input formats
- [CBOR](../../features/binary_formats/cbor.md) - the article on the CBOR format
## Version history
+2 -2
View File
@@ -1,4 +1,4 @@
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xmlns=http://www.w3.org/2000/svg viewbox="0 Line truncated
<span class=p>{</span>
<span class=w> </span><span class=n>error</span><span class=p>,</span>
<span class=w> </span><span class=n>ignore</span><span class=p>,</span>
@@ -35,4 +35,4 @@
</code></pre></div> <p>Output:</p> <div class=highlight><pre><span></span><code><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>.parse_error.</span><span class=mi>112</span><span class=p>]</span><span class=w> </span><span class=err>parse</span><span class=w> </span><span class=err>error</span><span class=w> </span><span class=err>a</span><span class=kc>t</span><span class=w> </span><span class=err>by</span><span class=kc>te</span><span class=w> </span><span class=mi>1</span><span class=p>:</span><span class=w> </span><span class=err>sy</span><span class=kc>nta</span><span class=err>x</span><span class=w> </span><span class=err>error</span><span class=w> </span><span class=err>while</span><span class=w> </span><span class=err>parsi</span><span class=kc>n</span><span class=err>g</span><span class=w> </span><span class=err>CBOR</span><span class=w> </span><span class=err>value</span><span class=p>:</span><span class=w> </span><span class=err>i</span><span class=kc>n</span><span class=err>valid</span><span class=w> </span><span class=err>by</span><span class=kc>te</span><span class=p>:</span><span class=w> </span><span class=mi>0</span><span class=err>xD</span><span class=mi>8</span>
<span class=p>{</span><span class=nt>"bytes"</span><span class=p>:[</span><span class=mi>202</span><span class=p>,</span><span class=mi>254</span><span class=p>,</span><span class=mi>186</span><span class=p>,</span><span class=mi>190</span><span class=p>],</span><span class=nt>"subtype"</span><span class=p>:</span><span class=kc>null</span><span class=p>}</span>
<span class=p>{</span><span class=nt>"bytes"</span><span class=p>:[</span><span class=mi>202</span><span class=p>,</span><span class=mi>254</span><span class=p>,</span><span class=mi>186</span><span class=p>,</span><span class=mi>190</span><span class=p>],</span><span class=nt>"subtype"</span><span class=p>:</span><span class=mi>66</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=../from_cbor/ >from_cbor</a> deserializes a <abbr title="JavaScript Object Notation">JSON</abbr> value from <abbr title="Concise Binary Object Representation">CBOR</abbr></li> <li><a href=../input_format_t/ >input_format_t</a> the enumeration of supported input formats</li> <li><a href=../../../features/binary_formats/cbor/ ><abbr title="Concise Binary Object Representation">CBOR</abbr></a> - the article on the <abbr title="Concise Binary Object Representation">CBOR</abbr> format</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. 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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/binary_values/ >Binary values</a> - how binary values and subtypes are handled</li> <li><a href=../from_cbor/ ><code>from_cbor</code></a> - deserializes a <abbr title="JavaScript Object Notation">JSON</abbr> value from <abbr title="Concise Binary Object Representation">CBOR</abbr></li> <li><a href=../input_format_t/ ><code>input_format_t</code></a> - the enumeration of supported input formats</li> <li><a href=../../../features/binary_formats/cbor/ ><abbr title="Concise Binary Object Representation">CBOR</abbr></a> - the article on the <abbr title="Concise Binary Object Representation">CBOR</abbr> format</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. 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+3 -2
View File
@@ -64,8 +64,9 @@ Output:
## See also
- [from_cbor](https://json.nlohmann.me/api/basic_json/from_cbor/index.md) deserializes a JSON value from CBOR
- [input_format_t](https://json.nlohmann.me/api/basic_json/input_format_t/index.md) the enumeration of supported input formats
- [Binary values](https://json.nlohmann.me/features/binary_values/index.md) - how binary values and subtypes are handled
- [`from_cbor`](https://json.nlohmann.me/api/basic_json/from_cbor/index.md) - deserializes a JSON value from CBOR
- [`input_format_t`](https://json.nlohmann.me/api/basic_json/input_format_t/index.md) - the enumeration of supported input formats
- [CBOR](https://json.nlohmann.me/features/binary_formats/cbor/index.md) - the article on the CBOR format
## Version history
+38 -5
View File
@@ -6,7 +6,40 @@ const_iterator cend() const noexcept;
Returns an iterator to one past the last element.
![Illustration from cppreference.com](../../images/range-begin-end.svg)
<div class="nj-fig-wrap" markdown>
<svg class="nj-fig nj-fig--range" viewBox="0 0 600 150" role="img" aria-labelledby="fig-be-title" xmlns="http://www.w3.org/2000/svg">
<title id="fig-be-title">A row of fifteen elements followed by a dashed past-the-last position. begin() points to the first element and end() points to the past-the-last position.</title>
<defs><marker id="fig-be-arrow" viewBox="0 0 10 10" refX="9" refY="5" markerWidth="7" markerHeight="7" orient="auto"><path class="fg-head" d="M0 1 L10 5 L0 9 z"/></marker></defs>
<rect class="fg-cell" x="30" y="62" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="64" y="62" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="98" y="62" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="132" y="62" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="166" y="62" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="200" y="62" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="234" y="62" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="268" y="62" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="302" y="62" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="336" y="62" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="370" y="62" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="404" y="62" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="438" y="62" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="472" y="62" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="506" y="62" width="30" height="30" rx="5"/>
<rect class="fg-cell fg-cell--end" x="540" y="62" width="30" height="30" rx="5"/>
<rect class="fg-pill" x="15" y="8" width="60" height="24" rx="6"/>
<text class="fg-pilltext" x="45" y="24">begin</text>
<line class="fg-arrow" x1="45" y1="32" x2="45" y2="60" marker-end="url(#fig-be-arrow)"/>
<rect class="fg-pill" x="531" y="8" width="48" height="24" rx="6"/>
<text class="fg-pilltext" x="555" y="24">end</text>
<line class="fg-arrow" x1="555" y1="32" x2="555" y2="60" marker-end="url(#fig-be-arrow)"/>
<text class="fg-note fg-note--r" x="537" y="132">Past-the-last element</text>
<line class="fg-arrow" x1="555" y1="124" x2="555" y2="96" marker-end="url(#fig-be-arrow)"/>
</svg>
</div>
<p class="nj-caption" markdown>`cend()` points to the position after the last element, like `end()`, and `begin()` to
the first element; the dashed cell is the past-the-last position, which must not be dereferenced.</p>
## Return value
@@ -58,11 +91,11 @@ Constant.
## See also
- [end](end.md) returns an iterator to one past the last element
- [cbegin](cbegin.md) returns a const iterator to the first element
- [crend](crend.md) returns a const reverse iterator to one before the first element
- [`end`](end.md) - returns an iterator to one past the last element
- [`cbegin`](cbegin.md) - returns a const iterator to the first element
- [`crend`](crend.md) - returns a const reverse iterator to one before the first element
- [Iterators](../../features/iterators.md) - the article on iterators
- [basic_json_view::cend](../basic_json_view/cend.md) - the same iteration on a zero-copy view
- [`basic_json_view::cend`](../basic_json_view/cend.md) - the same iteration on a zero-copy view
## Version history
+3 -3
View File
@@ -1,5 +1,5 @@
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</code></pre></div> <p>Returns an iterator to one past the last element.</p> <p><img alt="Illustration from cppreference.com" src=../../../images/range-begin-end.svg></p> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <p>iterator one past the last element</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">&para;</a></h2> <p>No-throw guarantee: this member function never throws exceptions.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">&para;</a></h2> <p>Constant.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The following code shows an example for <code>cend()</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=description content="JSON for Modern C++ is a header-only C++11 library that makes JSON a first-class data type."><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/cend/" rel="canonical"><link href=../cbor_tag_handler_t/ rel=prev><link href=../clear/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>cend - 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=../../../css/custom.css><link rel=stylesheet href=../../../css/brand.css><link rel=stylesheet href=../../../css/fig-sax.css><link rel=stylesheet href=../../../css/fig-jsonview.css><link rel=stylesheet 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</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> <img src=../../../images/wordmark-header.svg alt=logo> </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> cend </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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</code></pre></div> <p>Returns an iterator to one past the last element.</p> <div class=nj-fig-wrap> <p><svg class="nj-fig nj-fig--range" viewbox="0 0 600 150" role=img aria-labelledby=fig-be-title xmlns=http://www.w3.org/2000/svg> <title id=fig-be-title>A row of fifteen elements followed by a dashed past-the-last position. begin() points to the first element and end() points to the past-the-last position.</title> <defs><marker id=fig-be-arrow viewbox="0 0 10 10" refx=9 refy=5 markerwidth=7 markerheight=7 orient=auto><path class=fg-head d="M0 1 L10 5 L0 9 z"/></marker></defs> <rect class=fg-cell x=30 y=62 width=30 height=30 rx=5 /> <rect class=fg-cell x=64 y=62 width=30 height=30 rx=5 /> <rect class=fg-cell x=98 y=62 width=30 height=30 rx=5 /> <rect class=fg-cell x=132 y=62 width=30 height=30 rx=5 /> <rect class=fg-cell x=166 y=62 width=30 height=30 rx=5 /> <rect class=fg-cell x=200 y=62 width=30 height=30 rx=5 /> <rect class=fg-cell x=234 y=62 width=30 height=30 rx=5 /> <rect class=fg-cell x=268 y=62 width=30 height=30 rx=5 /> <rect class=fg-cell x=302 y=62 width=30 height=30 rx=5 /> <rect class=fg-cell x=336 y=62 width=30 height=30 rx=5 /> <rect class=fg-cell x=370 y=62 width=30 height=30 rx=5 /> <rect class=fg-cell x=404 y=62 width=30 height=30 rx=5 /> <rect class=fg-cell x=438 y=62 width=30 height=30 rx=5 /> <rect class=fg-cell x=472 y=62 width=30 height=30 rx=5 /> <rect class=fg-cell x=506 y=62 width=30 height=30 rx=5 /> <rect x=540 y=62 width=30 height=30 rx=5 class="fg-cell fg-cell--end"/> <rect class=fg-pill x=15 y=8 width=60 height=24 rx=6 /> <text class=fg-pilltext x=45 y=24>begin</text> <line class=fg-arrow x1=45 y1=32 x2=45 y2=60 marker-end=url(#fig-be-arrow) /> <rect class=fg-pill x=531 y=8 width=48 height=24 rx=6 /> <text class=fg-pilltext x=555 y=24>end</text> <line class=fg-arrow x1=555 y1=32 x2=555 y2=60 marker-end=url(#fig-be-arrow) /> <text class="fg-note fg-note--r" x=537 y=132>Past-the-last element</text> <line class=fg-arrow x1=555 y1=124 x2=555 y2=96 marker-end=url(#fig-be-arrow) /> </svg></p> </div> <p class=nj-caption><code>cend()</code> points to the position after the last element, like <code>end()</code>, and <code>begin()</code> to the first element; the dashed cell is the past-the-last position, which must not be dereferenced.</p> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <p>iterator one past the last element</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">&para;</a></h2> <p>No-throw guarantee: this member function never throws exceptions.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">&para;</a></h2> <p>Constant.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The following code shows an example for <code>cend()</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>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
@@ -19,4 +19,4 @@
<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=o>*</span><span class=n>it</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>5</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=../end/ >end</a> returns an iterator to one past the last element</li> <li><a href=../cbegin/ >cbegin</a> returns a const iterator to the first element</li> <li><a href=../crend/ >crend</a> returns a const reverse iterator to one before the first element</li> <li><a href=../../../features/iterators/ >Iterators</a> - the article on iterators</li> <li><a href=../../basic_json_view/cend/ >basic_json_view::cend</a> - the same iteration on a 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 1.0.0.</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 21, 2026 08:21:27 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=../end/ ><code>end</code></a> - returns an iterator to one past the last element</li> <li><a href=../cbegin/ ><code>cbegin</code></a> - returns a const iterator to the first element</li> <li><a href=../crend/ ><code>crend</code></a> - returns a const reverse iterator to one before the first element</li> <li><a href=../../../features/iterators/ >Iterators</a> - the article on iterators</li> <li><a href=../../basic_json_view/cend/ ><code>basic_json_view::cend</code></a> - the same iteration on a 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 1.0.0.</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 27, 2026 06:41:42 UTC">October 27, 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> <nav class="md-footer__inner md-grid" aria-label=Footer> <a href=../cbor_tag_handler_t/ class="md-footer__link md-footer__link--prev" aria-label="Previous: cbor_tag_handler_t"> <div class="md-footer__button md-icon"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M20 11v2H8l5.5 5.5-1.42 1.42L4.16 12l7.92-7.92L13.5 5.5 8 11z"/></svg> </div> <div class=md-footer__title> <span class=md-footer__direction> Previous </span> <div class=md-ellipsis> cbor_tag_handler_t </div> </div> </a> <a href=../clear/ class="md-footer__link md-footer__link--next" aria-label="Next: clear"> <div class=md-footer__title> <span class=md-footer__direction> Next </span> <div class=md-ellipsis> clear </div> </div> <div class="md-footer__button md-icon"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M4 11v2h12l-5.5 5.5 1.42 1.42L19.84 12l-7.92-7.92L10.5 5.5 16 11z"/></svg> </div> </a> </nav> <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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+6 -4
View File
@@ -6,6 +6,8 @@ const_iterator cend() const noexcept;
Returns an iterator to one past the last element.
`cend()` points to the position after the last element, like `end()`, and `begin()` to the first element; the dashed cell is the past-the-last position, which must not be dereferenced.
## Return value
iterator one past the last element
@@ -54,11 +56,11 @@ Output:
## See also
- [end](https://json.nlohmann.me/api/basic_json/end/index.md) returns an iterator to one past the last element
- [cbegin](https://json.nlohmann.me/api/basic_json/cbegin/index.md) returns a const iterator to the first element
- [crend](https://json.nlohmann.me/api/basic_json/crend/index.md) returns a const reverse iterator to one before the first element
- [`end`](https://json.nlohmann.me/api/basic_json/end/index.md) - returns an iterator to one past the last element
- [`cbegin`](https://json.nlohmann.me/api/basic_json/cbegin/index.md) - returns a const iterator to the first element
- [`crend`](https://json.nlohmann.me/api/basic_json/crend/index.md) - returns a const reverse iterator to one before the first element
- [Iterators](https://json.nlohmann.me/features/iterators/index.md) - the article on iterators
- [basic_json_view::cend](https://json.nlohmann.me/api/basic_json_view/cend/index.md) - the same iteration on a zero-copy view
- [`basic_json_view::cend`](https://json.nlohmann.me/api/basic_json_view/cend/index.md) - the same iteration on a zero-copy view
## Version history
+3 -2
View File
@@ -95,8 +95,9 @@ All iterators, pointers, and references related to this container are invalidate
## See also
- [erase](erase.md) removes elements from a JSON value
- [empty](empty.md) checks whether the JSON value has no elements
- [`erase`](erase.md) - removes elements from a JSON value
- [`empty`](empty.md) - checks whether the JSON value has no elements
- [Modifying values](../../features/modifying_values.md) - the article on modifying values
## Version history
+2 -2
View File
@@ -1,4 +1,4 @@
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</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> <img src=../../../images/wordmark-header.svg alt=logo> </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> clear </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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</code></pre></div> <p>Clears the content of a <abbr title="JavaScript Object Notation">JSON</abbr> value and resets it to the default value as if <a href=../basic_json/ ><code>basic_json(value_t)</code></a> would have been called with the current value type from <a href=../type/ ><code>type()</code></a>:</p> <table> <thead> <tr> <th>Value type</th> <th>initial value</th> </tr> </thead> <tbody> <tr> <td>null</td> <td><code>null</code></td> </tr> <tr> <td>boolean</td> <td><code>false</code></td> </tr> <tr> <td>string</td> <td><code>""</code></td> </tr> <tr> <td>number</td> <td><code>0</code></td> </tr> <tr> <td>binary</td> <td>An empty byte vector with no subtype</td> </tr> <tr> <td>object</td> <td><code>{}</code></td> </tr> <tr> <td>array</td> <td><code>[]</code></td> </tr> </tbody> </table> <p>Has the same effect as calling</p> <div class=highlight><pre><span></span><code><span class=o>*</span><span class=k>this</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>basic_json</span><span class=p>(</span><span class=n>type</span><span class=p>());</span>
</code></pre></div> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">&para;</a></h2> <p>No-throw guarantee: this function never throws exceptions.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">&para;</a></h2> <p>Linear in the size of the <abbr title="JavaScript Object Notation">JSON</abbr> value.</p> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <p>All iterators, pointers, and references related to this container are invalidated.</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 the effect of <code>clear()</code> to different <abbr title="JavaScript Object Notation">JSON</abbr> types.</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>
@@ -41,4 +41,4 @@
<span class=p>{}</span>
<span class=p>[]</span>
<span class=s2>""</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=../erase/ >erase</a> removes elements from a <abbr title="JavaScript Object Notation">JSON</abbr> value</li> <li><a href=../empty/ >empty</a> checks whether the <abbr title="JavaScript Object Notation">JSON</abbr> value has no elements</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 1.0.0.</li> <li>Added support for binary types in version 3.8.0.</li> <li>Fixed 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> to also clear the subtype of a binary value; before, the subtype was left unchanged.</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=../erase/ ><code>erase</code></a> - removes elements from a <abbr title="JavaScript Object Notation">JSON</abbr> value</li> <li><a href=../empty/ ><code>empty</code></a> - checks whether the <abbr title="JavaScript Object Notation">JSON</abbr> value has no elements</li> <li><a href=../../../features/modifying_values/ >Modifying values</a> - the article on modifying values</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 1.0.0.</li> <li>Added support for binary types in version 3.8.0.</li> <li>Fixed 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> to also clear the subtype of a binary value; before, the subtype was left unchanged.</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 27, 2026 06:41:42 UTC">October 27, 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> <nav class="md-footer__inner md-grid" aria-label=Footer> <a href=../cend/ class="md-footer__link md-footer__link--prev" aria-label="Previous: cend"> <div class="md-footer__button md-icon"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M20 11v2H8l5.5 5.5-1.42 1.42L4.16 12l7.92-7.92L13.5 5.5 8 11z"/></svg> </div> <div class=md-footer__title> <span class=md-footer__direction> Previous </span> <div class=md-ellipsis> cend </div> </div> </a> <a href=../contains/ class="md-footer__link md-footer__link--next" aria-label="Next: contains"> <div class=md-footer__title> <span class=md-footer__direction> Next </span> <div class=md-ellipsis> contains </div> </div> <div class="md-footer__button md-icon"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M4 11v2h12l-5.5 5.5 1.42 1.42L19.84 12l-7.92-7.92L10.5 5.5 16 11z"/></svg> </div> </a> </nav> <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
@@ -91,8 +91,9 @@ false
## See also
- [erase](https://json.nlohmann.me/api/basic_json/erase/index.md) removes elements from a JSON value
- [empty](https://json.nlohmann.me/api/basic_json/empty/index.md) checks whether the JSON value has no elements
- [`erase`](https://json.nlohmann.me/api/basic_json/erase/index.md) - removes elements from a JSON value
- [`empty`](https://json.nlohmann.me/api/basic_json/empty/index.md) - checks whether the JSON value has no elements
- [Modifying values](https://json.nlohmann.me/features/modifying_values/index.md) - the article on modifying values
## Version history
+4 -3
View File
@@ -221,9 +221,10 @@ Strong exception safety: if an exception occurs, the original value stays intact
## See also
- [find](find.md) find a value in an object
- [count](count.md) returns the number of occurrences of a key
- [basic_json_view::contains](../basic_json_view/contains.md) - the same check on a zero-copy view
- [`find`](find.md) - find a value in an object
- [`count`](count.md) - returns the number of occurrences of a key
- [`basic_json_view::contains`](../basic_json_view/contains.md) - the same check on a zero-copy view
- [Element Access](../../features/element_access/index.md#does-this-key-exist) - how to test whether a key exists
## Version history
+2 -2
View File
@@ -1,4 +1,4 @@
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<span class=kt>bool</span><span class=w> </span><span class=nf>contains</span><span class=p>(</span><span class=k>const</span><span class=w> </span><span class=k>typename</span><span class=w> </span><span class=nc>object_t</span><span class=o>::</span><span class=n>key_type</span><span class=o>&amp;</span><span class=w> </span><span class=n>key</span><span class=p>)</span><span class=w> </span><span class=k>const</span><span class=p>;</span>
<span class=c1>// (2)</span>
@@ -91,4 +91,4 @@
<span class=kc>false</span>
<span class=kc>false</span>
<span class=kc>false</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=../find/ >find</a> find a value in an object</li> <li><a href=../count/ >count</a> returns the number of occurrences of a key</li> <li><a href=../../basic_json_view/contains/ >basic_json_view::contains</a> - the same check on a zero-copy view</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 3.11.0.</li> <li>Added in version 3.6.0. Extended template <code>KeyType</code> to support comparable types in version 3.11.0. Support for keys convertible to <code>std::string_view</code> 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>, consistently across the lookup functions.</li> <li>Added in version 3.7.0.</li> <li>Deleted overloads for integral key types 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> to reject such calls at compile time instead of causing undefined behavior at runtime.</li> </ol> <!-- 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 16:11:46 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://fontaweLine 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=../find/ ><code>find</code></a> - find a value in an object</li> <li><a href=../count/ ><code>count</code></a> - returns the number of occurrences of a key</li> <li><a href=../../basic_json_view/contains/ ><code>basic_json_view::contains</code></a> - the same check on a zero-copy view</li> <li><a href=../../../features/element_access/#does-this-key-exist>Element Access</a> - how to test whether a key exists</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 3.11.0.</li> <li>Added in version 3.6.0. Extended template <code>KeyType</code> to support comparable types in version 3.11.0. Support for keys convertible to <code>std::string_view</code> 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>, consistently across the lookup functions.</li> <li>Added in version 3.7.0.</li> <li>Deleted overloads for integral key types 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> to reject such calls at compile time instead of causing undefined behavior at runtime.</li> </ol> <!-- 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 27, 2026 06:41:42 UTC">October 27, 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> <nav class="md-footer__inner md-grid" aria-label=Footer> <a href=../clear/ class="md-footer__link md-footer__link--prev" aria-label="Previous: clear"> <div class="md-footer__button md-icon"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M20 11v2H8l5.5 5.5-1.42 1.42L4.16 12l7.92-7.92L13.5 5.5 8 11z"/></svg> </div> <div class=md-footer__title> <span class=md-footer__direction> Previous </span> <div class=md-ellipsis> clear </div> </div> </a> <a href=../count/ class="md-footer__link md-footer__link--next" aria-label="Next: count"> <div class=md-footer__title> <span class=md-footer__direction> Next </span> <div class=md-ellipsis> count </div> </div> <div class="md-footer__button md-icon"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M4 11v2h12l-5.5 5.5 1.42 1.42L19.84 12l-7.92-7.92L10.5 5.5 16 11z"/></svg> </div> </a> </nav> <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-Line truncated
+4 -3
View File
@@ -194,9 +194,10 @@ false
## See also
- [find](https://json.nlohmann.me/api/basic_json/find/index.md) find a value in an object
- [count](https://json.nlohmann.me/api/basic_json/count/index.md) returns the number of occurrences of a key
- [basic_json_view::contains](https://json.nlohmann.me/api/basic_json_view/contains/index.md) - the same check on a zero-copy view
- [`find`](https://json.nlohmann.me/api/basic_json/find/index.md) - find a value in an object
- [`count`](https://json.nlohmann.me/api/basic_json/count/index.md) - returns the number of occurrences of a key
- [`basic_json_view::contains`](https://json.nlohmann.me/api/basic_json_view/contains/index.md) - the same check on a zero-copy view
- [Element Access](https://json.nlohmann.me/features/element_access/#does-this-key-exist) - how to test whether a key exists
## Version history
+4 -3
View File
@@ -127,9 +127,10 @@ Logarithmic in the size of the JSON object.
## See also
- [find](find.md) find a value in an object
- [contains](contains.md) checks whether a key exists
- [basic_json_view::count](../basic_json_view/count.md) - the same check on a zero-copy view
- [`find`](find.md) - find a value in an object
- [`contains`](contains.md) - checks whether a key exists
- [`basic_json_view::count`](../basic_json_view/count.md) - the same check on a zero-copy view
- [Element Access](../../features/element_access/index.md#does-this-key-exist) - how to test whether a key exists
## Version history
+2 -2
View File
@@ -1,4 +1,4 @@
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0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0Line truncated
<span class=n>size_type</span><span class=w> </span><span class=nf>count</span><span class=p>(</span><span class=k>const</span><span class=w> </span><span class=k>typename</span><span class=w> </span><span class=nc>object_t</span><span class=o>::</span><span class=n>key_type</span><span class=o>&amp;</span><span class=w> </span><span class=n>key</span><span class=p>)</span><span class=w> </span><span class=k>const</span><span class=p>;</span>
<span class=c1>// (2)</span>
@@ -50,4 +50,4 @@
<span class=p>}</span>
</code></pre></div> <p>Output:</p> <div class=highlight><pre><span></span><code><span class=kc>nu</span><span class=err>mber</span><span class=w> </span><span class=err>o</span><span class=kc>f</span><span class=w> </span><span class=err>eleme</span><span class=kc>nts</span><span class=w> </span><span class=err>wi</span><span class=kc>t</span><span class=err>h</span><span class=w> </span><span class=err>key</span><span class=w> </span><span class=nt>"two"</span><span class=p>:</span><span class=w> </span><span class=mi>1</span>
<span class=kc>nu</span><span class=err>mber</span><span class=w> </span><span class=err>o</span><span class=kc>f</span><span class=w> </span><span class=err>eleme</span><span class=kc>nts</span><span class=w> </span><span class=err>wi</span><span class=kc>t</span><span class=err>h</span><span class=w> </span><span class=err>key</span><span class=w> </span><span class=nt>"three"</span><span class=p>:</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=../find/ >find</a> find a value in an object</li> <li><a href=../contains/ >contains</a> checks whether a key exists</li> <li><a href=../../basic_json_view/count/ >basic_json_view::count</a> - the same check on a zero-copy view</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 3.11.0.</li> <li>Added in version 1.0.0. Changed to support comparable key types in version 3.11.0. Support for keys convertible to <code>std::string_view</code> 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>, consistently across the lookup functions.</li> <li>Deleted overload for integral key types 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> to reject such calls at compile time instead of causing undefined behavior at runtime.</li> </ol> <!-- 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 24, 2026 15:57:44 UTC">October 24, 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 LicenLine 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=../find/ ><code>find</code></a> - find a value in an object</li> <li><a href=../contains/ ><code>contains</code></a> - checks whether a key exists</li> <li><a href=../../basic_json_view/count/ ><code>basic_json_view::count</code></a> - the same check on a zero-copy view</li> <li><a href=../../../features/element_access/#does-this-key-exist>Element Access</a> - how to test whether a key exists</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 3.11.0.</li> <li>Added in version 1.0.0. Changed to support comparable key types in version 3.11.0. Support for keys convertible to <code>std::string_view</code> 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>, consistently across the lookup functions.</li> <li>Deleted overload for integral key types 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> to reject such calls at compile time instead of causing undefined behavior at runtime.</li> </ol> <!-- 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 27, 2026 06:41:42 UTC">October 27, 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> <nav class="md-footer__inner md-grid" aria-label=Footer> <a href=../contains/ class="md-footer__link md-footer__link--prev" aria-label="Previous: contains"> <div class="md-footer__button md-icon"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M20 11v2H8l5.5 5.5-1.42 1.42L4.16 12l7.92-7.92L13.5 5.5 8 11z"/></svg> </div> <div class=md-footer__title> <span class=md-footer__direction> Previous </span> <div class=md-ellipsis> contains </div> </div> </a> <a href=../crbegin/ class="md-footer__link md-footer__link--next" aria-label="Next: crbegin"> <div class=md-footer__title> <span class=md-footer__direction> Next </span> <div class=md-ellipsis> crbegin </div> </div> <div class="md-footer__button md-icon"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M4 11v2h12l-5.5 5.5 1.42 1.42L19.84 12l-7.92-7.92L10.5 5.5 16 11z"/></svg> </div> </a> </nav> <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 Line truncated
+4 -3
View File
@@ -112,9 +112,10 @@ number of elements with key "three": 0
## See also
- [find](https://json.nlohmann.me/api/basic_json/find/index.md) find a value in an object
- [contains](https://json.nlohmann.me/api/basic_json/contains/index.md) checks whether a key exists
- [basic_json_view::count](https://json.nlohmann.me/api/basic_json_view/count/index.md) - the same check on a zero-copy view
- [`find`](https://json.nlohmann.me/api/basic_json/find/index.md) - find a value in an object
- [`contains`](https://json.nlohmann.me/api/basic_json/contains/index.md) - checks whether a key exists
- [`basic_json_view::count`](https://json.nlohmann.me/api/basic_json_view/count/index.md) - the same check on a zero-copy view
- [Element Access](https://json.nlohmann.me/features/element_access/#does-this-key-exist) - how to test whether a key exists
## Version history
+64 -4
View File
@@ -6,7 +6,67 @@ const_reverse_iterator crbegin() const noexcept;
Returns an iterator to the reverse-beginning; that is, the last element.
![Illustration from cppreference.com](../../images/range-rbegin-rend.svg)
<div class="nj-fig-wrap" markdown>
<svg class="nj-fig nj-fig--range" viewBox="0 0 600 236" role="img" aria-labelledby="fig-rbe-title" xmlns="http://www.w3.org/2000/svg">
<title id="fig-rbe-title">Two rows of sixteen cells. The upper row shows the reversed sequence: rend() points to a dashed position before the first element and rbegin() to the last element. The lower row shows the forward sequence: begin() points to the first element and end() to a dashed position after the last element. A reverse iterator stores an iterator to the next element, so rend() corresponds to begin() and rbegin() to end().</title>
<defs><marker id="fig-rbe-arrow" viewBox="0 0 10 10" refX="9" refY="5" markerWidth="7" markerHeight="7" orient="auto"><path class="fg-head" d="M0 1 L10 5 L0 9 z"/></marker></defs>
<rect class="fg-cell fg-cell--end" x="30" y="62" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="64" y="62" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="98" y="62" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="132" y="62" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="166" y="62" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="200" y="62" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="234" y="62" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="268" y="62" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="302" y="62" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="336" y="62" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="370" y="62" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="404" y="62" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="438" y="62" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="472" y="62" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="506" y="62" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="540" y="62" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="30" y="144" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="64" y="144" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="98" y="144" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="132" y="144" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="166" y="144" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="200" y="144" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="234" y="144" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="268" y="144" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="302" y="144" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="336" y="144" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="370" y="144" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="404" y="144" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="438" y="144" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="472" y="144" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="506" y="144" width="30" height="30" rx="5"/>
<rect class="fg-cell fg-cell--end" x="540" y="144" width="30" height="30" rx="5"/>
<rect class="fg-pill" x="19" y="8" width="52" height="24" rx="6"/>
<text class="fg-pilltext" x="45" y="24">rend</text>
<line class="fg-arrow" x1="45" y1="32" x2="45" y2="60" marker-end="url(#fig-rbe-arrow)"/>
<rect class="fg-pill" x="521" y="8" width="68" height="24" rx="6"/>
<text class="fg-pilltext" x="555" y="24">rbegin</text>
<line class="fg-arrow" x1="555" y1="32" x2="555" y2="60" marker-end="url(#fig-rbe-arrow)"/>
<text class="fg-note fg-note--l" x="81" y="24">Reverse past-the-last element</text>
<line class="fg-arrow fg-arrow--dash" x1="45" y1="94" x2="45" y2="142"/>
<line class="fg-arrow fg-arrow--dash" x1="555" y1="94" x2="555" y2="142"/>
<text class="fg-note" x="300" y="123">A reverse iterator stores an iterator to the next element</text>
<text class="fg-note" x="300" y="141" dy="0" style="display:none"></text>
<rect class="fg-pill" x="15" y="204" width="60" height="24" rx="6"/>
<text class="fg-pilltext" x="45" y="220">begin</text>
<line class="fg-arrow" x1="45" y1="202" x2="45" y2="178" marker-end="url(#fig-rbe-arrow)"/>
<rect class="fg-pill" x="531" y="204" width="48" height="24" rx="6"/>
<text class="fg-pilltext" x="555" y="220">end</text>
<line class="fg-arrow" x1="555" y1="202" x2="555" y2="178" marker-end="url(#fig-rbe-arrow)"/>
<text class="fg-note fg-note--r" x="515" y="221">Past-the-last element</text>
</svg>
</div>
<p class="nj-caption" markdown>`crbegin()` points to the last element, like `rbegin()`, and `rend()` to the position
before the first element. The upper row is the reversed sequence and the lower row the forward sequence; dashed arrows
link each reverse iterator to the forward iterator it stores, and dashed cells are past-the-last positions.</p>
## Return value
@@ -55,9 +115,9 @@ Constant.
## See also
- [crend](crend.md) returns a const reverse iterator to one before the first element
- [rbegin](rbegin.md) returns a reverse iterator to the last element
- [cbegin](cbegin.md) returns a const iterator to the first element
- [`crend`](crend.md) - returns a const reverse iterator to one before the first element
- [`rbegin`](rbegin.md) - returns a reverse iterator to the last element
- [`cbegin`](cbegin.md) - returns a const iterator to the first element
- [Iterators](../../features/iterators.md) - the article on iterators
## Version history
+3 -3
View File
@@ -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/basic_json/crbegin/" rel="canonical"><link href=../count/ rel=prev><link href=../crend/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>crbegin - 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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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> </label>Line truncated
</code></pre></div> <p>Returns an iterator to the reverse-beginning; that is, the last element.</p> <p><img alt="Illustration from cppreference.com" src=../../../images/range-rbegin-rend.svg></p> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <p>reverse iterator to the last element</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">&para;</a></h2> <p>No-throw guarantee: this member function never throws exceptions.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">&para;</a></h2> <p>Constant.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The following code shows an example for <code>crbegin()</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=description content="JSON for Modern C++ is a header-only C++11 library that makes JSON a first-class data type."><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/crbegin/" rel="canonical"><link href=../count/ rel=prev><link href=../crend/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>crbegin - 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=../../../css/custom.css><link rel=stylesheet href=../../../css/brand.css><link rel=stylesheet href=../../../css/fig-sax.css><link rel=stylesheet href=../../../css/fig-jsonview.css><link rel=stylesheet 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</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> <img src=../../../images/wordmark-header.svg alt=logo> </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> crbegin </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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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.Line truncated
</code></pre></div> <p>Returns an iterator to the reverse-beginning; that is, the last element.</p> <div class=nj-fig-wrap> <p><svg class="nj-fig nj-fig--range" viewbox="0 0 600 236" role=img aria-labelledby=fig-rbe-title xmlns=http://www.w3.org/2000/svg> <title id=fig-rbe-title>Two rows of sixteen cells. The upper row shows the reversed sequence: rend() points to a dashed position before the first element and rbegin() to the last element. The lower row shows the forward sequence: begin() points to the first element and end() to a dashed position after the last element. A reverse iterator stores an iterator to the next element, so rend() corresponds to begin() and rbegin() to end().</title> <defs><marker id=fig-rbe-arrow viewbox="0 0 10 10" refx=9 refy=5 markerwidth=7 markerheight=7 orient=auto><path class=fg-head d="M0 1 L10 5 L0 9 z"/></marker></defs> <rect x=30 y=62 width=30 height=30 rx=5 class="fg-cell fg-cell--end"/> <rect class=fg-cell x=64 y=62 width=30 height=30 rx=5 /> <rect class=fg-cell x=98 y=62 width=30 height=30 rx=5 /> <rect class=fg-cell x=132 y=62 width=30 height=30 rx=5 /> <rect class=fg-cell x=166 y=62 width=30 height=30 rx=5 /> <rect class=fg-cell x=200 y=62 width=30 height=30 rx=5 /> <rect class=fg-cell x=234 y=62 width=30 height=30 rx=5 /> <rect class=fg-cell x=268 y=62 width=30 height=30 rx=5 /> <rect class=fg-cell x=302 y=62 width=30 height=30 rx=5 /> <rect class=fg-cell x=336 y=62 width=30 height=30 rx=5 /> <rect class=fg-cell x=370 y=62 width=30 height=30 rx=5 /> <rect class=fg-cell x=404 y=62 width=30 height=30 rx=5 /> <rect class=fg-cell x=438 y=62 width=30 height=30 rx=5 /> <rect class=fg-cell x=472 y=62 width=30 height=30 rx=5 /> <rect class=fg-cell x=506 y=62 width=30 height=30 rx=5 /> <rect class=fg-cell x=540 y=62 width=30 height=30 rx=5 /> <rect class=fg-cell x=30 y=144 width=30 height=30 rx=5 /> <rect class=fg-cell x=64 y=144 width=30 height=30 rx=5 /> <rect class=fg-cell x=98 y=144 width=30 height=30 rx=5 /> <rect class=fg-cell x=132 y=144 width=30 height=30 rx=5 /> <rect class=fg-cell x=166 y=144 width=30 height=30 rx=5 /> <rect class=fg-cell x=200 y=144 width=30 height=30 rx=5 /> <rect class=fg-cell x=234 y=144 width=30 height=30 rx=5 /> <rect class=fg-cell x=268 y=144 width=30 height=30 rx=5 /> <rect class=fg-cell x=302 y=144 width=30 height=30 rx=5 /> <rect class=fg-cell x=336 y=144 width=30 height=30 rx=5 /> <rect class=fg-cell x=370 y=144 width=30 height=30 rx=5 /> <rect class=fg-cell x=404 y=144 width=30 height=30 rx=5 /> <rect class=fg-cell x=438 y=144 width=30 height=30 rx=5 /> <rect class=fg-cell x=472 y=144 width=30 height=30 rx=5 /> <rect class=fg-cell x=506 y=144 width=30 height=30 rx=5 /> <rect x=540 y=144 width=30 height=30 rx=5 class="fg-cell fg-cell--end"/> <rect class=fg-pill x=19 y=8 width=52 height=24 rx=6 /> <text class=fg-pilltext x=45 y=24>rend</text> <line class=fg-arrow x1=45 y1=32 x2=45 y2=60 marker-end=url(#fig-rbe-arrow) /> <rect class=fg-pill x=521 y=8 width=68 height=24 rx=6 /> <text class=fg-pilltext x=555 y=24>rbegin</text> <line class=fg-arrow x1=555 y1=32 x2=555 y2=60 marker-end=url(#fig-rbe-arrow) /> <text class="fg-note fg-note--l" x=81 y=24>Reverse past-the-last element</text> <line x1=45 y1=94 x2=45 y2=142 class="fg-arrow fg-arrow--dash"/> <line x1=555 y1=94 x2=555 y2=142 class="fg-arrow fg-arrow--dash"/> <text class=fg-note x=300 y=123>A reverse iterator stores an iterator to the next element</text> <text class=fg-note x=300 y=141 dy=0 style=display:none></text> <rect class=fg-pill x=15 y=204 width=60 height=24 rx=6 /> <text class=fg-pilltext x=45 y=220>begin</text> <line class=fg-arrow x1=45 y1=202 x2=45 y2=178 marker-end=url(#fig-rbe-arrow) /> <rect class=fg-pill x=531 y=204 width=48 height=24 rx=6 /> <text class=fg-pilltext x=555 y=220>end</text> <line class=fg-arrow x1=555 y1=202 x2=555 y2=178 marker-end=url(#fig-rbe-arrow) /> <text class="fg-note fg-note--r" x=515 y=221>Past-the-last element</text> </svg></p> </div> <p class=nj-caption><code>crbegin()</code> points to the last element, like <code>rbegin()</code>, and <code>rend()</code> to the position before the first element. The upper row is the reversed sequence and the lower row the forward sequence; dashed arrows link each reverse iterator to the forward iterator it stores, and dashed cells are past-the-last positions.</p> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <p>reverse iterator to the last element</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">&para;</a></h2> <p>No-throw guarantee: this member function never throws exceptions.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">&para;</a></h2> <p>Constant.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The following code shows an example foLine truncated
<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>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
@@ -16,4 +16,4 @@
<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=o>*</span><span class=n>it</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>5</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=../crend/ >crend</a> returns a const reverse iterator to one before the first element</li> <li><a href=../rbegin/ >rbegin</a> returns a reverse iterator to the last element</li> <li><a href=../cbegin/ >cbegin</a> returns a const iterator to the first element</li> <li><a href=../../../features/iterators/ >Iterators</a> - the article on iterators</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 1.0.0.</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=../crend/ ><code>crend</code></a> - returns a const reverse iterator to one before the first element</li> <li><a href=../rbegin/ ><code>rbegin</code></a> - returns a reverse iterator to the last element</li> <li><a href=../cbegin/ ><code>cbegin</code></a> - returns a const iterator to the first element</li> <li><a href=../../../features/iterators/ >Iterators</a> - the article on iterators</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 1.0.0.</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 27, 2026 06:41:42 UTC">October 27, 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> <nav class="md-footer__inner md-grid" aria-label=Footer> <a href=../count/ class="md-footer__link md-footer__link--prev" aria-label="Previous: count"> <div class="md-footer__button md-icon"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M20 11v2H8l5.5 5.5-1.42 1.42L4.16 12l7.92-7.92L13.5 5.5 8 11z"/></svg> </div> <div class=md-footer__title> <span class=md-footer__direction> Previous </span> <div class=md-ellipsis> count </div> </div> </a> <a href=../crend/ class="md-footer__link md-footer__link--next" aria-label="Next: crend"> <div class=md-footer__title> <span class=md-footer__direction> Next </span> <div class=md-ellipsis> crend </div> </div> <div class="md-footer__button md-icon"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M4 11v2h12l-5.5 5.5 1.42 1.42L19.84 12l-7.92-7.92L10.5 5.5 16 11z"/></svg> </div> </a> </nav> <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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+5 -3
View File
@@ -6,6 +6,8 @@ const_reverse_iterator crbegin() const noexcept;
Returns an iterator to the reverse-beginning; that is, the last element.
`crbegin()` points to the last element, like `rbegin()`, and `rend()` to the position before the first element. The upper row is the reversed sequence and the lower row the forward sequence; dashed arrows link each reverse iterator to the forward iterator it stores, and dashed cells are past-the-last positions.
## Return value
reverse iterator to the last element
@@ -51,9 +53,9 @@ Output:
## See also
- [crend](https://json.nlohmann.me/api/basic_json/crend/index.md) returns a const reverse iterator to one before the first element
- [rbegin](https://json.nlohmann.me/api/basic_json/rbegin/index.md) returns a reverse iterator to the last element
- [cbegin](https://json.nlohmann.me/api/basic_json/cbegin/index.md) returns a const iterator to the first element
- [`crend`](https://json.nlohmann.me/api/basic_json/crend/index.md) - returns a const reverse iterator to one before the first element
- [`rbegin`](https://json.nlohmann.me/api/basic_json/rbegin/index.md) - returns a reverse iterator to the last element
- [`cbegin`](https://json.nlohmann.me/api/basic_json/cbegin/index.md) - returns a const iterator to the first element
- [Iterators](https://json.nlohmann.me/features/iterators/index.md) - the article on iterators
## Version history
+64 -4
View File
@@ -7,7 +7,67 @@ const_reverse_iterator crend() const noexcept;
Returns an iterator to the reverse-end; that is, one before the first element. This element acts as a placeholder,
attempting to access it results in undefined behavior.
![Illustration from cppreference.com](../../images/range-rbegin-rend.svg)
<div class="nj-fig-wrap" markdown>
<svg class="nj-fig nj-fig--range" viewBox="0 0 600 236" role="img" aria-labelledby="fig-rbe-title" xmlns="http://www.w3.org/2000/svg">
<title id="fig-rbe-title">Two rows of sixteen cells. The upper row shows the reversed sequence: rend() points to a dashed position before the first element and rbegin() to the last element. The lower row shows the forward sequence: begin() points to the first element and end() to a dashed position after the last element. A reverse iterator stores an iterator to the next element, so rend() corresponds to begin() and rbegin() to end().</title>
<defs><marker id="fig-rbe-arrow" viewBox="0 0 10 10" refX="9" refY="5" markerWidth="7" markerHeight="7" orient="auto"><path class="fg-head" d="M0 1 L10 5 L0 9 z"/></marker></defs>
<rect class="fg-cell fg-cell--end" x="30" y="62" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="64" y="62" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="98" y="62" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="132" y="62" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="166" y="62" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="200" y="62" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="234" y="62" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="268" y="62" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="302" y="62" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="336" y="62" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="370" y="62" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="404" y="62" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="438" y="62" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="472" y="62" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="506" y="62" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="540" y="62" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="30" y="144" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="64" y="144" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="98" y="144" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="132" y="144" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="166" y="144" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="200" y="144" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="234" y="144" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="268" y="144" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="302" y="144" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="336" y="144" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="370" y="144" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="404" y="144" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="438" y="144" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="472" y="144" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="506" y="144" width="30" height="30" rx="5"/>
<rect class="fg-cell fg-cell--end" x="540" y="144" width="30" height="30" rx="5"/>
<rect class="fg-pill" x="19" y="8" width="52" height="24" rx="6"/>
<text class="fg-pilltext" x="45" y="24">rend</text>
<line class="fg-arrow" x1="45" y1="32" x2="45" y2="60" marker-end="url(#fig-rbe-arrow)"/>
<rect class="fg-pill" x="521" y="8" width="68" height="24" rx="6"/>
<text class="fg-pilltext" x="555" y="24">rbegin</text>
<line class="fg-arrow" x1="555" y1="32" x2="555" y2="60" marker-end="url(#fig-rbe-arrow)"/>
<text class="fg-note fg-note--l" x="81" y="24">Reverse past-the-last element</text>
<line class="fg-arrow fg-arrow--dash" x1="45" y1="94" x2="45" y2="142"/>
<line class="fg-arrow fg-arrow--dash" x1="555" y1="94" x2="555" y2="142"/>
<text class="fg-note" x="300" y="123">A reverse iterator stores an iterator to the next element</text>
<text class="fg-note" x="300" y="141" dy="0" style="display:none"></text>
<rect class="fg-pill" x="15" y="204" width="60" height="24" rx="6"/>
<text class="fg-pilltext" x="45" y="220">begin</text>
<line class="fg-arrow" x1="45" y1="202" x2="45" y2="178" marker-end="url(#fig-rbe-arrow)"/>
<rect class="fg-pill" x="531" y="204" width="48" height="24" rx="6"/>
<text class="fg-pilltext" x="555" y="220">end</text>
<line class="fg-arrow" x1="555" y1="202" x2="555" y2="178" marker-end="url(#fig-rbe-arrow)"/>
<text class="fg-note fg-note--r" x="515" y="221">Past-the-last element</text>
</svg>
</div>
<p class="nj-caption" markdown>`crend()` points to the position before the first element, like `rend()`, and `rbegin()`
to the last element. The upper row is the reversed sequence and the lower row the forward sequence; dashed arrows link
each reverse iterator to the forward iterator it stores, and dashed cells are past-the-last positions.</p>
## Return value
@@ -59,9 +119,9 @@ Constant.
## See also
- [crbegin](crbegin.md) returns a const reverse iterator to the last element
- [rend](rend.md) returns a reverse iterator to one before the first element
- [cend](cend.md) returns a const iterator to one past the last element
- [`crbegin`](crbegin.md) - returns a const reverse iterator to the last element
- [`rend`](rend.md) - returns a reverse iterator to one before the first element
- [`cend`](cend.md) - returns a const iterator to one past the last element
- [Iterators](../../features/iterators.md) - the article on iterators
## Version history
+3 -3
View File
@@ -1,5 +1,5 @@
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</code></pre></div> <p>Returns an iterator to the reverse-end; that is, one before the first element. This element acts as a placeholder, attempting to access it results in undefined behavior.</p> <p><img alt="Illustration from cppreference.com" src=../../../images/range-rbegin-rend.svg></p> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <p>reverse iterator to the element following the last element</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">&para;</a></h2> <p>No-throw guarantee: this member function never throws exceptions.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">&para;</a></h2> <p>Constant.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The following code shows an example for <code>crend()</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>
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</code></pre></div> <p>Returns an iterator to the reverse-end; that is, one before the first element. This element acts as a placeholder, attempting to access it results in undefined behavior.</p> <div class=nj-fig-wrap> <p><svg class="nj-fig nj-fig--range" viewbox="0 0 600 236" role=img aria-labelledby=fig-rbe-title xmlns=http://www.w3.org/2000/svg> <title id=fig-rbe-title>Two rows of sixteen cells. The upper row shows the reversed sequence: rend() points to a dashed position before the first element and rbegin() to the last element. The lower row shows the forward sequence: begin() points to the first element and end() to a dashed position after the last element. A reverse iterator stores an iterator to the next element, so rend() corresponds to begin() and rbegin() to end().</title> <defs><marker id=fig-rbe-arrow viewbox="0 0 10 10" refx=9 refy=5 markerwidth=7 markerheight=7 orient=auto><path class=fg-head d="M0 1 L10 5 L0 9 z"/></marker></defs> <rect x=30 y=62 width=30 height=30 rx=5 class="fg-cell fg-cell--end"/> <rect class=fg-cell x=64 y=62 width=30 height=30 rx=5 /> <rect class=fg-cell x=98 y=62 width=30 height=30 rx=5 /> <rect class=fg-cell x=132 y=62 width=30 height=30 rx=5 /> <rect class=fg-cell x=166 y=62 width=30 height=30 rx=5 /> <rect class=fg-cell x=200 y=62 width=30 height=30 rx=5 /> <rect class=fg-cell x=234 y=62 width=30 height=30 rx=5 /> <rect class=fg-cell x=268 y=62 width=30 height=30 rx=5 /> <rect class=fg-cell x=302 y=62 width=30 height=30 rx=5 /> <rect class=fg-cell x=336 y=62 width=30 height=30 rx=5 /> <rect class=fg-cell x=370 y=62 width=30 height=30 rx=5 /> <rect class=fg-cell x=404 y=62 width=30 height=30 rx=5 /> <rect class=fg-cell x=438 y=62 width=30 height=30 rx=5 /> <rect class=fg-cell x=472 y=62 width=30 height=30 rx=5 /> <rect class=fg-cell x=506 y=62 width=30 height=30 rx=5 /> <rect class=fg-cell x=540 y=62 width=30 height=30 rx=5 /> <rect class=fg-cell x=30 y=144 width=30 height=30 rx=5 /> <rect class=fg-cell x=64 y=144 width=30 height=30 rx=5 /> <rect class=fg-cell x=98 y=144 width=30 height=30 rx=5 /> <rect class=fg-cell x=132 y=144 width=30 height=30 rx=5 /> <rect class=fg-cell x=166 y=144 width=30 height=30 rx=5 /> <rect class=fg-cell x=200 y=144 width=30 height=30 rx=5 /> <rect class=fg-cell x=234 y=144 width=30 height=30 rx=5 /> <rect class=fg-cell x=268 y=144 width=30 height=30 rx=5 /> <rect class=fg-cell x=302 y=144 width=30 height=30 rx=5 /> <rect class=fg-cell x=336 y=144 width=30 height=30 rx=5 /> <rect class=fg-cell x=370 y=144 width=30 height=30 rx=5 /> <rect class=fg-cell x=404 y=144 width=30 height=30 rx=5 /> <rect class=fg-cell x=438 y=144 width=30 height=30 rx=5 /> <rect class=fg-cell x=472 y=144 width=30 height=30 rx=5 /> <rect class=fg-cell x=506 y=144 width=30 height=30 rx=5 /> <rect x=540 y=144 width=30 height=30 rx=5 class="fg-cell fg-cell--end"/> <rect class=fg-pill x=19 y=8 width=52 height=24 rx=6 /> <text class=fg-pilltext x=45 y=24>rend</text> <line class=fg-arrow x1=45 y1=32 x2=45 y2=60 marker-end=url(#fig-rbe-arrow) /> <rect class=fg-pill x=521 y=8 width=68 height=24 rx=6 /> <text class=fg-pilltext x=555 y=24>rbegin</text> <line class=fg-arrow x1=555 y1=32 x2=555 y2=60 marker-end=url(#fig-rbe-arrow) /> <text class="fg-note fg-note--l" x=81 y=24>Reverse past-the-last element</text> <line x1=45 y1=94 x2=45 y2=142 class="fg-arrow fg-arrow--dash"/> <line x1=555 y1=94 x2=555 y2=142 class="fg-arrow fg-arrow--dash"/> <text class=fg-note x=300 y=123>A reverse iterator stores an iterator to the next element</text> <text class=fg-note x=300 y=141 dy=0 style=display:none></text> <rect class=fg-pill x=15 y=204 width=60 height=24 rx=6 /> <text class=fg-pilltext x=45 y=220>begin</text> <line class=fg-arrow x1=45 y1=202 x2=45 y2=178 marker-end=url(#fig-rbe-arrow) /> <rect class=fg-pill x=531 y=204 width=48 height=24 rx=6 /> <text class=fg-pilltext x=555 y=220>end</text> <line class=fg-arrow x1=555 y1=202 x2=555 y2=178 marker-end=url(#fig-rbe-arrow) /> <text class="fg-note fg-note--r" x=515 y=221>Past-the-last element</text> </svg></p> </div> <p class=nj-caption><code>crend()</code> points to the position before the first element, like <code>rend()</code>, and <code>rbegin()</code> to the last element. The upper row is the reversed sequence and the lower row the forward sequence; dashed arrows link each reverse iterator to the forward iterator it stores, and dashed cells are past-the-last positions.</p> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <p>reverse iterator to the element following the last element</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">&para;</a></h2> <p>No-throw guarantee: this member function never throws exceptions.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">&para;</a></h2> <p>Constant.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="PermaneLine truncated
<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>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
@@ -19,4 +19,4 @@
<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=o>*</span><span class=n>it</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>1</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=../crbegin/ >crbegin</a> returns a const reverse iterator to the last element</li> <li><a href=../rend/ >rend</a> returns a reverse iterator to one before the first element</li> <li><a href=../cend/ >cend</a> returns a const iterator to one past the last element</li> <li><a href=../../../features/iterators/ >Iterators</a> - the article on iterators</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 1.0.0.</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=../crbegin/ ><code>crbegin</code></a> - returns a const reverse iterator to the last element</li> <li><a href=../rend/ ><code>rend</code></a> - returns a reverse iterator to one before the first element</li> <li><a href=../cend/ ><code>cend</code></a> - returns a const iterator to one past the last element</li> <li><a href=../../../features/iterators/ >Iterators</a> - the article on iterators</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 1.0.0.</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 27, 2026 06:41:42 UTC">October 27, 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> <nav class="md-footer__inner md-grid" aria-label=Footer> <a href=../crbegin/ class="md-footer__link md-footer__link--prev" aria-label="Previous: crbegin"> <div class="md-footer__button md-icon"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M20 11v2H8l5.5 5.5-1.42 1.42L4.16 12l7.92-7.92L13.5 5.5 8 11z"/></svg> </div> <div class=md-footer__title> <span class=md-footer__direction> Previous </span> <div class=md-ellipsis> crbegin </div> </div> </a> <a href=../default_object_comparator_t/ class="md-footer__link md-footer__link--next" aria-label="Next: default_object_comparator_t"> <div class=md-footer__title> <span class=md-footer__direction> Next </span> <div class=md-ellipsis> default_object_comparator_t </div> </div> <div class="md-footer__button md-icon"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M4 11v2h12l-5.5 5.5 1.42 1.42L19.84 12l-7.92-7.92L10.5 5.5 16 11z"/></svg> </div> </a> </nav> <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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+5 -3
View File
@@ -6,6 +6,8 @@ const_reverse_iterator crend() const noexcept;
Returns an iterator to the reverse-end; that is, one before the first element. This element acts as a placeholder, attempting to access it results in undefined behavior.
`crend()` points to the position before the first element, like `rend()`, and `rbegin()` to the last element. The upper row is the reversed sequence and the lower row the forward sequence; dashed arrows link each reverse iterator to the forward iterator it stores, and dashed cells are past-the-last positions.
## Return value
reverse iterator to the element following the last element
@@ -54,9 +56,9 @@ Output:
## See also
- [crbegin](https://json.nlohmann.me/api/basic_json/crbegin/index.md) returns a const reverse iterator to the last element
- [rend](https://json.nlohmann.me/api/basic_json/rend/index.md) returns a reverse iterator to one before the first element
- [cend](https://json.nlohmann.me/api/basic_json/cend/index.md) returns a const iterator to one past the last element
- [`crbegin`](https://json.nlohmann.me/api/basic_json/crbegin/index.md) - returns a const reverse iterator to the last element
- [`rend`](https://json.nlohmann.me/api/basic_json/rend/index.md) - returns a reverse iterator to one before the first element
- [`cend`](https://json.nlohmann.me/api/basic_json/cend/index.md) - returns a const iterator to one past the last element
- [Iterators](https://json.nlohmann.me/features/iterators/index.md) - the article on iterators
## Version history
@@ -45,8 +45,10 @@ The actual comparator used depends on [`object_t`](object_t.md) and can be obtai
## See also
- [object_comparator_t](object_comparator_t.md) the comparator actually used by `object_t`
- [object_t](object_t.md) the type used to store JSON objects
- [`object_comparator_t`](object_comparator_t.md) - the comparator actually used by `object_t`
- [`object_t`](object_t.md) - the type used to store JSON objects
- [Template Parameter Requirements](../../features/types/template_parameters.md) - requirements on the `ObjectType` template parameter
- [Object order](../../features/object_order.md) - preserve the insertion order of keys
## Version history
@@ -1,4 +1,4 @@
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<span class=k>using</span><span class=w> </span><span class=n>default_object_comparator_t</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>less</span><span class=o>&lt;&gt;</span><span class=p>;</span><span class=w> </span><span class=c1>// since C++14</span>
</code></pre></div> <p>The default comparator used by <a href=../object_t/ ><code>object_t</code></a>.</p> <p>Since C++14 a transparent comparator is used which prevents unnecessary string construction when looking up a key in an object.</p> <p>The actual comparator used depends on <a href=../object_t/ ><code>object_t</code></a> and can be obtained via <a href=../object_comparator_t/ ><code>object_comparator_t</code></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 example below demonstrates the default comparator.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
@@ -14,4 +14,4 @@
<span class=p>}</span>
</code></pre></div> <p>Output:</p> <div class=highlight><pre><span></span><code><span class=err>o</span><span class=kc>ne</span><span class=w> </span><span class=err>&lt;</span><span class=w> </span><span class=kc>t</span><span class=err>wo</span><span class=w> </span><span class=p>:</span><span class=w> </span><span class=kc>true</span>
<span class=kc>t</span><span class=err>hree</span><span class=w> </span><span class=err>&lt;</span><span class=w> </span><span class=kc>f</span><span class=err>our</span><span class=w> </span><span class=p>:</span><span class=w> </span><span class=kc>false</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=../object_comparator_t/ >object_comparator_t</a> the comparator actually used by <code>object_t</code></li> <li><a href=../object_t/ >object_t</a> the type used to store <abbr title="JavaScript Object Notation">JSON</abbr> objects</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=../object_comparator_t/ ><code>object_comparator_t</code></a> - the comparator actually used by <code>object_t</code></li> <li><a href=../object_t/ ><code>object_t</code></a> - the type used to store <abbr title="JavaScript Object Notation">JSON</abbr> objects</li> <li><a href=../../../features/types/template_parameters/ >Template Parameter Requirements</a> - requirements on the <code>ObjectType</code> template parameter</li> <li><a href=../../../features/object_order/ >Object order</a> - preserve the insertion order of keys</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 27, 2026 06:41:42 UTC">October 27, 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> <nav class="md-footer__inner md-grid" aria-label=Footer> <a href=../crend/ class="md-footer__link md-footer__link--prev" aria-label="Previous: crend"> <div class="md-footer__button md-icon"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M20 11v2H8l5.5 5.5-1.42 1.42L4.16 12l7.92-7.92L13.5 5.5 8 11z"/></svg> </div> <div class=md-footer__title> <span class=md-footer__direction> Previous </span> <div class=md-ellipsis> crend </div> </div> </a> <a href=../diff/ class="md-footer__link md-footer__link--next" aria-label="Next: diff"> <div class=md-footer__title> <span class=md-footer__direction> Next </span> <div class=md-ellipsis> diff </div> </div> <div class="md-footer__button md-icon"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M4 11v2h12l-5.5 5.5 1.42 1.42L19.84 12l-7.92-7.92L10.5 5.5 16 11z"/></svg> </div> </a> </nav> <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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@@ -41,8 +41,10 @@ three < four : false
## See also
- [object_comparator_t](https://json.nlohmann.me/api/basic_json/object_comparator_t/index.md) the comparator actually used by `object_t`
- [object_t](https://json.nlohmann.me/api/basic_json/object_t/index.md) the type used to store JSON objects
- [`object_comparator_t`](https://json.nlohmann.me/api/basic_json/object_comparator_t/index.md) - the comparator actually used by `object_t`
- [`object_t`](https://json.nlohmann.me/api/basic_json/object_t/index.md) - the type used to store JSON objects
- [Template Parameter Requirements](https://json.nlohmann.me/features/types/template_parameters/index.md) - requirements on the `ObjectType` template parameter
- [Object order](https://json.nlohmann.me/features/object_order/index.md) - preserve the insertion order of keys
## Version history
+6 -5
View File
@@ -154,11 +154,12 @@ operations times the length of their paths, so a small change deep inside a valu
## See also
- [RFC 6902 (JSON Patch)](https://tools.ietf.org/html/rfc6902)
- [patch](patch.md) applies a JSON Patch
- [patch_inplace](patch_inplace.md) applies a JSON Patch in place
- [merge_patch](merge_patch.md) applies a JSON Merge Patch
- [merge_diff](merge_diff.md) creates a diff as a JSON Merge Patch
- [RFC 6902 (JSON Patch)](https://tools.ietf.org/html/rfc6902) - specification of JSON Patch
- [`patch`](patch.md) - applies a JSON Patch
- [`patch_inplace`](patch_inplace.md) - applies a JSON Patch in place
- [`merge_patch`](merge_patch.md) - applies a JSON Merge Patch
- [`merge_diff`](merge_diff.md) - creates a diff as a JSON Merge Patch
- [JSON Patch and Diff](../../features/json_patch.md) - the article on JSON Patch
## Version history
+2 -2
View File
@@ -1,4 +1,4 @@
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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=description content="JSON for Modern C++ is a header-only C++11 library that makes JSON a first-class data type."><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/diff/" rel="canonical"><link href=../default_object_comparator_t/ rel=prev><link href=../dump/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>diff - 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=../../../css/custom.css><link rel=stylesheet href=../../../css/brand.css><link rel=stylesheet href=../../../css/fig-sax.css><link rel=stylesheet href=../../../css/fig-jsonview.css><link rel=stylesheet 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<span class=w> </span><span class=k>const</span><span class=w> </span><span class=n>basic_json</span><span class=o>&amp;</span><span class=w> </span><span class=n>target</span><span class=p>,</span>
<span class=w> </span><span class=k>const</span><span class=w> </span><span class=n>string_t</span><span class=o>&amp;</span><span class=w> </span><span class=n>path</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=s>""</span><span class=p>);</span>
</code></pre></div> <p>Creates a <a href="http://jsonpatch.com"><abbr title="JavaScript Object Notation">JSON</abbr> Patch</a> so that value <code>source</code> can be changed into the value <code>target</code> by calling <a href=../patch/ ><code>patch</code></a> function.</p> <p>For two <abbr title="JavaScript Object Notation">JSON</abbr> values <code>source</code> and <code>target</code>, the following code yields <code class=highlight><span class=nb>true</span></code>: <div class=highlight><pre><span></span><code><span class=n>source</span><span class=p>.</span><span class=n>patch</span><span class=p>(</span><span class=n>diff</span><span class=p>(</span><span class=n>source</span><span class=p>,</span><span class=w> </span><span class=n>target</span><span class=p>))</span><span class=w> </span><span class=o>==</span><span class=w> </span><span class=n>target</span><span class=p>;</span>
@@ -64,4 +64,4 @@
<span class=w> </span><span class=s2>"world"</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="https://tools.ietf.org/html/rfc6902"><abbr title="Request for Comments">RFC</abbr> 6902 (<abbr title="JavaScript Object Notation">JSON</abbr> Patch)</a></li> <li><a href=../patch/ >patch</a> applies a <abbr title="JavaScript Object Notation">JSON</abbr> Patch</li> <li><a href=../patch_inplace/ >patch_inplace</a> applies a <abbr title="JavaScript Object Notation">JSON</abbr> Patch in place</li> <li><a href=../merge_patch/ >merge_patch</a> applies a <abbr title="JavaScript Object Notation">JSON</abbr> Merge Patch</li> <li><a href=../merge_diff/ >merge_diff</a> creates a diff as a <abbr title="JavaScript Object Notation">JSON</abbr> Merge Patch</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 2.0.0.</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 26, 2026 16:12:05 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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</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="https://tools.ietf.org/html/rfc6902"><abbr title="Request for Comments">RFC</abbr> 6902 (<abbr title="JavaScript Object Notation">JSON</abbr> Patch)</a> - specification of <abbr title="JavaScript Object Notation">JSON</abbr> Patch</li> <li><a href=../patch/ ><code>patch</code></a> - applies a <abbr title="JavaScript Object Notation">JSON</abbr> Patch</li> <li><a href=../patch_inplace/ ><code>patch_inplace</code></a> - applies a <abbr title="JavaScript Object Notation">JSON</abbr> Patch in place</li> <li><a href=../merge_patch/ ><code>merge_patch</code></a> - applies a <abbr title="JavaScript Object Notation">JSON</abbr> Merge Patch</li> <li><a href=../merge_diff/ ><code>merge_diff</code></a> - creates a diff as a <abbr title="JavaScript Object Notation">JSON</abbr> Merge Patch</li> <li><a href=../../../features/json_patch/ ><abbr title="JavaScript Object Notation">JSON</abbr> Patch and Diff</a> - the article on <abbr title="JavaScript Object Notation">JSON</abbr> Patch</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 2.0.0.</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 27, 2026 06:41:42 UTC">October 27, 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> <nav class="md-footer__inner md-grid" aria-label=Footer> <a href=../default_object_comparator_t/ class="md-footer__link md-footer__link--prev" aria-label="Previous: default_object_comparator_t"> <div class="md-footer__button md-icon"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M20 11v2H8l5.5 5.5-1.42 1.42L4.16 12l7.92-7.92L13.5 5.5 8 11z"/></svg> </div> <div class=md-footer__title> <span class=md-footer__direction> Previous </span> <div class=md-ellipsis> default_object_comparator_t </div> </div> </a> <a href=../dump/ class="md-footer__link md-footer__link--next" aria-label="Next: dump"> <div class=md-footer__title> <span class=md-footer__direction> Next </span> <div class=md-ellipsis> dump </div> </div> <div class="md-footer__button md-icon"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M4 11v2h12l-5.5 5.5 1.42 1.42L19.84 12l-7.92-7.92L10.5 5.5 16 11z"/></svg> </div> </a> </nav> <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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+6 -5
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@@ -127,11 +127,12 @@ Output:
## See also
- [RFC 6902 (JSON Patch)](https://tools.ietf.org/html/rfc6902)
- [patch](https://json.nlohmann.me/api/basic_json/patch/index.md) applies a JSON Patch
- [patch_inplace](https://json.nlohmann.me/api/basic_json/patch_inplace/index.md) applies a JSON Patch in place
- [merge_patch](https://json.nlohmann.me/api/basic_json/merge_patch/index.md) applies a JSON Merge Patch
- [merge_diff](https://json.nlohmann.me/api/basic_json/merge_diff/index.md) creates a diff as a JSON Merge Patch
- [RFC 6902 (JSON Patch)](https://tools.ietf.org/html/rfc6902) - specification of JSON Patch
- [`patch`](https://json.nlohmann.me/api/basic_json/patch/index.md) - applies a JSON Patch
- [`patch_inplace`](https://json.nlohmann.me/api/basic_json/patch_inplace/index.md) - applies a JSON Patch in place
- [`merge_patch`](https://json.nlohmann.me/api/basic_json/merge_patch/index.md) - applies a JSON Merge Patch
- [`merge_diff`](https://json.nlohmann.me/api/basic_json/merge_diff/index.md) - creates a diff as a JSON Merge Patch
- [JSON Patch and Diff](https://json.nlohmann.me/features/json_patch/index.md) - the article on JSON Patch
## Version history
+3 -3
View File
@@ -192,9 +192,9 @@ Binary values are serialized as an object containing two keys:
## See also
- [to_string](to_string.md) returns a string representation of a JSON value
- [operator<<](../operator_ltlt.md) serialize to stream
- [`basic_json_view::dump`](../basic_json_view/dump.md) the corresponding function of `basic_json_view`, serializing
- [`to_string`](to_string.md) - returns a string representation of a JSON value
- [`operator<<`](../operator_ltlt.md) - serialize to stream
- [`basic_json_view::dump`](../basic_json_view/dump.md) - the corresponding function of `basic_json_view`, serializing
directly from a flat index without building a `basic_json` value
- [Serialization](../../features/serialization.md) - the serialization article
+2 -2
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@@ -1,4 +1,4 @@
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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=description content="JSON for Modern C++ is a header-only C++11 library that makes JSON a first-class data type."><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/dump/" rel="canonical"><link href=../diff/ rel=prev><link href=../emplace/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>dump - 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=../../../css/custom.css><link rel=stylesheet href=../../../css/brand.css><link rel=stylesheet href=../../../css/fig-sax.css><link rel=stylesheet href=../../../css/fig-jsonview.css><link rel=stylesheet 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</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> <img src=../../../images/wordmark-header.svg alt=logo> </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> dump </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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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-.5Line truncated
<span class=w> </span><span class=k>const</span><span class=w> </span><span class=kt>char</span><span class=w> </span><span class=n>indent_char</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=sc>' '</span><span class=p>,</span>
<span class=w> </span><span class=k>const</span><span class=w> </span><span class=kt>bool</span><span class=w> </span><span class=n>ensure_ascii</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=nb>false</span><span class=p>,</span>
<span class=w> </span><span class=k>const</span><span class=w> </span><span class=n>error_handler_t</span><span class=w> </span><span class=n>error_handler</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>error_handler_t</span><span class=o>::</span><span class=n>strict</span><span class=p>)</span><span class=w> </span><span class=k>const</span><span class=p>;</span>
@@ -105,4 +105,4 @@
<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>.</span><span class=kc>t</span><span class=err>ype_error.</span><span class=mi>316</span><span class=p>]</span><span class=w> </span><span class=err>i</span><span class=kc>n</span><span class=err>valid</span><span class=w> </span><span class=err>UTF</span><span class=mi>-8</span><span class=w> </span><span class=err>by</span><span class=kc>te</span><span class=w> </span><span class=err>a</span><span class=kc>t</span><span class=w> </span><span class=err>i</span><span class=kc>n</span><span class=err>dex</span><span class=w> </span><span class=mi>2</span><span class=p>:</span><span class=w> </span><span class=mi>0</span><span class=err>xA</span><span class=mi>9</span>
<span class=err>s</span><span class=kc>tr</span><span class=err>i</span><span class=kc>n</span><span class=err>g</span><span class=w> </span><span class=err>wi</span><span class=kc>t</span><span class=err>h</span><span class=w> </span><span class=err>replaced</span><span class=w> </span><span class=err>i</span><span class=kc>n</span><span class=err>valid</span><span class=w> </span><span class=err>charac</span><span class=kc>ters</span><span class=p>:</span><span class=w> </span><span class=s2>"ä�ü"</span>
<span class=err>s</span><span class=kc>tr</span><span class=err>i</span><span class=kc>n</span><span class=err>g</span><span class=w> </span><span class=err>wi</span><span class=kc>t</span><span class=err>h</span><span class=w> </span><span class=err>ig</span><span class=kc>n</span><span class=err>ored</span><span class=w> </span><span class=err>i</span><span class=kc>n</span><span class=err>valid</span><span class=w> </span><span class=err>charac</span><span class=kc>ters</span><span class=p>:</span><span class=w> </span><span class=s2>"äü"</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=../to_string/ >to_string</a> returns a string representation of a <abbr title="JavaScript Object Notation">JSON</abbr> value</li> <li><a href=../../operator_ltlt/ >operator&lt;&lt;</a> serialize to stream</li> <li><a href=../../basic_json_view/dump/ ><code>basic_json_view::dump</code></a> the corresponding function of <code>basic_json_view</code>, serializing directly from a flat index without building a <code>basic_json</code> value</li> <li><a href=../../../features/serialization/ >Serialization</a> - the serialization article</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 1.0.0.</li> <li>Indentation character <code>indent_char</code>, option <code>ensure_ascii</code> and exceptions added in version 3.0.0.</li> <li>Error handlers added in version 3.4.0.</li> <li>Serialization of binary values added in version 3.8.0.</li> <li>Error handler <code>keep</code> 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>Doubles are written with the shortest digits (Żmij instead of Grisu2) 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>; about 0.1% of doubles are written differently, most of them with fewer digits.</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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</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=../to_string/ ><code>to_string</code></a> - returns a string representation of a <abbr title="JavaScript Object Notation">JSON</abbr> value</li> <li><a href=../../operator_ltlt/ ><code>operator&lt;&lt;</code></a> - serialize to stream</li> <li><a href=../../basic_json_view/dump/ ><code>basic_json_view::dump</code></a> - the corresponding function of <code>basic_json_view</code>, serializing directly from a flat index without building a <code>basic_json</code> value</li> <li><a href=../../../features/serialization/ >Serialization</a> - the serialization article</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 1.0.0.</li> <li>Indentation character <code>indent_char</code>, option <code>ensure_ascii</code> and exceptions added in version 3.0.0.</li> <li>Error handlers added in version 3.4.0.</li> <li>Serialization of binary values added in version 3.8.0.</li> <li>Error handler <code>keep</code> 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>Doubles are written with the shortest digits (Żmij instead of Grisu2) 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>; about 0.1% of doubles are written differently, most of them with fewer digits.</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 27, 2026 06:41:42 UTC">October 27, 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> <nav class="md-footer__inner md-grid" aria-label=Footer> <a href=../diff/ class="md-footer__link md-footer__link--prev" aria-label="Previous: diff"> <div class="md-footer__button md-icon"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M20 11v2H8l5.5 5.5-1.42 1.42L4.16 12l7.92-7.92L13.5 5.5 8 11z"/></svg> </div> <div class=md-footer__title> <span class=md-footer__direction> Previous </span> <div class=md-ellipsis> diff </div> </div> </a> <a href=../emplace/ class="md-footer__link md-footer__link--next" aria-label="Next: emplace"> <div class=md-footer__title> <span class=md-footer__direction> Next </span> <div class=md-ellipsis> emplace </div> </div> <div class="md-footer__button md-icon"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M4 11v2h12l-5.5 5.5 1.42 1.42L19.84 12l-7.92-7.92L10.5 5.5 16 11z"/></svg> </div> </a> </nav> <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 -3
View File
@@ -169,9 +169,9 @@ string with ignored invalid characters: "äü"
## See also
- [to_string](https://json.nlohmann.me/api/basic_json/to_string/index.md) returns a string representation of a JSON value
- [operator\<<](https://json.nlohmann.me/api/operator_ltlt/index.md) serialize to stream
- [`basic_json_view::dump`](https://json.nlohmann.me/api/basic_json_view/dump/index.md) the corresponding function of `basic_json_view`, serializing directly from a flat index without building a `basic_json` value
- [`to_string`](https://json.nlohmann.me/api/basic_json/to_string/index.md) - returns a string representation of a JSON value
- [`operator<<`](https://json.nlohmann.me/api/operator_ltlt/index.md) - serialize to stream
- [`basic_json_view::dump`](https://json.nlohmann.me/api/basic_json_view/dump/index.md) - the corresponding function of `basic_json_view`, serializing directly from a flat index without building a `basic_json` value
- [Serialization](https://json.nlohmann.me/features/serialization/index.md) - the serialization article
## Version history
+2 -2
View File
@@ -100,8 +100,8 @@ Logarithmic in the size of the container, O(log(`size()`)).
## See also
- [emplace_back](emplace_back.md) add a value to an array
- [insert](insert.md) add values to an array/object
- [`emplace_back`](emplace_back.md) - add a value to an array
- [`insert`](insert.md) - add values to an array/object
- [Modifying values](../../features/modifying_values.md) - the article on modifying values
## Version history
+2 -2
View File
@@ -1,4 +1,4 @@
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<span class=n>std</span><span class=o>::</span><span class=n>pair</span><span class=o>&lt;</span><span class=n>iterator</span><span class=p>,</span><span class=w> </span><span class=kt>bool</span><span class=o>&gt;</span><span class=w> </span><span class=n>emplace</span><span class=p>(</span><span class=n>Args</span><span class=o>&amp;&amp;</span><span class=w> </span><span class=p>...</span><span class=w> </span><span class=n>args</span><span class=p>);</span>
</code></pre></div> <p>Inserts a new element into a <abbr title="JavaScript Object Notation">JSON</abbr> object constructed in-place with the given <code>args</code> if there is no element with the key in the container. If the function is called on a <abbr title="JavaScript Object Notation">JSON</abbr> null value, an empty object is created before appending the value created from <code>args</code>.</p> <h2 id=template-parameters>Template parameters<a class=headerlink href=#template-parameters title="Permanent link">&para;</a></h2> <dl> <dt><code>Args</code></dt> <dd>compatible types to create a <code>basic_json</code> object</dd> </dl> <h2 id=iterator-invalidation>Iterator invalidation<a class=headerlink href=#iterator-invalidation title="Permanent link">&para;</a></h2> <p>For <a href=../../ordered_json/ ><code>ordered_json</code></a>, adding a value to an object can yield a reallocation, in which case all iterators (including the <code>end()</code> iterator) and all references to the elements are invalidated.</p> <h2 id=parameters>Parameters<a class=headerlink href=#parameters title="Permanent link">&para;</a></h2> <dl> <dt><code>args</code> (in)</dt> <dd>arguments to forward to a constructor of <code>basic_json</code></dd> </dl> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <p>a pair consisting of an iterator to the inserted element, or the already-existing element if no insertion happened, and a <code class=highlight><span class=kt>bool</span></code> denoting whether the insertion took place.</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">&para;</a></h2> <p>Strong guarantee: if an exception is thrown, there are no changes to any <abbr title="JavaScript Object Notation">JSON</abbr> value. As an exception, a <code class=highlight><span class=kc>null</span></code> value is converted to an empty object before the element is added and keeps that type if adding the element throws.</p> <h2 id=exceptions>Exceptions<a class=headerlink href=#exceptions title="Permanent link">&para;</a></h2> <p>Throws <a href=../../../home/exceptions/#jsonexceptiontype_error311><code>type_error.311</code></a> when called on a type other than <abbr title="JavaScript Object Notation">JSON</abbr> object or <code class=highlight><span class=kc>null</span></code>; example: <code>"cannot use emplace() with number"</code></p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">&para;</a></h2> <p>Logarithmic in the size of the container, O(log(<code>size()</code>)).</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 <code>emplace()</code> can be used to add elements to a <abbr title="JavaScript Object Notation">JSON</abbr> object. Note how the <code class=highlight><span class=kc>null</span></code> value was silently converted to a <abbr title="JavaScript Object Notation">JSON</abbr> object. Further note how no value is added if there was already one value stored with the same key.</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>
@@ -37,4 +37,4 @@
<span class=mi>3</span><span class=w> </span><span class=kc>true</span>
<span class=p>{</span><span class=nt>"A"</span><span class=p>:</span><span class=s2>"a"</span><span class=p>,</span><span class=nt>"B"</span><span class=p>:</span><span class=s2>"b"</span><span class=p>}</span>
<span class=s2>"b"</span><span class=w> </span><span class=kc>false</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=../emplace_back/ >emplace_back</a> add a value to an array</li> <li><a href=../insert/ >insert</a> add values to an array/object</li> <li><a href=../../../features/modifying_values/ >Modifying values</a> - the article on modifying values</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 2.0.8.</li> <li>Fixed 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>: for <a href=../../ordered_json/ ><code>ordered_json</code></a>, the value could previously only be passed as an rvalue; it can now also be passed as an lvalue or a <code class=highlight><span class=k>const</span></code> lvalue, matching the behavior of <code>json</code>.</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 24, 2026 15:57:44 UTC">October 24, 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=../emplace_back/ ><code>emplace_back</code></a> - add a value to an array</li> <li><a href=../insert/ ><code>insert</code></a> - add values to an array/object</li> <li><a href=../../../features/modifying_values/ >Modifying values</a> - the article on modifying values</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 2.0.8.</li> <li>Fixed 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>: for <a href=../../ordered_json/ ><code>ordered_json</code></a>, the value could previously only be passed as an rvalue; it can now also be passed as an lvalue or a <code class=highlight><span class=k>const</span></code> lvalue, matching the behavior of <code>json</code>.</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 27, 2026 06:41:42 UTC">October 27, 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> <nav class="md-footer__inner md-grid" aria-label=Footer> <a href=../dump/ class="md-footer__link md-footer__link--prev" aria-label="Previous: dump"> <div class="md-footer__button md-icon"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M20 11v2H8l5.5 5.5-1.42 1.42L4.16 12l7.92-7.92L13.5 5.5 8 11z"/></svg> </div> <div class=md-footer__title> <span class=md-footer__direction> Previous </span> <div class=md-ellipsis> dump </div> </div> </a> <a href=../emplace_back/ class="md-footer__link md-footer__link--next" aria-label="Next: emplace_back"> <div class=md-footer__title> <span class=md-footer__direction> Next </span> <div class=md-ellipsis> emplace_back </div> </div> <div class="md-footer__button md-icon"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M4 11v2h12l-5.5 5.5 1.42 1.42L19.84 12l-7.92-7.92L10.5 5.5 16 11z"/></svg> </div> </a> </nav> <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
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@@ -88,8 +88,8 @@ null
## See also
- [emplace_back](https://json.nlohmann.me/api/basic_json/emplace_back/index.md) add a value to an array
- [insert](https://json.nlohmann.me/api/basic_json/insert/index.md) add values to an array/object
- [`emplace_back`](https://json.nlohmann.me/api/basic_json/emplace_back/index.md) - add a value to an array
- [`insert`](https://json.nlohmann.me/api/basic_json/insert/index.md) - add values to an array/object
- [Modifying values](https://json.nlohmann.me/features/modifying_values/index.md) - the article on modifying values
## Version history
+2 -2
View File
@@ -89,8 +89,8 @@ Amortized constant.
## See also
- [operator+=](operator+=.md) add a value to an array/object
- [push_back](push_back.md) add a value to an array/object
- [`operator+=`](operator+=.md) - add a value to an array/object
- [`push_back`](push_back.md) - add a value to an array/object
- [Modifying values](../../features/modifying_values.md) - the article on modifying values
## Version history
+2 -2
View File
@@ -1,4 +1,4 @@
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</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> <img src=../../../images/wordmark-header.svg alt=logo> </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> emplace_back </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="M9.5Line truncated
<span class=n>reference</span><span class=w> </span><span class=n>emplace_back</span><span class=p>(</span><span class=n>Args</span><span class=o>&amp;&amp;</span><span class=w> </span><span class=p>...</span><span class=w> </span><span class=n>args</span><span class=p>);</span>
</code></pre></div> <p>Creates a <abbr title="JavaScript Object Notation">JSON</abbr> value from the passed parameters <code>args</code> to the end of the <abbr title="JavaScript Object Notation">JSON</abbr> value. If the function is called on a <abbr title="JavaScript Object Notation">JSON</abbr> <code class=highlight><span class=kc>null</span></code> value, an empty array is created before appending the value created from <code>args</code>.</p> <h2 id=template-parameters>Template parameters<a class=headerlink href=#template-parameters title="Permanent link">&para;</a></h2> <dl> <dt><code>Args</code></dt> <dd>compatible types to create a <code>basic_json</code> object</dd> </dl> <h2 id=iterator-invalidation>Iterator invalidation<a class=headerlink href=#iterator-invalidation title="Permanent link">&para;</a></h2> <p>By adding an element to the end of the array, a reallocation can happen, in which case all iterators (including the <a href=../end/ ><code>end()</code></a> iterator) and all references to the elements are invalidated. Otherwise, only the <a href=../end/ ><code>end()</code></a> iterator is invalidated.</p> <h2 id=parameters>Parameters<a class=headerlink href=#parameters title="Permanent link">&para;</a></h2> <dl> <dt><code>args</code> (in)</dt> <dd>arguments to forward to a constructor of <code>basic_json</code></dd> </dl> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <p>reference to the inserted element</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">&para;</a></h2> <p>Strong guarantee: if an exception is thrown, there are no changes to any <abbr title="JavaScript Object Notation">JSON</abbr> value. As an exception, a <code class=highlight><span class=kc>null</span></code> value is converted to an empty array before the element is added and keeps that type if adding the element throws.</p> <h2 id=exceptions>Exceptions<a class=headerlink href=#exceptions title="Permanent link">&para;</a></h2> <p>Throws <a href=../../../home/exceptions/#jsonexceptiontype_error311><code>type_error.311</code></a> when called on a type other than <abbr title="JavaScript Object Notation">JSON</abbr> array or <code class=highlight><span class=kc>null</span></code>; example: <code>"cannot use emplace_back() with number"</code></p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">&para;</a></h2> <p>Amortized constant.</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 <code>emplace_back()</code> can be used to add elements to a <abbr title="JavaScript Object Notation">JSON</abbr> array. Note how the <code>null</code> value was silently converted to a <abbr title="JavaScript Object Notation">JSON</abbr> array.</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>
@@ -28,4 +28,4 @@
<span class=kc>null</span>
<span class=p>[</span><span class=mi>1</span><span class=p>,</span><span class=mi>2</span><span class=p>,</span><span class=mi>3</span><span class=p>,</span><span class=mi>4</span><span class=p>,</span><span class=mi>5</span><span class=p>,</span><span class=mi>6</span><span class=p>]</span>
<span class=p>[</span><span class=s2>"first"</span><span class=p>,[</span><span class=s2>"second"</span><span class=p>,</span><span class=s2>"second"</span><span class=p>,</span><span class=s2>"second"</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%2B%3D/ >operator+=</a> add a value to an array/object</li> <li><a href=../push_back/ >push_back</a> add a value to an array/object</li> <li><a href=../../../features/modifying_values/ >Modifying values</a> - the article on modifying values</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 2.0.8.</li> <li>Returns reference since 3.7.0.</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 24, 2026 15:57:44 UTC">October 24, 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%2B%3D/ ><code>operator+=</code></a> - add a value to an array/object</li> <li><a href=../push_back/ ><code>push_back</code></a> - add a value to an array/object</li> <li><a href=../../../features/modifying_values/ >Modifying values</a> - the article on modifying values</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 2.0.8.</li> <li>Returns reference since 3.7.0.</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 27, 2026 06:41:42 UTC">October 27, 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> <nav class="md-footer__inner md-grid" aria-label=Footer> <a href=../emplace/ class="md-footer__link md-footer__link--prev" aria-label="Previous: emplace"> <div class="md-footer__button md-icon"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M20 11v2H8l5.5 5.5-1.42 1.42L4.16 12l7.92-7.92L13.5 5.5 8 11z"/></svg> </div> <div class=md-footer__title> <span class=md-footer__direction> Previous </span> <div class=md-ellipsis> emplace </div> </div> </a> <a href=../empty/ class="md-footer__link md-footer__link--next" aria-label="Next: empty"> <div class=md-footer__title> <span class=md-footer__direction> Next </span> <div class=md-ellipsis> empty </div> </div> <div class="md-footer__button md-icon"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M4 11v2h12l-5.5 5.5 1.42 1.42L19.84 12l-7.92-7.92L10.5 5.5 16 11z"/></svg> </div> </a> </nav> <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
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@@ -79,8 +79,8 @@ null
## See also
- [operator+=](https://json.nlohmann.me/api/basic_json/operator%2B%3D/index.md) add a value to an array/object
- [push_back](https://json.nlohmann.me/api/basic_json/push_back/index.md) add a value to an array/object
- [`operator+=`](https://json.nlohmann.me/api/basic_json/operator%2B%3D/index.md) - add a value to an array/object
- [`push_back`](https://json.nlohmann.me/api/basic_json/push_back/index.md) - add a value to an array/object
- [Modifying values](https://json.nlohmann.me/features/modifying_values/index.md) - the article on modifying values
## Version history
+4 -4
View File
@@ -41,7 +41,7 @@ bool empty() const noexcept
## Notes
This function does not return whether a string stored as JSON value is empty -- it returns whether the JSON container
This function does not return whether a string stored as JSON value is empty — it returns whether the JSON container
itself is empty which is `#!cpp false` in the case of a string.
## Examples
@@ -101,9 +101,9 @@ itself is empty which is `#!cpp false` in the case of a string.
## See also
- [size](size.md) returns the number of elements
- [clear](clear.md) clears the content and resets the value to the default value
- [basic_json_view::empty](../basic_json_view/empty.md) - the same check on a zero-copy view
- [`size`](size.md) - returns the number of elements
- [`clear`](clear.md) - clears the content and resets the value to the default value
- [`basic_json_view::empty`](../basic_json_view/empty.md) - the same check on a zero-copy view
## Version history
+3 -3
View File
@@ -1,9 +1,9 @@
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</code></pre></div> <p>Checks if a <abbr title="JavaScript Object Notation">JSON</abbr> value has no elements (i.e., whether its <a href=../size/ ><code>size()</code></a> is <code>0</code>).</p> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <p>The return value depends on the different types and is defined as follows:</p> <table> <thead> <tr> <th>Value type</th> <th>return value</th> </tr> </thead> <tbody> <tr> <td>null</td> <td><code class=highlight><span class=nb>true</span></code></td> </tr> <tr> <td>boolean</td> <td><code class=highlight><span class=nb>false</span></code></td> </tr> <tr> <td>string</td> <td><code class=highlight><span class=nb>false</span></code></td> </tr> <tr> <td>number</td> <td><code class=highlight><span class=nb>false</span></code></td> </tr> <tr> <td>binary</td> <td><code class=highlight><span class=nb>false</span></code></td> </tr> <tr> <td>object</td> <td>result of function <code>object_t::empty()</code></td> </tr> <tr> <td>array</td> <td>result of function <code>array_t::empty()</code></td> </tr> </tbody> </table> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">&para;</a></h2> <p>No-throw guarantee: this function never throws exceptions.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">&para;</a></h2> <p>Constant, as long as <a href=../array_t/ ><code>array_t</code></a> and <a href=../object_t/ ><code>object_t</code></a> satisfy the <a href="https://en.cppreference.com/w/cpp/named_req/Container">Container</a> concept; that is, their <code>empty()</code> functions have constant complexity.</p> <h2 id=possible-implementation>Possible implementation<a class=headerlink href=#possible-implementation title="Permanent link">&para;</a></h2> <div class=highlight><pre><span></span><code><span class=kt>bool</span><span class=w> </span><span class=nf>empty</span><span class=p>()</span><span class=w> </span><span class=k>const</span><span class=w> </span><span class=k>noexcept</span>
<span class=p>{</span>
<span class=w> </span><span class=k>return</span><span class=w> </span><span class=n>size</span><span class=p>()</span><span class=w> </span><span class=o>==</span><span class=w> </span><span class=mi>0</span><span class=p>;</span>
<span class=p>}</span>
</code></pre></div> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <p>This function does not return whether a string stored as <abbr title="JavaScript Object Notation">JSON</abbr> value is empty -- it returns whether the <abbr title="JavaScript Object Notation">JSON</abbr> container itself is empty which is <code class=highlight><span class=nb>false</span></code> in the case of a string.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The following code uses <code>empty()</code> to check if a <abbr title="JavaScript Object Notation">JSON</abbr> object contains any elements.</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> <p>This function does not return whether a string stored as <abbr title="JavaScript Object Notation">JSON</abbr> value is empty — it returns whether the <abbr title="JavaScript Object Notation">JSON</abbr> container itself is empty which is <code class=highlight><span class=nb>false</span></code> in the case of a string.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The following code uses <code>empty()</code> to check if a <abbr title="JavaScript Object Notation">JSON</abbr> object contains any elements.</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>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
@@ -42,4 +42,4 @@
<span class=kc>false</span>
<span class=kc>true</span>
<span class=kc>false</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=../size/ >size</a> returns the number of elements</li> <li><a href=../clear/ >clear</a> clears the content and resets the value to the default value</li> <li><a href=../../basic_json_view/empty/ >basic_json_view::empty</a> - the same check on a 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 1.0.0.</li> <li>Extended to return <code class=highlight><span class=nb>false</span></code> for binary types in version 3.8.0.</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 21, 2026 08:21:27 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=../size/ ><code>size</code></a> - returns the number of elements</li> <li><a href=../clear/ ><code>clear</code></a> - clears the content and resets the value to the default value</li> <li><a href=../../basic_json_view/empty/ ><code>basic_json_view::empty</code></a> - the same check on a 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 1.0.0.</li> <li>Extended to return <code class=highlight><span class=nb>false</span></code> for binary types in version 3.8.0.</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 27, 2026 06:41:42 UTC">October 27, 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> <nav class="md-footer__inner md-grid" aria-label=Footer> <a href=../emplace_back/ class="md-footer__link md-footer__link--prev" aria-label="Previous: emplace_back"> <div class="md-footer__button md-icon"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M20 11v2H8l5.5 5.5-1.42 1.42L4.16 12l7.92-7.92L13.5 5.5 8 11z"/></svg> </div> <div class=md-footer__title> <span class=md-footer__direction> Previous </span> <div class=md-ellipsis> emplace_back </div> </div> </a> <a href=../end/ class="md-footer__link md-footer__link--next" aria-label="Next: end"> <div class=md-footer__title> <span class=md-footer__direction> Next </span> <div class=md-ellipsis> end </div> </div> <div class="md-footer__button md-icon"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M4 11v2h12l-5.5 5.5 1.42 1.42L19.84 12l-7.92-7.92L10.5 5.5 16 11z"/></svg> </div> </a> </nav> <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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+4 -4
View File
@@ -39,7 +39,7 @@ bool empty() const noexcept
## Notes
This function does not return whether a string stored as JSON value is empty -- it returns whether the JSON container itself is empty which is `false` in the case of a string.
This function does not return whether a string stored as JSON value is empty — it returns whether the JSON container itself is empty which is `false` in the case of a string.
## Examples
@@ -96,9 +96,9 @@ false
## See also
- [size](https://json.nlohmann.me/api/basic_json/size/index.md) returns the number of elements
- [clear](https://json.nlohmann.me/api/basic_json/clear/index.md) clears the content and resets the value to the default value
- [basic_json_view::empty](https://json.nlohmann.me/api/basic_json_view/empty/index.md) - the same check on a zero-copy view
- [`size`](https://json.nlohmann.me/api/basic_json/size/index.md) - returns the number of elements
- [`clear`](https://json.nlohmann.me/api/basic_json/clear/index.md) - clears the content and resets the value to the default value
- [`basic_json_view::empty`](https://json.nlohmann.me/api/basic_json_view/empty/index.md) - the same check on a zero-copy view
## Version history
+38 -5
View File
@@ -7,7 +7,40 @@ const_iterator end() const noexcept;
Returns an iterator to one past the last element.
![Illustration from cppreference.com](../../images/range-begin-end.svg)
<div class="nj-fig-wrap" markdown>
<svg class="nj-fig nj-fig--range" viewBox="0 0 600 150" role="img" aria-labelledby="fig-be-title" xmlns="http://www.w3.org/2000/svg">
<title id="fig-be-title">A row of fifteen elements followed by a dashed past-the-last position. begin() points to the first element and end() points to the past-the-last position.</title>
<defs><marker id="fig-be-arrow" viewBox="0 0 10 10" refX="9" refY="5" markerWidth="7" markerHeight="7" orient="auto"><path class="fg-head" d="M0 1 L10 5 L0 9 z"/></marker></defs>
<rect class="fg-cell" x="30" y="62" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="64" y="62" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="98" y="62" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="132" y="62" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="166" y="62" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="200" y="62" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="234" y="62" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="268" y="62" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="302" y="62" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="336" y="62" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="370" y="62" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="404" y="62" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="438" y="62" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="472" y="62" width="30" height="30" rx="5"/>
<rect class="fg-cell" x="506" y="62" width="30" height="30" rx="5"/>
<rect class="fg-cell fg-cell--end" x="540" y="62" width="30" height="30" rx="5"/>
<rect class="fg-pill" x="15" y="8" width="60" height="24" rx="6"/>
<text class="fg-pilltext" x="45" y="24">begin</text>
<line class="fg-arrow" x1="45" y1="32" x2="45" y2="60" marker-end="url(#fig-be-arrow)"/>
<rect class="fg-pill" x="531" y="8" width="48" height="24" rx="6"/>
<text class="fg-pilltext" x="555" y="24">end</text>
<line class="fg-arrow" x1="555" y1="32" x2="555" y2="60" marker-end="url(#fig-be-arrow)"/>
<text class="fg-note fg-note--r" x="537" y="132">Past-the-last element</text>
<line class="fg-arrow" x1="555" y1="124" x2="555" y2="96" marker-end="url(#fig-be-arrow)"/>
</svg>
</div>
<p class="nj-caption" markdown>`end()` points to the position after the last element and `begin()` to the first element;
the dashed cell is the past-the-last position, which must not be dereferenced.</p>
## Return value
@@ -59,11 +92,11 @@ Constant.
## See also
- [begin](begin.md) returns an iterator to the first element
- [cend](cend.md) returns a const iterator to one past the last element
- [rend](rend.md) returns a reverse iterator to one before the first element
- [`begin`](begin.md) - returns an iterator to the first element
- [`cend`](cend.md) - returns a const iterator to one past the last element
- [`rend`](rend.md) - returns a reverse iterator to one before the first element
- [Iterators](../../features/iterators.md) - the article on iterators
- [basic_json_view::end](../basic_json_view/end.md) - the same iteration on a zero-copy view
- [`basic_json_view::end`](../basic_json_view/end.md) - the same iteration on a zero-copy view
## Version history
+3 -3
View File
@@ -1,6 +1,6 @@
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<span class=n>const_iterator</span><span class=w> </span><span class=nf>end</span><span class=p>()</span><span class=w> </span><span class=k>const</span><span class=w> </span><span class=k>noexcept</span><span class=p>;</span>
</code></pre></div> <p>Returns an iterator to one past the last element.</p> <p><img alt="Illustration from cppreference.com" src=../../../images/range-begin-end.svg></p> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <p>iterator one past the last element</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">&para;</a></h2> <p>No-throw guarantee: this member function never throws exceptions.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">&para;</a></h2> <p>Constant.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The following code shows an example for <code>end()</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>
</code></pre></div> <p>Returns an iterator to one past the last element.</p> <div class=nj-fig-wrap> <p><svg class="nj-fig nj-fig--range" viewbox="0 0 600 150" role=img aria-labelledby=fig-be-title xmlns=http://www.w3.org/2000/svg> <title id=fig-be-title>A row of fifteen elements followed by a dashed past-the-last position. begin() points to the first element and end() points to the past-the-last position.</title> <defs><marker id=fig-be-arrow viewbox="0 0 10 10" refx=9 refy=5 markerwidth=7 markerheight=7 orient=auto><path class=fg-head d="M0 1 L10 5 L0 9 z"/></marker></defs> <rect class=fg-cell x=30 y=62 width=30 height=30 rx=5 /> <rect class=fg-cell x=64 y=62 width=30 height=30 rx=5 /> <rect class=fg-cell x=98 y=62 width=30 height=30 rx=5 /> <rect class=fg-cell x=132 y=62 width=30 height=30 rx=5 /> <rect class=fg-cell x=166 y=62 width=30 height=30 rx=5 /> <rect class=fg-cell x=200 y=62 width=30 height=30 rx=5 /> <rect class=fg-cell x=234 y=62 width=30 height=30 rx=5 /> <rect class=fg-cell x=268 y=62 width=30 height=30 rx=5 /> <rect class=fg-cell x=302 y=62 width=30 height=30 rx=5 /> <rect class=fg-cell x=336 y=62 width=30 height=30 rx=5 /> <rect class=fg-cell x=370 y=62 width=30 height=30 rx=5 /> <rect class=fg-cell x=404 y=62 width=30 height=30 rx=5 /> <rect class=fg-cell x=438 y=62 width=30 height=30 rx=5 /> <rect class=fg-cell x=472 y=62 width=30 height=30 rx=5 /> <rect class=fg-cell x=506 y=62 width=30 height=30 rx=5 /> <rect x=540 y=62 width=30 height=30 rx=5 class="fg-cell fg-cell--end"/> <rect class=fg-pill x=15 y=8 width=60 height=24 rx=6 /> <text class=fg-pilltext x=45 y=24>begin</text> <line class=fg-arrow x1=45 y1=32 x2=45 y2=60 marker-end=url(#fig-be-arrow) /> <rect class=fg-pill x=531 y=8 width=48 height=24 rx=6 /> <text class=fg-pilltext x=555 y=24>end</text> <line class=fg-arrow x1=555 y1=32 x2=555 y2=60 marker-end=url(#fig-be-arrow) /> <text class="fg-note fg-note--r" x=537 y=132>Past-the-last element</text> <line class=fg-arrow x1=555 y1=124 x2=555 y2=96 marker-end=url(#fig-be-arrow) /> </svg></p> </div> <p class=nj-caption><code>end()</code> points to the position after the last element and <code>begin()</code> to the first element; the dashed cell is the past-the-last position, which must not be dereferenced.</p> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <p>iterator one past the last element</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">&para;</a></h2> <p>No-throw guarantee: this member function never throws exceptions.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">&para;</a></h2> <p>Constant.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The following code shows an example for <code>end()</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>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
@@ -20,4 +20,4 @@
<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=o>*</span><span class=n>it</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>5</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=../begin/ >begin</a> returns an iterator to the first element</li> <li><a href=../cend/ >cend</a> returns a const iterator to one past the last element</li> <li><a href=../rend/ >rend</a> returns a reverse iterator to one before the first element</li> <li><a href=../../../features/iterators/ >Iterators</a> - the article on iterators</li> <li><a href=../../basic_json_view/end/ >basic_json_view::end</a> - the same iteration on a 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 1.0.0.</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 21, 2026 08:21:27 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=../begin/ ><code>begin</code></a> - returns an iterator to the first element</li> <li><a href=../cend/ ><code>cend</code></a> - returns a const iterator to one past the last element</li> <li><a href=../rend/ ><code>rend</code></a> - returns a reverse iterator to one before the first element</li> <li><a href=../../../features/iterators/ >Iterators</a> - the article on iterators</li> <li><a href=../../basic_json_view/end/ ><code>basic_json_view::end</code></a> - the same iteration on a 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 1.0.0.</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 27, 2026 06:41:42 UTC">October 27, 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> <nav class="md-footer__inner md-grid" aria-label=Footer> <a href=../empty/ class="md-footer__link md-footer__link--prev" aria-label="Previous: empty"> <div class="md-footer__button md-icon"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M20 11v2H8l5.5 5.5-1.42 1.42L4.16 12l7.92-7.92L13.5 5.5 8 11z"/></svg> </div> <div class=md-footer__title> <span class=md-footer__direction> Previous </span> <div class=md-ellipsis> empty </div> </div> </a> <a href=../end_pos/ class="md-footer__link md-footer__link--next" aria-label="Next: end_pos"> <div class=md-footer__title> <span class=md-footer__direction> Next </span> <div class=md-ellipsis> end_pos </div> </div> <div class="md-footer__button md-icon"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M4 11v2h12l-5.5 5.5 1.42 1.42L19.84 12l-7.92-7.92L10.5 5.5 16 11z"/></svg> </div> </a> </nav> <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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+6 -4
View File
@@ -7,6 +7,8 @@ const_iterator end() const noexcept;
Returns an iterator to one past the last element.
`end()` points to the position after the last element and `begin()` to the first element; the dashed cell is the past-the-last position, which must not be dereferenced.
## Return value
iterator one past the last element
@@ -55,11 +57,11 @@ Output:
## See also
- [begin](https://json.nlohmann.me/api/basic_json/begin/index.md) returns an iterator to the first element
- [cend](https://json.nlohmann.me/api/basic_json/cend/index.md) returns a const iterator to one past the last element
- [rend](https://json.nlohmann.me/api/basic_json/rend/index.md) returns a reverse iterator to one before the first element
- [`begin`](https://json.nlohmann.me/api/basic_json/begin/index.md) - returns an iterator to the first element
- [`cend`](https://json.nlohmann.me/api/basic_json/cend/index.md) - returns a const iterator to one past the last element
- [`rend`](https://json.nlohmann.me/api/basic_json/rend/index.md) - returns a reverse iterator to one before the first element
- [Iterators](https://json.nlohmann.me/features/iterators/index.md) - the article on iterators
- [basic_json_view::end](https://json.nlohmann.me/api/basic_json_view/end/index.md) - the same iteration on a zero-copy view
- [`basic_json_view::end`](https://json.nlohmann.me/api/basic_json_view/end/index.md) - the same iteration on a zero-copy view
## Version history
+3 -2
View File
@@ -161,8 +161,9 @@ Constant.
## See also
- [start_pos](start_pos.md) to access the start position
- [JSON_DIAGNOSTIC_POSITIONS](../macros/json_diagnostic_positions.md) for an overview of the diagnostic positions
- [`start_pos`](start_pos.md) - to access the start position
- [`JSON_DIAGNOSTIC_POSITIONS`](../macros/json_diagnostic_positions.md) - overview of the supported conversions
- [Parsing and Exceptions](../../features/parsing/parse_exceptions.md) - handling parse errors and locating them in the input
## Version history
+2 -2
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/basic_json/end_pos/" rel="canonical"><link href=../end/ rel=prev><link href=../erase/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>end_pos - 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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</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> <img src=../../../images/wordmark-header.svg alt=logo> </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> end_pos </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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<span class=k>constexpr</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=kt>size_t</span><span class=w> </span><span class=nf>end_pos</span><span class=p>()</span><span class=w> </span><span class=k>const</span><span class=w> </span><span class=k>noexcept</span><span class=p>;</span>
<span class=cp>#endif</span>
</code></pre></div> <p>Returns the position immediately following the last character of the <abbr title="JavaScript Object Notation">JSON</abbr> string from which the value was parsed from.</p> <table> <thead> <tr> <th><abbr title="JavaScript Object Notation">JSON</abbr> type</th> <th>return value</th> </tr> </thead> <tbody> <tr> <td>object</td> <td>position after the closing <code>}</code></td> </tr> <tr> <td>array</td> <td>position after the closing <code>]</code></td> </tr> <tr> <td>string</td> <td>position after the closing <code>"</code></td> </tr> <tr> <td>number</td> <td>position after the last character</td> </tr> <tr> <td>boolean</td> <td>position after <code>e</code></td> </tr> <tr> <td>null</td> <td>position after <code>l</code></td> </tr> </tbody> </table> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <p>the position of the character <em>following</em> the last character of the given value in the parsed <abbr title="JavaScript Object Notation">JSON</abbr> string, if the value was created by the <a href=../parse/ ><code>parse</code></a> function, or <code>std::string::npos</code> if the value was constructed otherwise</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">&para;</a></h2> <p>No-throw guarantee: this member function never throws exceptions.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">&para;</a></h2> <p>Constant.</p> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <div class="admonition note"> <p class=admonition-title>Note</p> <p>The function is only available if macro <a href=../../macros/json_diagnostic_positions/ ><code>JSON_DIAGNOSTIC_POSITIONS</code></a> has been defined to <code class=highlight><span class=mi>1</span></code> before including the library header.</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</summary> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
@@ -101,4 +101,4 @@ Original string:
1
Parsed string:
1
</code></pre></div> <p>The output shows the start/end positions of all the objects and fields in the <abbr title="JavaScript Object Notation">JSON</abbr> string.</p> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../start_pos/ >start_pos</a> to access the start position</li> <li><a href=../../macros/json_diagnostic_positions/ >JSON_DIAGNOSTIC_POSITIONS</a> for an overview of the diagnostic positions</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 3.12.0.</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="January 17, 2025 05:53:35 UTC">January 17, 2025</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>The output shows the start/end positions of all the objects and fields in the <abbr title="JavaScript Object Notation">JSON</abbr> string.</p> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../start_pos/ ><code>start_pos</code></a> - to access the start position</li> <li><a href=../../macros/json_diagnostic_positions/ ><code>JSON_DIAGNOSTIC_POSITIONS</code></a> - overview of the supported conversions</li> <li><a href=../../../features/parsing/parse_exceptions/ >Parsing and Exceptions</a> - handling parse errors and locating them in the input</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 3.12.0.</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 27, 2026 06:41:42 UTC">October 27, 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> <nav class="md-footer__inner md-grid" aria-label=Footer> <a href=../end/ class="md-footer__link md-footer__link--prev" aria-label="Previous: end"> <div class="md-footer__button md-icon"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M20 11v2H8l5.5 5.5-1.42 1.42L4.16 12l7.92-7.92L13.5 5.5 8 11z"/></svg> </div> <div class=md-footer__title> <span class=md-footer__direction> Previous </span> <div class=md-ellipsis> end </div> </div> </a> <a href=../erase/ class="md-footer__link md-footer__link--next" aria-label="Next: erase"> <div class=md-footer__title> <span class=md-footer__direction> Next </span> <div class=md-ellipsis> erase </div> </div> <div class="md-footer__button md-icon"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M4 11v2h12l-5.5 5.5 1.42 1.42L19.84 12l-7.92-7.92L10.5 5.5 16 11z"/></svg> </div> </a> </nav> <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
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@@ -155,8 +155,9 @@ The output shows the start/end positions of all the objects and fields in the JS
## See also
- [start_pos](https://json.nlohmann.me/api/basic_json/start_pos/index.md) to access the start position
- [JSON_DIAGNOSTIC_POSITIONS](https://json.nlohmann.me/api/macros/json_diagnostic_positions/index.md) for an overview of the diagnostic positions
- [`start_pos`](https://json.nlohmann.me/api/basic_json/start_pos/index.md) - to access the start position
- [`JSON_DIAGNOSTIC_POSITIONS`](https://json.nlohmann.me/api/macros/json_diagnostic_positions/index.md) - overview of the supported conversions
- [Parsing and Exceptions](https://json.nlohmann.me/features/parsing/parse_exceptions/index.md) - handling parse errors and locating them in the input
## Version history
+2 -2
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@@ -337,8 +337,8 @@ Strong exception safety: if an exception occurs, the original value stays intact
## See also
- [clear](clear.md) clears the contents
- [insert](insert.md) add values to an array/object
- [`clear`](clear.md) - clears the contents
- [`insert`](insert.md) - add values to an array/object
- [Modifying values](../../features/modifying_values.md) - the article on modifying values
## Version history
+2 -2
View File
@@ -1,4 +1,4 @@
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<span class=n>iterator</span><span class=w> </span><span class=nf>erase</span><span class=p>(</span><span class=n>iterator</span><span class=w> </span><span class=n>pos</span><span class=p>);</span>
<span class=n>const_iterator</span><span class=w> </span><span class=nf>erase</span><span class=p>(</span><span class=n>const_iterator</span><span class=w> </span><span class=n>pos</span><span class=p>);</span>
@@ -148,4 +148,4 @@
<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_array</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>0</span><span class=p>,</span><span class=mi>1</span><span class=p>,</span><span class=mi>3</span><span class=p>,</span><span class=mi>4</span><span class=p>,</span><span class=mi>5</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=../clear/ >clear</a> clears the contents</li> <li><a href=../insert/ >insert</a> add values to an array/object</li> <li><a href=../../../features/modifying_values/ >Modifying values</a> - the article on modifying values</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 1.0.0. Added support for binary types in version 3.8.0.</li> <li>Added in version 1.0.0. Added support for binary types in version 3.8.0.</li> <li>Added in version 1.0.0.</li> <li>Added in version 3.11.0. Support for keys convertible to <code>std::string_view</code> 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>, consistently across the lookup functions.</li> <li>Added in version 1.0.0.</li> </ol> <!-- 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 24, 2026 15:57:44 UTC">October 24, 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 32-32.3V64.3Line 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=../clear/ ><code>clear</code></a> - clears the contents</li> <li><a href=../insert/ ><code>insert</code></a> - add values to an array/object</li> <li><a href=../../../features/modifying_values/ >Modifying values</a> - the article on modifying values</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 1.0.0. Added support for binary types in version 3.8.0.</li> <li>Added in version 1.0.0. Added support for binary types in version 3.8.0.</li> <li>Added in version 1.0.0.</li> <li>Added in version 3.11.0. Support for keys convertible to <code>std::string_view</code> 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>, consistently across the lookup functions.</li> <li>Added in version 1.0.0.</li> </ol> <!-- 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 27, 2026 06:41:42 UTC">October 27, 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> <nav class="md-footer__inner md-grid" aria-label=Footer> <a href=../end_pos/ class="md-footer__link md-footer__link--prev" aria-label="Previous: end_pos"> <div class="md-footer__button md-icon"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M20 11v2H8l5.5 5.5-1.42 1.42L4.16 12l7.92-7.92L13.5 5.5 8 11z"/></svg> </div> <div class=md-footer__title> <span class=md-footer__direction> Previous </span> <div class=md-ellipsis> end_pos </div> </div> </a> <a href=../error_handler_t/ class="md-footer__link md-footer__link--next" aria-label="Next: error_handler_t"> <div class=md-footer__title> <span class=md-footer__direction> Next </span> <div class=md-ellipsis> error_handler_t </div> </div> <div class="md-footer__button md-icon"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M4 11v2h12l-5.5 5.5 1.42 1.42L19.84 12l-7.92-7.92L10.5 5.5 16 11z"/></svg> </div> </a> </nav> <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.Line truncated
+2 -2
View File
@@ -300,8 +300,8 @@ Output:
## See also
- [clear](https://json.nlohmann.me/api/basic_json/clear/index.md) clears the contents
- [insert](https://json.nlohmann.me/api/basic_json/insert/index.md) add values to an array/object
- [`clear`](https://json.nlohmann.me/api/basic_json/clear/index.md) - clears the contents
- [`insert`](https://json.nlohmann.me/api/basic_json/insert/index.md) - add values to an array/object
- [Modifying values](https://json.nlohmann.me/features/modifying_values/index.md) - the article on modifying values
## Version history
+1 -1
View File
@@ -90,7 +90,7 @@ keep
## See also
- [dump](dump.md) serializes a JSON value, with an `error_handler_t` parameter to configure invalid UTF-8 handling
- [`dump`](dump.md) - serializes a JSON value, with an `error_handler_t` parameter to configure invalid UTF-8 handling
- [Handling invalid UTF-8](../../features/serialization.md#handling-invalid-utf-8) - the article on handling invalid UTF-8
## Version history
+2 -2
View File
@@ -1,4 +1,4 @@
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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"Line truncated
<span class=w> </span><span class=n>strict</span><span class=p>,</span>
<span class=w> </span><span class=n>replace</span><span class=p>,</span>
<span class=w> </span><span class=n>ignore</span><span class=p>,</span>
@@ -33,4 +33,4 @@
<span class=err>s</span><span class=kc>tr</span><span class=err>i</span><span class=kc>n</span><span class=err>g</span><span class=w> </span><span class=err>wi</span><span class=kc>t</span><span class=err>h</span><span class=w> </span><span class=err>replaced</span><span class=w> </span><span class=err>i</span><span class=kc>n</span><span class=err>valid</span><span class=w> </span><span class=err>charac</span><span class=kc>ters</span><span class=p>:</span><span class=w> </span><span class=s2>"ä�ü"</span>
<span class=err>s</span><span class=kc>tr</span><span class=err>i</span><span class=kc>n</span><span class=err>g</span><span class=w> </span><span class=err>wi</span><span class=kc>t</span><span class=err>h</span><span class=w> </span><span class=err>ig</span><span class=kc>n</span><span class=err>ored</span><span class=w> </span><span class=err>i</span><span class=kc>n</span><span class=err>valid</span><span class=w> </span><span class=err>charac</span><span class=kc>ters</span><span class=p>:</span><span class=w> </span><span class=s2>"äü"</span>
<span class=err>s</span><span class=kc>tr</span><span class=err>i</span><span class=kc>n</span><span class=err>g</span><span class=w> </span><span class=err>wi</span><span class=kc>t</span><span class=err>h</span><span class=w> </span><span class=kc>t</span><span class=err>he</span><span class=w> </span><span class=err>i</span><span class=kc>n</span><span class=err>valid</span><span class=w> </span><span class=err>by</span><span class=kc>te</span><span class=w> </span><span class=err>kep</span><span class=kc>t</span><span class=w> </span><span class=err>as</span><span class=w> </span><span class=err>is</span><span class=w> </span><span class=err>(</span><span class=mi>7</span><span class=w> </span><span class=err>by</span><span class=kc>tes</span><span class=p>,</span><span class=w> </span><span class=kc>n</span><span class=err>o</span><span class=kc>t</span><span class=w> </span><span class=err>valid</span><span class=w> </span><span class=err>UTF</span><span class=mi>-8</span><span class=w> </span><span class=err>i</span><span class=kc>tself</span><span class=err>)</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=../dump/ >dump</a> serializes a <abbr title="JavaScript Object Notation">JSON</abbr> value, with an <code>error_handler_t</code> parameter to configure invalid <abbr title="Unicode Transformation Format">UTF</abbr>-8 handling</li> <li><a href=../../../features/serialization/#handling-invalid-utf-8>Handling invalid <abbr title="Unicode Transformation Format">UTF</abbr>-8</a> - the article on handling invalid <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 3.4.0.</li> <li>Added <code>keep</code>, and made this enumeration apply to the binary readers and writers in addition to <code>dump</code>, in version 3.13.0.</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=../dump/ ><code>dump</code></a> - serializes a <abbr title="JavaScript Object Notation">JSON</abbr> value, with an <code>error_handler_t</code> parameter to configure invalid <abbr title="Unicode Transformation Format">UTF</abbr>-8 handling</li> <li><a href=../../../features/serialization/#handling-invalid-utf-8>Handling invalid <abbr title="Unicode Transformation Format">UTF</abbr>-8</a> - the article on handling invalid <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 3.4.0.</li> <li>Added <code>keep</code>, and made this enumeration apply to the binary readers and writers in addition to <code>dump</code>, in version 3.13.0.</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 27, 2026 06:41:42 UTC">October 27, 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> <nav class="md-footer__inner md-grid" aria-label=Footer> <a href=../erase/ class="md-footer__link md-footer__link--prev" aria-label="Previous: erase"> <div class="md-footer__button md-icon"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M20 11v2H8l5.5 5.5-1.42 1.42L4.16 12l7.92-7.92L13.5 5.5 8 11z"/></svg> </div> <div class=md-footer__title> <span class=md-footer__direction> Previous </span> <div class=md-ellipsis> erase </div> </div> </a> <a href=../exception/ class="md-footer__link md-footer__link--next" aria-label="Next: exception"> <div class=md-footer__title> <span class=md-footer__direction> Next </span> <div class=md-ellipsis> exception </div> </div> <div class="md-footer__button md-icon"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M4 11v2h12l-5.5 5.5 1.42 1.42L19.84 12l-7.92-7.92L10.5 5.5 16 11z"/></svg> </div> </a> </nav> <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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+1 -1
View File
@@ -70,7 +70,7 @@ string with the invalid byte kept as is (7 bytes, not valid UTF-8 itself)
## See also
- [dump](https://json.nlohmann.me/api/basic_json/dump/index.md) serializes a JSON value, with an `error_handler_t` parameter to configure invalid UTF-8 handling
- [`dump`](https://json.nlohmann.me/api/basic_json/dump/index.md) - serializes a JSON value, with an `error_handler_t` parameter to configure invalid UTF-8 handling
- [Handling invalid UTF-8](https://json.nlohmann.me/features/serialization/#handling-invalid-utf-8) - the article on handling invalid UTF-8
## Version history
+8 -1
View File
@@ -40,6 +40,9 @@ classDiagram
style json_exception fill:#CCCCFF
```
<p class="nj-caption" markdown>Class hierarchy of the library's exceptions; arrows point from a derived class to its
base class, and the highlighted box is `basic_json::exception`.</p>
Subclasses:
- [`parse_error`](parse_error.md) for exceptions indicating a parse error
@@ -102,7 +105,11 @@ constructor.
## See also
[List of exceptions](../../home/exceptions.md)
- [List of exceptions](../../home/exceptions.md) - overview of all exceptions thrown by the library
- [Working Without Exceptions](../../features/no_exceptions.md) - using the library without exceptions
- [`JSON_DIAGNOSTICS`](../macros/json_diagnostics.md) - extended exception messages with the path of the failing value
- [Parsing and Exceptions](../../features/parsing/parse_exceptions.md) - parsing alternatives that do not throw
- [Debugging](../../home/debugging.md) - debugging aids
## Version history
+3 -3
View File
@@ -1,4 +1,4 @@
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</code></pre></div> <p>This class is an extension of <a href="https://en.cppreference.com/w/cpp/error/exception"><code>std::exception</code></a> objects with a member <code>id</code> for exception ids. It is used as the base class for all exceptions thrown by the <code>basic_json</code> class. This class can hence be used as "wildcard" to catch exceptions, see example below.</p> <pre class=mermaid><code>classDiagram
direction LR
@@ -27,7 +27,7 @@
json_exception &lt;|-- json_out_of_range
json_exception &lt;|-- json_other_error
style json_exception fill:#CCCCFF</code></pre> <p>Subclasses:</p> <ul> <li><a href=../parse_error/ ><code>parse_error</code></a> for exceptions indicating a parse error</li> <li><a href=../invalid_iterator/ ><code>invalid_iterator</code></a> for exceptions indicating errors with iterators</li> <li><a href=../type_error/ ><code>type_error</code></a> for exceptions indicating executing a member function with a wrong type</li> <li><a href=../out_of_range/ ><code>out_of_range</code></a> for exceptions indicating access out of the defined range</li> <li><a href=../other_error/ ><code>other_error</code></a> for exceptions indicating other library errors</li> </ul> <h2 id=member-functions>Member functions<a class=headerlink href=#member-functions title="Permanent link">&para;</a></h2> <ul> <li><strong>what</strong> - returns explanatory string</li> </ul> <h2 id=member-variables>Member variables<a class=headerlink href=#member-variables title="Permanent link">&para;</a></h2> <ul> <li><strong>id</strong> - the id of the exception</li> </ul> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <p>To have nothrow-copy-constructible exceptions, we internally use <code>std::runtime_error</code> which can cope with arbitrary-length error messages. Intermediate strings are built with static functions and then passed to the actual constructor.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The following code shows how arbitrary library exceptions can be caught.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
style json_exception fill:#CCCCFF</code></pre> <p class=nj-caption>Class hierarchy of the library's exceptions; arrows point from a derived class to its base class, and the highlighted box is <code>basic_json::exception</code>.</p> <p>Subclasses:</p> <ul> <li><a href=../parse_error/ ><code>parse_error</code></a> for exceptions indicating a parse error</li> <li><a href=../invalid_iterator/ ><code>invalid_iterator</code></a> for exceptions indicating errors with iterators</li> <li><a href=../type_error/ ><code>type_error</code></a> for exceptions indicating executing a member function with a wrong type</li> <li><a href=../out_of_range/ ><code>out_of_range</code></a> for exceptions indicating access out of the defined range</li> <li><a href=../other_error/ ><code>other_error</code></a> for exceptions indicating other library errors</li> </ul> <h2 id=member-functions>Member functions<a class=headerlink href=#member-functions title="Permanent link">&para;</a></h2> <ul> <li><strong>what</strong> - returns explanatory string</li> </ul> <h2 id=member-variables>Member variables<a class=headerlink href=#member-variables title="Permanent link">&para;</a></h2> <ul> <li><strong>id</strong> - the id of the exception</li> </ul> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <p>To have nothrow-copy-constructible exceptions, we internally use <code>std::runtime_error</code> which can cope with arbitrary-length error messages. Intermediate strings are built with static functions and then passed to the actual constructor.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The following code shows how arbitrary library exceptions can be caught.</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>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
@@ -49,4 +49,4 @@
<span class=p>}</span>
</code></pre></div> <p>Output:</p> <div class=highlight><pre><span></span><code><span class=err>message</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>403</span><span class=p>]</span><span class=w> </span><span class=err>key</span><span class=w> </span><span class=err>'</span><span class=kc>n</span><span class=err>o</span><span class=kc>n</span><span class=mf>-e</span><span class=err>xis</span><span class=kc>t</span><span class=err>i</span><span class=kc>n</span><span class=err>g'</span><span class=w> </span><span class=kc>n</span><span class=err>o</span><span class=kc>t</span><span class=w> </span><span class=kc>f</span><span class=err>ou</span><span class=kc>n</span><span class=err>d</span>
<span class=err>excep</span><span class=kc>t</span><span class=err>io</span><span class=kc>n</span><span class=w> </span><span class=err>id</span><span class=p>:</span><span class=w> </span><span class=mi>403</span>
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <p><a href=../../../home/exceptions/ >List of exceptions</a></p> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ul> <li>Added in version 3.0.0.</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 24, 2026 15:57:44 UTC">October 24, 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/exceptions/ >List of exceptions</a> - overview of all exceptions thrown by the library</li> <li><a href=../../../features/no_exceptions/ >Working Without Exceptions</a> - using the library without exceptions</li> <li><a href=../../macros/json_diagnostics/ ><code>JSON_DIAGNOSTICS</code></a> - extended exception messages with the path of the failing value</li> <li><a href=../../../features/parsing/parse_exceptions/ >Parsing and Exceptions</a> - parsing alternatives that do not throw</li> <li><a href=../../../home/debugging/ >Debugging</a> - debugging aids</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 3.0.0.</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 27, 2026 06:41:42 UTC">October 27, 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> <nav class="md-footer__inner md-grid" aria-label=Footer> <a href=../error_handler_t/ class="md-footer__link md-footer__link--prev" aria-label="Previous: error_handler_t"> <div class="md-footer__button md-icon"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M20 11v2H8l5.5 5.5-1.42 1.42L4.16 12l7.92-7.92L13.5 5.5 8 11z"/></svg> </div> <div class=md-footer__title> <span class=md-footer__direction> Previous </span> <div class=md-ellipsis> error_handler_t </div> </div> </a> <a href=../find/ class="md-footer__link md-footer__link--next" aria-label="Next: find"> <div class=md-footer__title> <span class=md-footer__direction> Next </span> <div class=md-ellipsis> find </div> </div> <div class="md-footer__button md-icon"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M4 11v2h12l-5.5 5.5 1.42 1.42L19.84 12l-7.92-7.92L10.5 5.5 16 11z"/></svg> </div> </a> </nav> <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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