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<span class=w> </span><span class=c1>// a simple struct to model a person</span>
<span class=w> </span><span class=k>struct</span><span class=w> </span><span class=nc>person</span><span class=w> </span><span class=p>{</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>string</span><span class=w> </span><span class=n>name</span><span class=p>;</span>
@@ -50,7 +50,7 @@
<span class=w> </span><span class=n>j</span><span class=p>.</span><span class=n>at</span><span class=p>(</span><span class=s>&quot;age&quot;</span><span class=p>).</span><span class=n>get_to</span><span class=p>(</span><span class=n>p</span><span class=p>.</span><span class=n>age</span><span class=p>);</span>
<span class=w> </span><span class=p>}</span>
<span class=p>}</span><span class=w> </span><span class=c1>// namespace ns</span>
</code></pre></div> <p>That's all! When calling the <code>json</code> constructor with your type, your custom <code>to_json</code> method will be automatically called. Likewise, when calling <code>template get&lt;your_type&gt;()</code> or <code>get_to(your_type&amp;)</code>, the <code>from_json</code> method will be called.</p> <p>Some important things:</p> <ul> <li>Those methods <strong>MUST</strong> be in your type's namespace (which can be the global namespace), or the library will not be able to locate them (in this example, they are in namespace <code>ns</code>, where <code>person</code> is defined).</li> <li>Those methods <strong>MUST</strong> be available (e.g., proper headers must be included) everywhere you use these conversions. Look at <a href=https://github.com/nlohmann/json/issues/1108>#1108</a> for errors that may occur otherwise.</li> <li>When using <code>template get&lt;your_type&gt;()</code>, <code>your_type</code> <strong>MUST</strong> be <a href=https://en.cppreference.com/w/cpp/named_req/DefaultConstructible>DefaultConstructible</a>. (There is a way to bypass this requirement described later.)</li> <li>In function <code>from_json</code>, use function <a href=../../api/basic_json/at/ ><code>at()</code></a> to access the object values rather than <code>operator[]</code>. In case a key does not exist, <code>at</code> throws an exception that you can handle, whereas <code>operator[]</code> exhibits undefined behavior.</li> <li>You do not need to add serializers or deserializers for STL types like <code>std::vector</code>: the library already implements these.</li> </ul> <h2 id=simplify-your-life-with-macros>Simplify your life with macros<a class=headerlink href=#simplify-your-life-with-macros title="Permanent link">&para;</a></h2> <p>If you just want to serialize/deserialize some structs, the <code>to_json</code>/<code>from_json</code> functions can be a lot of boilerplate.</p> <p>There are four macros to make your life easier as long as you (1) want to use a JSON object as serialization and (2) want to use the member variable names as object keys in that object:</p> <ul> <li><a href=../../api/macros/nlohmann_define_type_non_intrusive/ ><code>NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE(name, member1, member2, ...)</code></a> is to be defined inside the namespace of the class/struct to create code for. It will throw an exception in <code>from_json()</code> due to a missing value in the JSON object.</li> <li><a href=../../api/macros/nlohmann_define_type_non_intrusive/ ><code>NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT(name, member1, member2, ...)</code></a> is to be defined inside the namespace of the class/struct to create code for. It will not throw an exception in <code>from_json()</code> due to a missing value in the JSON object, but fills in values from object which is default-constructed by the type.</li> <li><a href=../../api/macros/nlohmann_define_type_intrusive/ ><code>NLOHMANN_DEFINE_TYPE_INTRUSIVE(name, member1, member2, ...)</code></a> is to be defined inside the class/struct to create code for. This macro can also access private members. It will throw an exception in <code>from_json()</code> due to a missing value in the JSON object.</li> <li><a href=../../api/macros/nlohmann_define_type_intrusive/ ><code>NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT(name, member1, member2, ...)</code></a> is to be defined inside the class/struct to create code for. This macro can also access private members. It will not throw an exception in <code>from_json()</code> due to a missing value in the JSON object, but fills in values from object which is default-constructed by the type.</li> </ul> <p>In all macros, the first parameter is the name of the class/struct, and all remaining parameters name the members. You can read more docs about them starting from <a href=../macros/#nlohmann_define_type_intrusivetype-member>here</a>.</p> <div class="admonition info"> <p class=admonition-title>Implementation limits</p> <ul> <li>The current macro implementations are limited to at most 64 member variables. If you want to serialize/deserialize types with more than 64 member variables, you need to define the <code>to_json</code>/<code>from_json</code> functions manually.</li> <li>The macros only work for the <a href=../../api/json/ ><code>nlohmann::json</code></a> type; other specializations such as <a href=../../api/ordered_json/ ><code>nlohmann::ordered_json</code></a> are currently unsupported.</li> </ul> </div> <details class=example> <summary>Example</summary> <p>The <code>to_json</code>/<code>from_json</code> functions for the <code>person</code> struct above can be created with:</p> <div class=highlight><pre><span></span><code><span class=k>namespace</span><span class=w> </span><span class=nn>ns</span><span class=w> </span><span class=p>{</span>
</code></pre></div> <p>That's all! When calling the <code>json</code> constructor with your type, your custom <code>to_json</code> method will be automatically called. Likewise, when calling <code>template get&lt;your_type&gt;()</code> or <code>get_to(your_type&amp;)</code>, the <code>from_json</code> method will be called.</p> <p>Some important things:</p> <ul> <li>Those methods <strong>MUST</strong> be in your type's namespace (which can be the global namespace), or the library will not be able to locate them (in this example, they are in namespace <code>ns</code>, where <code>person</code> is defined).</li> <li>Those methods <strong>MUST</strong> be available (e.g., proper headers must be included) everywhere you use these conversions. Look at <a href="https://github.com/nlohmann/json/issues/1108">#1108</a> for errors that may occur otherwise.</li> <li>When using <code>template get&lt;your_type&gt;()</code>, <code>your_type</code> <strong>MUST</strong> be <a href="https://en.cppreference.com/w/cpp/named_req/DefaultConstructible">DefaultConstructible</a>. (There is a way to bypass this requirement described later.)</li> <li>In function <code>from_json</code>, use function <a href=../../api/basic_json/at/ ><code>at()</code></a> to access the object values rather than <code>operator[]</code>. In case a key does not exist, <code>at</code> throws an exception that you can handle, whereas <code>operator[]</code> exhibits undefined behavior.</li> <li>You do not need to add serializers or deserializers for <abbr title="Standard Template Library">STL</abbr> types like <code>std::vector</code>: the library already implements these.</li> </ul> <h2 id=simplify-your-life-with-macros>Simplify your life with macros<a class=headerlink href=#simplify-your-life-with-macros title="Permanent link">&para;</a></h2> <p>If you just want to serialize/deserialize some structs, the <code>to_json</code>/<code>from_json</code> functions can be a lot of boilerplate.</p> <p>There are six macros to make your life easier as long as you (1) want to use a <abbr title="JavaScript Object Notation">JSON</abbr> object as serialization and (2) want to use the member variable names as object keys in that object:</p> <ul> <li><a href=../../api/macros/nlohmann_define_type_non_intrusive/ ><code>NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE(name, member1, member2, ...)</code></a> is to be defined inside the namespace of the class/struct to create code for. It will throw an exception in <code>from_json()</code> due to a missing value in the <abbr title="JavaScript Object Notation">JSON</abbr> object.</li> <li><a href=../../api/macros/nlohmann_define_type_non_intrusive/ ><code>NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT(name, member1, member2, ...)</code></a> is to be defined inside the namespace of the class/struct to create code for. It will not throw an exception in <code>from_json()</code> due to a missing value in the <abbr title="JavaScript Object Notation">JSON</abbr> object, but fills in values from object which is default-constructed by the type.</li> <li><a href=../../api/macros/nlohmann_define_type_non_intrusive/ ><code>NLOHMANN_DEFINE_TYPE_INTRUSIVE_ONLY_SERIALIZE(name, member1, member2, ...)</code></a> is to be defined inside the namespace of the class/struct to create code for. It does not define a <code>fron_json()</code> function which is needed in case the type does not have a default constructor.</li> <li><a href=../../api/macros/nlohmann_define_type_intrusive/ ><code>NLOHMANN_DEFINE_TYPE_INTRUSIVE(name, member1, member2, ...)</code></a> is to be defined inside the class/struct to create code for. This macro can also access private members. It will throw an exception in <code>from_json()</code> due to a missing value in the <abbr title="JavaScript Object Notation">JSON</abbr> object.</li> <li><a href=../../api/macros/nlohmann_define_type_intrusive/ ><code>NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT(name, member1, member2, ...)</code></a> is to be defined inside the class/struct to create code for. This macro can also access private members. It will not throw an exception in <code>from_json()</code> due to a missing value in the <abbr title="JavaScript Object Notation">JSON</abbr> object, but fills in values from object which is default-constructed by the type.</li> <li><a href=../../api/macros/nlohmann_define_type_intrusive/ ><code>NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE(name, member1, member2, ...)</code></a> is to be defined inside the class/struct to create code for. This macro can also access private members. It does not define a <code>fron_json()</code> function which is needed in case the type does not have a default constructor.</li> </ul> <p>Furthermore, there exist versions to use in case of derived classes:</p> <table> <thead> <tr> <th>Need access to private members</th> <th>Need only de-serialization</th> <th>Allow missing values when de-serializing</th> <th>macro</th> </tr> </thead> <tbody> <tr> <td><div style="colorLine truncated
<span class=w> </span><span class=n>NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE</span><span class=p>(</span><span class=n>person</span><span class=p>,</span><span class=w> </span><span class=n>name</span><span class=p>,</span><span class=w> </span><span class=n>address</span><span class=p>,</span><span class=w> </span><span class=n>age</span><span class=p>)</span>
<span class=p>}</span>
</code></pre></div> <p>Here is an example with private members, where <code>NLOHMANN_DEFINE_TYPE_INTRUSIVE</code> is needed:</p> <div class=highlight><pre><span></span><code><span class=k>namespace</span><span class=w> </span><span class=nn>ns</span><span class=w> </span><span class=p>{</span>
@@ -64,7 +64,7 @@
<span class=w> </span><span class=n>NLOHMANN_DEFINE_TYPE_INTRUSIVE</span><span class=p>(</span><span class=n>address</span><span class=p>,</span><span class=w> </span><span class=n>street</span><span class=p>,</span><span class=w> </span><span class=n>housenumber</span><span class=p>,</span><span class=w> </span><span class=n>postcode</span><span class=p>)</span>
<span class=w> </span><span class=p>};</span>
<span class=p>}</span>
</code></pre></div> </details> <h2 id=how-do-i-convert-third-party-types>How do I convert third-party types?<a class=headerlink href=#how-do-i-convert-third-party-types title="Permanent link">&para;</a></h2> <p>This requires a bit more advanced technique. But first, let's see how this conversion mechanism works:</p> <p>The library uses <strong>JSON Serializers</strong> to convert types to json. The default serializer for <code>nlohmann::json</code> is <code>nlohmann::adl_serializer</code> (ADL means <a href=https://en.cppreference.com/w/cpp/language/adl>Argument-Dependent Lookup</a>).</p> <p>It is implemented like this (simplified):</p> <div class=highlight><pre><span></span><code><span class=k>template</span><span class=w> </span><span class=o>&lt;</span><span class=k>typename</span><span class=w> </span><span class=nc>T</span><span class=o>&gt;</span>
</code></pre></div> </details> <h2 id=how-do-i-convert-third-party-types>How do I convert third-party types?<a class=headerlink href=#how-do-i-convert-third-party-types title="Permanent link">&para;</a></h2> <p>This requires a bit more advanced technique. But first, let's see how this conversion mechanism works:</p> <p>The library uses <strong><abbr title="JavaScript Object Notation">JSON</abbr> Serializers</strong> to convert types to json. The default serializer for <code>nlohmann::json</code> is <code>nlohmann::adl_serializer</code> (<abbr title="Argument-dependent lookup">ADL</abbr> means <a href="https://en.cppreference.com/w/cpp/language/adl">Argument-Dependent Lookup</a>).</p> <p>It is implemented like this (simplified):</p> <div class=highlight><pre><span></span><code><span class=k>template</span><span class=w> </span><span class=o>&lt;</span><span class=k>typename</span><span class=w> </span><span class=nc>T</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>
<span class=w> </span><span class=k>static</span><span class=w> </span><span class=kt>void</span><span class=w> </span><span class=nf>to_json</span><span class=p>(</span><span class=n>json</span><span class=o>&amp;</span><span class=w> </span><span class=n>j</span><span class=p>,</span><span class=w> </span><span class=k>const</span><span class=w> </span><span class=n>T</span><span class=o>&amp;</span><span class=w> </span><span class=n>value</span><span class=p>)</span><span class=w> </span><span class=p>{</span>
<span class=w> </span><span class=c1>// calls the &quot;to_json&quot; method in T&#39;s namespace</span>
@@ -97,7 +97,7 @@
<span class=w> </span><span class=p>}</span>
<span class=p>};</span>
<span class=n>NLOHMANN_JSON_NAMESPACE_END</span>
</code></pre></div> <div class="admonition note"> <p class=admonition-title>ABI compatibility</p> <p>Use <a href=../../api/macros/nlohmann_json_namespace_begin/ ><code>NLOHMANN_JSON_NAMESPACE_BEGIN</code></a> and <code>NLOHMANN_JSON_NAMESPACE_END</code> instead of <code class=highlight><span class=k>namespace</span><span class=w> </span><span class=nn>nlohmann</span><span class=w> </span><span class=p>{</span><span class=w> </span><span class=p>}</span></code> in code which may be linked with different versions of this library.</p> </div> <h2 id=how-can-i-use-get-for-non-default-constructiblenon-copyable-types>How can I use <code>get()</code> for non-default constructible/non-copyable types?<a class=headerlink href=#how-can-i-use-get-for-non-default-constructiblenon-copyable-types title="Permanent link">&para;</a></h2> <p>There is a way, if your type is <a href=https://en.cppreference.com/w/cpp/named_req/MoveConstructible>MoveConstructible</a>. You will need to specialize the <code>adl_serializer</code> as well, but with a special <code>from_json</code> overload:</p> <div class=highlight><pre><span></span><code><span class=k>struct</span><span class=w> </span><span class=nc>move_only_type</span><span class=w> </span><span class=p>{</span>
</code></pre></div> <div class="admonition note"> <p class=admonition-title>ABI compatibility</p> <p>Use <a href=../../api/macros/nlohmann_json_namespace_begin/ ><code>NLOHMANN_JSON_NAMESPACE_BEGIN</code></a> and <code>NLOHMANN_JSON_NAMESPACE_END</code> instead of <code class=highlight><span class=k>namespace</span><span class=w> </span><span class=nn>nlohmann</span><span class=w> </span><span class=p>{</span><span class=w> </span><span class=p>}</span></code> in code which may be linked with different versions of this library.</p> </div> <h2 id=how-can-i-use-get-for-non-default-constructiblenon-copyable-types>How can I use <code>get()</code> for non-default constructible/non-copyable types?<a class=headerlink href=#how-can-i-use-get-for-non-default-constructiblenon-copyable-types title="Permanent link">&para;</a></h2> <p>There is a way, if your type is <a href="https://en.cppreference.com/w/cpp/named_req/MoveConstructible">MoveConstructible</a>. You will need to specialize the <code>adl_serializer</code> as well, but with a special <code>from_json</code> overload:</p> <div class=highlight><pre><span></span><code><span class=k>struct</span><span class=w> </span><span class=nc>move_only_type</span><span class=w> </span><span class=p>{</span>
<span class=w> </span><span class=n>move_only_type</span><span class=p>()</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=k>delete</span><span class=p>;</span>
<span class=w> </span><span class=n>move_only_type</span><span class=p>(</span><span class=kt>int</span><span class=w> </span><span class=n>ii</span><span class=p>)</span><span class=o>:</span><span class=w> </span><span class=n>i</span><span class=p>(</span><span class=n>ii</span><span class=p>)</span><span class=w> </span><span class=p>{}</span>
<span class=w> </span><span class=n>move_only_type</span><span class=p>(</span><span class=k>const</span><span class=w> </span><span class=n>move_only_type</span><span class=o>&amp;</span><span class=p>)</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=k>delete</span><span class=p>;</span>
@@ -123,7 +123,7 @@
<span class=w> </span><span class=p>}</span>
<span class=w> </span><span class=p>};</span>
<span class=p>}</span>
</code></pre></div> <h2 id=can-i-write-my-own-serializer-advanced-use>Can I write my own serializer? (Advanced use)<a class=headerlink href=#can-i-write-my-own-serializer-advanced-use title="Permanent link">&para;</a></h2> <p>Yes. You might want to take a look at <a href=https://github.com/nlohmann/json/blob/develop/tests/src/unit-udt.cpp><code>unit-udt.cpp</code></a> in the test suite, to see a few examples.</p> <p>If you write your own serializer, you'll need to do a few things:</p> <ul> <li>use a different <code>basic_json</code> alias than <code>nlohmann::json</code> (the last template parameter of <code>basic_json</code> is the <code>JSONSerializer</code>)</li> <li>use your <code>basic_json</code> alias (or a template parameter) in all your <code>to_json</code>/<code>from_json</code> methods</li> <li>use <code>nlohmann::to_json</code> and <code>nlohmann::from_json</code> when you need ADL</li> </ul> <p>Here is an example, without simplifications, that only accepts types with a size &lt;= 32, and uses ADL.</p> <div class=highlight><pre><span></span><code><span class=c1>// You should use void as a second template argument</span>
</code></pre></div> <h2 id=can-i-write-my-own-serializer-advanced-use>Can I write my own serializer? (Advanced use)<a class=headerlink href=#can-i-write-my-own-serializer-advanced-use title="Permanent link">&para;</a></h2> <p>Yes. You might want to take a look at <a href="https://github.com/nlohmann/json/blob/develop/tests/src/unit-udt.cpp"><code>unit-udt.cpp</code></a> in the test suite, to see a few examples.</p> <p>If you write your own serializer, you'll need to do a few things:</p> <ul> <li>use a different <code>basic_json</code> alias than <code>nlohmann::json</code> (the last template parameter of <code>basic_json</code> is the <code>JSONSerializer</code>)</li> <li>use your <code>basic_json</code> alias (or a template parameter) in all your <code>to_json</code>/<code>from_json</code> methods</li> <li>use <code>nlohmann::to_json</code> and <code>nlohmann::from_json</code> when you need <abbr title="Argument-dependent lookup">ADL</abbr></li> </ul> <p>Here is an example, without simplifications, that only accepts types with a size &lt;= 32, and uses <abbr title="Argument-dependent lookup">ADL</abbr>.</p> <div class=highlight><pre><span></span><code><span class=c1>// You should use void as a second template argument</span>
<span class=c1>// if you don&#39;t need compile-time checks on T</span>
<span class=k>template</span><span class=o>&lt;</span><span class=k>typename</span><span class=w> </span><span class=nc>T</span><span class=p>,</span><span class=w> </span><span class=k>typename</span><span class=w> </span><span class=nc>SFINAE</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=k>typename</span><span class=w> </span><span class=nc>std</span><span class=o>::</span><span class=n>enable_if</span><span class=o>&lt;</span><span class=k>sizeof</span><span class=p>(</span><span class=n>T</span><span class=p>)</span><span class=w> </span><span class=o>&lt;=</span><span class=w> </span><span class=mi>32</span><span class=o>&gt;::</span><span class=n>type</span><span class=o>&gt;</span>
<span class=k>struct</span><span class=w> </span><span class=nc>less_than_32_serializer</span><span class=w> </span><span class=p>{</span>
@@ -159,4 +159,4 @@
<span class=w> </span><span class=n>value</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>j</span><span class=p>.</span><span class=k>template</span><span class=w> </span><span class=k>template</span><span class=w> </span><span class=n>get</span><span class=o>&lt;</span><span class=n>T</span><span class=o>&gt;</span><span class=p>();</span><span class=w> </span><span class=c1>// oops!</span>
<span class=w> </span><span class=p>}</span>
<span class=p>};</span>
</code></pre></div> <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">January 10, 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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15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.52 6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9.5 5Line truncated
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
@@ -8,7 +8,7 @@
<span class=w> </span><span class=k>auto</span><span class=w> </span><span class=n>v</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>j</span><span class=p>[</span><span class=s>&quot;missing&quot;</span><span class=p>];</span>
<span class=p>}</span>
</code></pre></div> <p>Output:</p> <div class=highlight><pre><span></span><code>Assertion failed: (m_value.object-&gt;find(key) != m_value.object-&gt;end()), function operator[], file json.hpp, line 2144.
</code></pre></div> </details> <h3 id=constructing-from-an-uninitialized-iterator-range>Constructing from an uninitialized iterator range<a class=headerlink href=#constructing-from-an-uninitialized-iterator-range title="Permanent link">&para;</a></h3> <p>Constructing a JSON value from an iterator range (see <a href=../../api/basic_json/basic_json/ >constructor</a>) with an uninitialized iterator is undefined behavior and yields a runtime assertion.</p> <details class=example> <summary>Example 2: Uninitialized iterator range</summary> <p>The following code will trigger an assertion at runtime:</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
</code></pre></div> </details> <h3 id=constructing-from-an-uninitialized-iterator-range>Constructing from an uninitialized iterator range<a class=headerlink href=#constructing-from-an-uninitialized-iterator-range title="Permanent link">&para;</a></h3> <p>Constructing a <abbr title="JavaScript Object Notation">JSON</abbr> value from an iterator range (see <a href=../../api/basic_json/basic_json/ >constructor</a>) with an uninitialized iterator is undefined behavior and yields a runtime assertion.</p> <details class=example> <summary>Example 2: Uninitialized iterator range</summary> <p>The following code will trigger an assertion at runtime:</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
@@ -18,7 +18,7 @@
<span class=w> </span><span class=n>json</span><span class=w> </span><span class=n>j</span><span class=p>(</span><span class=n>it1</span><span class=p>,</span><span class=w> </span><span class=n>it2</span><span class=p>);</span>
<span class=p>}</span>
</code></pre></div> <p>Output:</p> <div class=highlight><pre><span></span><code>Assertion failed: (m_object != nullptr), function operator++, file iter_impl.hpp, line 368.
</code></pre></div> </details> <h3 id=operations-on-uninitialized-iterators>Operations on uninitialized iterators<a class=headerlink href=#operations-on-uninitialized-iterators title="Permanent link">&para;</a></h3> <p>Any operation on uninitialized iterators (i.e., iterators that are not associated with any JSON value) is undefined behavior and yields a runtime assertion.</p> <details class=example> <summary>Example 3: Uninitialized iterator</summary> <p>The following code will trigger an assertion at runtime:</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
</code></pre></div> </details> <h3 id=operations-on-uninitialized-iterators>Operations on uninitialized iterators<a class=headerlink href=#operations-on-uninitialized-iterators title="Permanent link">&para;</a></h3> <p>Any operation on uninitialized iterators (i.e., iterators that are not associated with any <abbr title="JavaScript Object Notation">JSON</abbr> value) is undefined behavior and yields a runtime assertion.</p> <details class=example> <summary>Example 3: Uninitialized iterator</summary> <p>The following code will trigger an assertion at runtime:</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
@@ -43,4 +43,4 @@
<span class=w> </span><span class=p>}</span>
<span class=p>}</span>
</code></pre></div> <p>Output:</p> <div class=highlight><pre><span></span><code>[json.exception.parse_error.101] parse error: attempting to parse an empty input; check that your input string or stream contains the expected JSON
</code></pre></div> </details> <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">January 10, 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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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> <div class=md-searLine truncated
<span class=w> </span><span class=nt>&quot;_ArrayType_&quot;</span><span class=p>:</span><span class=w> </span><span class=s2>&quot;uint8&quot;</span><span class=p>,</span>
<span class=w> </span><span class=nt>&quot;_ArraySize_&quot;</span><span class=p>:</span><span class=w> </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=w> </span><span class=nt>&quot;_ArrayData_&quot;</span><span class=p>:</span><span class=w> </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>
</code></pre></div> <p>Likewise, when a JSON object in the above form is serialzed using <a href=../../../api/basic_json/to_bjdata/ ><code>to_bjdata</code></a>, it is automatically converted into a compact BJData ND-array. The only exception is, that when the 1-dimensional vector stored in <code>"_ArraySize_"</code> contains a single integer or two integers with one being 1, a regular 1-D optimized array is generated.</p> <p>The current version of this library does not yet support automatic detection of and conversion from a nested JSON array input to a BJData ND-array.</p> </div> <div class="admonition info"> <p class=admonition-title>Restrictions in optimized data types for arrays and objects</p> <p>Due to diminished space saving, hampered readability, and increased security risks, in BJData, the allowed data types following the <code>$</code> marker in an optimized array and object container are restricted to <strong>non-zero-fixed-length</strong> data types. Therefore, the valid optimized type markers can only be one of <code>UiuImlMLhdDCB</code>. This also means other variable (<code>[{SH</code>) or zero-length types (<code>TFN</code>) can not be used in an optimized array or object in BJData.</p> </div> <div class="admonition info"> <p class=admonition-title>Binary values</p> <p>BJData provides a dedicated <code>B</code> marker (defined in the <a href=https://github.com/NeuroJSON/bjdata/blob/master/Binary_JData_Specification.md#optimized-binary-array)>BJData specification (Draft 3)</a>) that is used in optimized arrays to designate binary data. This means that, unlike UBJSON, binary data can be both serialized and deserialized.</p> <p>To preserve compatibility with BJData Draft 2, the Draft 3 optimized binary array must be explicitly enabled using the <code>version</code> parameter of <a href=../../../api/basic_json/to_bjdata/ ><code>to_bjdata</code></a>.</p> <p>In Draft2 mode (default), if the JSON data contains the binary type, the value stored as a list of integers, as suggested by the BJData documentation. In particular, this means that the serialization and the deserialization of JSON containing binary values into BJData and back will result in a different JSON object.</p> </div> <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>
</code></pre></div> <p>Likewise, when a <abbr title="JavaScript Object Notation">JSON</abbr> object in the above form is serialzed using <a href=../../../api/basic_json/to_bjdata/ ><code>to_bjdata</code></a>, it is automatically converted into a compact <abbr title="Binary JData">BJData</abbr> ND-array. The only exception is, that when the 1-dimensional vector stored in <code>"_ArraySize_"</code> contains a single integer or two integers with one being 1, a regular 1-D optimized array is generated.</p> <p>The current version of this library does not yet support automatic detection of and conversion from a nested <abbr title="JavaScript Object Notation">JSON</abbr> array input to a <abbr title="Binary JData">BJData</abbr> ND-array.</p> </div> <div class="admonition info"> <p class=admonition-title>Restrictions in optimized data types for arrays and objects</p> <p>Due to diminished space saving, hampered readability, and increased security risks, in <abbr title="Binary JData">BJData</abbr>, the allowed data types following the <code>$</code> marker in an optimized array and object container are restricted to <strong>non-zero-fixed-length</strong> data types. Therefore, the valid optimized type markers can only be one of <code>UiuImlMLhdDCB</code>. This also means other variable (<code>[{SH</code>) or zero-length types (<code>TFN</code>) can not be used in an optimized array or object in <abbr title="Binary JData">BJData</abbr>.</p> </div> <div class="admonition info"> <p class=admonition-title>Binary values</p> <p><abbr title="Binary JData">BJData</abbr> provides a dedicated <code>B</code> marker (defined in the <a href="https://github.com/NeuroJSON/bjdata/blob/master/Binary_JData_Specification.md#optimized-binary-array)"><abbr title="Binary JData">BJData</abbr> specification (Draft 3)</a>) that is used in optimized arrays to designate binary data. This means that, unlike <abbr title="Universal Binary JSON">UBJSON</abbr>, binary data can be both serialized and deserialized.</p> <p>To preserve compatibility with <abbr title="Binary JData">BJData</abbr> Draft 2, the Draft 3 optimized binary array must be explicitly enabled using the <code>version</code> parameter of <a href=../../../api/basic_json/to_bjdata/ ><code>to_bjdata</code></a>.</p> <p>In Draft2 mode (default), if the <abbr title="JavaScript Object Notation">JSON</abbr> data contains the binary type, the value stored as a list of integers, as suggested by the <abbr title="Binary JData">BJData</abbr> documentation. In particular, this means that the serialization and the deserialization of <abbr title="JavaScript Object Notation">JSON</abbr> containing binary values into <abbr title="Binary JData">BJData</abbr> and back will result in a different <abbr title="JavaScript Object Notation">JSON</abbr> object.</p> </div> <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>
<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>
@@ -71,7 +71,7 @@
<span class=p>[</span><span class=n>i1i2i3i4i5i6i7i8</span><span class=p>]</span>
<span class=p>[</span><span class=err>#</span><span class=n>i8i1i2i3i4i5i6i7i8</span>
<span class=p>[</span><span class=n>$i</span><span class=err>#</span><span class=n>i812345678</span>
</code></pre></div> </details> <h2 id=deserialization>Deserialization<a class=headerlink href=#deserialization title="Permanent link">&para;</a></h2> <p>The library maps BJData types to JSON value types as follows:</p> <table> <thead> <tr> <th>BJData type</th> <th>JSON value type</th> <th>marker</th> </tr> </thead> <tbody> <tr> <td>no-op</td> <td><em>no value, next value is read</em></td> <td><code>N</code></td> </tr> <tr> <td>null</td> <td><code>null</code></td> <td><code>Z</code></td> </tr> <tr> <td>false</td> <td><code>false</code></td> <td><code>F</code></td> </tr> <tr> <td>true</td> <td><code>true</code></td> <td><code>T</code></td> </tr> <tr> <td>float16</td> <td>number_float</td> <td><code>h</code></td> </tr> <tr> <td>float32</td> <td>number_float</td> <td><code>d</code></td> </tr> <tr> <td>float64</td> <td>number_float</td> <td><code>D</code></td> </tr> <tr> <td>uint8</td> <td>number_unsigned</td> <td><code>U</code></td> </tr> <tr> <td>int8</td> <td>number_integer</td> <td><code>i</code></td> </tr> <tr> <td>uint16</td> <td>number_unsigned</td> <td><code>u</code></td> </tr> <tr> <td>int16</td> <td>number_integer</td> <td><code>I</code></td> </tr> <tr> <td>uint32</td> <td>number_unsigned</td> <td><code>m</code></td> </tr> <tr> <td>int32</td> <td>number_integer</td> <td><code>l</code></td> </tr> <tr> <td>uint64</td> <td>number_unsigned</td> <td><code>M</code></td> </tr> <tr> <td>int64</td> <td>number_integer</td> <td><code>L</code></td> </tr> <tr> <td>byte</td> <td>number_unsigned</td> <td><code>B</code></td> </tr> <tr> <td>string</td> <td>string</td> <td><code>S</code></td> </tr> <tr> <td>char</td> <td>string</td> <td><code>C</code></td> </tr> <tr> <td>array</td> <td>array (optimized values are supported)</td> <td><code>[</code></td> </tr> <tr> <td>ND-array</td> <td>object (in JData annotated array format)</td> <td><code>[$.#[.</code></td> </tr> <tr> <td>object</td> <td>object (optimized values are supported)</td> <td><code>{</code></td> </tr> <tr> <td>binary</td> <td>binary (strongly-typed byte array)</td> <td><code>[$B</code></td> </tr> </tbody> </table> <div class="admonition success"> <p class=admonition-title>Complete mapping</p> <p>The mapping is <strong>complete</strong> in the sense that any BJData value can be converted to a JSON value.</p> </div> <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>
</code></pre></div> </details> <h2 id=deserialization>Deserialization<a class=headerlink href=#deserialization title="Permanent link">&para;</a></h2> <p>The library maps <abbr title="Binary JData">BJData</abbr> types to <abbr title="JavaScript Object Notation">JSON</abbr> value types as follows:</p> <table> <thead> <tr> <th><abbr title="Binary JData">BJData</abbr> type</th> <th><abbr title="JavaScript Object Notation">JSON</abbr> value type</th> <th>marker</th> </tr> </thead> <tbody> <tr> <td>no-op</td> <td><em>no value, next value is read</em></td> <td><code>N</code></td> </tr> <tr> <td>null</td> <td><code>null</code></td> <td><code>Z</code></td> </tr> <tr> <td>false</td> <td><code>false</code></td> <td><code>F</code></td> </tr> <tr> <td>true</td> <td><code>true</code></td> <td><code>T</code></td> </tr> <tr> <td>float16</td> <td>number_float</td> <td><code>h</code></td> </tr> <tr> <td>float32</td> <td>number_float</td> <td><code>d</code></td> </tr> <tr> <td>float64</td> <td>number_float</td> <td><code>D</code></td> </tr> <tr> <td>uint8</td> <td>number_unsigned</td> <td><code>U</code></td> </tr> <tr> <td>int8</td> <td>number_integer</td> <td><code>i</code></td> </tr> <tr> <td>uint16</td> <td>number_unsigned</td> <td><code>u</code></td> </tr> <tr> <td>int16</td> <td>number_integer</td> <td><code>I</code></td> </tr> <tr> <td>uint32</td> <td>number_unsigned</td> <td><code>m</code></td> </tr> <tr> <td>int32</td> <td>number_integer</td> <td><code>l</code></td> </tr> <tr> <td>uint64</td> <td>number_unsigned</td> <td><code>M</code></td> </tr> <tr> <td>int64</td> <td>number_integer</td> <td><code>L</code></td> </tr> <tr> <td>byte</td> <td>number_unsigned</td> <td><code>B</code></td> </tr> <tr> <td>string</td> <td>string</td> <td><code>S</code></td> </tr> <tr> <td>char</td> <td>string</td> <td><code>C</code></td> </tr> <tr> <td>array</td> <td>array (optimized values are supported)</td> <td><code>[</code></td> </tr> <tr> <td>ND-array</td> <td>object (in JData annotated array format)</td> <td><code>[$.#[.</code></td> </tr> <tr> <td>object</td> <td>object (optimized values are supported)</td> <td><code>{</code></td> </tr> <tr> <td>binary</td> <td>binary (strongly-typed byte array)</td> <td><code>[$B</code></td> </tr> </tbody> </table> <div class="admonition success"> <p class=admonition-title>Complete mapping</p> <p>The mapping is <strong>complete</strong> in the sense that any <abbr title="Binary JData">BJData</abbr> value can be converted to a <abbr title="JavaScript Object Notation">JSON</abbr> value.</p> </div> <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>
<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>
@@ -95,4 +95,4 @@
<span class=w> </span><span class=nt>&quot;compact&quot;</span><span class=p>:</span><span class=w> </span><span class=kc>true</span><span class=p>,</span>
<span class=w> </span><span class=nt>&quot;schema&quot;</span><span class=p>:</span><span class=w> </span><span class=mi>0</span>
<span class=p>}</span>
</code></pre></div> </details> <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">January 10, 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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<!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/features/binary_formats/bson/" rel="canonical"><link href=../bjdata/ rel=prev><link href=../cbor/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.5.49"><title>BSON - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.6f8fc17f.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.06af60db.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new 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xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> BSON </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark mode" type=radio name=__palette 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<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>
@@ -21,7 +21,7 @@
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>endl</span><span class=p>;</span>
<span class=p>}</span>
</code></pre></div> <p>Output:</p> <div class=highlight><pre><span></span><code><span class=mh>0x1b</span><span class=w> </span><span class=mh>0x00</span><span class=w> </span><span class=mh>0x00</span><span class=w> </span><span class=mh>0x00</span><span class=w> </span><span class=mh>0x08</span><span class=w> </span><span class=mh>0x63</span><span class=w> </span><span class=mh>0x6f</span><span class=w> </span><span class=mh>0x6d</span><span class=w> </span><span class=mh>0x70</span><span class=w> </span><span class=mh>0x61</span><span class=w> </span><span class=mh>0x63</span><span class=w> </span><span class=mh>0x74</span><span class=w> </span><span class=mh>0x00</span><span class=w> </span><span class=mh>0x01</span><span class=w> </span><span class=mh>0x10</span><span class=w> </span><span class=mh>0x73</span><span class=w> </span><span class=mh>0x63</span><span class=w> </span><span class=mh>0x68</span><span class=w> </span><span class=mh>0x65</span><span class=w> </span><span class=mh>0x6d</span><span class=w> </span><span class=mh>0x61</span><span class=w> </span><span class=mh>0x00</span><span class=w> </span><span class=mh>0x00</span><span class=w> </span><span class=mh>0x00</span><span class=w> </span><span class=mh>0x00</span><span class=w> </span><span class=mh>0x00</span><span class=w> </span><span class=mh>0x00</span><span class=w> </span>
</code></pre></div> </details> <h2 id=deserialization>Deserialization<a class=headerlink href=#deserialization title="Permanent link">&para;</a></h2> <p>The library maps BSON record types to JSON value types as follows:</p> <table> <thead> <tr> <th>BSON type</th> <th>BSON marker byte</th> <th>JSON value type</th> </tr> </thead> <tbody> <tr> <td>double</td> <td>0x01</td> <td>number_float</td> </tr> <tr> <td>string</td> <td>0x02</td> <td>string</td> </tr> <tr> <td>document</td> <td>0x03</td> <td>object</td> </tr> <tr> <td>array</td> <td>0x04</td> <td>array</td> </tr> <tr> <td>binary</td> <td>0x05</td> <td>binary</td> </tr> <tr> <td>undefined</td> <td>0x06</td> <td><em>unsupported</em></td> </tr> <tr> <td>ObjectId</td> <td>0x07</td> <td><em>unsupported</em></td> </tr> <tr> <td>boolean</td> <td>0x08</td> <td>boolean</td> </tr> <tr> <td>UTC Date-Time</td> <td>0x09</td> <td><em>unsupported</em></td> </tr> <tr> <td>null</td> <td>0x0A</td> <td>null</td> </tr> <tr> <td>Regular Expr.</td> <td>0x0B</td> <td><em>unsupported</em></td> </tr> <tr> <td>DB Pointer</td> <td>0x0C</td> <td><em>unsupported</em></td> </tr> <tr> <td>JavaScript Code</td> <td>0x0D</td> <td><em>unsupported</em></td> </tr> <tr> <td>Symbol</td> <td>0x0E</td> <td><em>unsupported</em></td> </tr> <tr> <td>JavaScript Code</td> <td>0x0F</td> <td><em>unsupported</em></td> </tr> <tr> <td>int32</td> <td>0x10</td> <td>number_integer</td> </tr> <tr> <td>uint64(Timestamp)</td> <td>0x11</td> <td>number_unsigned</td> </tr> <tr> <td>128-bit decimal float</td> <td>0x13</td> <td><em>unsupported</em></td> </tr> <tr> <td>Max Key</td> <td>0x7F</td> <td><em>unsupported</em></td> </tr> <tr> <td>Min Key</td> <td>0xFF</td> <td><em>unsupported</em></td> </tr> </tbody> </table> <div class="admonition warning"> <p class=admonition-title>Incomplete mapping</p> <p>The mapping is <strong>incomplete</strong>. The unsupported mappings are indicated in the table above.</p> </div> <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>
</code></pre></div> </details> <h2 id=deserialization>Deserialization<a class=headerlink href=#deserialization title="Permanent link">&para;</a></h2> <p>The library maps <abbr title="Binary JSON">BSON</abbr> record types to <abbr title="JavaScript Object Notation">JSON</abbr> value types as follows:</p> <table> <thead> <tr> <th><abbr title="Binary JSON">BSON</abbr> type</th> <th><abbr title="Binary JSON">BSON</abbr> marker byte</th> <th><abbr title="JavaScript Object Notation">JSON</abbr> value type</th> </tr> </thead> <tbody> <tr> <td>double</td> <td>0x01</td> <td>number_float</td> </tr> <tr> <td>string</td> <td>0x02</td> <td>string</td> </tr> <tr> <td>document</td> <td>0x03</td> <td>object</td> </tr> <tr> <td>array</td> <td>0x04</td> <td>array</td> </tr> <tr> <td>binary</td> <td>0x05</td> <td>binary</td> </tr> <tr> <td>undefined</td> <td>0x06</td> <td><em>unsupported</em></td> </tr> <tr> <td>ObjectId</td> <td>0x07</td> <td><em>unsupported</em></td> </tr> <tr> <td>boolean</td> <td>0x08</td> <td>boolean</td> </tr> <tr> <td>UTC Date-Time</td> <td>0x09</td> <td><em>unsupported</em></td> </tr> <tr> <td>null</td> <td>0x0A</td> <td>null</td> </tr> <tr> <td>Regular Expr.</td> <td>0x0B</td> <td><em>unsupported</em></td> </tr> <tr> <td>DB Pointer</td> <td>0x0C</td> <td><em>unsupported</em></td> </tr> <tr> <td>JavaScript Code</td> <td>0x0D</td> <td><em>unsupported</em></td> </tr> <tr> <td>Symbol</td> <td>0x0E</td> <td><em>unsupported</em></td> </tr> <tr> <td>JavaScript Code</td> <td>0x0F</td> <td><em>unsupported</em></td> </tr> <tr> <td>int32</td> <td>0x10</td> <td>number_integer</td> </tr> <tr> <td>uint64(Timestamp)</td> <td>0x11</td> <td>number_unsigned</td> </tr> <tr> <td>128-bit decimal float</td> <td>0x13</td> <td><em>unsupported</em></td> </tr> <tr> <td>Max Key</td> <td>0x7F</td> <td><em>unsupported</em></td> </tr> <tr> <td>Min Key</td> <td>0xFF</td> <td><em>unsupported</em></td> </tr> </tbody> </table> <div class="admonition warning"> <p class=admonition-title>Incomplete mapping</p> <p>The mapping is <strong>incomplete</strong>. The unsupported mappings are indicated in the table above.</p> </div> <div class="admonition note"> <p class=admonition-title>Handling of <abbr title="Binary JSON">BSON</abbr> type 0x11</p> <p><abbr title="Binary JSON">BSON</abbr> type 0x11 is used to represent uint64 numbers. This library treats these values purely as uint64 numbers and does not parse them into date-related formats.</p> </div> <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>
<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>
@@ -46,4 +46,4 @@
<span class=w> </span><span class=nt>&quot;compact&quot;</span><span class=p>:</span><span class=w> </span><span class=kc>true</span><span class=p>,</span>
<span class=w> </span><span class=nt>&quot;schema&quot;</span><span class=p>:</span><span class=w> </span><span class=mi>0</span>
<span class=p>}</span>
</code></pre></div> </details> <div class="admonition note"> <p class=admonition-title>Handling of BSON type 0x11</p> <p>BSON type 0x11 is used to represent uint64 numbers. This library treats these values purely as uint64 numbers and does not parse them into date-related formats.</p> </div> <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">January 10, 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; 2013 - 2024 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 0 496 512"><!-- Font Awesome Free 6.7.1 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 2024 Fonticons, Inc.--><path d="M165.9 397.4c0 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-.3-1.9-3-3.2-5.9-2.9M244.8 8C106.1 8 0 113.3 0 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 12.1C428.2 457.8 496 362.9 496 252 496 113.3 383.5 8 244.8 8M97.2 352.9c-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 6.7.1 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 2024 Fonticons, Inc.--><path d="M416 32H31.9C14.3 32 0 46.5 0 64.3v383.4C0 465.5 14.3 480 31.9 480H416c17.6 0 32-14.5 32-32.3V64.3c0-17.8-14.4-32.3-32-32.3M135.4 416H69V202.2h66.5V416zm-33.2-243c-21.3 0-38.5-17.3-38.5-38.5S80.9 96 102.2 96c21.2 0 38.5 17.3 38.5 38.5 0 21.3-17.2 38.5-38.5 38.5m282.1 243h-66.4V312c0-24.8-.5-56.7-34.5-56.7-34.6 0-39.9 27-39.9 54.9V416h-66.4V202.2h63.7v29.2h.9c8.9-16.8 30.6-34.5 62.9-34.5 67.2 0 79.7 44.3 79.7 101.9z"/></svg> </a> <a href=https://www.xing.com/profile/Niels_Lohmann target=_blank rel=noopener title=www.xing.com class=md-social__link> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 384 512"><!-- Font Awesome Free 6.7.1 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 2024 Fonticons, Inc.--><path d="M162.7 210c-1.8 3.3-25.2 44.4-70.1 123.5-4.9 8.3-10.8 12.5-17.7 12.5H9.8c-7.7 0-12.1-7.5-8.5-14.4l69-121.3q.3 0 0-.3l-43.9-75.6c-4.3-7.8Line truncated
</code></pre></div> </details> <!-- 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">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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<!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/features/binary_formats/cbor/" rel="canonical"><link href=../bson/ rel=prev><link href=../messagepack/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.5.49"><title>CBOR - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.6f8fc17f.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.06af60db.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new 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xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> CBOR </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark mode" type=radio name=__palette 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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> <div class=md-Line truncated
<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>
@@ -21,7 +21,7 @@
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>endl</span><span class=p>;</span>
<span class=p>}</span>
</code></pre></div> <p>Output:</p> <div class=highlight><pre><span></span><code><span class=mh>0xa2</span><span class=w> </span><span class=mh>0x67</span><span class=w> </span><span class=mh>0x63</span><span class=w> </span><span class=mh>0x6f</span><span class=w> </span><span class=mh>0x6d</span><span class=w> </span><span class=mh>0x70</span><span class=w> </span><span class=mh>0x61</span><span class=w> </span><span class=mh>0x63</span><span class=w> </span><span class=mh>0x74</span><span class=w> </span><span class=mh>0xf5</span><span class=w> </span><span class=mh>0x66</span><span class=w> </span><span class=mh>0x73</span><span class=w> </span><span class=mh>0x63</span><span class=w> </span><span class=mh>0x68</span><span class=w> </span><span class=mh>0x65</span><span class=w> </span><span class=mh>0x6d</span><span class=w> </span><span class=mh>0x61</span><span class=w> </span><span class=mh>0x00</span><span class=w> </span>
</code></pre></div> </details> <h2 id=deserialization>Deserialization<a class=headerlink href=#deserialization title="Permanent link">&para;</a></h2> <p>The library maps CBOR types to JSON value types as follows:</p> <table> <thead> <tr> <th>CBOR type</th> <th>JSON value type</th> <th>first byte</th> </tr> </thead> <tbody> <tr> <td>Integer</td> <td>number_unsigned</td> <td>0x00..0x17</td> </tr> <tr> <td>Unsigned integer</td> <td>number_unsigned</td> <td>0x18</td> </tr> <tr> <td>Unsigned integer</td> <td>number_unsigned</td> <td>0x19</td> </tr> <tr> <td>Unsigned integer</td> <td>number_unsigned</td> <td>0x1A</td> </tr> <tr> <td>Unsigned integer</td> <td>number_unsigned</td> <td>0x1B</td> </tr> <tr> <td>Negative integer</td> <td>number_integer</td> <td>0x20..0x37</td> </tr> <tr> <td>Negative integer</td> <td>number_integer</td> <td>0x38</td> </tr> <tr> <td>Negative integer</td> <td>number_integer</td> <td>0x39</td> </tr> <tr> <td>Negative integer</td> <td>number_integer</td> <td>0x3A</td> </tr> <tr> <td>Negative integer</td> <td>number_integer</td> <td>0x3B</td> </tr> <tr> <td>Byte string</td> <td>binary</td> <td>0x40..0x57</td> </tr> <tr> <td>Byte string</td> <td>binary</td> <td>0x58</td> </tr> <tr> <td>Byte string</td> <td>binary</td> <td>0x59</td> </tr> <tr> <td>Byte string</td> <td>binary</td> <td>0x5A</td> </tr> <tr> <td>Byte string</td> <td>binary</td> <td>0x5B</td> </tr> <tr> <td>UTF-8 string</td> <td>string</td> <td>0x60..0x77</td> </tr> <tr> <td>UTF-8 string</td> <td>string</td> <td>0x78</td> </tr> <tr> <td>UTF-8 string</td> <td>string</td> <td>0x79</td> </tr> <tr> <td>UTF-8 string</td> <td>string</td> <td>0x7A</td> </tr> <tr> <td>UTF-8 string</td> <td>string</td> <td>0x7B</td> </tr> <tr> <td>UTF-8 string</td> <td>string</td> <td>0x7F</td> </tr> <tr> <td>array</td> <td>array</td> <td>0x80..0x97</td> </tr> <tr> <td>array</td> <td>array</td> <td>0x98</td> </tr> <tr> <td>array</td> <td>array</td> <td>0x99</td> </tr> <tr> <td>array</td> <td>array</td> <td>0x9A</td> </tr> <tr> <td>array</td> <td>array</td> <td>0x9B</td> </tr> <tr> <td>array</td> <td>array</td> <td>0x9F</td> </tr> <tr> <td>map</td> <td>object</td> <td>0xA0..0xB7</td> </tr> <tr> <td>map</td> <td>object</td> <td>0xB8</td> </tr> <tr> <td>map</td> <td>object</td> <td>0xB9</td> </tr> <tr> <td>map</td> <td>object</td> <td>0xBA</td> </tr> <tr> <td>map</td> <td>object</td> <td>0xBB</td> </tr> <tr> <td>map</td> <td>object</td> <td>0xBF</td> </tr> <tr> <td>False</td> <td><code>false</code></td> <td>0xF4</td> </tr> <tr> <td>True</td> <td><code>true</code></td> <td>0xF5</td> </tr> <tr> <td>Null</td> <td><code>null</code></td> <td>0xF6</td> </tr> <tr> <td>Half-Precision Float</td> <td>number_float</td> <td>0xF9</td> </tr> <tr> <td>Single-Precision Float</td> <td>number_float</td> <td>0xFA</td> </tr> <tr> <td>Double-Precision Float</td> <td>number_float</td> <td>0xFB</td> </tr> </tbody> </table> <div class="admonition warning"> <p class=admonition-title>Incomplete mapping</p> <p>The mapping is <strong>incomplete</strong> in the sense that not all CBOR types can be converted to a JSON value. The following CBOR types are not supported and will yield parse errors:</p> <ul> <li>date/time (0xC0..0xC1)</li> <li>bignum (0xC2..0xC3)</li> <li>decimal fraction (0xC4)</li> <li>bigfloat (0xC5)</li> <li>expected conversions (0xD5..0xD7)</li> <li>simple values (0xE0..0xF3, 0xF8)</li> <li>undefined (0xF7)</li> </ul> </div> <div class="admonition warning"> <p class=admonition-title>Object keys</p> <p>CBOR allows map keys of any type, whereas JSON only allows strings as keys in object values. Therefore, CBOR maps with keys other than UTF-8 strings are rejected.</p> </div> <div class="admonition warning"> <p class=admonition-title>Tagged items</p> <p>Tagged items will throw a parse error by default. They can be ignored by passing <code>cbor_tag_handler_t::ignore</code> to function <code>from_cbor</code>. They can be stored by passing <code>cbor_tag_handler_t::store</code> to function <code>from_cbor</code>.</p> </div> <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>
</code></pre></div> </details> <h2 id=deserialization>Deserialization<a class=headerlink href=#deserialization title="Permanent link">&para;</a></h2> <p>The library maps <abbr title="Concise Binary Object Representation">CBOR</abbr> types to <abbr title="JavaScript Object Notation">JSON</abbr> value types as follows:</p> <table> <thead> <tr> <th><abbr title="Concise Binary Object Representation">CBOR</abbr> type</th> <th><abbr title="JavaScript Object Notation">JSON</abbr> value type</th> <th>first byte</th> </tr> </thead> <tbody> <tr> <td>Integer</td> <td>number_unsigned</td> <td>0x00..0x17</td> </tr> <tr> <td>Unsigned integer</td> <td>number_unsigned</td> <td>0x18</td> </tr> <tr> <td>Unsigned integer</td> <td>number_unsigned</td> <td>0x19</td> </tr> <tr> <td>Unsigned integer</td> <td>number_unsigned</td> <td>0x1A</td> </tr> <tr> <td>Unsigned integer</td> <td>number_unsigned</td> <td>0x1B</td> </tr> <tr> <td>Negative integer</td> <td>number_integer</td> <td>0x20..0x37</td> </tr> <tr> <td>Negative integer</td> <td>number_integer</td> <td>0x38</td> </tr> <tr> <td>Negative integer</td> <td>number_integer</td> <td>0x39</td> </tr> <tr> <td>Negative integer</td> <td>number_integer</td> <td>0x3A</td> </tr> <tr> <td>Negative integer</td> <td>number_integer</td> <td>0x3B</td> </tr> <tr> <td>Byte string</td> <td>binary</td> <td>0x40..0x57</td> </tr> <tr> <td>Byte string</td> <td>binary</td> <td>0x58</td> </tr> <tr> <td>Byte string</td> <td>binary</td> <td>0x59</td> </tr> <tr> <td>Byte string</td> <td>binary</td> <td>0x5A</td> </tr> <tr> <td>Byte string</td> <td>binary</td> <td>0x5B</td> </tr> <tr> <td><abbr title="Unicode Transformation Format">UTF</abbr>-8 string</td> <td>string</td> <td>0x60..0x77</td> </tr> <tr> <td><abbr title="Unicode Transformation Format">UTF</abbr>-8 string</td> <td>string</td> <td>0x78</td> </tr> <tr> <td><abbr title="Unicode Transformation Format">UTF</abbr>-8 string</td> <td>string</td> <td>0x79</td> </tr> <tr> <td><abbr title="Unicode Transformation Format">UTF</abbr>-8 string</td> <td>string</td> <td>0x7A</td> </tr> <tr> <td><abbr title="Unicode Transformation Format">UTF</abbr>-8 string</td> <td>string</td> <td>0x7B</td> </tr> <tr> <td><abbr title="Unicode Transformation Format">UTF</abbr>-8 string</td> <td>string</td> <td>0x7F</td> </tr> <tr> <td>array</td> <td>array</td> <td>0x80..0x97</td> </tr> <tr> <td>array</td> <td>array</td> <td>0x98</td> </tr> <tr> <td>array</td> <td>array</td> <td>0x99</td> </tr> <tr> <td>array</td> <td>array</td> <td>0x9A</td> </tr> <tr> <td>array</td> <td>array</td> <td>0x9B</td> </tr> <tr> <td>array</td> <td>array</td> <td>0x9F</td> </tr> <tr> <td>map</td> <td>object</td> <td>0xA0..0xB7</td> </tr> <tr> <td>map</td> <td>object</td> <td>0xB8</td> </tr> <tr> <td>map</td> <td>object</td> <td>0xB9</td> </tr> <tr> <td>map</td> <td>object</td> <td>0xBA</td> </tr> <tr> <td>map</td> <td>object</td> <td>0xBB</td> </tr> <tr> <td>map</td> <td>object</td> <td>0xBF</td> </tr> <tr> <td>False</td> <td><code>false</code></td> <td>0xF4</td> </tr> <tr> <td>True</td> <td><code>true</code></td> <td>0xF5</td> </tr> <tr> <td>Null</td> <td><code>null</code></td> <td>0xF6</td> </tr> <tr> <td>Half-Precision Float</td> <td>number_float</td> <td>0xF9</td> </tr> <tr> <td>Single-Precision Float</td> <td>number_float</td> <td>0xFA</td> </tr> <tr> <td>Double-Precision Float</td> <td>number_float</td> <td>0xFB</td> </tr> </tbody> </table> <div class="admonition warning"> <p class=admonition-title>Incomplete mapping</p> <p>The mapping is <strong>incomplete</strong> in the sense that not all <abbr title="Concise Binary Object Representation">CBOR</abbr> types can be converted to a <abbr title="JavaScript Object Notation">JSON</abbr> value. The following <abbr title="Concise Binary Object Representation">CBOR</abbr> types are not supported and will yield parse errors:</p> <ul> <li>date/time (0xC0..0xC1)</li> <li>bignum (0xC2..0xC3)</li> <li>decimal fraction (0xC4)</li> <li>bigfloat (0xC5)</li> <li>expected conversions (0xD5..0xD7)</li> <li>simple values (0xE0..0xF3, 0xF8)</li> <li>undefined (0xF7)</li> </ul> </div> <div class="admonition warning"> <p class=admonition-title>Object keys</p> <p><abbr title="Concise Binary Object Representation">CBOR</abbr> allows map keys of any type, whereas <abbr title="JavaScript Object Notation">JSON</abbr> only allows strings as keys in object values. Therefore, <abbr title="Concise Binary Object Representation">CBOR</abbr> maps with keys other than <abbr title="Unicode Transformation Format">UTF</abbr>-8 strings are rejected.</p> </div> <div class="admonition warning"> <p class=admonition-title>Tagged items</p> <p>Tagged items will throw a parse error by default. They can be ignored by passing <code>cbor_tag_handler_t::ignore</code> to function <code>from_cbor</code>. They can be stored by passing <code>cbor_tag_handler_t::store</code> to function <code>from_cbor</code>.</p> </div> <details class=example> <summary>Example</summary> <div class=highlight><Line truncated
<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>
@@ -45,4 +45,4 @@
<span class=w> </span><span class=nt>&quot;compact&quot;</span><span class=p>:</span><span class=w> </span><span class=kc>true</span><span class=p>,</span>
<span class=w> </span><span class=nt>&quot;schema&quot;</span><span class=p>:</span><span class=w> </span><span class=mi>0</span>
<span class=p>}</span>
</code></pre></div> </details> <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">January 10, 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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15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.52 6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9.5 5"/></svg> </label> <div clLine truncated
@@ -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/features/binary_formats/messagepack/ rel=canonical><link href=../cbor/ rel=prev><link href=../ubjson/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.5.49"><title>MessagePack - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.6f8fc17f.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.06af60db.min.css><link rel=preconnect href=https://fonts.gstatic.com crossorigin><link rel=stylesheet href="https://fonts.googleapis.com/css?family=Roboto:300,300i,400,400i,700,700i%7CJetBrains+Mono:400,400i,700,700i&display=fallback"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet 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6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9.5 5"/></svg> Line truncated
<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>
@@ -21,7 +21,7 @@
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>endl</span><span class=p>;</span>
<span class=p>}</span>
</code></pre></div> <p>Output:</p> <div class=highlight><pre><span></span><code><span class=mh>0x82</span><span class=w> </span><span class=mh>0xa7</span><span class=w> </span><span class=mh>0x63</span><span class=w> </span><span class=mh>0x6f</span><span class=w> </span><span class=mh>0x6d</span><span class=w> </span><span class=mh>0x70</span><span class=w> </span><span class=mh>0x61</span><span class=w> </span><span class=mh>0x63</span><span class=w> </span><span class=mh>0x74</span><span class=w> </span><span class=mh>0xc3</span><span class=w> </span><span class=mh>0xa6</span><span class=w> </span><span class=mh>0x73</span><span class=w> </span><span class=mh>0x63</span><span class=w> </span><span class=mh>0x68</span><span class=w> </span><span class=mh>0x65</span><span class=w> </span><span class=mh>0x6d</span><span class=w> </span><span class=mh>0x61</span><span class=w> </span><span class=mh>0x00</span><span class=w> </span>
</code></pre></div> </details> <h2 id=deserialization>Deserialization<a class=headerlink href=#deserialization title="Permanent link">&para;</a></h2> <p>The library maps MessagePack types to JSON value types as follows:</p> <table> <thead> <tr> <th>MessagePack type</th> <th>JSON value type</th> <th>first byte</th> </tr> </thead> <tbody> <tr> <td>positive fixint</td> <td>number_unsigned</td> <td>0x00..0x7F</td> </tr> <tr> <td>fixmap</td> <td>object</td> <td>0x80..0x8F</td> </tr> <tr> <td>fixarray</td> <td>array</td> <td>0x90..0x9F</td> </tr> <tr> <td>fixstr</td> <td>string</td> <td>0xA0..0xBF</td> </tr> <tr> <td>nil</td> <td><code>null</code></td> <td>0xC0</td> </tr> <tr> <td>false</td> <td><code>false</code></td> <td>0xC2</td> </tr> <tr> <td>true</td> <td><code>true</code></td> <td>0xC3</td> </tr> <tr> <td>float 32</td> <td>number_float</td> <td>0xCA</td> </tr> <tr> <td>float 64</td> <td>number_float</td> <td>0xCB</td> </tr> <tr> <td>uint 8</td> <td>number_unsigned</td> <td>0xCC</td> </tr> <tr> <td>uint 16</td> <td>number_unsigned</td> <td>0xCD</td> </tr> <tr> <td>uint 32</td> <td>number_unsigned</td> <td>0xCE</td> </tr> <tr> <td>uint 64</td> <td>number_unsigned</td> <td>0xCF</td> </tr> <tr> <td>int 8</td> <td>number_integer</td> <td>0xD0</td> </tr> <tr> <td>int 16</td> <td>number_integer</td> <td>0xD1</td> </tr> <tr> <td>int 32</td> <td>number_integer</td> <td>0xD2</td> </tr> <tr> <td>int 64</td> <td>number_integer</td> <td>0xD3</td> </tr> <tr> <td>str 8</td> <td>string</td> <td>0xD9</td> </tr> <tr> <td>str 16</td> <td>string</td> <td>0xDA</td> </tr> <tr> <td>str 32</td> <td>string</td> <td>0xDB</td> </tr> <tr> <td>array 16</td> <td>array</td> <td>0xDC</td> </tr> <tr> <td>array 32</td> <td>array</td> <td>0xDD</td> </tr> <tr> <td>map 16</td> <td>object</td> <td>0xDE</td> </tr> <tr> <td>map 32</td> <td>object</td> <td>0xDF</td> </tr> <tr> <td>bin 8</td> <td>binary</td> <td>0xC4</td> </tr> <tr> <td>bin 16</td> <td>binary</td> <td>0xC5</td> </tr> <tr> <td>bin 32</td> <td>binary</td> <td>0xC6</td> </tr> <tr> <td>ext 8</td> <td>binary</td> <td>0xC7</td> </tr> <tr> <td>ext 16</td> <td>binary</td> <td>0xC8</td> </tr> <tr> <td>ext 32</td> <td>binary</td> <td>0xC9</td> </tr> <tr> <td>fixext 1</td> <td>binary</td> <td>0xD4</td> </tr> <tr> <td>fixext 2</td> <td>binary</td> <td>0xD5</td> </tr> <tr> <td>fixext 4</td> <td>binary</td> <td>0xD6</td> </tr> <tr> <td>fixext 8</td> <td>binary</td> <td>0xD7</td> </tr> <tr> <td>fixext 16</td> <td>binary</td> <td>0xD8</td> </tr> <tr> <td>negative fixint</td> <td>number_integer</td> <td>0xE0-0xFF</td> </tr> </tbody> </table> <div class="admonition info"> <p class=admonition-title>Info</p> <p>Any MessagePack output created by <code>to_msgpack</code> can be successfully parsed by <code>from_msgpack</code>.</p> </div> <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>
</code></pre></div> </details> <h2 id=deserialization>Deserialization<a class=headerlink href=#deserialization title="Permanent link">&para;</a></h2> <p>The library maps MessagePack types to <abbr title="JavaScript Object Notation">JSON</abbr> value types as follows:</p> <table> <thead> <tr> <th>MessagePack type</th> <th><abbr title="JavaScript Object Notation">JSON</abbr> value type</th> <th>first byte</th> </tr> </thead> <tbody> <tr> <td>positive fixint</td> <td>number_unsigned</td> <td>0x00..0x7F</td> </tr> <tr> <td>fixmap</td> <td>object</td> <td>0x80..0x8F</td> </tr> <tr> <td>fixarray</td> <td>array</td> <td>0x90..0x9F</td> </tr> <tr> <td>fixstr</td> <td>string</td> <td>0xA0..0xBF</td> </tr> <tr> <td>nil</td> <td><code>null</code></td> <td>0xC0</td> </tr> <tr> <td>false</td> <td><code>false</code></td> <td>0xC2</td> </tr> <tr> <td>true</td> <td><code>true</code></td> <td>0xC3</td> </tr> <tr> <td>float 32</td> <td>number_float</td> <td>0xCA</td> </tr> <tr> <td>float 64</td> <td>number_float</td> <td>0xCB</td> </tr> <tr> <td>uint 8</td> <td>number_unsigned</td> <td>0xCC</td> </tr> <tr> <td>uint 16</td> <td>number_unsigned</td> <td>0xCD</td> </tr> <tr> <td>uint 32</td> <td>number_unsigned</td> <td>0xCE</td> </tr> <tr> <td>uint 64</td> <td>number_unsigned</td> <td>0xCF</td> </tr> <tr> <td>int 8</td> <td>number_integer</td> <td>0xD0</td> </tr> <tr> <td>int 16</td> <td>number_integer</td> <td>0xD1</td> </tr> <tr> <td>int 32</td> <td>number_integer</td> <td>0xD2</td> </tr> <tr> <td>int 64</td> <td>number_integer</td> <td>0xD3</td> </tr> <tr> <td>str 8</td> <td>string</td> <td>0xD9</td> </tr> <tr> <td>str 16</td> <td>string</td> <td>0xDA</td> </tr> <tr> <td>str 32</td> <td>string</td> <td>0xDB</td> </tr> <tr> <td>array 16</td> <td>array</td> <td>0xDC</td> </tr> <tr> <td>array 32</td> <td>array</td> <td>0xDD</td> </tr> <tr> <td>map 16</td> <td>object</td> <td>0xDE</td> </tr> <tr> <td>map 32</td> <td>object</td> <td>0xDF</td> </tr> <tr> <td>bin 8</td> <td>binary</td> <td>0xC4</td> </tr> <tr> <td>bin 16</td> <td>binary</td> <td>0xC5</td> </tr> <tr> <td>bin 32</td> <td>binary</td> <td>0xC6</td> </tr> <tr> <td>ext 8</td> <td>binary</td> <td>0xC7</td> </tr> <tr> <td>ext 16</td> <td>binary</td> <td>0xC8</td> </tr> <tr> <td>ext 32</td> <td>binary</td> <td>0xC9</td> </tr> <tr> <td>fixext 1</td> <td>binary</td> <td>0xD4</td> </tr> <tr> <td>fixext 2</td> <td>binary</td> <td>0xD5</td> </tr> <tr> <td>fixext 4</td> <td>binary</td> <td>0xD6</td> </tr> <tr> <td>fixext 8</td> <td>binary</td> <td>0xD7</td> </tr> <tr> <td>fixext 16</td> <td>binary</td> <td>0xD8</td> </tr> <tr> <td>negative fixint</td> <td>number_integer</td> <td>0xE0-0xFF</td> </tr> </tbody> </table> <div class="admonition info"> <p class=admonition-title>Info</p> <p>Any MessagePack output created by <code>to_msgpack</code> can be successfully parsed by <code>from_msgpack</code>.</p> </div> <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>
<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>
@@ -45,4 +45,4 @@
<span class=w> </span><span class=nt>&quot;compact&quot;</span><span class=p>:</span><span class=w> </span><span class=kc>true</span><span class=p>,</span>
<span class=w> </span><span class=nt>&quot;schema&quot;</span><span class=p>:</span><span class=w> </span><span class=mi>0</span>
<span class=p>}</span>
</code></pre></div> </details> <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">January 10, 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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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> UBJSON </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark mode" type=radio name=__palette 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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> </lLine truncated
<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>
@@ -66,7 +66,7 @@
<span class=p>[</span><span class=n>i1i2i3i4i5i6i7i8</span><span class=p>]</span>
<span class=p>[</span><span class=err>#</span><span class=n>i8i1i2i3i4i5i6i7i8</span>
<span class=p>[</span><span class=n>$i</span><span class=err>#</span><span class=n>i812345678</span>
</code></pre></div> </details> <h2 id=deserialization>Deserialization<a class=headerlink href=#deserialization title="Permanent link">&para;</a></h2> <p>The library maps UBJSON types to JSON value types as follows:</p> <table> <thead> <tr> <th>UBJSON type</th> <th>JSON value type</th> <th>marker</th> </tr> </thead> <tbody> <tr> <td>no-op</td> <td><em>no value, next value is read</em></td> <td><code>N</code></td> </tr> <tr> <td>null</td> <td><code>null</code></td> <td><code>Z</code></td> </tr> <tr> <td>false</td> <td><code>false</code></td> <td><code>F</code></td> </tr> <tr> <td>true</td> <td><code>true</code></td> <td><code>T</code></td> </tr> <tr> <td>float32</td> <td>number_float</td> <td><code>d</code></td> </tr> <tr> <td>float64</td> <td>number_float</td> <td><code>D</code></td> </tr> <tr> <td>uint8</td> <td>number_unsigned</td> <td><code>U</code></td> </tr> <tr> <td>int8</td> <td>number_integer</td> <td><code>i</code></td> </tr> <tr> <td>int16</td> <td>number_integer</td> <td><code>I</code></td> </tr> <tr> <td>int32</td> <td>number_integer</td> <td><code>l</code></td> </tr> <tr> <td>int64</td> <td>number_integer</td> <td><code>L</code></td> </tr> <tr> <td>string</td> <td>string</td> <td><code>S</code></td> </tr> <tr> <td>char</td> <td>string</td> <td><code>C</code></td> </tr> <tr> <td>array</td> <td>array (optimized values are supported)</td> <td><code>[</code></td> </tr> <tr> <td>object</td> <td>object (optimized values are supported)</td> <td><code>{</code></td> </tr> </tbody> </table> <div class="admonition success"> <p class=admonition-title>Complete mapping</p> <p>The mapping is <strong>complete</strong> in the sense that any UBJSON value can be converted to a JSON value.</p> </div> <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>
</code></pre></div> </details> <h2 id=deserialization>Deserialization<a class=headerlink href=#deserialization title="Permanent link">&para;</a></h2> <p>The library maps <abbr title="Universal Binary JSON">UBJSON</abbr> types to <abbr title="JavaScript Object Notation">JSON</abbr> value types as follows:</p> <table> <thead> <tr> <th><abbr title="Universal Binary JSON">UBJSON</abbr> type</th> <th><abbr title="JavaScript Object Notation">JSON</abbr> value type</th> <th>marker</th> </tr> </thead> <tbody> <tr> <td>no-op</td> <td><em>no value, next value is read</em></td> <td><code>N</code></td> </tr> <tr> <td>null</td> <td><code>null</code></td> <td><code>Z</code></td> </tr> <tr> <td>false</td> <td><code>false</code></td> <td><code>F</code></td> </tr> <tr> <td>true</td> <td><code>true</code></td> <td><code>T</code></td> </tr> <tr> <td>float32</td> <td>number_float</td> <td><code>d</code></td> </tr> <tr> <td>float64</td> <td>number_float</td> <td><code>D</code></td> </tr> <tr> <td>uint8</td> <td>number_unsigned</td> <td><code>U</code></td> </tr> <tr> <td>int8</td> <td>number_integer</td> <td><code>i</code></td> </tr> <tr> <td>int16</td> <td>number_integer</td> <td><code>I</code></td> </tr> <tr> <td>int32</td> <td>number_integer</td> <td><code>l</code></td> </tr> <tr> <td>int64</td> <td>number_integer</td> <td><code>L</code></td> </tr> <tr> <td>string</td> <td>string</td> <td><code>S</code></td> </tr> <tr> <td>char</td> <td>string</td> <td><code>C</code></td> </tr> <tr> <td>array</td> <td>array (optimized values are supported)</td> <td><code>[</code></td> </tr> <tr> <td>object</td> <td>object (optimized values are supported)</td> <td><code>{</code></td> </tr> </tbody> </table> <div class="admonition success"> <p class=admonition-title>Complete mapping</p> <p>The mapping is <strong>complete</strong> in the sense that any <abbr title="Universal Binary JSON">UBJSON</abbr> value can be converted to a <abbr title="JavaScript Object Notation">JSON</abbr> value.</p> </div> <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>
<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>
@@ -90,4 +90,4 @@
<span class=w> </span><span class=nt>&quot;compact&quot;</span><span class=p>:</span><span class=w> </span><span class=kc>true</span><span class=p>,</span>
<span class=w> </span><span class=nt>&quot;schema&quot;</span><span class=p>:</span><span class=w> </span><span class=mi>0</span>
<span class=p>}</span>
</code></pre></div> </details> <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">January 10, 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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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
class binary_t ["json::binary_t"] {
+void set_subtype(std::uint64_t subtype)
@@ -23,18 +23,18 @@ vector &lt;|-- binary_t</code></pre> <p>By default, binary values are stored as
<span class=n>binary</span><span class=p>.</span><span class=n>subtype</span><span class=p>();</span><span class=w> </span><span class=c1>// returns 23</span>
</code></pre></div> <p>As <code>json::binary_t</code> is subclassing <code>std::vector&lt;std::uint8_t&gt;</code>, all member functions are available:</p> <div class=highlight><pre><span></span><code><span class=n>binary</span><span class=p>.</span><span class=n>size</span><span class=p>();</span><span class=w> </span><span class=c1>// returns 4</span>
<span class=n>binary</span><span class=p>[</span><span class=mi>1</span><span class=p>];</span><span class=w> </span><span class=c1>// returns 0xFE</span>
</code></pre></div> <p>JSON values can be constructed from <code>json::binary_t</code>:</p> <div class=highlight><pre><span></span><code><span class=n>json</span><span class=w> </span><span class=n>j</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>binary</span><span class=p>;</span>
</code></pre></div> <p><abbr title="JavaScript Object Notation">JSON</abbr> values can be constructed from <code>json::binary_t</code>:</p> <div class=highlight><pre><span></span><code><span class=n>json</span><span class=w> </span><span class=n>j</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>binary</span><span class=p>;</span>
</code></pre></div> <p>Binary values are primitive values just like numbers or strings:</p> <div class=highlight><pre><span></span><code><span class=n>j</span><span class=p>.</span><span class=n>is_binary</span><span class=p>();</span><span class=w> </span><span class=c1>// returns true</span>
<span class=n>j</span><span class=p>.</span><span class=n>is_primitive</span><span class=p>();</span><span class=w> </span><span class=c1>// returns true</span>
</code></pre></div> <p>Given a binary JSON value, the <code>binary_t</code> can be accessed by reference as via <code>get_binary()</code>:</p> <div class=highlight><pre><span></span><code><span class=n>j</span><span class=p>.</span><span class=n>get_binary</span><span class=p>().</span><span class=n>has_subtype</span><span class=p>();</span><span class=w> </span><span class=c1>// returns true</span>
</code></pre></div> <p>Given a binary <abbr title="JavaScript Object Notation">JSON</abbr> value, the <code>binary_t</code> can be accessed by reference as via <code>get_binary()</code>:</p> <div class=highlight><pre><span></span><code><span class=n>j</span><span class=p>.</span><span class=n>get_binary</span><span class=p>().</span><span class=n>has_subtype</span><span class=p>();</span><span class=w> </span><span class=c1>// returns true</span>
<span class=n>j</span><span class=p>.</span><span class=n>get_binary</span><span class=p>().</span><span class=n>size</span><span class=p>();</span><span class=w> </span><span class=c1>// returns 4</span>
</code></pre></div> <p>For convenience, binary JSON values can be constructed via <code>json::binary</code>:</p> <div class=highlight><pre><span></span><code><span class=k>auto</span><span class=w> </span><span class=n>j2</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>json</span><span class=o>::</span><span class=n>binary</span><span class=p>({</span><span class=mh>0xCA</span><span class=p>,</span><span class=w> </span><span class=mh>0xFE</span><span class=p>,</span><span class=w> </span><span class=mh>0xBA</span><span class=p>,</span><span class=w> </span><span class=mh>0xBE</span><span class=p>},</span><span class=w> </span><span class=mi>23</span><span class=p>);</span>
</code></pre></div> <p>For convenience, binary <abbr title="JavaScript Object Notation">JSON</abbr> values can be constructed via <code>json::binary</code>:</p> <div class=highlight><pre><span></span><code><span class=k>auto</span><span class=w> </span><span class=n>j2</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>json</span><span class=o>::</span><span class=n>binary</span><span class=p>({</span><span class=mh>0xCA</span><span class=p>,</span><span class=w> </span><span class=mh>0xFE</span><span class=p>,</span><span class=w> </span><span class=mh>0xBA</span><span class=p>,</span><span class=w> </span><span class=mh>0xBE</span><span class=p>},</span><span class=w> </span><span class=mi>23</span><span class=p>);</span>
<span class=k>auto</span><span class=w> </span><span class=n>j3</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>json</span><span class=o>::</span><span class=n>binary</span><span class=p>({</span><span class=mh>0xCA</span><span class=p>,</span><span class=w> </span><span class=mh>0xFE</span><span class=p>,</span><span class=w> </span><span class=mh>0xBA</span><span class=p>,</span><span class=w> </span><span class=mh>0xBE</span><span class=p>});</span>
<span class=n>j2</span><span class=w> </span><span class=o>==</span><span class=w> </span><span class=n>j</span><span class=p>;</span><span class=w> </span><span class=c1>// returns true</span>
<span class=n>j3</span><span class=p>.</span><span class=n>get_binary</span><span class=p>().</span><span class=n>has_subtype</span><span class=p>();</span><span class=w> </span><span class=c1>// returns false</span>
<span class=n>j3</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=c1>// returns std::uint64_t(-1) as j3 has no subtype</span>
</code></pre></div> <h2 id=serialization>Serialization<a class=headerlink href=#serialization title="Permanent link">&para;</a></h2> <p>Binary values are serialized differently according to the formats.</p> <h3 id=json>JSON<a class=headerlink href=#json title="Permanent link">&para;</a></h3> <p>JSON does not have a binary type, and this library does not introduce a new type as this would break conformance. Instead, binary values are serialized as an object with two keys: <code>bytes</code> holds an array of integers, and <code>subtype</code> is an integer or <code>null</code>.</p> <details class=example> <summary>Example</summary> <p>Code:</p> <div class=highlight><pre><span></span><code><span class=c1>// create a binary value of subtype 42</span>
</code></pre></div> <h2 id=serialization>Serialization<a class=headerlink href=#serialization title="Permanent link">&para;</a></h2> <p>Binary values are serialized differently according to the formats.</p> <h3 id=json><abbr title="JavaScript Object Notation">JSON</abbr><a class=headerlink href=#json title="Permanent link">&para;</a></h3> <p><abbr title="JavaScript Object Notation">JSON</abbr> does not have a binary type, and this library does not introduce a new type as this would break conformance. Instead, binary values are serialized as an object with two keys: <code>bytes</code> holds an array of integers, and <code>subtype</code> is an integer or <code>null</code>.</p> <details class=example> <summary>Example</summary> <p>Code:</p> <div class=highlight><pre><span></span><code><span class=c1>// create a binary value of subtype 42</span>
<span class=n>json</span><span class=w> </span><span class=n>j</span><span class=p>;</span>
<span class=n>j</span><span class=p>[</span><span class=s>&quot;binary&quot;</span><span class=p>]</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>json</span><span class=o>::</span><span class=n>binary</span><span class=p>({</span><span class=mh>0xCA</span><span class=p>,</span><span class=w> </span><span class=mh>0xFE</span><span class=p>,</span><span class=w> </span><span class=mh>0xBA</span><span class=p>,</span><span class=w> </span><span class=mh>0xBE</span><span class=p>},</span><span class=w> </span><span class=mi>42</span><span class=p>);</span>
@@ -46,7 +46,7 @@ vector &lt;|-- binary_t</code></pre> <p>By default, binary values are stored as
<span class=w> </span><span class=nt>&quot;subtype&quot;</span><span class=p>:</span><span class=w> </span><span class=mi>42</span>
<span class=w> </span><span class=p>}</span>
<span class=p>}</span>
</code></pre></div> </details> <div class="admonition warning"> <p class=admonition-title>No roundtrip for binary values</p> <p>The JSON parser will not parse the objects generated by binary values back to binary values. This is by design to remain standards compliant. Serializing binary values to JSON is only implemented for debugging purposes.</p> </div> <h3 id=bjdata>BJData<a class=headerlink href=#bjdata title="Permanent link">&para;</a></h3> <p><a href=../binary_formats/bjdata/ >BJData</a> neither supports binary values nor subtypes, and proposes to serialize binary values as array of uint8 values. This translation is implemented by the library.</p> <details class=example> <summary>Example</summary> <p>Code:</p> <div class=highlight><pre><span></span><code><span class=c1>// create a binary value of subtype 42 (will be ignored in BJData)</span>
</code></pre></div> </details> <div class="admonition warning"> <p class=admonition-title>No roundtrip for binary values</p> <p>The <abbr title="JavaScript Object Notation">JSON</abbr> parser will not parse the objects generated by binary values back to binary values. This is by design to remain standards compliant. Serializing binary values to <abbr title="JavaScript Object Notation">JSON</abbr> is only implemented for debugging purposes.</p> </div> <h3 id=bjdata><abbr title="Binary JData">BJData</abbr><a class=headerlink href=#bjdata title="Permanent link">&para;</a></h3> <p><a href=../binary_formats/bjdata/ ><abbr title="Binary JData">BJData</abbr></a> neither supports binary values nor subtypes, and proposes to serialize binary values as array of uint8 values. This translation is implemented by the library.</p> <details class=example> <summary>Example</summary> <p>Code:</p> <div class=highlight><pre><span></span><code><span class=c1>// create a binary value of subtype 42 (will be ignored in BJData)</span>
<span class=n>json</span><span class=w> </span><span class=n>j</span><span class=p>;</span>
<span class=n>j</span><span class=p>[</span><span class=s>&quot;binary&quot;</span><span class=p>]</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>json</span><span class=o>::</span><span class=n>binary</span><span class=p>({</span><span class=mh>0xCA</span><span class=p>,</span><span class=w> </span><span class=mh>0xFE</span><span class=p>,</span><span class=w> </span><span class=mh>0xBA</span><span class=p>,</span><span class=w> </span><span class=mh>0xBE</span><span class=p>},</span><span class=w> </span><span class=mi>42</span><span class=p>);</span>
@@ -59,7 +59,7 @@ vector &lt;|-- binary_t</code></pre> <p>By default, binary values are stored as
<span class=w> </span><span class=mh>0x55</span><span class=w> </span><span class=mh>0xCA</span><span class=w> </span><span class=mh>0x55</span><span class=w> </span><span class=mh>0xFE</span><span class=w> </span><span class=mh>0x55</span><span class=w> </span><span class=mh>0xBA</span><span class=w> </span><span class=mh>0x55</span><span class=w> </span><span class=mh>0xBE</span><span class=w> </span><span class=c1>// content (each byte prefixed with &#39;U&#39;)</span>
<span class=w> </span><span class=mh>0x5D</span><span class=w> </span><span class=c1>// &#39;]&#39;</span>
<span class=mh>0x7D</span><span class=w> </span><span class=c1>// &#39;}&#39;</span>
</code></pre></div> <p>The following code uses the type and size optimization for UBJSON:</p> <div class=highlight><pre><span></span><code><span class=c1>// convert to UBJSON using the size and type optimization</span>
</code></pre></div> <p>The following code uses the type and size optimization for <abbr title="Universal Binary JSON">UBJSON</abbr>:</p> <div class=highlight><pre><span></span><code><span class=c1>// convert to UBJSON using the size and type optimization</span>
<span class=k>auto</span><span class=w> </span><span class=n>v</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>json</span><span class=o>::</span><span class=n>to_bjdata</span><span class=p>(</span><span class=n>j</span><span class=p>,</span><span class=w> </span><span class=nb>true</span><span class=p>,</span><span class=w> </span><span class=nb>true</span><span class=p>);</span>
</code></pre></div> <p>The resulting vector has 22 elements; the optimization is not effective for examples with few values:</p> <div class=highlight><pre><span></span><code><span class=mh>0x7B</span><span class=w> </span><span class=c1>// &#39;{&#39;</span>
<span class=w> </span><span class=mh>0x23</span><span class=w> </span><span class=mh>0x69</span><span class=w> </span><span class=mh>0x01</span><span class=w> </span><span class=c1>// &#39;#&#39; &#39;i&#39; type of the array elements: unsigned integers</span>
@@ -69,10 +69,10 @@ vector &lt;|-- binary_t</code></pre> <p>By default, binary values are stored as
<span class=w> </span><span class=mh>0x24</span><span class=w> </span><span class=mh>0x55</span><span class=w> </span><span class=c1>// &#39;$&#39; &#39;U&#39; type of the array elements: unsigned integers</span>
<span class=w> </span><span class=mh>0x23</span><span class=w> </span><span class=mh>0x69</span><span class=w> </span><span class=mh>0x04</span><span class=w> </span><span class=c1>// &#39;#&#39; i 4 number of array elements</span>
<span class=w> </span><span class=mh>0xCA</span><span class=w> </span><span class=mh>0xFE</span><span class=w> </span><span class=mh>0xBA</span><span class=w> </span><span class=mh>0xBE</span><span class=w> </span><span class=c1>// content</span>
</code></pre></div> <p>Note that subtype (42) is <strong>not</strong> serialized and that UBJSON has <strong>no binary type</strong>, and deserializing <code>v</code> would yield the following value:</p> <div class=highlight><pre><span></span><code><span class=p>{</span>
</code></pre></div> <p>Note that subtype (42) is <strong>not</strong> serialized and that <abbr title="Universal Binary JSON">UBJSON</abbr> has <strong>no binary type</strong>, and deserializing <code>v</code> would yield the following value:</p> <div class=highlight><pre><span></span><code><span class=p>{</span>
<span class=w> </span><span class=nt>&quot;binary&quot;</span><span class=p>:</span><span class=w> </span><span class=p>[</span><span class=mi>202</span><span class=p>,</span><span class=w> </span><span class=mi>254</span><span class=p>,</span><span class=w> </span><span class=mi>186</span><span class=p>,</span><span class=w> </span><span class=mi>190</span><span class=p>]</span>
<span class=p>}</span>
</code></pre></div> </details> <h3 id=bson>BSON<a class=headerlink href=#bson title="Permanent link">&para;</a></h3> <p><a href=../binary_formats/bson/ >BSON</a> supports binary values and subtypes. If a subtype is given, it is used and added as unsigned 8-bit integer. If no subtype is given, the generic binary subtype 0x00 is used.</p> <details class=example> <summary>Example</summary> <p>Code:</p> <div class=highlight><pre><span></span><code><span class=c1>// create a binary value of subtype 42</span>
</code></pre></div> </details> <h3 id=bson><abbr title="Binary JSON">BSON</abbr><a class=headerlink href=#bson title="Permanent link">&para;</a></h3> <p><a href=../binary_formats/bson/ ><abbr title="Binary JSON">BSON</abbr></a> supports binary values and subtypes. If a subtype is given, it is used and added as unsigned 8-bit integer. If no subtype is given, the generic binary subtype 0x00 is used.</p> <details class=example> <summary>Example</summary> <p>Code:</p> <div class=highlight><pre><span></span><code><span class=c1>// create a binary value of subtype 42</span>
<span class=n>json</span><span class=w> </span><span class=n>j</span><span class=p>;</span>
<span class=n>j</span><span class=p>[</span><span class=s>&quot;binary&quot;</span><span class=p>]</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>json</span><span class=o>::</span><span class=n>binary</span><span class=p>({</span><span class=mh>0xCA</span><span class=p>,</span><span class=w> </span><span class=mh>0xFE</span><span class=p>,</span><span class=w> </span><span class=mh>0xBA</span><span class=p>,</span><span class=w> </span><span class=mh>0xBE</span><span class=p>},</span><span class=w> </span><span class=mi>42</span><span class=p>);</span>
@@ -91,7 +91,7 @@ vector &lt;|-- binary_t</code></pre> <p>By default, binary values are stored as
<span class=w> </span><span class=nt>&quot;subtype&quot;</span><span class=p>:</span><span class=w> </span><span class=mi>42</span>
<span class=w> </span><span class=p>}</span>
<span class=p>}</span>
</code></pre></div> </details> <h3 id=cbor>CBOR<a class=headerlink href=#cbor title="Permanent link">&para;</a></h3> <p><a href=../binary_formats/cbor/ >CBOR</a> supports binary values, but no subtypes. Subtypes will be serialized as tags. Any binary value will be serialized as byte strings. The library will choose the smallest representation using the length of the byte array.</p> <details class=example> <summary>Example</summary> <p>Code:</p> <div class=highlight><pre><span></span><code><span class=c1>// create a binary value of subtype 42</span>
</code></pre></div> </details> <h3 id=cbor><abbr title="Concise Binary Object Representation">CBOR</abbr><a class=headerlink href=#cbor title="Permanent link">&para;</a></h3> <p><a href=../binary_formats/cbor/ ><abbr title="Concise Binary Object Representation">CBOR</abbr></a> supports binary values, but no subtypes. Subtypes will be serialized as tags. Any binary value will be serialized as byte strings. The library will choose the smallest representation using the length of the byte array.</p> <details class=example> <summary>Example</summary> <p>Code:</p> <div class=highlight><pre><span></span><code><span class=c1>// create a binary value of subtype 42</span>
<span class=n>json</span><span class=w> </span><span class=n>j</span><span class=p>;</span>
<span class=n>j</span><span class=p>[</span><span class=s>&quot;binary&quot;</span><span class=p>]</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>json</span><span class=o>::</span><span class=n>binary</span><span class=p>({</span><span class=mh>0xCA</span><span class=p>,</span><span class=w> </span><span class=mh>0xFE</span><span class=p>,</span><span class=w> </span><span class=mh>0xBA</span><span class=p>,</span><span class=w> </span><span class=mh>0xBE</span><span class=p>},</span><span class=w> </span><span class=mi>42</span><span class=p>);</span>
@@ -127,7 +127,7 @@ vector &lt;|-- binary_t</code></pre> <p>By default, binary values are stored as
<span class=w> </span><span class=nt>&quot;subtype&quot;</span><span class=p>:</span><span class=w> </span><span class=mi>42</span>
<span class=w> </span><span class=p>}</span>
<span class=p>}</span>
</code></pre></div> </details> <h3 id=ubjson>UBJSON<a class=headerlink href=#ubjson title="Permanent link">&para;</a></h3> <p><a href=../binary_formats/ubjson/ >UBJSON</a> neither supports binary values nor subtypes, and proposes to serialize binary values as array of uint8 values. This translation is implemented by the library.</p> <details class=example> <summary>Example</summary> <p>Code:</p> <div class=highlight><pre><span></span><code><span class=c1>// create a binary value of subtype 42 (will be ignored in UBJSON)</span>
</code></pre></div> </details> <h3 id=ubjson><abbr title="Universal Binary JSON">UBJSON</abbr><a class=headerlink href=#ubjson title="Permanent link">&para;</a></h3> <p><a href=../binary_formats/ubjson/ ><abbr title="Universal Binary JSON">UBJSON</abbr></a> neither supports binary values nor subtypes, and proposes to serialize binary values as array of uint8 values. This translation is implemented by the library.</p> <details class=example> <summary>Example</summary> <p>Code:</p> <div class=highlight><pre><span></span><code><span class=c1>// create a binary value of subtype 42 (will be ignored in UBJSON)</span>
<span class=n>json</span><span class=w> </span><span class=n>j</span><span class=p>;</span>
<span class=n>j</span><span class=p>[</span><span class=s>&quot;binary&quot;</span><span class=p>]</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>json</span><span class=o>::</span><span class=n>binary</span><span class=p>({</span><span class=mh>0xCA</span><span class=p>,</span><span class=w> </span><span class=mh>0xFE</span><span class=p>,</span><span class=w> </span><span class=mh>0xBA</span><span class=p>,</span><span class=w> </span><span class=mh>0xBE</span><span class=p>},</span><span class=w> </span><span class=mi>42</span><span class=p>);</span>
@@ -140,7 +140,7 @@ vector &lt;|-- binary_t</code></pre> <p>By default, binary values are stored as
<span class=w> </span><span class=mh>0x55</span><span class=w> </span><span class=mh>0xCA</span><span class=w> </span><span class=mh>0x55</span><span class=w> </span><span class=mh>0xFE</span><span class=w> </span><span class=mh>0x55</span><span class=w> </span><span class=mh>0xBA</span><span class=w> </span><span class=mh>0x55</span><span class=w> </span><span class=mh>0xBE</span><span class=w> </span><span class=c1>// content (each byte prefixed with &#39;U&#39;)</span>
<span class=w> </span><span class=mh>0x5D</span><span class=w> </span><span class=c1>// &#39;]&#39;</span>
<span class=mh>0x7D</span><span class=w> </span><span class=c1>// &#39;}&#39;</span>
</code></pre></div> <p>The following code uses the type and size optimization for UBJSON:</p> <div class=highlight><pre><span></span><code><span class=c1>// convert to UBJSON using the size and type optimization</span>
</code></pre></div> <p>The following code uses the type and size optimization for <abbr title="Universal Binary JSON">UBJSON</abbr>:</p> <div class=highlight><pre><span></span><code><span class=c1>// convert to UBJSON using the size and type optimization</span>
<span class=k>auto</span><span class=w> </span><span class=n>v</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>json</span><span class=o>::</span><span class=n>to_ubjson</span><span class=p>(</span><span class=n>j</span><span class=p>,</span><span class=w> </span><span class=nb>true</span><span class=p>,</span><span class=w> </span><span class=nb>true</span><span class=p>);</span>
</code></pre></div> <p>The resulting vector has 23 elements; the optimization is not effective for examples with few values:</p> <div class=highlight><pre><span></span><code><span class=mh>0x7B</span><span class=w> </span><span class=c1>// &#39;{&#39;</span>
<span class=w> </span><span class=mh>0x24</span><span class=w> </span><span class=c1>// &#39;$&#39; type of the object elements</span>
@@ -151,7 +151,7 @@ vector &lt;|-- binary_t</code></pre> <p>By default, binary values are stored as
<span class=w> </span><span class=mh>0x24</span><span class=w> </span><span class=mh>0x55</span><span class=w> </span><span class=c1>// &#39;$&#39; &#39;U&#39; type of the array elements: unsigned integers</span>
<span class=w> </span><span class=mh>0x23</span><span class=w> </span><span class=mh>0x69</span><span class=w> </span><span class=mh>0x04</span><span class=w> </span><span class=c1>// &#39;#&#39; i 4 number of array elements</span>
<span class=w> </span><span class=mh>0xCA</span><span class=w> </span><span class=mh>0xFE</span><span class=w> </span><span class=mh>0xBA</span><span class=w> </span><span class=mh>0xBE</span><span class=w> </span><span class=c1>// content</span>
</code></pre></div> <p>Note that subtype (42) is <strong>not</strong> serialized and that UBJSON has <strong>no binary type</strong>, and deserializing <code>v</code> would yield the following value:</p> <div class=highlight><pre><span></span><code><span class=p>{</span>
</code></pre></div> <p>Note that subtype (42) is <strong>not</strong> serialized and that <abbr title="Universal Binary JSON">UBJSON</abbr> has <strong>no binary type</strong>, and deserializing <code>v</code> would yield the following value:</p> <div class=highlight><pre><span></span><code><span class=p>{</span>
<span class=w> </span><span class=nt>&quot;binary&quot;</span><span class=p>:</span><span class=w> </span><span class=p>[</span><span class=mi>202</span><span class=p>,</span><span class=w> </span><span class=mi>254</span><span class=p>,</span><span class=w> </span><span class=mi>186</span><span class=p>,</span><span class=w> </span><span class=mi>190</span><span class=p>]</span>
<span class=p>}</span>
</code></pre></div> </details> <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">January 10, 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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<span class=w> </span><span class=c1>// update in 2006: removed Pluto</span>
<span class=w> </span><span class=nt>&quot;planets&quot;</span><span class=p>:</span><span class=w> </span><span class=p>[</span><span class=s2>&quot;Mercury&quot;</span><span class=p>,</span><span class=w> </span><span class=s2>&quot;Venus&quot;</span><span class=p>,</span><span class=w> </span><span class=s2>&quot;Earth&quot;</span><span class=p>,</span><span class=w> </span><span class=s2>&quot;Mars&quot;</span><span class=p>,</span>
<span class=w> </span><span class=s2>&quot;Jupiter&quot;</span><span class=p>,</span><span class=w> </span><span class=s2>&quot;Uranus&quot;</span><span class=p>,</span><span class=w> </span><span class=s2>&quot;Neptune&quot;</span><span class=w> </span><span class=cm>/*, &quot;Pluto&quot; */</span><span class=p>]</span>
@@ -47,4 +47,4 @@ last read: &#39;&lt;U+000A&gt; {&lt;U+000A&gt; /&#39;; expected string
<span class=w> </span><span class=s2>&quot;Neptune&quot;</span>
<span class=w> </span><span class=p>]</span>
<span class=p>}</span>
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15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.52 6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 1Line truncated
<span class=w> </span><span class=nt>&quot;name&quot;</span><span class=p>:</span><span class=w> </span><span class=s2>&quot;Mary Smith&quot;</span><span class=p>,</span>
<span class=w> </span><span class=nt>&quot;age&quot;</span><span class=p>:</span><span class=w> </span><span class=mi>42</span><span class=p>,</span>
<span class=w> </span><span class=nt>&quot;hobbies&quot;</span><span class=p>:</span><span class=w> </span><span class=p>[</span><span class=s2>&quot;hiking&quot;</span><span class=p>,</span><span class=w> </span><span class=s2>&quot;reading&quot;</span><span class=p>]</span>
<span class=p>}</span>
</code></pre></div> <p>Assume the value is parsed to a <code>json</code> variable <code>j</code>.</p> <table> <thead> <tr> <th>expression</th> <th>value</th> </tr> </thead> <tbody> <tr> <td><code class=highlight><span class=n>j</span></code></td> <td><code class=highlight><span class=p>{</span><span class=nt>&quot;name&quot;</span><span class=p>:</span><span class=w> </span><span class=s2>&quot;Mary Smith&quot;</span><span class=p>,</span><span class=w> </span><span class=nt>&quot;age&quot;</span><span class=p>:</span><span class=w> </span><span class=mi>42</span><span class=p>,</span><span class=w> </span><span class=nt>&quot;hobbies&quot;</span><span class=p>:</span><span class=w> </span><span class=p>[</span><span class=s2>&quot;hiking&quot;</span><span class=p>,</span><span class=w> </span><span class=s2>&quot;reading&quot;</span><span class=p>]}</span></code></td> </tr> <tr> <td><code class=highlight><span class=n>j</span><span class=p>.</span><span class=n>at</span><span class=p>(</span><span class=s>&quot;name&quot;</span><span class=p>)</span></code></td> <td><code class=highlight><span class=s2>&quot;Mary Smith&quot;</span></code></td> </tr> <tr> <td><code class=highlight><span class=n>j</span><span class=p>.</span><span class=n>at</span><span class=p>(</span><span class=s>&quot;age&quot;</span><span class=p>)</span></code></td> <td><code class=highlight><span class=mi>42</span></code></td> </tr> <tr> <td><code class=highlight><span class=n>j</span><span class=p>.</span><span class=n>at</span><span class=p>(</span><span class=s>&quot;hobbies&quot;</span><span class=p>)</span></code></td> <td><code class=highlight><span class=p>[</span><span class=s2>&quot;hiking&quot;</span><span class=p>,</span><span class=w> </span><span class=s2>&quot;reading&quot;</span><span class=p>]</span></code></td> </tr> <tr> <td><code class=highlight><span class=n>j</span><span class=p>.</span><span class=n>at</span><span class=p>(</span><span class=s>&quot;hobbies&quot;</span><span class=p>).</span><span class=n>at</span><span class=p>(</span><span class=mi>0</span><span class=p>)</span></code></td> <td><code class=highlight><span class=s2>&quot;hiking&quot;</span></code></td> </tr> <tr> <td><code class=highlight><span class=n>j</span><span class=p>.</span><span class=n>at</span><span class=p>(</span><span class=s>&quot;hobbies&quot;</span><span class=p>).</span><span class=n>at</span><span class=p>(</span><span class=mi>1</span><span class=p>)</span></code></td> <td><code class=highlight><span class=s2>&quot;reading&quot;</span></code></td> </tr> </tbody> </table> </details> <p>The return value is a reference, so it can be modified by the original value.</p> <details class=example> <summary>Write access</summary> <div class=highlight><pre><span></span><code><span class=n>j</span><span class=p>.</span><span class=n>at</span><span class=p>(</span><span class=s>&quot;name&quot;</span><span class=p>)</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=s>&quot;John Smith&quot;</span><span class=p>;</span>
</code></pre></div> <p>This code produces the following JSON value:</p> <div class=highlight><pre><span></span><code><span class=p>{</span>
</code></pre></div> <p>This code produces the following <abbr title="JavaScript Object Notation">JSON</abbr> value:</p> <div class=highlight><pre><span></span><code><span class=p>{</span>
<span class=w> </span><span class=nt>&quot;name&quot;</span><span class=p>:</span><span class=w> </span><span class=s2>&quot;John Smith&quot;</span><span class=p>,</span>
<span class=w> </span><span class=nt>&quot;age&quot;</span><span class=p>:</span><span class=w> </span><span class=mi>42</span><span class=p>,</span>
<span class=w> </span><span class=nt>&quot;hobbies&quot;</span><span class=p>:</span><span class=w> </span><span class=p>[</span><span class=s2>&quot;hiking&quot;</span><span class=p>,</span><span class=w> </span><span class=s2>&quot;reading&quot;</span><span class=p>]</span>
@@ -12,4 +12,4 @@
</code></pre></div> </details> <p>When accessing an invalid index (i.e., an index greater than or equal to the array size) or the passed object key is non-existing, an exception is thrown.</p> <details class=example> <summary>Accessing via invalid index or missing key</summary> <div class=highlight><pre><span></span><code><span class=n>j</span><span class=p>.</span><span class=n>at</span><span class=p>(</span><span class=s>&quot;hobbies&quot;</span><span class=p>).</span><span class=n>at</span><span class=p>(</span><span class=mi>3</span><span class=p>)</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=s>&quot;cooking&quot;</span><span class=p>;</span>
</code></pre></div> <p>This code produces the following exception:</p> <div class=highlight><pre><span></span><code>[json.exception.out_of_range.401] array index 3 is out of range
</code></pre></div> <p>When you <a href=../../../home/exceptions/#extended-diagnostic-messages>extended diagnostic messages</a> are enabled by defining <a href=../../../api/macros/json_diagnostics/ ><code>JSON_DIAGNOSTICS</code></a>, the exception further gives information where the key or index is missing or out of range.</p> <div class=highlight><pre><span></span><code>[json.exception.out_of_range.401] (/hobbies) array index 3 is out of range
</code></pre></div> </details> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <div class="admonition failure"> <p class=admonition-title>Exceptions</p> <ul> <li><a href=../../../api/basic_json/at/ ><code>at</code></a> can only be used with objects (with a string argument) or with arrays (with a numeric argument). For other types, a <a href=../../../home/exceptions/#jsonexceptiontype_error304><code>basic_json::type_error</code></a> is thrown.</li> <li><a href=../../../home/exceptions/#out-of-range><code>basic_json::out_of_range</code> exception</a> exceptions are thrown if the provided key is not found in an object or the provided index is invalid.</li> </ul> </div> <h2 id=summary>Summary<a class=headerlink href=#summary title="Permanent link">&para;</a></h2> <table> <thead> <tr> <th>scenario</th> <th>non-const value</th> <th>const value</th> </tr> </thead> <tbody> <tr> <td>access to existing object key</td> <td>reference to existing value is returned</td> <td>const reference to existing value is returned</td> </tr> <tr> <td>access to valid array index</td> <td>reference to existing value is returned</td> <td>const reference to existing value is returned</td> </tr> <tr> <td>access to non-existing object key</td> <td><code>basic_json::out_of_range</code> exception is thrown</td> <td><code>basic_json::out_of_range</code> exception is thrown</td> </tr> <tr> <td>access to invalid array index</td> <td><code>basic_json::out_of_range</code> exception is thrown</td> <td><code>basic_json::out_of_range</code> exception is thrown</td> </tr> </tbody> </table> <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">January 10, 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; 2013 - 2024 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 0 496 512"><!-- Font Awesome Free 6.7.1 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 2024 Fonticons, Inc.--><path d="M165.9 397.4c0 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-.3-1.9-3-3.2-5.9-2.9M244.8 8C106.1 8 0 113.3 0 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 12.1C428.2 457.8 496 362.9 496 252 496 113.3 383.5 8 244.8 8M97.2 352.9c-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/nielslohmaLine truncated
</code></pre></div> </details> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <div class="admonition failure"> <p class=admonition-title>Exceptions</p> <ul> <li><a href=../../../api/basic_json/at/ ><code>at</code></a> can only be used with objects (with a string argument) or with arrays (with a numeric argument). For other types, a <a href=../../../home/exceptions/#jsonexceptiontype_error304><code>basic_json::type_error</code></a> is thrown.</li> <li><a href=../../../home/exceptions/#out-of-range><code>basic_json::out_of_range</code> exception</a> exceptions are thrown if the provided key is not found in an object or the provided index is invalid.</li> </ul> </div> <h2 id=summary>Summary<a class=headerlink href=#summary title="Permanent link">&para;</a></h2> <table> <thead> <tr> <th>scenario</th> <th>non-const value</th> <th>const value</th> </tr> </thead> <tbody> <tr> <td>access to existing object key</td> <td>reference to existing value is returned</td> <td>const reference to existing value is returned</td> </tr> <tr> <td>access to valid array index</td> <td>reference to existing value is returned</td> <td>const reference to existing value is returned</td> </tr> <tr> <td>access to non-existing object key</td> <td><code>basic_json::out_of_range</code> exception is thrown</td> <td><code>basic_json::out_of_range</code> exception is thrown</td> </tr> <tr> <td>access to invalid array index</td> <td><code>basic_json::out_of_range</code> exception is thrown</td> <td><code>basic_json::out_of_range</code> exception is thrown</td> </tr> </tbody> </table> <!-- 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">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; 2013-2025 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 0 496 512"><!-- Font Awesome Free 6.7.1 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 2024 Fonticons, Inc.--><path d="M165.9 397.4c0 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-.3-1.9-3-3.2-5.9-2.9M244.8 8C106.1 8 0 113.3 0 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 12.1C428.2 457.8 496 362.9 496 252 496 113.3 383.5 8 244.8 8M97.2 352.9c-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 2.3c1.6Line truncated
@@ -1,5 +1,5 @@
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<span class=w> </span><span class=nt>&quot;logOutput&quot;</span><span class=p>:</span><span class=w> </span><span class=s2>&quot;result.log&quot;</span><span class=p>,</span>
<span class=w> </span><span class=nt>&quot;append&quot;</span><span class=p>:</span><span class=w> </span><span class=kc>true</span>
<span class=p>}</span>
</code></pre></div> <p>Assume the value is parsed to a <code>json</code> variable <code>j</code>.</p> <table> <thead> <tr> <th>expression</th> <th>value</th> </tr> </thead> <tbody> <tr> <td><code class=highlight><span class=n>j</span></code></td> <td><code class=highlight><span class=p>{</span><span class=nt>&quot;logOutput&quot;</span><span class=p>:</span><span class=w> </span><span class=s2>&quot;result.log&quot;</span><span class=p>,</span><span class=w> </span><span class=nt>&quot;append&quot;</span><span class=p>:</span><span class=w> </span><span class=kc>true</span><span class=p>}</span></code></td> </tr> <tr> <td><code class=highlight><span class=n>j</span><span class=p>.</span><span class=n>value</span><span class=p>(</span><span class=s>&quot;logOutput&quot;</span><span class=p>,</span><span class=w> </span><span class=s>&quot;logfile.log&quot;</span><span class=p>)</span></code></td> <td><code class=highlight><span class=s2>&quot;result.log&quot;</span></code></td> </tr> <tr> <td><code class=highlight><span class=n>j</span><span class=p>.</span><span class=n>value</span><span class=p>(</span><span class=s>&quot;append&quot;</span><span class=p>,</span><span class=w> </span><span class=nb>true</span><span class=p>)</span></code></td> <td><code class=highlight><span class=kc>true</span></code></td> </tr> <tr> <td><code class=highlight><span class=n>j</span><span class=p>.</span><span class=n>value</span><span class=p>(</span><span class=s>&quot;append&quot;</span><span class=p>,</span><span class=w> </span><span class=nb>false</span><span class=p>)</span></code></td> <td><code class=highlight><span class=kc>true</span></code></td> </tr> <tr> <td><code class=highlight><span class=n>j</span><span class=p>.</span><span class=n>value</span><span class=p>(</span><span class=s>&quot;logLevel&quot;</span><span class=p>,</span><span class=w> </span><span class=s>&quot;verbose&quot;</span><span class=p>)</span></code></td> <td><code class=highlight><span class=s2>&quot;verbose&quot;</span></code></td> </tr> </tbody> </table> </details> <h2 id=note>Note<a class=headerlink href=#note title="Permanent link">&para;</a></h2> <div class="admonition failure"> <p class=admonition-title>Exceptions</p> <ul> <li><code>value</code> can only be used with objects. For other types, a <a href=../../../home/exceptions/#jsonexceptiontype_error306><code>basic_json::type_error</code></a> is thrown.</li> </ul> </div> <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">January 10, 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; 2013 - 2024 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 0 496 512"><!-- Font Awesome Free 6.7.1 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 2024 Fonticons, Inc.--><path d="M165.9 397.4c0 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-.3-1.9-3-3.2-5.9-2.9M244.8 8C106.1 8 0 113.3 0 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 8.8-27Line truncated
</code></pre></div> <p>Assume the value is parsed to a <code>json</code> variable <code>j</code>.</p> <table> <thead> <tr> <th>expression</th> <th>value</th> </tr> </thead> <tbody> <tr> <td><code class=highlight><span class=n>j</span></code></td> <td><code class=highlight><span class=p>{</span><span class=nt>&quot;logOutput&quot;</span><span class=p>:</span><span class=w> </span><span class=s2>&quot;result.log&quot;</span><span class=p>,</span><span class=w> </span><span class=nt>&quot;append&quot;</span><span class=p>:</span><span class=w> </span><span class=kc>true</span><span class=p>}</span></code></td> </tr> <tr> <td><code class=highlight><span class=n>j</span><span class=p>.</span><span class=n>value</span><span class=p>(</span><span class=s>&quot;logOutput&quot;</span><span class=p>,</span><span class=w> </span><span class=s>&quot;logfile.log&quot;</span><span class=p>)</span></code></td> <td><code class=highlight><span class=s2>&quot;result.log&quot;</span></code></td> </tr> <tr> <td><code class=highlight><span class=n>j</span><span class=p>.</span><span class=n>value</span><span class=p>(</span><span class=s>&quot;append&quot;</span><span class=p>,</span><span class=w> </span><span class=nb>true</span><span class=p>)</span></code></td> <td><code class=highlight><span class=kc>true</span></code></td> </tr> <tr> <td><code class=highlight><span class=n>j</span><span class=p>.</span><span class=n>value</span><span class=p>(</span><span class=s>&quot;append&quot;</span><span class=p>,</span><span class=w> </span><span class=nb>false</span><span class=p>)</span></code></td> <td><code class=highlight><span class=kc>true</span></code></td> </tr> <tr> <td><code class=highlight><span class=n>j</span><span class=p>.</span><span class=n>value</span><span class=p>(</span><span class=s>&quot;logLevel&quot;</span><span class=p>,</span><span class=w> </span><span class=s>&quot;verbose&quot;</span><span class=p>)</span></code></td> <td><code class=highlight><span class=s2>&quot;verbose&quot;</span></code></td> </tr> </tbody> </table> </details> <h2 id=note>Note<a class=headerlink href=#note title="Permanent link">&para;</a></h2> <div class="admonition failure"> <p class=admonition-title>Exceptions</p> <ul> <li><code>value</code> can only be used with objects. For other types, a <a href=../../../home/exceptions/#jsonexceptiontype_error306><code>basic_json::type_error</code></a> is thrown.</li> </ul> </div> <!-- 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">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; 2013-2025 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 0 496 512"><!-- Font Awesome Free 6.7.1 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 2024 Fonticons, Inc.--><path d="M165.9 397.4c0 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-.3-1.9-3-3.2-5.9-2.9M244.8 8C106.1 8 0 113.3 0 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.Line truncated
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6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9.5 5"/></svg> </label> <divLine truncated
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<span class=w> </span><span class=nt>&quot;name&quot;</span><span class=p>:</span><span class=w> </span><span class=s2>&quot;Mary Smith&quot;</span><span class=p>,</span>
<span class=w> </span><span class=nt>&quot;age&quot;</span><span class=p>:</span><span class=w> </span><span class=mi>42</span><span class=p>,</span>
<span class=w> </span><span class=nt>&quot;hobbies&quot;</span><span class=p>:</span><span class=w> </span><span class=p>[</span><span class=s2>&quot;hiking&quot;</span><span class=p>,</span><span class=w> </span><span class=s2>&quot;reading&quot;</span><span class=p>]</span>
<span class=p>}</span>
</code></pre></div> <p>Assume the value is parsed to a <code>json</code> variable <code>j</code>.</p> <table> <thead> <tr> <th>expression</th> <th>value</th> </tr> </thead> <tbody> <tr> <td><code class=highlight><span class=n>j</span></code></td> <td><code class=highlight><span class=p>{</span><span class=nt>&quot;name&quot;</span><span class=p>:</span><span class=w> </span><span class=s2>&quot;Mary Smith&quot;</span><span class=p>,</span><span class=w> </span><span class=nt>&quot;age&quot;</span><span class=p>:</span><span class=w> </span><span class=mi>42</span><span class=p>,</span><span class=w> </span><span class=nt>&quot;hobbies&quot;</span><span class=p>:</span><span class=w> </span><span class=p>[</span><span class=s2>&quot;hiking&quot;</span><span class=p>,</span><span class=w> </span><span class=s2>&quot;reading&quot;</span><span class=p>]}</span></code></td> </tr> <tr> <td><code class=highlight><span class=n>j</span><span class=p>[</span><span class=s>&quot;name&quot;</span><span class=p>]</span></code></td> <td><code class=highlight><span class=s2>&quot;Mary Smith&quot;</span></code></td> </tr> <tr> <td><code class=highlight><span class=n>j</span><span class=p>[</span><span class=s>&quot;age&quot;</span><span class=p>]</span></code></td> <td><code class=highlight><span class=mi>42</span></code></td> </tr> <tr> <td><code class=highlight><span class=n>j</span><span class=p>[</span><span class=s>&quot;hobbies&quot;</span><span class=p>]</span></code></td> <td><code class=highlight><span class=p>[</span><span class=s2>&quot;hiking&quot;</span><span class=p>,</span><span class=w> </span><span class=s2>&quot;reading&quot;</span><span class=p>]</span></code></td> </tr> <tr> <td><code class=highlight><span class=n>j</span><span class=p>[</span><span class=s>&quot;hobbies&quot;</span><span class=p>][</span><span class=mi>0</span><span class=p>]</span></code></td> <td><code class=highlight><span class=s2>&quot;hiking&quot;</span></code></td> </tr> <tr> <td><code class=highlight><span class=n>j</span><span class=p>[</span><span class=s>&quot;hobbies&quot;</span><span class=p>][</span><span class=mi>1</span><span class=p>]</span></code></td> <td><code class=highlight><span class=s2>&quot;reading&quot;</span></code></td> </tr> </tbody> </table> </details> <p>The return value is a reference, so it can modify the original value. In case the passed object key is non-existing, a <code class=highlight><span class=kc>null</span></code> value is inserted which can be immediately be overwritten.</p> <details class=example> <summary>Write access</summary> <div class=highlight><pre><span></span><code><span class=n>j</span><span class=p>[</span><span class=s>&quot;name&quot;</span><span class=p>]</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=s>&quot;John Smith&quot;</span><span class=p>;</span>
<span class=n>j</span><span class=p>[</span><span class=s>&quot;maidenName&quot;</span><span class=p>]</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=s>&quot;Jones&quot;</span><span class=p>;</span>
</code></pre></div> <p>This code produces the following JSON value:</p> <div class=highlight><pre><span></span><code><span class=p>{</span>
</code></pre></div> <p>This code produces the following <abbr title="JavaScript Object Notation">JSON</abbr> value:</p> <div class=highlight><pre><span></span><code><span class=p>{</span>
<span class=w> </span><span class=nt>&quot;name&quot;</span><span class=p>:</span><span class=w> </span><span class=s2>&quot;John Smith&quot;</span><span class=p>,</span>
<span class=w> </span><span class=nt>&quot;maidenName&quot;</span><span class=p>:</span><span class=w> </span><span class=s2>&quot;Jones&quot;</span><span class=p>,</span>
<span class=w> </span><span class=nt>&quot;age&quot;</span><span class=p>:</span><span class=w> </span><span class=mi>42</span><span class=p>,</span>
<span class=w> </span><span class=nt>&quot;hobbies&quot;</span><span class=p>:</span><span class=w> </span><span class=p>[</span><span class=s2>&quot;hiking&quot;</span><span class=p>,</span><span class=w> </span><span class=s2>&quot;reading&quot;</span><span class=p>]</span>
<span class=p>}</span>
</code></pre></div> </details> <p>When accessing an invalid index (i.e., an index greater than or equal to the array size), the JSON array is resized such that the passed index is the new maximal index. Intermediate values are filled with <code class=highlight><span class=kc>null</span></code>.</p> <details class=example> <summary>Filling up arrays with <code class=highlight><span class=kc>null</span></code> values</summary> <div class=highlight><pre><span></span><code><span class=n>j</span><span class=p>[</span><span class=s>&quot;hobbies&quot;</span><span class=p>][</span><span class=mi>0</span><span class=p>]</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=s>&quot;running&quot;</span><span class=p>;</span>
</code></pre></div> </details> <p>When accessing an invalid index (i.e., an index greater than or equal to the array size), the <abbr title="JavaScript Object Notation">JSON</abbr> array is resized such that the passed index is the new maximal index. Intermediate values are filled with <code class=highlight><span class=kc>null</span></code>.</p> <details class=example> <summary>Filling up arrays with <code class=highlight><span class=kc>null</span></code> values</summary> <div class=highlight><pre><span></span><code><span class=n>j</span><span class=p>[</span><span class=s>&quot;hobbies&quot;</span><span class=p>][</span><span class=mi>0</span><span class=p>]</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=s>&quot;running&quot;</span><span class=p>;</span>
<span class=n>j</span><span class=p>[</span><span class=s>&quot;hobbies&quot;</span><span class=p>][</span><span class=mi>3</span><span class=p>]</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=s>&quot;cooking&quot;</span><span class=p>;</span>
</code></pre></div> <p>This code produces the following JSON value:</p> <div class=highlight><pre><span></span><code><span class=p>{</span>
</code></pre></div> <p>This code produces the following <abbr title="JavaScript Object Notation">JSON</abbr> value:</p> <div class=highlight><pre><span></span><code><span class=p>{</span>
<span class=w> </span><span class=nt>&quot;name&quot;</span><span class=p>:</span><span class=w> </span><span class=s2>&quot;John Smith&quot;</span><span class=p>,</span>
<span class=w> </span><span class=nt>&quot;maidenName&quot;</span><span class=p>:</span><span class=w> </span><span class=s2>&quot;Jones&quot;</span><span class=p>,</span>
<span class=w> </span><span class=nt>&quot;age&quot;</span><span class=p>:</span><span class=w> </span><span class=mi>42</span><span class=p>,</span>
<span class=w> </span><span class=nt>&quot;hobbies&quot;</span><span class=p>:</span><span class=w> </span><span class=p>[</span><span class=s2>&quot;running&quot;</span><span class=p>,</span><span class=w> </span><span class=s2>&quot;reading&quot;</span><span class=p>,</span><span class=w> </span><span class=kc>null</span><span class=p>,</span><span class=w> </span><span class=s2>&quot;cooking&quot;</span><span class=p>]</span>
<span class=p>}</span>
</code></pre></div> </details> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <div class="admonition info"> <p class=admonition-title>Design rationale</p> <p>The library behaves differently to <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>map</span></code>:</p> <ul> <li><code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>vector</span><span class=o>::</span><span class=k>operator</span><span class=p>[]</span></code> never inserts a new element.</li> <li><code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>map</span><span class=o>::</span><span class=k>operator</span><span class=p>[]</span></code> is not available for const values.</li> </ul> <p>The type <code class=highlight><span class=n>json</span></code> wraps all JSON value types. It would be impossible to remove <a href=../../../api/basic_json/operator%5B%5D/ ><code>operator[]</code></a> for const objects. At the same time, inserting elements for non-const objects is really convenient as it avoids awkward <code>insert</code> calls. To this end, we decided to have an inserting non-const behavior for both arrays and objects.</p> </div> <div class="admonition info"> <p class=admonition-title>Info</p> <p>The access is unchecked. In case the passed object key does not exist or the passed array index is invalid, no exception is thrown.</p> </div> <div class="admonition danger"> <p class=admonition-title>Danger</p> <ul> <li>It is <strong>undefined behavior</strong> to access a const object with a non-existing key.</li> <li>It is <strong>undefined behavior</strong> to access a const array with an invalid index.</li> <li>In debug mode, an <strong>assertion</strong> will fire in both cases. You can disable assertions by defining the preprocessor symbol <code class=highlight><span class=n>NDEBUG</span></code> or redefine the macro <a href=../../macros/#json_assertx><code>JSON_ASSERT(x)</code></a>. See the documentation on <a href=../../assertions/ >runtime assertions</a> for more information.</li> </ul> </div> <div class="admonition failure"> <p class=admonition-title>Exceptions</p> <p><code>operator[]</code> can only be used with objects (with a string argument) or with arrays (with a numeric argument). For other types, a <a href=../../../home/exceptions/#jsonexceptiontype_error305><code>basic_json::type_error</code></a> is thrown.</p> </div> <h2 id=summary>Summary<a class=headerlink href=#summary title="Permanent link">&para;</a></h2> <table> <thead> <tr> <th>scenario</th> <th>non-const value</th> <th>const value</th> </tr> </thead> <tbody> <tr> <td>access to existing object key</td> <td>reference to existing value is returned</td> <td>const reference to existing value is returned</td> </tr> <tr> <td>access to valid array index</td> <td>reference to existing value is returned</td> <td>const reference to existing value is returned</td> </tr> <tr> <td>access to non-existing object key</td> <td>reference to newly inserted <code class=highlight><span class=kc>null</span></code> value is returned</td> <td><strong>undefined behavior</strong>; <a href=../../assertions/ >runtime assertion</a> in debug mode</td> </tr> <tr> <td>access to invalid array index</td> <td>reference to newly inserted <code class=highlight><span class=kc>null</span></code> value is returned; any index between previous maximal index and passed index are filled with <code class=highlight><span class=kc>null</span></code></td> <td><strong>undefined behavior</strong>; <a href=../../assertions/ >runtime assertion</a> in debug mode</td> </tr> </tbody> </table> <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">January 10, 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-componentLine truncated
</code></pre></div> </details> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <div class="admonition info"> <p class=admonition-title>Design rationale</p> <p>The library behaves differently to <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>map</span></code>:</p> <ul> <li><code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>vector</span><span class=o>::</span><span class=k>operator</span><span class=p>[]</span></code> never inserts a new element.</li> <li><code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>map</span><span class=o>::</span><span class=k>operator</span><span class=p>[]</span></code> is not available for const values.</li> </ul> <p>The type <code class=highlight><span class=n>json</span></code> wraps all <abbr title="JavaScript Object Notation">JSON</abbr> value types. It would be impossible to remove <a href=../../../api/basic_json/operator%5B%5D/ ><code>operator[]</code></a> for const objects. At the same time, inserting elements for non-const objects is really convenient as it avoids awkward <code>insert</code> calls. To this end, we decided to have an inserting non-const behavior for both arrays and objects.</p> </div> <div class="admonition info"> <p class=admonition-title>Info</p> <p>The access is unchecked. In case the passed object key does not exist or the passed array index is invalid, no exception is thrown.</p> </div> <div class="admonition danger"> <p class=admonition-title>Danger</p> <ul> <li>It is <strong>undefined behavior</strong> to access a const object with a non-existing key.</li> <li>It is <strong>undefined behavior</strong> to access a const array with an invalid index.</li> <li>In debug mode, an <strong>assertion</strong> will fire in both cases. You can disable assertions by defining the preprocessor symbol <code class=highlight><span class=n>NDEBUG</span></code> or redefine the macro <a href=../../macros/#json_assertx><code>JSON_ASSERT(x)</code></a>. See the documentation on <a href=../../assertions/ >runtime assertions</a> for more information.</li> </ul> </div> <div class="admonition failure"> <p class=admonition-title>Exceptions</p> <p><code>operator[]</code> can only be used with objects (with a string argument) or with arrays (with a numeric argument). For other types, a <a href=../../../home/exceptions/#jsonexceptiontype_error305><code>basic_json::type_error</code></a> is thrown.</p> </div> <h2 id=summary>Summary<a class=headerlink href=#summary title="Permanent link">&para;</a></h2> <table> <thead> <tr> <th>scenario</th> <th>non-const value</th> <th>const value</th> </tr> </thead> <tbody> <tr> <td>access to existing object key</td> <td>reference to existing value is returned</td> <td>const reference to existing value is returned</td> </tr> <tr> <td>access to valid array index</td> <td>reference to existing value is returned</td> <td>const reference to existing value is returned</td> </tr> <tr> <td>access to non-existing object key</td> <td>reference to newly inserted <code class=highlight><span class=kc>null</span></code> value is returned</td> <td><strong>undefined behavior</strong>; <a href=../../assertions/ >runtime assertion</a> in debug mode</td> </tr> <tr> <td>access to invalid array index</td> <td>reference to newly inserted <code class=highlight><span class=kc>null</span></code> value is returned; any index between previous maximal index and passed index are filled with <code class=highlight><span class=kc>null</span></code></td> <td><strong>undefined behavior</strong>; <a href=../../assertions/ >runtime assertion</a> in debug mode</td> </tr> </tbody> </table> <!-- 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">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&&tarLine truncated
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<span class=k>enum</span><span class=w> </span><span class=nc>TaskState</span><span class=w> </span><span class=p>{</span>
<span class=w> </span><span class=n>TS_STOPPED</span><span class=p>,</span>
<span class=w> </span><span class=n>TS_RUNNING</span><span class=p>,</span>
@@ -24,4 +24,4 @@
<span class=c1>// undefined json value to enum (where the first map entry above is the default)</span>
<span class=n>json</span><span class=w> </span><span class=n>jPi</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=mf>3.14</span><span class=p>;</span>
<span class=n>assert</span><span class=p>(</span><span class=n>jPi</span><span class=p>.</span><span class=k>template</span><span class=w> </span><span class=n>get</span><span class=o>&lt;</span><span class=n>TaskState</span><span class=o>&gt;</span><span class=p>()</span><span class=w> </span><span class=o>==</span><span class=w> </span><span class=n>TS_INVALID</span><span class=w> </span><span class=p>);</span>
</code></pre></div> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <p>Just as in <a href=../arbitrary_types/ >Arbitrary Type Conversions</a> above,</p> <ul> <li><a href=../../api/macros/nlohmann_json_serialize_enum/ ><code>NLOHMANN_JSON_SERIALIZE_ENUM()</code></a> MUST be declared in your enum type's namespace (which can be the global namespace), or the library will not be able to locate it, and it will default to integer serialization.</li> <li>It MUST be available (e.g., proper headers must be included) everywhere you use the conversions.</li> </ul> <p>Other Important points:</p> <ul> <li>When using <code>template get&lt;ENUM_TYPE&gt;()</code>, undefined JSON values will default to the first pair specified in your map. Select this default pair carefully.</li> <li>If an enum or JSON value is specified more than once in your map, the first matching occurrence from the top of the map will be returned when converting to or from JSON.</li> <li>To disable the default serialization of enumerators as integers and force a compiler error instead, see <a href=../../api/macros/json_disable_enum_serialization/ ><code>JSON_DISABLE_ENUM_SERIALIZATION</code></a>.</li> </ul> <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">January 10, 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; 2013 - 2024 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 0 496 512"><!-- Font Awesome Free 6.7.1 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 2024 Fonticons, Inc.--><path d="M165.9 397.4c0 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-.3-1.9-3-3.2-5.9-2.9M244.8 8C106.1 8 0 113.3 0 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 12.1C428.2 457.8 496 362.9 496 252 496 113.3 383.5 8 244.8 8M97.2 352.9c-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 6.7.1 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 2024 Fonticons, Inc.--><path d="M416 32H31.9C14.3 32 0 46.5 0 64.3v383.Line truncated
</code></pre></div> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <p>Just as in <a href=../arbitrary_types/ >Arbitrary Type Conversions</a> above,</p> <ul> <li><a href=../../api/macros/nlohmann_json_serialize_enum/ ><code>NLOHMANN_JSON_SERIALIZE_ENUM()</code></a> MUST be declared in your enum type's namespace (which can be the global namespace), or the library will not be able to locate it, and it will default to integer serialization.</li> <li>It MUST be available (e.g., proper headers must be included) everywhere you use the conversions.</li> </ul> <p>Other Important points:</p> <ul> <li>When using <code>template get&lt;ENUM_TYPE&gt;()</code>, undefined <abbr title="JavaScript Object Notation">JSON</abbr> values will default to the first pair specified in your map. Select this default pair carefully.</li> <li>If an enum or <abbr title="JavaScript Object Notation">JSON</abbr> value is specified more than once in your map, the first matching occurrence from the top of the map will be returned when converting to or from <abbr title="JavaScript Object Notation">JSON</abbr>.</li> <li>To disable the default serialization of enumerators as integers and force a compiler error instead, see <a href=../../api/macros/json_disable_enum_serialization/ ><code>JSON_DISABLE_ENUM_SERIALIZATION</code></a>.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date">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; 2013-2025 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 0 496 512"><!-- Font Awesome Free 6.7.1 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 2024 Fonticons, Inc.--><path d="M165.9 397.4c0 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-.3-1.9-3-3.2-5.9-2.9M244.8 8C106.1 8 0 113.3 0 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 12.1C428.2 457.8 496 362.9 496 252 496 113.3 383.5 8 244.8 8M97.2 352.9c-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"><!--Line truncated
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6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9.5 5"/></svg> </label> <div Line truncated
<span class=n>json</span><span class=w> </span><span class=n>j</span><span class=p>;</span>
<span class=n>j</span><span class=p>[</span><span class=s>&quot;one&quot;</span><span class=p>]</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=mi>1</span><span class=p>;</span>
<span class=n>j</span><span class=p>[</span><span class=s>&quot;two&quot;</span><span class=p>]</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=mi>2</span><span class=p>;</span>
@@ -11,7 +11,7 @@
</code></pre></div> <p>Output:</p> <div class=highlight><pre><span></span><code><span class=mi>1</span>
<span class=mi>3</span>
<span class=mi>2</span>
</code></pre></div> <p>The reason for the order is the lexicographic ordering of the object keys "one", "three", "two".</p> </details> <h3 id=access-object-key-during-iteration>Access object key during iteration<a class=headerlink href=#access-object-key-during-iteration title="Permanent link">&para;</a></h3> <p>The JSON iterators have two member functions, <code>key()</code> and <code>value()</code> to access the object key and stored value, respectively. When calling <code>key()</code> on a non-object iterator, an <a href=../../home/exceptions/#jsonexceptioninvalid_iterator207>invalid_iterator.207</a> exception is thrown.</p> <details class=example> <summary>Example</summary> <div class=highlight><pre><span></span><code><span class=c1>// create JSON object {&quot;one&quot;: 1, &quot;two&quot;: 2, &quot;three&quot;: 3}</span>
</code></pre></div> <p>The reason for the order is the lexicographic ordering of the object keys "one", "three", "two".</p> </details> <h3 id=access-object-key-during-iteration>Access object key during iteration<a class=headerlink href=#access-object-key-during-iteration title="Permanent link">&para;</a></h3> <p>The <abbr title="JavaScript Object Notation">JSON</abbr> iterators have two member functions, <code>key()</code> and <code>value()</code> to access the object key and stored value, respectively. When calling <code>key()</code> on a non-object iterator, an <a href=../../home/exceptions/#jsonexceptioninvalid_iterator207>invalid_iterator.207</a> exception is thrown.</p> <details class=example> <summary>Example</summary> <div class=highlight><pre><span></span><code><span class=c1>// create JSON object {&quot;one&quot;: 1, &quot;two&quot;: 2, &quot;three&quot;: 3}</span>
<span class=n>json</span><span class=w> </span><span class=n>j</span><span class=p>;</span>
<span class=n>j</span><span class=p>[</span><span class=s>&quot;one&quot;</span><span class=p>]</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=mi>1</span><span class=p>;</span>
<span class=n>j</span><span class=p>[</span><span class=s>&quot;two&quot;</span><span class=p>]</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=mi>2</span><span class=p>;</span>
@@ -29,7 +29,7 @@
<span class=w> </span><span class=c1>// &quot;it&quot; is of type json::reference and has no key() member</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>&quot;value: &quot;</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>it</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=sc>&#39;\n&#39;</span><span class=p>;</span>
<span class=p>}</span>
</code></pre></div> <p>For this reason, the <code>items()</code> function allows accessing <code>iterator::key()</code> and <code>iterator::value()</code> during range-based for loops. In these loops, a reference to the JSON values is returned, so there is no access to the underlying iterator.</p> <div class=highlight><pre><span></span><code><span class=k>for</span><span class=w> </span><span class=p>(</span><span class=k>auto</span><span class=o>&amp;</span><span class=w> </span><span class=n>el</span><span class=w> </span><span class=o>:</span><span class=w> </span><span class=n>j_object</span><span class=p>.</span><span class=n>items</span><span class=p>())</span>
</code></pre></div> <p>For this reason, the <code>items()</code> function allows accessing <code>iterator::key()</code> and <code>iterator::value()</code> during range-based for loops. In these loops, a reference to the <abbr title="JavaScript Object Notation">JSON</abbr> values is returned, so there is no access to the underlying iterator.</p> <div class=highlight><pre><span></span><code><span class=k>for</span><span class=w> </span><span class=p>(</span><span class=k>auto</span><span class=o>&amp;</span><span class=w> </span><span class=n>el</span><span class=w> </span><span class=o>:</span><span class=w> </span><span class=n>j_object</span><span class=p>.</span><span class=n>items</span><span class=p>())</span>
<span class=p>{</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>&quot;key: &quot;</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>el</span><span class=p>.</span><span class=n>key</span><span class=p>()</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>&quot;, value:&quot;</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>el</span><span class=p>.</span><span class=n>value</span><span class=p>()</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=sc>&#39;\n&#39;</span><span class=p>;</span>
<span class=p>}</span>
@@ -37,7 +37,7 @@
<span class=p>{</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>&quot;key: &quot;</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>key</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>&quot;, value:&quot;</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>val</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=sc>&#39;\n&#39;</span><span class=p>;</span>
<span class=p>}</span>
</code></pre></div> <div class="admonition note"> <p class=admonition-title>Note</p> <p>When iterating over an array, <code>key()</code> will return the index of the element as string. For primitive types (e.g., numbers), <code>key()</code> returns an empty string.</p> </div> <div class="admonition warning"> <p class=admonition-title>Warning</p> <p>Using <code>items()</code> on temporary objects is dangerous. Make sure the object's lifetime exceeds the iteration. See <a href=https://github.com/nlohmann/json/issues/2040>#2040</a> for more information.</p> </div> <h3 id=reverse-iteration-order>Reverse iteration order<a class=headerlink href=#reverse-iteration-order title="Permanent link">&para;</a></h3> <p><code>rbegin()</code> and <code>rend()</code> return iterators in the reverse sequence.</p> <p><img alt="Illustration from cppreference.com" src=../../images/range-rbegin-rend.svg></p> <details class=example> <summary>Example</summary> <div class=highlight><pre><span></span><code><span class=n>json</span><span class=w> </span><span class=n>j</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=p>{</span><span class=mi>1</span><span class=p>,</span><span class=w> </span><span class=mi>2</span><span class=p>,</span><span class=w> </span><span class=mi>3</span><span class=p>,</span><span class=w> </span><span class=mi>4</span><span class=p>};</span>
</code></pre></div> <div class="admonition note"> <p class=admonition-title>Note</p> <p>When iterating over an array, <code>key()</code> will return the index of the element as string. For primitive types (e.g., numbers), <code>key()</code> returns an empty string.</p> </div> <div class="admonition warning"> <p class=admonition-title>Warning</p> <p>Using <code>items()</code> on temporary objects is dangerous. Make sure the object's lifetime exceeds the iteration. See <a href="https://github.com/nlohmann/json/issues/2040">#2040</a> for more information.</p> </div> <h3 id=reverse-iteration-order>Reverse iteration order<a class=headerlink href=#reverse-iteration-order title="Permanent link">&para;</a></h3> <p><code>rbegin()</code> and <code>rend()</code> return iterators in the reverse sequence.</p> <p><img alt="Illustration from cppreference.com" src=../../images/range-rbegin-rend.svg></p> <details class=example> <summary>Example</summary> <div class=highlight><pre><span></span><code><span class=n>json</span><span class=w> </span><span class=n>j</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=p>{</span><span class=mi>1</span><span class=p>,</span><span class=w> </span><span class=mi>2</span><span class=p>,</span><span class=w> </span><span class=mi>3</span><span class=p>,</span><span class=w> </span><span class=mi>4</span><span class=p>};</span>
<span class=k>for</span><span class=w> </span><span class=p>(</span><span class=k>auto</span><span class=w> </span><span class=n>it</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>j</span><span class=p>.</span><span class=n>rbegin</span><span class=p>();</span><span class=w> </span><span class=n>it</span><span class=w> </span><span class=o>!=</span><span class=w> </span><span class=n>j</span><span class=p>.</span><span class=n>rend</span><span class=p>();</span><span class=w> </span><span class=o>++</span><span class=n>it</span><span class=p>)</span>
<span class=p>{</span>
@@ -47,10 +47,10 @@
<span class=mi>3</span>
<span class=mi>2</span>
<span class=mi>1</span>
</code></pre></div> </details> <h3 id=iterating-strings-and-binary-values>Iterating strings and binary values<a class=headerlink href=#iterating-strings-and-binary-values title="Permanent link">&para;</a></h3> <p>Note that "value" means a JSON value in this setting, not values stored in the underlying containers. That is, <code>*begin()</code> returns the complete string or binary array and is also safe the underlying string or binary array is empty.</p> <details class=example> <summary>Example</summary> <div class=highlight><pre><span></span><code><span class=n>json</span><span class=w> </span><span class=n>j</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=s>&quot;Hello, world&quot;</span><span class=p>;</span>
</code></pre></div> </details> <h3 id=iterating-strings-and-binary-values>Iterating strings and binary values<a class=headerlink href=#iterating-strings-and-binary-values title="Permanent link">&para;</a></h3> <p>Note that "value" means a <abbr title="JavaScript Object Notation">JSON</abbr> value in this setting, not values stored in the underlying containers. That is, <code>*begin()</code> returns the complete string or binary array and is also safe the underlying string or binary array is empty.</p> <details class=example> <summary>Example</summary> <div class=highlight><pre><span></span><code><span class=n>json</span><span class=w> </span><span class=n>j</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=s>&quot;Hello, world&quot;</span><span class=p>;</span>
<span class=k>for</span><span class=w> </span><span class=p>(</span><span class=k>auto</span><span class=w> </span><span class=n>it</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>j</span><span class=p>.</span><span class=n>begin</span><span class=p>();</span><span class=w> </span><span class=n>it</span><span class=w> </span><span class=o>!=</span><span class=w> </span><span class=n>j</span><span class=p>.</span><span class=n>end</span><span class=p>();</span><span class=w> </span><span class=o>++</span><span class=n>it</span><span class=p>)</span>
<span class=p>{</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=o>*</span><span class=n>it</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>endl</span><span class=p>;</span>
<span class=p>}</span>
</code></pre></div> <p>Output:</p> <div class=highlight><pre><span></span><code><span class=s2>&quot;Hello, world&quot;</span>
</code></pre></div> </details> <h2 id=iterator-invalidation>Iterator invalidation<a class=headerlink href=#iterator-invalidation title="Permanent link">&para;</a></h2> <table> <thead> <tr> <th>Operations</th> <th>invalidated iterators</th> </tr> </thead> <tbody> <tr> <td><code>clear</code></td> <td>all</td> </tr> </tbody> </table> <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">January 10, 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> </details> <h2 id=iterator-invalidation>Iterator invalidation<a class=headerlink href=#iterator-invalidation title="Permanent link">&para;</a></h2> <table> <thead> <tr> <th>Operations</th> <th>invalidated iterators</th> </tr> </thead> <tbody> <tr> <td><code>clear</code></td> <td>all</td> </tr> </tbody> </table> <!-- 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">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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<!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/features/json_patch/" rel="canonical"><link href=../json_pointer/ rel=prev><link href=../merge_patch/ rel=next><link rel=icon href=../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.5.49"><title>JSON Patch and Diff - JSON for Modern C++</title><link rel=stylesheet href=../../assets/stylesheets/main.6f8fc17f.min.css><link rel=stylesheet href=../../assets/stylesheets/palette.06af60db.min.css><link rel="stylesheet" href="../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../css/custom.css><script>__md_scope=new 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<svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> JSON Patch and Diff </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark mode" 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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> Line truncated
<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>
@@ -42,8 +42,8 @@
<span class=w> </span><span class=s2>&quot;world&quot;</span>
<span class=w> </span><span class=p>]</span>
<span class=p>}</span>
</code></pre></div> </details> <h2 id=diff>Diff<a class=headerlink href=#diff title="Permanent link">&para;</a></h2> <p>The library can also calculate a JSON patch (i.e., a <strong>diff</strong>) given two JSON values.</p> <div class="admonition success"> <p class=admonition-title>Invariant</p> <p>For two JSON values <em>source</em> and <em>target</em>, the following code yields always true:</p> <div class=highlight><pre><span></span><code>source.patch(diff(source, target)) == target;
</code></pre></div> </div> <details class=example> <summary>Example</summary> <p>The following code shows how a JSON patch is created as a diff for two JSON values.</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> </details> <h2 id=diff>Diff<a class=headerlink href=#diff title="Permanent link">&para;</a></h2> <p>The library can also calculate a <abbr title="JavaScript Object Notation">JSON</abbr> patch (i.e., a <strong>diff</strong>) given two <abbr title="JavaScript Object Notation">JSON</abbr> values.</p> <div class="admonition success"> <p class=admonition-title>Invariant</p> <p>For two <abbr title="JavaScript Object Notation">JSON</abbr> values <em>source</em> and <em>target</em>, the following code yields always true:</p> <div class=highlight><pre><span></span><code>source.patch(diff(source, target)) == target;
</code></pre></div> </div> <details class=example> <summary>Example</summary> <p>The following code shows how a <abbr title="JavaScript Object Notation">JSON</abbr> patch is created as a diff for two <abbr title="JavaScript Object Notation">JSON</abbr> values.</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>
@@ -105,4 +105,4 @@
<span class=w> </span><span class=s2>&quot;world&quot;</span>
<span class=w> </span><span class=p>]</span>
<span class=p>}</span>
</code></pre></div> </details> <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">January 10, 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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@@ -1,4 +1,4 @@
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6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9.5 5"/></svg> </label> <div class=md-Line truncated
<span class=w> </span><span class=nt>&quot;array&quot;</span><span class=p>:</span><span class=w> </span><span class=p>[</span><span class=s2>&quot;A&quot;</span><span class=p>,</span><span class=w> </span><span class=s2>&quot;B&quot;</span><span class=p>,</span><span class=w> </span><span class=s2>&quot;C&quot;</span><span class=p>],</span>
<span class=w> </span><span class=nt>&quot;nested&quot;</span><span class=p>:</span><span class=w> </span><span class=p>{</span>
<span class=w> </span><span class=nt>&quot;one&quot;</span><span class=p>:</span><span class=w> </span><span class=mi>1</span><span class=p>,</span>
@@ -6,9 +6,9 @@
<span class=w> </span><span class=nt>&quot;three&quot;</span><span class=p>:</span><span class=w> </span><span class=p>[</span><span class=kc>true</span><span class=p>,</span><span class=w> </span><span class=kc>false</span><span class=p>]</span>
<span class=w> </span><span class=p>}</span>
<span class=p>}</span>
</code></pre></div> <p>Then every value inside the JSON document can be identified as follows:</p> <table> <thead> <tr> <th>JSON Pointer</th> <th>JSON value</th> </tr> </thead> <tbody> <tr> <td>``</td> <td><code class=highlight><span class=p>{</span><span class=nt>&quot;array&quot;</span><span class=p>:[</span><span class=s2>&quot;A&quot;</span><span class=p>,</span><span class=s2>&quot;B&quot;</span><span class=p>,</span><span class=s2>&quot;C&quot;</span><span class=p>],</span><span class=nt>&quot;nested&quot;</span><span class=p>:{</span><span class=nt>&quot;one&quot;</span><span class=p>:</span><span class=mi>1</span><span class=p>,</span><span class=nt>&quot;two&quot;</span><span class=p>:</span><span class=mi>2</span><span class=p>,</span><span class=nt>&quot;three&quot;</span><span class=p>:[</span><span class=kc>true</span><span class=p>,</span><span class=kc>false</span><span class=p>]}}</span></code></td> </tr> <tr> <td><code>/array</code></td> <td><code class=highlight><span class=p>[</span><span class=s2>&quot;A&quot;</span><span class=p>,</span><span class=s2>&quot;B&quot;</span><span class=p>,</span><span class=s2>&quot;C&quot;</span><span class=p>]</span></code></td> </tr> <tr> <td><code>/array/0</code></td> <td><code class=highlight><span class=err>A</span></code></td> </tr> <tr> <td><code>/array/1</code></td> <td><code class=highlight><span class=err>B</span></code></td> </tr> <tr> <td><code>/array/2</code></td> <td><code class=highlight><span class=err>C</span></code></td> </tr> <tr> <td><code>/nested</code></td> <td><code class=highlight><span class=p>{</span><span class=nt>&quot;one&quot;</span><span class=p>:</span><span class=mi>1</span><span class=p>,</span><span class=nt>&quot;two&quot;</span><span class=p>:</span><span class=mi>2</span><span class=p>,</span><span class=nt>&quot;three&quot;</span><span class=p>:[</span><span class=kc>true</span><span class=p>,</span><span class=kc>false</span><span class=p>]}</span></code></td> </tr> <tr> <td><code>/nested/one</code></td> <td><code class=highlight><span class=mi>1</span></code></td> </tr> <tr> <td><code>/nested/two</code></td> <td><code class=highlight><span class=mi>2</span></code></td> </tr> <tr> <td><code>/nested/three</code></td> <td><code class=highlight><span class=p>[</span><span class=kc>true</span><span class=p>,</span><span class=kc>false</span><span class=p>]</span></code></td> </tr> <tr> <td><code>/nested/three/0</code></td> <td><code class=highlight><span class=kc>true</span></code></td> </tr> <tr> <td><code>/nested/three/1</code></td> <td><code class=highlight><span class=kc>false</span></code></td> </tr> </tbody> </table> <p>Note <code>/</code> does not identify the root (i.e., the whole document), but an object entry with empty key <code>""</code>. See <a href=https://tools.ietf.org/html/rfc6901>RFC 6901</a> for more information.</p> <h2 id=json-pointer-creation>JSON Pointer creation<a class=headerlink href=#json-pointer-creation title="Permanent link">&para;</a></h2> <p>JSON Pointers can be created from a string:</p> <div class=highlight><pre><span></span><code><span class=n>json</span><span class=o>::</span><span class=n>json_pointer</span><span class=w> </span><span class=n>p</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=s>&quot;/nested/one&quot;</span><span class=p>;</span>
</code></pre></div> <p>Then every value inside the <abbr title="JavaScript Object Notation">JSON</abbr> document can be identified as follows:</p> <table> <thead> <tr> <th><abbr title="JavaScript Object Notation">JSON</abbr> Pointer</th> <th><abbr title="JavaScript Object Notation">JSON</abbr> value</th> </tr> </thead> <tbody> <tr> <td>``</td> <td><code class=highlight><span class=p>{</span><span class=nt>&quot;array&quot;</span><span class=p>:[</span><span class=s2>&quot;A&quot;</span><span class=p>,</span><span class=s2>&quot;B&quot;</span><span class=p>,</span><span class=s2>&quot;C&quot;</span><span class=p>],</span><span class=nt>&quot;nested&quot;</span><span class=p>:{</span><span class=nt>&quot;one&quot;</span><span class=p>:</span><span class=mi>1</span><span class=p>,</span><span class=nt>&quot;two&quot;</span><span class=p>:</span><span class=mi>2</span><span class=p>,</span><span class=nt>&quot;three&quot;</span><span class=p>:[</span><span class=kc>true</span><span class=p>,</span><span class=kc>false</span><span class=p>]}}</span></code></td> </tr> <tr> <td><code>/array</code></td> <td><code class=highlight><span class=p>[</span><span class=s2>&quot;A&quot;</span><span class=p>,</span><span class=s2>&quot;B&quot;</span><span class=p>,</span><span class=s2>&quot;C&quot;</span><span class=p>]</span></code></td> </tr> <tr> <td><code>/array/0</code></td> <td><code class=highlight><span class=err>A</span></code></td> </tr> <tr> <td><code>/array/1</code></td> <td><code class=highlight><span class=err>B</span></code></td> </tr> <tr> <td><code>/array/2</code></td> <td><code class=highlight><span class=err>C</span></code></td> </tr> <tr> <td><code>/nested</code></td> <td><code class=highlight><span class=p>{</span><span class=nt>&quot;one&quot;</span><span class=p>:</span><span class=mi>1</span><span class=p>,</span><span class=nt>&quot;two&quot;</span><span class=p>:</span><span class=mi>2</span><span class=p>,</span><span class=nt>&quot;three&quot;</span><span class=p>:[</span><span class=kc>true</span><span class=p>,</span><span class=kc>false</span><span class=p>]}</span></code></td> </tr> <tr> <td><code>/nested/one</code></td> <td><code class=highlight><span class=mi>1</span></code></td> </tr> <tr> <td><code>/nested/two</code></td> <td><code class=highlight><span class=mi>2</span></code></td> </tr> <tr> <td><code>/nested/three</code></td> <td><code class=highlight><span class=p>[</span><span class=kc>true</span><span class=p>,</span><span class=kc>false</span><span class=p>]</span></code></td> </tr> <tr> <td><code>/nested/three/0</code></td> <td><code class=highlight><span class=kc>true</span></code></td> </tr> <tr> <td><code>/nested/three/1</code></td> <td><code class=highlight><span class=kc>false</span></code></td> </tr> </tbody> </table> <p>Note <code>/</code> does not identify the root (i.e., the whole document), but an object entry with empty key <code>""</code>. See <a href="https://tools.ietf.org/html/rfc6901"><abbr title="Request for Comments">RFC</abbr> 6901</a> for more information.</p> <h2 id=json-pointer-creation><abbr title="JavaScript Object Notation">JSON</abbr> Pointer creation<a class=headerlink href=#json-pointer-creation title="Permanent link">&para;</a></h2> <p><abbr title="JavaScript Object Notation">JSON</abbr> Pointers can be created from a string:</p> <div class=highlight><pre><span></span><code><span class=n>json</span><span class=o>::</span><span class=n>json_pointer</span><span class=w> </span><span class=n>p</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=s>&quot;/nested/one&quot;</span><span class=p>;</span>
</code></pre></div> <p>Furthermore, a user-defined string literal can be used to achieve the same result:</p> <div class=highlight><pre><span></span><code><span class=k>auto</span><span class=w> </span><span class=n>p</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=s>&quot;/nested/one&quot;</span><span class=n>_json_pointer</span><span class=p>;</span>
</code></pre></div> <p>The escaping rules of <a href=https://tools.ietf.org/html/rfc6901>RFC 6901</a> are implemented. See the <a href=../../api/json_pointer/json_pointer/ >constructor documentation</a> for more information.</p> <h2 id=value-access>Value access<a class=headerlink href=#value-access title="Permanent link">&para;</a></h2> <p>JSON Pointers can be used in the <a href=../../api/basic_json/at/ ><code>at</code></a>, <a href=../../api/basic_json/operator%5B%5D/ ><code>operator[]</code></a>, and <a href=../../api/basic_json/value/ ><code>value</code></a> functions just like object keys or array indices.</p> <div class=highlight><pre><span></span><code><span class=c1>// the JSON value from above</span>
</code></pre></div> <p>The escaping rules of <a href="https://tools.ietf.org/html/rfc6901"><abbr title="Request for Comments">RFC</abbr> 6901</a> are implemented. See the <a href=../../api/json_pointer/json_pointer/ >constructor documentation</a> for more information.</p> <h2 id=value-access>Value access<a class=headerlink href=#value-access title="Permanent link">&para;</a></h2> <p><abbr title="JavaScript Object Notation">JSON</abbr> Pointers can be used in the <a href=../../api/basic_json/at/ ><code>at</code></a>, <a href=../../api/basic_json/operator%5B%5D/ ><code>operator[]</code></a>, and <a href=../../api/basic_json/value/ ><code>value</code></a> functions just like object keys or array indices.</p> <div class=highlight><pre><span></span><code><span class=c1>// the JSON value from above</span>
<span class=k>auto</span><span class=w> </span><span class=n>j</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>json</span><span class=o>::</span><span class=n>parse</span><span class=p>(</span><span class=sa>R</span><span class=s>&quot;</span><span class=dl>(</span><span class=s>{</span>
<span class=s> &quot;array&quot;: [&quot;A&quot;, &quot;B&quot;, &quot;C&quot;],</span>
<span class=s> &quot;nested&quot;: {</span>
@@ -23,7 +23,7 @@
<span class=k>auto</span><span class=w> </span><span class=n>val1</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>j</span><span class=p>[</span><span class=s>&quot;/nested/one&quot;</span><span class=n>_json_pointer</span><span class=p>];</span><span class=w> </span><span class=c1>// 1</span>
<span class=k>auto</span><span class=w> </span><span class=n>val2</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>j</span><span class=p>.</span><span class=n>at</span><span class=p>(</span><span class=n>json</span><span class=o>::</span><span class=n>json_pointer</span><span class=p>(</span><span class=s>&quot;/nested/three/1&quot;</span><span class=p>));</span><span class=w> </span><span class=c1>// false</span>
<span class=k>auto</span><span class=w> </span><span class=n>val3</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>j</span><span class=p>.</span><span class=n>value</span><span class=p>(</span><span class=n>json</span><span class=o>::</span><span class=n>json_pointer</span><span class=p>(</span><span class=s>&quot;/nested/four&quot;</span><span class=p>),</span><span class=w> </span><span class=mi>0</span><span class=p>);</span><span class=w> </span><span class=c1>// 0</span>
</code></pre></div> <h2 id=flatten-unflatten>Flatten / unflatten<a class=headerlink href=#flatten-unflatten title="Permanent link">&para;</a></h2> <p>The library implements a function <a href=../../api/basic_json/flatten/ ><code>flatten</code></a> to convert any JSON document into a JSON object where each key is a JSON Pointer and each value is a primitive JSON value (i.e., a string, boolean, number, or null).</p> <div class=highlight><pre><span></span><code><span class=c1>// the JSON value from above</span>
</code></pre></div> <h2 id=flatten-unflatten>Flatten / unflatten<a class=headerlink href=#flatten-unflatten title="Permanent link">&para;</a></h2> <p>The library implements a function <a href=../../api/basic_json/flatten/ ><code>flatten</code></a> to convert any <abbr title="JavaScript Object Notation">JSON</abbr> document into a <abbr title="JavaScript Object Notation">JSON</abbr> object where each key is a <abbr title="JavaScript Object Notation">JSON</abbr> Pointer and each value is a primitive <abbr title="JavaScript Object Notation">JSON</abbr> value (i.e., a string, boolean, number, or null).</p> <div class=highlight><pre><span></span><code><span class=c1>// the JSON value from above</span>
<span class=k>auto</span><span class=w> </span><span class=n>j</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>json</span><span class=o>::</span><span class=n>parse</span><span class=p>(</span><span class=sa>R</span><span class=s>&quot;</span><span class=dl>(</span><span class=s>{</span>
<span class=s> &quot;array&quot;: [&quot;A&quot;, &quot;B&quot;, &quot;C&quot;],</span>
<span class=s> &quot;nested&quot;: {</span>
@@ -45,4 +45,4 @@
<span class=w> </span><span class=nt>&quot;/nested/three/1&quot;</span><span class=p>:</span><span class=w> </span><span class=kc>false</span>
<span class=p>}</span>
</code></pre></div> <p>The reverse function, <a href=../../api/basic_json/unflatten/ ><code>unflatten</code></a> recreates the original value.</p> <div class=highlight><pre><span></span><code><span class=k>auto</span><span class=w> </span><span class=n>j_original</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>j_flat</span><span class=p>.</span><span class=n>unflatten</span><span class=p>();</span>
</code></pre></div> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li>Class <a href=../../api/json_pointer/ ><code>json_pointer</code></a></li> <li>Function <a href=../../api/basic_json/flatten/ ><code>flatten</code></a></li> <li>Function <a href=../../api/basic_json/unflatten/ ><code>unflatten</code></a></li> <li><a href=../json_patch/ >JSON Patch</a></li> </ul> <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">January 10, 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> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li>Class <a href=../../api/json_pointer/ ><code>json_pointer</code></a></li> <li>Function <a href=../../api/basic_json/flatten/ ><code>flatten</code></a></li> <li>Function <a href=../../api/basic_json/unflatten/ ><code>unflatten</code></a></li> <li><a href=../json_patch/ ><abbr title="JavaScript Object Notation">JSON</abbr> Patch</a></li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date">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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<!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/features/macros/ rel=canonical><link href=../enum_conversion/ rel=prev><link href=../types/ rel=next><link rel=icon href=../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.5.49"><title>Supported Macros - JSON for Modern C++</title><link rel=stylesheet href=../../assets/stylesheets/main.6f8fc17f.min.css><link rel=stylesheet href=../../assets/stylesheets/palette.06af60db.min.css><link rel=preconnect href=https://fonts.gstatic.com crossorigin><link rel=stylesheet href="https://fonts.googleapis.com/css?family=Roboto:300,300i,400,400i,700,700i%7CJetBrains+Mono:400,400i,700,700i&display=fallback"><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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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> <diLine truncated
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iomanip&gt;</span><span class=c1> // for std::setw</span>
@@ -50,4 +50,4 @@
<span class=w> </span><span class=p>],</span>
<span class=w> </span><span class=nt>&quot;title&quot;</span><span class=p>:</span><span class=w> </span><span class=s2>&quot;Hello!&quot;</span>
<span class=p>}</span>
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</code></pre></div> <h2 id=purpose>Purpose<a class=headerlink href=#purpose title="Permanent link">&para;</a></h2> <p>Several incompatibilities have been observed. Amongst the most common ones is linking code compiled with different definitions of <a href=../../api/macros/json_diagnostics/ ><code>JSON_DIAGNOSTICS</code></a>. This is illustrated in the diagram below.</p> <pre class=mermaid><code>graph
json["&lt;strong&gt;nlohmann_json (v3.10.5)&lt;/strong&gt;&lt;br&gt;JSON_DIAGNOSTICS=0"]
json_diag["&lt;strong&gt;nlohmann_json (v3.10.5)&lt;/strong&gt;&lt;br&gt;JSON_DIAGNOSTICS=1"]
@@ -7,6 +7,6 @@
library --&gt; json
app --&gt; json_diag
app --&gt; library</code></pre> <p>In releases prior to 3.11.0, mixing any version of the JSON library with different <code>JSON_DIAGNOSTICS</code> settings would result in a crashing application. If <code>some_library</code> never passes instances of JSON library types to the application, this scenario became safe in version 3.11.0 and above due to the inline namespace yielding distinct symbol names.</p> <h2 id=limitations>Limitations<a class=headerlink href=#limitations title="Permanent link">&para;</a></h2> <p>Neither the compiler nor the linker will issue as much as a warning when translation units – intended to be linked together and that include different versions and/or configurations of the JSON library – exchange and use library types.</p> <p>There is an exception when forward declarations are used (i.e., when including <code>json_fwd.hpp</code>) in which case the linker may complain about undefined references.</p> <h2 id=disabling-the-version-component>Disabling the version component<a class=headerlink href=#disabling-the-version-component title="Permanent link">&para;</a></h2> <p>Different versions are not necessarily ABI-incompatible, but the project does not actively track changes in the ABI and recommends that all parts of a codebase exchanging library types be built with the same version. Users can, <strong>at their own risk</strong>, disable the version component of the linline namespace, allowing different versions – but not configurations – to be used in cases where the linker would otherwise output undefined reference errors.</p> <p>To do so, define <a href=../../api/macros/nlohmann_json_namespace_no_version/ ><code>NLOHMANN_JSON_NAMESPACE_NO_VERSION</code></a> to <code>1</code>.</p> <p>This applies to version 3.11.2 and above only, versions 3.11.0 and 3.11.1 can apply the technique described in the next section to emulate the effect of the <code>NLOHMANN_JSON_NAMESPACE_NO_VERSION</code> macro.</p> <div class="admonition danger"> <p class=admonition-title>Use at your own risk</p> <p>Disabling the namespace version component and mixing ABI-incompatible versions will result in crashes or incorrect behavior. You have been warned!</p> </div> <h2 id=disabling-the-inline-namespace-completely>Disabling the inline namespace completely<a class=headerlink href=#disabling-the-inline-namespace-completely title="Permanent link">&para;</a></h2> <p>When interoperability with code using a pre-3.11.0 version of the library is required, users can, <strong>at their own risk</strong> restore the old namespace layout by redefining <a href=../../api/macros/nlohmann_json_namespace_begin/ ><code>NLOHMANN_JSON_NAMESPACE_BEGIN, NLOHMANN_JSON_NAMESPACE_END</code></a> as follows:</p> <div class=highlight><pre><span></span><code><span class=cp>#define NLOHMANN_JSON_NAMESPACE_BEGIN namespace nlohmann {</span>
app --&gt; library</code></pre> <p>In releases prior to 3.11.0, mixing any version of the <abbr title="JavaScript Object Notation">JSON</abbr> library with different <code>JSON_DIAGNOSTICS</code> settings would result in a crashing application. If <code>some_library</code> never passes instances of <abbr title="JavaScript Object Notation">JSON</abbr> library types to the application, this scenario became safe in version 3.11.0 and above due to the inline namespace yielding distinct symbol names.</p> <h2 id=limitations>Limitations<a class=headerlink href=#limitations title="Permanent link">&para;</a></h2> <p>Neither the compiler nor the linker will issue as much as a warning when translation units – intended to be linked together and that include different versions and/or configurations of the <abbr title="JavaScript Object Notation">JSON</abbr> library – exchange and use library types.</p> <p>There is an exception when forward declarations are used (i.e., when including <code>json_fwd.hpp</code>) in which case the linker may complain about undefined references.</p> <h2 id=disabling-the-version-component>Disabling the version component<a class=headerlink href=#disabling-the-version-component title="Permanent link">&para;</a></h2> <p>Different versions are not necessarily ABI-incompatible, but the project does not actively track changes in the ABI and recommends that all parts of a codebase exchanging library types be built with the same version. Users can, <strong>at their own risk</strong>, disable the version component of the linline namespace, allowing different versions – but not configurations – to be used in cases where the linker would otherwise output undefined reference errors.</p> <p>To do so, define <a href=../../api/macros/nlohmann_json_namespace_no_version/ ><code>NLOHMANN_JSON_NAMESPACE_NO_VERSION</code></a> to <code>1</code>.</p> <p>This applies to version 3.11.2 and above only, versions 3.11.0 and 3.11.1 can apply the technique described in the next section to emulate the effect of the <code>NLOHMANN_JSON_NAMESPACE_NO_VERSION</code> macro.</p> <div class="admonition danger"> <p class=admonition-title>Use at your own risk</p> <p>Disabling the namespace version component and mixing ABI-incompatible versions will result in crashes or incorrect behavior. You have been warned!</p> </div> <h2 id=disabling-the-inline-namespace-completely>Disabling the inline namespace completely<a class=headerlink href=#disabling-the-inline-namespace-completely title="Permanent link">&para;</a></h2> <p>When interoperability with code using a pre-3.11.0 version of the library is required, users can, <strong>at their own risk</strong> restore the old namespace layout by redefining <a href=../../api/macros/nlohmann_json_namespace_begin/ ><code>NLOHMANN_JSON_NAMESPACE_BEGIN, NLOHMANN_JSON_NAMESPACE_END</code></a> as follows:</p> <div class=highlight><pre><span></span><code><span class=cp>#define NLOHMANN_JSON_NAMESPACE_BEGIN namespace nlohmann {</span>
<span class=cp>#define NLOHMANN_JSON_NAMESPACE_END }</span>
</code></pre></div> <div class="admonition danger"> <p class=admonition-title>Use at your own risk</p> <p>Overriding the namespace and mixing ABI-incompatible versions will result in crashes or incorrect behavior. You have been warned!</p> </div> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ul> <li>Introduced inline namespace (<code>json_v3_11_0[_abi-tag]*</code>) in version 3.11.0.</li> <li>Changed structure of inline namespace in version 3.11.2.</li> </ul> <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">January 10, 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; 2013 - 2024 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 0 496 512"><!-- Font Awesome Free 6.7.1 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 2024 Fonticons, Inc.--><path d="M165.9 397.4c0 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-.3-1.9-3-3.2-5.9-2.9M244.8 8C106.1 8 0 113.3 0 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 12.1C428.2 457.8 496 362.9 496 252 496 113.3 383.5 8 244.8 8M97.2 352.9c-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 6.7.1 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 2024 Fonticons, Inc.--><path d="M416 32H31.9C14.3 32 0 46.5 0 64.3v383.4C0 465.5 14.3 480 31.9 480H416c17.6 0 32-14.5 32-32.3V64.3c0-17.8-14.4-32.3-32-32.3M135.4 416H69V202.2h66.5V416zm-33.2-243c-21.3 0-38.5-17.3-38.5-38.5S80.9 96 102.2 96c21.2 0 38.5 17.3 38.5 38.5 0 21.3-17.2 38.5-38.5 38.5m282.1 243h-66.4V312c0-24.8-.5-56.7-34.5-56.7-34.6 0-39.9 27-39.9 54.9V416h-66.4V202.2h63.7v29.2h.9c8.9-16.8 30.6-34.5 62.9-34.5 67.2 0 79.7 44.3 79.7 101.9z"/></svg> </a> <a href=https://www.xing.com/profile/Niels_Lohmann target=_blank rel=noopener title=www.xing.com class=md-social__link> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 384 512"><!-- Font Awesome Free 6.7.1 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/liceLine truncated
</code></pre></div> <div class="admonition danger"> <p class=admonition-title>Use at your own risk</p> <p>Overriding the namespace and mixing ABI-incompatible versions will result in crashes or incorrect behavior. You have been warned!</p> </div> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ul> <li>Introduced inline namespace (<code>json_v3_11_0[_abi-tag]*</code>) in version 3.11.0.</li> <li>Changed structure of inline namespace in version 3.11.2.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date">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; 2013-2025 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 0 496 512"><!-- Font Awesome Free 6.7.1 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 2024 Fonticons, Inc.--><path d="M165.9 397.4c0 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-.3-1.9-3-3.2-5.9-2.9M244.8 8C106.1 8 0 113.3 0 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 12.1C428.2 457.8 496 362.9 496 252 496 113.3 383.5 8 244.8 8M97.2 352.9c-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 6.7.1 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 2024 Fonticons, Inc.--><path d="M416 32H31.9C14.3 32 0 46.5 0 64.3v383.4C0 465.5 14.3 480 31.9 480H416c17.6 0 32-14.5 32-32.3V64.3c0-17.8-14.4-32.3-32-32.3M135.4 416H69V202.2h66.5V416zm-33.2-243c-21.3 0-38.5-17.3-38.5-38.5S80.9 96 102.2 96c21.2 0 38.5 17.3 38.5 38.5 0 21.3-17.2 38.5-38.5 38.5m282.1 243h-66.4V312c0-24.8-.5-56.7-34.5-56.7-34.6 0-39.9 27-39.9 54.9V416h-66.4V202.2h63.7v29.2h.9c8.9-16.8 30.6-34.5 62.9-34.5 67.2 0 79.7 44.3 79.7 101.9z"/></svg> </a> <a href="https://www.xing.com/profile/Niels_Lohmann" target="_blank" rel="noopener" title="www.xing.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0Line truncated
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6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9.5 5"/></svg> </label> <div class=md-seaLine truncated
<span class=cp>#include</span><span class=w> </span><span class=cpf>&quot;json.hpp&quot;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
@@ -17,7 +17,7 @@
<span class=w> </span><span class=nt>&quot;three&quot;</span><span class=p>:</span><span class=w> </span><span class=mi>3</span><span class=p>,</span>
<span class=w> </span><span class=nt>&quot;two&quot;</span><span class=p>:</span><span class=w> </span><span class=mi>2</span>
<span class=p>}</span>
</code></pre></div> </details> <h2 id=alternative-behavior-preserve-insertion-order>Alternative behavior: preserve insertion order<a class=headerlink href=#alternative-behavior-preserve-insertion-order title="Permanent link">&para;</a></h2> <p>If you do want to preserve the <strong>insertion order</strong>, you can try the type <a href=https://github.com/nlohmann/json/issues/2179><code>nlohmann::ordered_json</code></a>.</p> <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>
</code></pre></div> </details> <h2 id=alternative-behavior-preserve-insertion-order>Alternative behavior: preserve insertion order<a class=headerlink href=#alternative-behavior-preserve-insertion-order title="Permanent link">&para;</a></h2> <p>If you do want to preserve the <strong>insertion order</strong>, you can try the type <a href="https://github.com/nlohmann/json/issues/2179"><code>nlohmann::ordered_json</code></a>.</p> <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>
<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>ordered_json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>ordered_json</span><span class=p>;</span>
@@ -36,7 +36,7 @@
<span class=w> </span><span class=nt>&quot;two&quot;</span><span class=p>:</span><span class=w> </span><span class=mi>2</span><span class=p>,</span>
<span class=w> </span><span class=nt>&quot;three&quot;</span><span class=p>:</span><span class=w> </span><span class=mi>3</span>
<span class=p>}</span>
</code></pre></div> </details> <p>Alternatively, you can use a more sophisticated ordered map like <a href=https://github.com/Tessil/ordered-map><code>tsl::ordered_map</code></a> (<a href=https://github.com/nlohmann/json/issues/546#issuecomment-304447518>integration</a>) or <a href=https://github.com/nlohmann/fifo_map><code>nlohmann::fifo_map</code></a> (<a href=https://github.com/nlohmann/json/issues/485#issuecomment-333652309>integration</a>).</p> <h3 id=notes-on-parsing>Notes on parsing<a class=headerlink href=#notes-on-parsing title="Permanent link">&para;</a></h3> <p>Note that you also need to call the right <a href=../../api/basic_json/parse/ ><code>parse</code></a> function when reading from a file. Assume file <code>input.json</code> contains the JSON object above:</p> <div class=highlight><pre><span></span><code><span class=p>{</span>
</code></pre></div> </details> <p>Alternatively, you can use a more sophisticated ordered map like <a href="https://github.com/Tessil/ordered-map"><code>tsl::ordered_map</code></a> (<a href="https://github.com/nlohmann/json/issues/546#issuecomment-304447518">integration</a>) or <a href="https://github.com/nlohmann/fifo_map"><code>nlohmann::fifo_map</code></a> (<a href="https://github.com/nlohmann/json/issues/485#issuecomment-333652309">integration</a>).</p> <h3 id=notes-on-parsing>Notes on parsing<a class=headerlink href=#notes-on-parsing title="Permanent link">&para;</a></h3> <p>Note that you also need to call the right <a href=../../api/basic_json/parse/ ><code>parse</code></a> function when reading from a file. Assume file <code>input.json</code> contains the <abbr title="JavaScript Object Notation">JSON</abbr> object above:</p> <div class=highlight><pre><span></span><code><span class=p>{</span>
<span class=w> </span><span class=nt>&quot;one&quot;</span><span class=p>:</span><span class=w> </span><span class=mi>1</span><span class=p>,</span>
<span class=w> </span><span class=nt>&quot;two&quot;</span><span class=p>:</span><span class=w> </span><span class=mi>2</span><span class=p>,</span>
<span class=w> </span><span class=nt>&quot;three&quot;</span><span class=p>:</span><span class=w> </span><span class=mi>3</span>
@@ -57,4 +57,4 @@
<span class=w> </span><span class=nt>&quot;three&quot;</span><span class=p>:</span><span class=w> </span><span class=mi>3</span>
<span class=w> </span><span class=nt>&quot;two&quot;</span><span class=p>:</span><span class=w> </span><span class=mi>2</span><span class=p>,</span>
<span class=p>}</span>
</code></pre></div> </details> <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">January 10, 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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<span class=p>{</span><span class=nt>&quot;name&quot;</span><span class=p>:</span><span class=w> </span><span class=s2>&quot;Alexa&quot;</span><span class=p>,</span><span class=w> </span><span class=nt>&quot;wins&quot;</span><span class=p>:</span><span class=w> </span><span class=p>[[</span><span class=s2>&quot;two pair&quot;</span><span class=p>,</span><span class=w> </span><span class=s2>&quot;4♠&quot;</span><span class=p>],</span><span class=w> </span><span class=p>[</span><span class=s2>&quot;two pair&quot;</span><span class=p>,</span><span class=w> </span><span class=s2>&quot;9♠&quot;</span><span class=p>]]}</span>
<span class=p>{</span><span class=nt>&quot;name&quot;</span><span class=p>:</span><span class=w> </span><span class=s2>&quot;May&quot;</span><span class=p>,</span><span class=w> </span><span class=nt>&quot;wins&quot;</span><span class=p>:</span><span class=w> </span><span class=p>[]}</span>
<span class=p>{</span><span class=nt>&quot;name&quot;</span><span class=p>:</span><span class=w> </span><span class=s2>&quot;Deloise&quot;</span><span class=p>,</span><span class=w> </span><span class=nt>&quot;wins&quot;</span><span class=p>:</span><span class=w> </span><span class=p>[[</span><span class=s2>&quot;three of a kind&quot;</span><span class=p>,</span><span class=w> </span><span class=s2>&quot;5♣&quot;</span><span class=p>]]}</span>
</code></pre></div> </div> <p>JSON Lines input with more than one value is treated as invalid JSON by the <a href=../../../api/basic_json/parse/ ><code>parse</code></a> or <a href=../../../api/basic_json/accept/ ><code>accept</code></a> functions. To process it line by line, functions like <a href=https://en.cppreference.com/w/cpp/string/basic_string/getline><code>std::getline</code></a> can be used:</p> <div class="admonition example"> <p class=admonition-title>Example: Parse JSON Text input line by line</p> <p>The example below demonstrates how JSON Lines can be processed.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;sstream&gt;</span>
</code></pre></div> </div> <p><abbr title="JavaScript Object Notation">JSON</abbr> Lines input with more than one value is treated as invalid <abbr title="JavaScript Object Notation">JSON</abbr> by the <a href=../../../api/basic_json/parse/ ><code>parse</code></a> or <a href=../../../api/basic_json/accept/ ><code>accept</code></a> functions. To process it line by line, functions like <a href="https://en.cppreference.com/w/cpp/string/basic_string/getline"><code>std::getline</code></a> can be used:</p> <div class="admonition example"> <p class=admonition-title>Example: Parse <abbr title="JavaScript Object Notation">JSON</abbr> Text input line by line</p> <p>The example below demonstrates how <abbr title="JavaScript Object Notation">JSON</abbr> Lines can be processed.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;sstream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
@@ -33,4 +33,4 @@
<span class=p>{</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>j</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>endl</span><span class=p>;</span>
<span class=p>}</span>
</code></pre></div> <p>with a JSON Lines input does not work, because the parser will try to parse one value after the last one.</p> </div> <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">January 10, 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>with a <abbr title="JavaScript Object Notation">JSON</abbr> Lines input does not work, because the parser will try to parse one value after the last one.</p> </div> <!-- 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">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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<!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/features/parsing/parse_exceptions/" rel="canonical"><link href=../json_lines/ rel=prev><link href=../parser_callbacks/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.5.49"><title>Parsing and Exceptions - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.6f8fc17f.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.06af60db.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new 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data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> Parsing and Exceptions </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo 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4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.52 6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.Line truncated
<span class=k>try</span>
<span class=p>{</span>
<span class=w> </span><span class=n>j</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>json</span><span class=o>::</span><span class=n>parse</span><span class=p>(</span><span class=n>my_input</span><span class=p>);</span>
@@ -12,11 +12,11 @@
<span class=p>{</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cerr</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>&quot;parse error&quot;</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>endl</span><span class=p>;</span>
<span class=p>}</span>
</code></pre></div> <p>Note there is no diagnostic information available in this scenario.</p> <h2 id=use-accept-function>Use accept() function<a class=headerlink href=#use-accept-function title="Permanent link">&para;</a></h2> <p>Alternatively, function <code>accept()</code> can be used which does not return a <code>json</code> value, but a <code class=highlight><span class=kt>bool</span></code> indicating whether the input is valid JSON.</p> <div class=highlight><pre><span></span><code><span class=k>if</span><span class=w> </span><span class=p>(</span><span class=o>!</span><span class=n>json</span><span class=o>::</span><span class=n>accept</span><span class=p>(</span><span class=n>my_input</span><span class=p>))</span>
</code></pre></div> <p>Note there is no diagnostic information available in this scenario.</p> <h2 id=use-accept-function>Use accept() function<a class=headerlink href=#use-accept-function title="Permanent link">&para;</a></h2> <p>Alternatively, function <code>accept()</code> can be used which does not return a <code>json</code> value, but a <code class=highlight><span class=kt>bool</span></code> indicating whether the input is valid <abbr title="JavaScript Object Notation">JSON</abbr>.</p> <div class=highlight><pre><span></span><code><span class=k>if</span><span class=w> </span><span class=p>(</span><span class=o>!</span><span class=n>json</span><span class=o>::</span><span class=n>accept</span><span class=p>(</span><span class=n>my_input</span><span class=p>))</span>
<span class=p>{</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cerr</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>&quot;parse error&quot;</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>endl</span><span class=p>;</span>
<span class=p>}</span>
</code></pre></div> <p>Again, there is no diagnostic information available.</p> <h2 id=user-defined-sax-interface>User-defined SAX interface<a class=headerlink href=#user-defined-sax-interface title="Permanent link">&para;</a></h2> <p>Finally, you can implement the <a href=../sax_interface/ >SAX interface</a> and decide what should happen in case of a parse error.</p> <p>This function has the following interface:</p> <div class=highlight><pre><span></span><code><span class=kt>bool</span><span class=w> </span><span class=nf>parse_error</span><span class=p>(</span><span class=n>std</span><span class=o>::</span><span class=kt>size_t</span><span class=w> </span><span class=n>position</span><span class=p>,</span>
</code></pre></div> <p>Again, there is no diagnostic information available.</p> <h2 id=user-defined-sax-interface>User-defined <abbr title="Simple API for XML">SAX</abbr> interface<a class=headerlink href=#user-defined-sax-interface title="Permanent link">&para;</a></h2> <p>Finally, you can implement the <a href=../sax_interface/ ><abbr title="Simple API for XML">SAX</abbr> interface</a> and decide what should happen in case of a parse error.</p> <p>This function has the following interface:</p> <div class=highlight><pre><span></span><code><span class=kt>bool</span><span class=w> </span><span class=nf>parse_error</span><span class=p>(</span><span class=n>std</span><span class=o>::</span><span class=kt>size_t</span><span class=w> </span><span class=n>position</span><span class=p>,</span>
<span class=w> </span><span class=k>const</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>string</span><span class=o>&amp;</span><span class=w> </span><span class=n>last_token</span><span class=p>,</span>
<span class=w> </span><span class=k>const</span><span class=w> </span><span class=n>json</span><span class=o>::</span><span class=n>exception</span><span class=o>&amp;</span><span class=w> </span><span class=n>ex</span><span class=p>);</span>
</code></pre></div> <p>The return value indicates whether the parsing should continue, so the function should usually return <code class=highlight><span class=nb>false</span></code>.</p> <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>
@@ -63,4 +63,4 @@
last read: &quot;3,]&quot;
parsing unsuccessful!
parsed value: [1,2,3]
</code></pre></div> </details> <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">January 10, 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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<span class=k>using</span><span class=w> </span><span class=n>parser_callback_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>function</span><span class=o>&lt;</span><span class=kt>bool</span><span class=p>(</span><span class=kt>int</span><span class=w> </span><span class=n>depth</span><span class=p>,</span><span class=w> </span><span class=n>parse_event_t</span><span class=w> </span><span class=n>event</span><span class=p>,</span><span class=w> </span><span class=n>BasicJsonType</span><span class=o>&amp;</span><span class=w> </span><span class=n>parsed</span><span class=p>)</span><span class=o>&gt;</span><span class=p>;</span>
</code></pre></div> <h2 id=callback-event-types>Callback event types<a class=headerlink href=#callback-event-types title="Permanent link">&para;</a></h2> <p>We distinguish six scenarios (determined by the event type) in which the callback function can be called. The following table describes the values of the parameters <code>depth</code>, <code>event</code>, and <code>parsed</code>.</p> <table> <thead> <tr> <th>parameter <code>event</code></th> <th>description</th> <th>parameter <code>depth</code></th> <th>parameter <code>parsed</code></th> </tr> </thead> <tbody> <tr> <td><code>parse_event_t::object_start</code></td> <td>the parser read <code>{</code> and started to process a JSON object</td> <td>depth of the parent of the JSON object</td> <td>a JSON value with type discarded</td> </tr> <tr> <td><code>parse_event_t::key</code></td> <td>the parser read a key of a value in an object</td> <td>depth of the currently parsed JSON object</td> <td>a JSON string containing the key</td> </tr> <tr> <td><code>parse_event_t::object_end</code></td> <td>the parser read <code>}</code> and finished processing a JSON object</td> <td>depth of the parent of the JSON object</td> <td>the parsed JSON object</td> </tr> <tr> <td><code>parse_event_t::array_start</code></td> <td>the parser read <code>[</code> and started to process a JSON array</td> <td>depth of the parent of the JSON array</td> <td>a JSON value with type discarded</td> </tr> <tr> <td><code>parse_event_t::array_end</code></td> <td>the parser read <code>]</code> and finished processing a JSON array</td> <td>depth of the parent of the JSON array</td> <td>the parsed JSON array</td> </tr> <tr> <td><code>parse_event_t::value</code></td> <td>the parser finished reading a JSON value</td> <td>depth of the value</td> <td>the parsed JSON value</td> </tr> </tbody> </table> <details class=example> <summary>Example</summary> <p>When parsing the following JSON text,</p> <div class=highlight><pre><span></span><code><span class=p>{</span>
</code></pre></div> <h2 id=callback-event-types>Callback event types<a class=headerlink href=#callback-event-types title="Permanent link">&para;</a></h2> <p>We distinguish six scenarios (determined by the event type) in which the callback function can be called. The following table describes the values of the parameters <code>depth</code>, <code>event</code>, and <code>parsed</code>.</p> <table> <thead> <tr> <th>parameter <code>event</code></th> <th>description</th> <th>parameter <code>depth</code></th> <th>parameter <code>parsed</code></th> </tr> </thead> <tbody> <tr> <td><code>parse_event_t::object_start</code></td> <td>the parser read <code>{</code> and started to process a <abbr title="JavaScript Object Notation">JSON</abbr> object</td> <td>depth of the parent of the <abbr title="JavaScript Object Notation">JSON</abbr> object</td> <td>a <abbr title="JavaScript Object Notation">JSON</abbr> value with type discarded</td> </tr> <tr> <td><code>parse_event_t::key</code></td> <td>the parser read a key of a value in an object</td> <td>depth of the currently parsed <abbr title="JavaScript Object Notation">JSON</abbr> object</td> <td>a <abbr title="JavaScript Object Notation">JSON</abbr> string containing the key</td> </tr> <tr> <td><code>parse_event_t::object_end</code></td> <td>the parser read <code>}</code> and finished processing a <abbr title="JavaScript Object Notation">JSON</abbr> object</td> <td>depth of the parent of the <abbr title="JavaScript Object Notation">JSON</abbr> object</td> <td>the parsed <abbr title="JavaScript Object Notation">JSON</abbr> object</td> </tr> <tr> <td><code>parse_event_t::array_start</code></td> <td>the parser read <code>[</code> and started to process a <abbr title="JavaScript Object Notation">JSON</abbr> array</td> <td>depth of the parent of the <abbr title="JavaScript Object Notation">JSON</abbr> array</td> <td>a <abbr title="JavaScript Object Notation">JSON</abbr> value with type discarded</td> </tr> <tr> <td><code>parse_event_t::array_end</code></td> <td>the parser read <code>]</code> and finished processing a <abbr title="JavaScript Object Notation">JSON</abbr> array</td> <td>depth of the parent of the <abbr title="JavaScript Object Notation">JSON</abbr> array</td> <td>the parsed <abbr title="JavaScript Object Notation">JSON</abbr> array</td> </tr> <tr> <td><code>parse_event_t::value</code></td> <td>the parser finished reading a <abbr title="JavaScript Object Notation">JSON</abbr> value</td> <td>depth of the value</td> <td>the parsed <abbr title="JavaScript Object Notation">JSON</abbr> value</td> </tr> </tbody> </table> <details class=example> <summary>Example</summary> <p>When parsing the following <abbr title="JavaScript Object Notation">JSON</abbr> text,</p> <div class=highlight><pre><span></span><code><span class=p>{</span>
<span class=w> </span><span class=nt>&quot;name&quot;</span><span class=p>:</span><span class=w> </span><span class=s2>&quot;Berlin&quot;</span><span class=p>,</span>
<span class=w> </span><span class=nt>&quot;location&quot;</span><span class=p>:</span><span class=w> </span><span class=p>[</span>
<span class=w> </span><span class=mf>52.519444</span><span class=p>,</span>
@@ -90,4 +90,4 @@
<span class=w> </span><span class=nt>&quot;Width&quot;</span><span class=p>:</span><span class=w> </span><span class=mi>800</span>
<span class=w> </span><span class=p>}</span>
<span class=p>}</span>
</code></pre></div> </details> <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">January 10, 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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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 Line truncated
class sax_t ["json::sax_t"] {
&lt;&lt;interface&gt;&gt;
@@ -49,4 +49,4 @@ class sax_t ["json::sax_t"] {
<span class=c1>// called when a parse error occurs; byte position, the last token, and an exception is passed</span>
<span class=kt>bool</span><span class=w> </span><span class=nf>parse_error</span><span class=p>(</span><span class=n>std</span><span class=o>::</span><span class=kt>size_t</span><span class=w> </span><span class=n>position</span><span class=p>,</span><span class=w> </span><span class=k>const</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>string</span><span class=o>&amp;</span><span class=w> </span><span class=n>last_token</span><span class=p>,</span><span class=w> </span><span class=k>const</span><span class=w> </span><span class=n>json</span><span class=o>::</span><span class=n>exception</span><span class=o>&amp;</span><span class=w> </span><span class=n>ex</span><span class=p>);</span>
</code></pre></div> <p>The return value of each function determines whether parsing should proceed.</p> <p>To implement your own SAX handler, proceed as follows:</p> <ol> <li>Implement the SAX interface in a class. You can use class <code>nlohmann::json_sax&lt;json&gt;</code> as base class, but you can also use any class where the functions described above are implemented and public.</li> <li>Create an object of your SAX interface class, e.g. <code>my_sax</code>.</li> <li>Call <code class=highlight><span class=kt>bool</span><span class=w> </span><span class=nf>json::sax_parse</span><span class=p>(</span><span class=n>input</span><span class=p>,</span><span class=w> </span><span class=o>&amp;</span><span class=n>my_sax</span><span class=p>);</span></code> where the first parameter can be any input like a string or an input stream and the second parameter is a pointer to your SAX interface.</li> </ol> <p>Note the <code>sax_parse</code> function only returns a <code class=highlight><span class=kt>bool</span></code> indicating the result of the last executed SAX event. It does not return <code>json</code> value - it is up to you to decide what to do with the SAX events. Furthermore, no exceptions are thrown in case of a parse error - it is up to you what to do with the exception object passed to your <code>parse_error</code> implementation. Internally, the SAX interface is used for the DOM parser (class <code>json_sax_dom_parser</code>) as well as the acceptor (<code>json_sax_acceptor</code>), see file <code>json_sax.hpp</code>.</p> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../../../api/json_sax/ >json_sax</a> - documentation of the SAX interface</li> <li><a href=../../../api/basic_json/sax_parse/ >sax_parse</a> - SAX parser</li> </ul> <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">January 10, 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; 2013 - 2024 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 0 496 512"><!-- Font Awesome Free 6.7.1 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 2024 Fonticons, Inc.--><path d="M165.9 397.4c0 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-.3-1.9-3-3.2-5.9-2.9M244.8 8C106.1 8 0 113.3 0 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 12.1C428.2 457.8 496 362.9 496 252 496 113.3 383.5 8 244.8 8M97.2 352.9c-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 Line truncated
</code></pre></div> <p>The return value of each function determines whether parsing should proceed.</p> <p>To implement your own <abbr title="Simple API for XML">SAX</abbr> handler, proceed as follows:</p> <ol> <li>Implement the <abbr title="Simple API for XML">SAX</abbr> interface in a class. You can use class <code>nlohmann::json_sax&lt;json&gt;</code> as base class, but you can also use any class where the functions described above are implemented and public.</li> <li>Create an object of your <abbr title="Simple API for XML">SAX</abbr> interface class, e.g. <code>my_sax</code>.</li> <li>Call <code class=highlight><span class=kt>bool</span><span class=w> </span><span class=nf>json::sax_parse</span><span class=p>(</span><span class=n>input</span><span class=p>,</span><span class=w> </span><span class=o>&amp;</span><span class=n>my_sax</span><span class=p>);</span></code> where the first parameter can be any input like a string or an input stream and the second parameter is a pointer to your <abbr title="Simple API for XML">SAX</abbr> interface.</li> </ol> <p>Note the <code>sax_parse</code> function only returns a <code class=highlight><span class=kt>bool</span></code> indicating the result of the last executed <abbr title="Simple API for XML">SAX</abbr> event. It does not return <code>json</code> value - it is up to you to decide what to do with the <abbr title="Simple API for XML">SAX</abbr> events. Furthermore, no exceptions are thrown in case of a parse error - it is up to you what to do with the exception object passed to your <code>parse_error</code> implementation. Internally, the <abbr title="Simple API for XML">SAX</abbr> interface is used for the <abbr title="Document Object Model">DOM</abbr> parser (class <code>json_sax_dom_parser</code>) as well as the acceptor (<code>json_sax_acceptor</code>), see file <code>json_sax.hpp</code>.</p> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../../../api/json_sax/ >json_sax</a> - documentation of the <abbr title="Simple API for XML">SAX</abbr> interface</li> <li><a href=../../../api/basic_json/sax_parse/ >sax_parse</a> - <abbr title="Simple API for XML">SAX</abbr> parser</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">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; 2013-2025 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 0 496 512"><!-- Font Awesome Free 6.7.1 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 2024 Fonticons, Inc.--><path d="M165.9 397.4c0 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-.3-1.9-3-3.2-5.9-2.9M244.8 8C106.1 8 0 113.3 0 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 20.9-6.5Line truncated
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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/features/types/ rel=canonical><link href=../macros/ rel=prev><link href=number_handling/ rel=next><link rel=icon href=../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.5.49"><title>Types - JSON for Modern C++</title><link rel=stylesheet href=../../assets/stylesheets/main.6f8fc17f.min.css><link rel=stylesheet href=../../assets/stylesheets/palette.06af60db.min.css><link rel=preconnect href=https://fonts.gstatic.com crossorigin><link rel=stylesheet href="https://fonts.googleapis.com/css?family=Roboto:300,300i,400,400i,700,700i%7CJetBrains+Mono:400,400i,700,700i&display=fallback"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../css/custom.css><script>__md_scope=new 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<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/features/types/" rel="canonical"><link href=../macros/ rel=prev><link href=number_handling/ rel=next><link rel=icon href=../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.5.49"><title>Types - JSON for Modern C++</title><link rel=stylesheet href=../../assets/stylesheets/main.6f8fc17f.min.css><link rel=stylesheet href=../../assets/stylesheets/palette.06af60db.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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class value_t {
&lt;&lt;enumeration&gt;&gt;
@@ -39,7 +39,7 @@ class basic_json {
}
basic_json .. json_value
basic_json .. value_t</code></pre> <h2 id=template-arguments>Template arguments<a class=headerlink href=#template-arguments title="Permanent link">&para;</a></h2> <p>The data types to store a JSON value are derived from the template arguments passed to class <code>basic_json</code>:</p> <div class=highlight><pre><span></span><code><span class=k>template</span><span class=o>&lt;</span>
basic_json .. value_t</code></pre> <h2 id=template-arguments>Template arguments<a class=headerlink href=#template-arguments title="Permanent link">&para;</a></h2> <p>The data types to store a <abbr title="JavaScript Object Notation">JSON</abbr> value are derived from the template arguments passed to class <code>basic_json</code>:</p> <div class=highlight><pre><span></span><code><span class=k>template</span><span class=o>&lt;</span>
<span class=w> </span><span class=k>template</span><span class=o>&lt;</span><span class=k>typename</span><span class=w> </span><span class=nc>U</span><span class=p>,</span><span class=w> </span><span class=k>typename</span><span class=w> </span><span class=nc>V</span><span class=p>,</span><span class=w> </span><span class=k>typename</span><span class=p>...</span><span class=w> </span><span class=n>Args</span><span class=o>&gt;</span><span class=w> </span><span class=k>class</span><span class=w> </span><span class=nc>ObjectType</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>map</span><span class=p>,</span>
<span class=w> </span><span class=k>template</span><span class=o>&lt;</span><span class=k>typename</span><span class=w> </span><span class=nc>U</span><span class=p>,</span><span class=w> </span><span class=k>typename</span><span class=p>...</span><span class=w> </span><span class=n>Args</span><span class=o>&gt;</span><span class=w> </span><span class=k>class</span><span class=w> </span><span class=nc>ArrayType</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>vector</span><span class=p>,</span>
<span class=w> </span><span class=k>class</span><span class=w> </span><span class=nc>StringType</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>string</span><span class=p>,</span>
@@ -67,14 +67,14 @@ basic_json .. value_t</code></pre> <h2 id=template-arguments>Template arguments<
<span class=k>using</span><span class=w> </span><span class=n>number_float_t</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>NumberFloatType</span><span class=p>;</span>
<span class=k>using</span><span class=w> </span><span class=n>binary_t</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>byte_container_with_subtype</span><span class=o>&lt;</span><span class=n>BinaryType</span><span class=o>&gt;</span><span class=p>;</span>
</code></pre></div> <h2 id=objects>Objects<a class=headerlink href=#objects title="Permanent link">&para;</a></h2> <p><a href=https://tools.ietf.org/html/rfc8259>RFC 8259</a> describes JSON objects as follows:</p> <blockquote> <p>An object is an unordered collection of zero or more name/value pairs, where a name is a string and a value is a string, number, boolean, null, object, or array.</p> </blockquote> <h3 id=default-type>Default type<a class=headerlink href=#default-type title="Permanent link">&para;</a></h3> <p>With the default values for <em>ObjectType</em> (<code>std::map</code>), <em>StringType</em> (<code>std::string</code>), and <em>AllocatorType</em> (<code>std::allocator</code>), the default value for <code>object_t</code> is:</p> <div class=highlight><pre><span></span><code><span class=n>std</span><span class=o>::</span><span class=n>map</span><span class=o>&lt;</span>
</code></pre></div> <h2 id=objects>Objects<a class=headerlink href=#objects title="Permanent link">&para;</a></h2> <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> objects as follows:</p> <blockquote> <p>An object is an unordered collection of zero or more name/value pairs, where a name is a string and a value is a string, number, boolean, null, object, or array.</p> </blockquote> <h3 id=default-type>Default type<a class=headerlink href=#default-type title="Permanent link">&para;</a></h3> <p>With the default values for <em>ObjectType</em> (<code>std::map</code>), <em>StringType</em> (<code>std::string</code>), and <em>AllocatorType</em> (<code>std::allocator</code>), the default value for <code>object_t</code> is:</p> <div class=highlight><pre><span></span><code><span class=n>std</span><span class=o>::</span><span class=n>map</span><span class=o>&lt;</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>string</span><span class=p>,</span><span class=w> </span><span class=c1>// key_type</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>less</span><span class=o>&lt;&gt;</span><span class=p>,</span><span class=w> </span><span class=c1>// key_compare</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>std</span><span class=o>::</span><span class=n>pair</span><span class=o>&lt;</span><span class=k>const</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>string</span><span class=p>,</span><span class=w> </span><span class=n>basic_json</span><span class=o>&gt;&gt;</span><span class=w> </span><span class=c1>// allocator_type</span>
<span class=o>&gt;</span>
</code></pre></div> <h3 id=behavior>Behavior<a class=headerlink href=#behavior title="Permanent link">&para;</a></h3> <p>The choice of <code>object_t</code> influences the behavior of the JSON class. With the default type, objects have the following behavior:</p> <ul> <li>When all names are unique, objects will be interoperable in the sense that all software implementations receiving that object will agree on the name-value mappings.</li> <li>When the names within an object are not unique, it is unspecified which one of the values for a given key will be chosen. For instance, <code class=highlight><span class=p>{</span><span class=nt>&quot;key&quot;</span><span class=p>:</span><span class=w> </span><span class=mi>2</span><span class=p>,</span><span class=w> </span><span class=nt>&quot;key&quot;</span><span class=p>:</span><span class=w> </span><span class=mi>1</span><span class=p>}</span></code> could be equal to either <code class=highlight><span class=p>{</span><span class=nt>&quot;key&quot;</span><span class=p>:</span><span class=w> </span><span class=mi>1</span><span class=p>}</span></code> or <code class=highlight><span class=p>{</span><span class=nt>&quot;key&quot;</span><span class=p>:</span><span class=w> </span><span class=mi>2</span><span class=p>}</span></code>.</li> <li>Internally, name/value pairs are stored in lexicographical order of the names. Objects will also be serialized (see <code>dump</code>) in this order. For instance, both <code class=highlight><span class=p>{</span><span class=nt>&quot;b&quot;</span><span class=p>:</span><span class=w> </span><span class=mi>1</span><span class=p>,</span><span class=w> </span><span class=nt>&quot;a&quot;</span><span class=p>:</span><span class=w> </span><span class=mi>2</span><span class=p>}</span></code> and <code class=highlight><span class=p>{</span><span class=nt>&quot;a&quot;</span><span class=p>:</span><span class=w> </span><span class=mi>2</span><span class=p>,</span><span class=w> </span><span class=nt>&quot;b&quot;</span><span class=p>:</span><span class=w> </span><span class=mi>1</span><span class=p>}</span></code> will be stored and serialized as <code class=highlight><span class=p>{</span><span class=nt>&quot;a&quot;</span><span class=p>:</span><span class=w> </span><span class=mi>2</span><span class=p>,</span><span class=w> </span><span class=nt>&quot;b&quot;</span><span class=p>:</span><span class=w> </span><span class=mi>1</span><span class=p>}</span></code>.</li> <li>When comparing objects, the order of the name/value pairs is irrelevant. This makes objects interoperable in the sense that they will not be affected by these differences. For instance, <code class=highlight><span class=p>{</span><span class=nt>&quot;b&quot;</span><span class=p>:</span><span class=w> </span><span class=mi>1</span><span class=p>,</span><span class=w> </span><span class=nt>&quot;a&quot;</span><span class=p>:</span><span class=w> </span><span class=mi>2</span><span class=p>}</span></code> and <code class=highlight><span class=p>{</span><span class=nt>&quot;a&quot;</span><span class=p>:</span><span class=w> </span><span class=mi>2</span><span class=p>,</span><span class=w> </span><span class=nt>&quot;b&quot;</span><span class=p>:</span><span class=w> </span><span class=mi>1</span><span class=p>}</span></code> will be treated as equal.</li> </ul> <h3 id=key-order>Key order<a class=headerlink href=#key-order title="Permanent link">&para;</a></h3> <p>The order name/value pairs are added to the object is <em>not</em> preserved by the library. Therefore, iterating an object may return name/value pairs in a different order than they were originally stored. In fact, keys will be traversed in alphabetical order as <code>std::map</code> with <code>std::less</code> is used by default. Please note this behavior conforms to <a href=https://tools.ietf.org/html/rfc8259>RFC 8259</a>, because any order implements the specified "unordered" nature of JSON objects.</p> <h3 id=limits>Limits<a class=headerlink href=#limits title="Permanent link">&para;</a></h3> <p><a href=https://tools.ietf.org/html/rfc8259>RFC 8259</a> specifies:</p> <blockquote> <p>An implementation may set limits on the maximum depth of nesting.</p> </blockquote> <p>In this class, the object's limit of nesting is not explicitly constrained. However, a maximum depth of nesting may be introduced by the compiler or runtime environment. A theoretical limit can be queried by calling the <code>max_size</code> function of a JSON object.</p> <h3 id=storage_1>Storage<a class=headerlink href=#storage_1 title="Permanent link">&para;</a></h3> <p>Objects are stored as pointers in a <code>basic_json</code> type. That is, for any access to object values, a pointer of type <code>object_t*</code> must be dereferenced.</p> <h2 id=arrays>Arrays<a class=headerlink href=#arrays title="Permanent link">&para;</a></h2> <p><a href=https://tools.ietf.org/html/rfc8259>RFC 8259</a> describes JSON arrays as follows:</p> <blockquote> <p>Line truncated
</code></pre></div> <h3 id=behavior>Behavior<a class=headerlink href=#behavior title="Permanent link">&para;</a></h3> <p>The choice of <code>object_t</code> influences the behavior of the <abbr title="JavaScript Object Notation">JSON</abbr> class. With the default type, objects have the following behavior:</p> <ul> <li>When all names are unique, objects will be interoperable in the sense that all software implementations receiving that object will agree on the name-value mappings.</li> <li>When the names within an object are not unique, it is unspecified which one of the values for a given key will be chosen. For instance, <code class=highlight><span class=p>{</span><span class=nt>&quot;key&quot;</span><span class=p>:</span><span class=w> </span><span class=mi>2</span><span class=p>,</span><span class=w> </span><span class=nt>&quot;key&quot;</span><span class=p>:</span><span class=w> </span><span class=mi>1</span><span class=p>}</span></code> could be equal to either <code class=highlight><span class=p>{</span><span class=nt>&quot;key&quot;</span><span class=p>:</span><span class=w> </span><span class=mi>1</span><span class=p>}</span></code> or <code class=highlight><span class=p>{</span><span class=nt>&quot;key&quot;</span><span class=p>:</span><span class=w> </span><span class=mi>2</span><span class=p>}</span></code>.</li> <li>Internally, name/value pairs are stored in lexicographical order of the names. Objects will also be serialized (see <code>dump</code>) in this order. For instance, both <code class=highlight><span class=p>{</span><span class=nt>&quot;b&quot;</span><span class=p>:</span><span class=w> </span><span class=mi>1</span><span class=p>,</span><span class=w> </span><span class=nt>&quot;a&quot;</span><span class=p>:</span><span class=w> </span><span class=mi>2</span><span class=p>}</span></code> and <code class=highlight><span class=p>{</span><span class=nt>&quot;a&quot;</span><span class=p>:</span><span class=w> </span><span class=mi>2</span><span class=p>,</span><span class=w> </span><span class=nt>&quot;b&quot;</span><span class=p>:</span><span class=w> </span><span class=mi>1</span><span class=p>}</span></code> will be stored and serialized as <code class=highlight><span class=p>{</span><span class=nt>&quot;a&quot;</span><span class=p>:</span><span class=w> </span><span class=mi>2</span><span class=p>,</span><span class=w> </span><span class=nt>&quot;b&quot;</span><span class=p>:</span><span class=w> </span><span class=mi>1</span><span class=p>}</span></code>.</li> <li>When comparing objects, the order of the name/value pairs is irrelevant. This makes objects interoperable in the sense that they will not be affected by these differences. For instance, <code class=highlight><span class=p>{</span><span class=nt>&quot;b&quot;</span><span class=p>:</span><span class=w> </span><span class=mi>1</span><span class=p>,</span><span class=w> </span><span class=nt>&quot;a&quot;</span><span class=p>:</span><span class=w> </span><span class=mi>2</span><span class=p>}</span></code> and <code class=highlight><span class=p>{</span><span class=nt>&quot;a&quot;</span><span class=p>:</span><span class=w> </span><span class=mi>2</span><span class=p>,</span><span class=w> </span><span class=nt>&quot;b&quot;</span><span class=p>:</span><span class=w> </span><span class=mi>1</span><span class=p>}</span></code> will be treated as equal.</li> </ul> <h3 id=key-order>Key order<a class=headerlink href=#key-order title="Permanent link">&para;</a></h3> <p>The order name/value pairs are added to the object is <em>not</em> preserved by the library. Therefore, iterating an object may return name/value pairs in a different order than they were originally stored. In fact, keys will be traversed in alphabetical order as <code>std::map</code> with <code>std::less</code> is used by default. Please note this behavior conforms to <a href="https://tools.ietf.org/html/rfc8259"><abbr title="Request for Comments">RFC</abbr> 8259</a>, because any order implements the specified "unordered" nature of <abbr title="JavaScript Object Notation">JSON</abbr> objects.</p> <h3 id=limits>Limits<a class=headerlink href=#limits title="Permanent link">&para;</a></h3> <p><a href="https://tools.ietf.org/html/rfc8259"><abbr title="Request for Comments">RFC</abbr> 8259</a> specifies:</p> <blockquote> <p>An implementation may set limits on the maximum depth of nesting.</p> </blockquote> <p>In this class, the object's limit of nesting is not explicitly constrained. However, a maximum depth of nesting may be introduced by the compiler or runtime environment. A theoretical limit can be queried by calling the <code>max_size</code> function of a <abbr title="JavaScript Object Notation">JSON</abbr> object.</p> <h3 id=storage_1>Storage<a class=headerlink href=#storage_1 title="Permanent link">&para;</a></h3> <p>Objects are stored as pointers in a <code>basic_json</code> type. That is, for any access to object values, a pointer of type <code>object_t*</code> Line truncated
<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>
<span class=o>&gt;</span>
</code></pre></div> <h3 id=limits_1>Limits<a class=headerlink href=#limits_1 title="Permanent link">&para;</a></h3> <p><a href=https://tools.ietf.org/html/rfc8259>RFC 8259</a> specifies:</p> <blockquote> <p>An implementation may set limits on the maximum depth of nesting.</p> </blockquote> <p>In this class, the array's limit of nesting is not explicitly constrained. However, a maximum depth of nesting may be introduced by the compiler or runtime environment. A theoretical limit can be queried by calling the <code>max_size</code> function of a JSON array.</p> <h3 id=storage_2>Storage<a class=headerlink href=#storage_2 title="Permanent link">&para;</a></h3> <p>Arrays are stored as pointers in a <code>basic_json</code> type. That is, for any access to array values, a pointer of type <code>array_t*</code> must be dereferenced.</p> <h2 id=strings>Strings<a class=headerlink href=#strings title="Permanent link">&para;</a></h2> <p><a href=https://tools.ietf.org/html/rfc8259>RFC 8259</a> describes JSON strings as follows:</p> <blockquote> <p>A string is a sequence of zero or more Unicode characters.</p> </blockquote> <p>Unicode values are split by the JSON class into byte-sized characters during deserialization.</p> <h3 id=default-type_2>Default type<a class=headerlink href=#default-type_2 title="Permanent link">&para;</a></h3> <p>With the default values for <em>StringType</em> (<code>std::string</code>), the default value for <code>string_t</code> is <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>string</span></code>.</p> <h3 id=encoding>Encoding<a class=headerlink href=#encoding title="Permanent link">&para;</a></h3> <p>Strings are stored in UTF-8 encoding. Therefore, functions like <code>std::string::size()</code> or <code>std::string::length()</code> return the number of <strong>bytes</strong> in the string rather than the number of characters or glyphs.</p> <h3 id=string-comparison>String comparison<a class=headerlink href=#string-comparison title="Permanent link">&para;</a></h3> <p><a href=https://tools.ietf.org/html/rfc8259>RFC 8259</a> states:</p> <blockquote> <p>Software implementations are typically required to test names of object members for equality. Implementations that transform the textual representation into sequences of Unicode code units and then perform the comparison numerically, code unit by code unit, are interoperable in the sense that implementations will agree in all cases on equality or inequality of two strings. For example, implementations that compare strings with escaped characters unconverted may incorrectly find that <code>"a\\b"</code> and <code>"a\u005Cb"</code> are not equal.</p> </blockquote> <p>This implementation is interoperable as it does compare strings code unit by code unit.</p> <h3 id=storage_3>Storage<a class=headerlink href=#storage_3 title="Permanent link">&para;</a></h3> <p>String values are stored as pointers in a <code>basic_json</code> type. That is, for any access to string values, a pointer of type <code>string_t*</code> must be dereferenced.</p> <h2 id=booleans>Booleans<a class=headerlink href=#booleans title="Permanent link">&para;</a></h2> <p><a href=https://tools.ietf.org/html/rfc8259>RFC 8259</a> implicitly describes a boolean as a type which differentiates the two literals <code>true</code> and <code>false</code>.</p> <h3 id=default-type_3>Default type<a class=headerlink href=#default-type_3 title="Permanent link">&para;</a></h3> <p>With the default values for <em>BooleanType</em> (<code class=highlight><span class=kt>bool</span></code>), the default value for <code>boolean_t</code> is <code class=highlight><span class=kt>bool</span></code>.</p> <h3 id=storage_4>Storage<a class=headerlink href=#storage_4 title="Permanent link">&para;</a></h3> <p>Boolean values are stored directly inside a <code>basic_json</code> type.</p> <h2 id=numbers>Numbers<a class=headerlink href=#numbers title="Permanent link">&para;</a></h2> <p>See the <a href=number_handling/ >number handling</a> article for a detailed discussion on how numbers are handled by this library.</p> <p><a href=https://tools.ietf.org/html/rfc8259>RFC 8259</a> describes numbers as follows:</p> <blockquote> <p>The representation of numbers is similar to that used in most programming languages. A number is represented in base 10 using decimal digits. It contains an integer component that may be prefixed with an optional minus sign, which may be followed by a fraction part and/or an exponent part. Leading zeros are not allowed. (...) Numeric values that cannot be represented in the grammar below (such as Infinity and NaN) are not permitted.</p> </blockquote> <p>This description includes both integer and floating-point numbers. However, C++ allows more precise storage if it is known whether the number is a signed integer, an unsigned integer or a floating-point number. Therefore, three different types, <code>number_integer_t</code>, <code>number_unsigned_t</code>, and <code>Line truncated
</code></pre></div> <h3 id=limits_1>Limits<a class=headerlink href=#limits_1 title="Permanent link">&para;</a></h3> <p><a href="https://tools.ietf.org/html/rfc8259"><abbr title="Request for Comments">RFC</abbr> 8259</a> specifies:</p> <blockquote> <p>An implementation may set limits on the maximum depth of nesting.</p> </blockquote> <p>In this class, the array's limit of nesting is not explicitly constrained. However, a maximum depth of nesting may be introduced by the compiler or runtime environment. A theoretical limit can be queried by calling the <code>max_size</code> function of a <abbr title="JavaScript Object Notation">JSON</abbr> array.</p> <h3 id=storage_2>Storage<a class=headerlink href=#storage_2 title="Permanent link">&para;</a></h3> <p>Arrays are stored as pointers in a <code>basic_json</code> type. That is, for any access to array values, a pointer of type <code>array_t*</code> must be dereferenced.</p> <h2 id=strings>Strings<a class=headerlink href=#strings title="Permanent link">&para;</a></h2> <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> strings as follows:</p> <blockquote> <p>A string is a sequence of zero or more Unicode characters.</p> </blockquote> <p>Unicode values are split by the <abbr title="JavaScript Object Notation">JSON</abbr> class into byte-sized characters during deserialization.</p> <h3 id=default-type_2>Default type<a class=headerlink href=#default-type_2 title="Permanent link">&para;</a></h3> <p>With the default values for <em>StringType</em> (<code>std::string</code>), the default value for <code>string_t</code> is <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>string</span></code>.</p> <h3 id=encoding>Encoding<a class=headerlink href=#encoding title="Permanent link">&para;</a></h3> <p>Strings are stored in <abbr title="Unicode Transformation Format">UTF</abbr>-8 encoding. Therefore, functions like <code>std::string::size()</code> or <code>std::string::length()</code> return the number of <strong>bytes</strong> in the string rather than the number of characters or glyphs.</p> <h3 id=string-comparison>String comparison<a class=headerlink href=#string-comparison title="Permanent link">&para;</a></h3> <p><a href="https://tools.ietf.org/html/rfc8259"><abbr title="Request for Comments">RFC</abbr> 8259</a> states:</p> <blockquote> <p>Software implementations are typically required to test names of object members for equality. Implementations that transform the textual representation into sequences of Unicode code units and then perform the comparison numerically, code unit by code unit, are interoperable in the sense that implementations will agree in all cases on equality or inequality of two strings. For example, implementations that compare strings with escaped characters unconverted may incorrectly find that <code>"a\\b"</code> and <code>"a\u005Cb"</code> are not equal.</p> </blockquote> <p>This implementation is interoperable as it does compare strings code unit by code unit.</p> <h3 id=storage_3>Storage<a class=headerlink href=#storage_3 title="Permanent link">&para;</a></h3> <p>String values are stored as pointers in a <code>basic_json</code> type. That is, for any access to string values, a pointer of type <code>string_t*</code> must be dereferenced.</p> <h2 id=booleans>Booleans<a class=headerlink href=#booleans title="Permanent link">&para;</a></h2> <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>true</code> and <code>false</code>.</p> <h3 id=default-type_3>Default type<a class=headerlink href=#default-type_3 title="Permanent link">&para;</a></h3> <p>With the default values for <em>BooleanType</em> (<code class=highlight><span class=kt>bool</span></code>), the default value for <code>boolean_t</code> is <code class=highlight><span class=kt>bool</span></code>.</p> <h3 id=storage_4>Storage<a class=headerlink href=#storage_4 title="Permanent link">&para;</a></h3> <p>Boolean values are stored directly inside a <code>basic_json</code> type.</p> <h2 id=numbers>Numbers<a class=headerlink href=#numbers title="Permanent link">&para;</a></h2> <p>See the <a href=number_handling/ >number handling</a> article for a detailed discussion on how numbers are handled by this library.</p> <p><a href="https://tools.ietf.org/html/rfc8259"><abbr title="Request for Comments">RFC</abbr> 8259</a> describes numbers as follows:</p> <blockquote> <p>The representation of numbers is similar to that used in most programming languages. A number is represented in base 10 using decimal digits. It contains an integer component that may be prefixed with an optional minus sign, which may be followed by a fraction part and/or an exponent part. Leading zeros are not allowed. (...) Numeric values that cannot be repLine truncated
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6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9.Line truncated
<span class=n>json</span><span class=w> </span><span class=n>j</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>f</span><span class=p>;</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>&#39;\n&#39;</span><span class=p>;</span>
</code></pre></div> yields <code class=highlight><span class=mf>0.30000001192092896</span></code>.</li> </ul> <p>All examples here can be reproduced by passing the original double value to</p> <div class=highlight><pre><span></span><code><span class=n>std</span><span class=o>::</span><span class=n>printf</span><span class=p>(</span><span class=s>&quot;%.*g</span><span class=se>\n</span><span class=s>&quot;</span><span class=p>,</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>numeric_limits</span><span class=o>&lt;</span><span class=kt>double</span><span class=o>&gt;::</span><span class=n>max_digits10</span><span class=p>,</span><span class=w> </span><span class=n>double_value</span><span class=p>);</span>
</code></pre></div> </div> <h4 id=nan-handling>NaN handling<a class=headerlink href=#nan-handling title="Permanent link">&para;</a></h4> <p>NaN (not-a-number) cannot be expressed with the number syntax described above and are in fact explicitly excluded:</p> <div class="admonition quote"> <p class=admonition-title><a href=https://tools.ietf.org/html/rfc8259#section-6>RFC 8259</a>, Section 6</p> <p>Numeric values that cannot be represented in the grammar below (such as Infinity and NaN) are not permitted.</p> </div> <p>That is, there is no way to <em>parse</em> a NaN value. However, NaN values can be stored in a JSON value by assignment.</p> <p>This library serializes NaN values as <code class=highlight><span class=kc>null</span></code>. This corresponds to the behavior of JavaScript's <a href=https://www.w3schools.com/js/js_json_stringify.asp><code>JSON.stringify</code></a> function.</p> <div class="admonition example"> <p class=admonition-title>Example</p> <p>The following example shows how a NaN value is stored in a <code>json</code> value.</p> <div class=highlight><pre><span></span><code><span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span>
</code></pre></div> </div> <h4 id=nan-handling><abbr title="Not a Number">NaN</abbr> handling<a class=headerlink href=#nan-handling title="Permanent link">&para;</a></h4> <p><abbr title="Not a Number">NaN</abbr> (not-a-number) cannot be expressed with the number syntax described above and are in fact explicitly excluded:</p> <div class="admonition quote"> <p class=admonition-title><a href="https://tools.ietf.org/html/rfc8259#section-6"><abbr title="Request for Comments">RFC</abbr> 8259</a>, Section 6</p> <p>Numeric values that cannot be represented in the grammar below (such as Infinity and <abbr title="Not a Number">NaN</abbr>) are not permitted.</p> </div> <p>That is, there is no way to <em>parse</em> a <abbr title="Not a Number">NaN</abbr> value. However, <abbr title="Not a Number">NaN</abbr> values can be stored in a <abbr title="JavaScript Object Notation">JSON</abbr> value by assignment.</p> <p>This library serializes <abbr title="Not a Number">NaN</abbr> values as <code class=highlight><span class=kc>null</span></code>. This corresponds to the behavior of JavaScript's <a href="https://www.w3schools.com/js/js_json_stringify.asp"><code>JSON.stringify</code></a> function.</p> <div class="admonition example"> <p class=admonition-title>Example</p> <p>The following example shows how a <abbr title="Not a Number">NaN</abbr> value is stored in a <code>json</code> value.</p> <div class=highlight><pre><span></span><code><span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span>
<span class=p>{</span>
<span class=w> </span><span class=kt>double</span><span class=w> </span><span class=n>val</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>numeric_limits</span><span class=o>&lt;</span><span class=kt>double</span><span class=o>&gt;::</span><span class=n>quiet_NaN</span><span class=p>();</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>&quot;val=&quot;</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>val</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>endl</span><span class=p>;</span>
@@ -14,7 +14,7 @@
</code></pre></div> <p>output:</p> <div class=highlight><pre><span></span><code>val=nan
j=null
val=nan
</code></pre></div> </div> <h3 id=number-comparison>Number comparison<a class=headerlink href=#number-comparison title="Permanent link">&para;</a></h3> <p>Floating-point inside JSON values numbers are compared with <code class=highlight><span class=n>json</span><span class=o>::</span><span class=n>number_float_t</span><span class=o>::</span><span class=n>operator</span><span class=o>==</span></code> which is <code class=highlight><span class=kt>double</span><span class=o>::</span><span class=n>operator</span><span class=o>==</span></code> by default.</p> <div class="admonition example"> <p class=admonition-title>Alternative comparison functions</p> <p>To compare floating-point while respecting an epsilon, an alternative <a href=https://github.com/mariokonrad/marnav/blob/master/include/marnav/math/floatingpoint.hpp#L34-#L39>comparison function</a> could be used, for instance</p> <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>T</span><span class=p>,</span><span class=w> </span><span class=k>typename</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=k>typename</span><span class=w> </span><span class=nc>std</span><span class=o>::</span><span class=n>enable_if</span><span class=o>&lt;</span><span class=n>std</span><span class=o>::</span><span class=n>is_floating_point</span><span class=o>&lt;</span><span class=n>T</span><span class=o>&gt;::</span><span class=n>value</span><span class=p>,</span><span class=w> </span><span class=n>T</span><span class=o>&gt;::</span><span class=n>type</span><span class=o>&gt;</span>
</code></pre></div> </div> <h3 id=number-comparison>Number comparison<a class=headerlink href=#number-comparison title="Permanent link">&para;</a></h3> <p>Floating-point inside <abbr title="JavaScript Object Notation">JSON</abbr> values numbers are compared with <code class=highlight><span class=n>json</span><span class=o>::</span><span class=n>number_float_t</span><span class=o>::</span><span class=n>operator</span><span class=o>==</span></code> which is <code class=highlight><span class=kt>double</span><span class=o>::</span><span class=n>operator</span><span class=o>==</span></code> by default.</p> <div class="admonition example"> <p class=admonition-title>Alternative comparison functions</p> <p>To compare floating-point while respecting an epsilon, an alternative <a href="https://github.com/mariokonrad/marnav/blob/master/include/marnav/math/floatingpoint.hpp#L34-#L39">comparison function</a> could be used, for instance</p> <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>T</span><span class=p>,</span><span class=w> </span><span class=k>typename</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=k>typename</span><span class=w> </span><span class=nc>std</span><span class=o>::</span><span class=n>enable_if</span><span class=o>&lt;</span><span class=n>std</span><span class=o>::</span><span class=n>is_floating_point</span><span class=o>&lt;</span><span class=n>T</span><span class=o>&gt;::</span><span class=n>value</span><span class=p>,</span><span class=w> </span><span class=n>T</span><span class=o>&gt;::</span><span class=n>type</span><span class=o>&gt;</span>
<span class=kr>inline</span><span class=w> </span><span class=kt>bool</span><span class=w> </span><span class=n>is_same</span><span class=p>(</span><span class=n>T</span><span class=w> </span><span class=n>a</span><span class=p>,</span><span class=w> </span><span class=n>T</span><span class=w> </span><span class=n>b</span><span class=p>,</span><span class=w> </span><span class=n>T</span><span class=w> </span><span class=n>epsilon</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>numeric_limits</span><span class=o>&lt;</span><span class=n>T</span><span class=o>&gt;::</span><span class=n>epsilon</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>return</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>abs</span><span class=p>(</span><span class=n>a</span><span class=w> </span><span class=o>-</span><span class=w> </span><span class=n>b</span><span class=p>)</span><span class=w> </span><span class=o>&lt;=</span><span class=w> </span><span class=n>epsilon</span><span class=p>;</span>
@@ -37,10 +37,10 @@ val=nan
<span class=w> </span><span class=p>}</span>
<span class=w> </span><span class=p>...</span>
<span class=p>}</span>
</code></pre></div> <p>(see <a href=https://github.com/nlohmann/json/issues/703>#703</a> for more information.)</p> </div> <div class="admonition note"> <p class=admonition-title>Note</p> <p>NaN values never compare equal to themselves or to other NaN values. See <a href=https://github.com/nlohmann/json/issues/514>#514</a>.</p> </div> <h3 id=number-conversion>Number conversion<a class=headerlink href=#number-conversion title="Permanent link">&para;</a></h3> <p>Just like the C++ language itself, the <code>get</code> family of functions allows conversions between unsigned and signed integers, and between integers and floating-point values to integers. This behavior may be surprising.</p> <div class="admonition warning"> <p class=admonition-title>Unconditional number conversions</p> <div class=highlight><pre><span></span><code><span class=kt>double</span><span class=w> </span><span class=n>d</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=mf>42.3</span><span class=p>;</span><span class=w> </span><span class=c1>// non-integer double value 42.3</span>
</code></pre></div> <p>(see <a href="https://github.com/nlohmann/json/issues/703">#703</a> for more information.)</p> </div> <div class="admonition note"> <p class=admonition-title>Note</p> <p><abbr title="Not a Number">NaN</abbr> values never compare equal to themselves or to other <abbr title="Not a Number">NaN</abbr> values. See <a href="https://github.com/nlohmann/json/issues/514">#514</a>.</p> </div> <h3 id=number-conversion>Number conversion<a class=headerlink href=#number-conversion title="Permanent link">&para;</a></h3> <p>Just like the C++ language itself, the <code>get</code> family of functions allows conversions between unsigned and signed integers, and between integers and floating-point values to integers. This behavior may be surprising.</p> <div class="admonition warning"> <p class=admonition-title>Unconditional number conversions</p> <div class=highlight><pre><span></span><code><span class=kt>double</span><span class=w> </span><span class=n>d</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=mf>42.3</span><span class=p>;</span><span class=w> </span><span class=c1>// non-integer double value 42.3</span>
<span class=n>json</span><span class=w> </span><span class=n>jd</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>d</span><span class=p>;</span><span class=w> </span><span class=c1>// stores double value 42.3</span>
<span class=hll><span class=n>std</span><span class=o>::</span><span class=kt>int64_t</span><span class=w> </span><span class=n>i</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>jd</span><span class=p>.</span><span class=k>template</span><span class=w> </span><span class=n>get</span><span class=o>&lt;</span><span class=n>std</span><span class=o>::</span><span class=kt>int64_t</span><span class=o>&gt;</span><span class=p>();</span><span class=w> </span><span class=c1>// now i==42; no warning or error is produced</span>
</span></code></pre></div> <p>Note the last line with throw a <a href=../../../home/exceptions/#jsonexceptiontype_error302><code>json.exception.type_error.302</code></a> exception if <code>jd</code> is not a numerical type, for instance a string.</p> </div> <p>The rationale is twofold:</p> <ol> <li>JSON does not define a number type or precision (see above).</li> <li>C++ also allows to silently convert between number types.</li> </ol> <div class="admonition success"> <p class=admonition-title>Conditional number conversion</p> <p>The code above can be solved by explicitly checking the nature of the value with members such as <a href=../../../api/basic_json/is_number_integer/ ><code>is_number_integer()</code></a> or <a href=../../../api/basic_json/is_number_unsigned/ ><code>is_number_unsigned()</code></a>:</p> <div class=highlight><pre><span></span><code><span class=c1>// check if jd is really integer-valued</span>
</span></code></pre></div> <p>Note the last line with throw a <a href=../../../home/exceptions/#jsonexceptiontype_error302><code>json.exception.type_error.302</code></a> exception if <code>jd</code> is not a numerical type, for instance a string.</p> </div> <p>The rationale is twofold:</p> <ol> <li><abbr title="JavaScript Object Notation">JSON</abbr> does not define a number type or precision (see above).</li> <li>C++ also allows to silently convert between number types.</li> </ol> <div class="admonition success"> <p class=admonition-title>Conditional number conversion</p> <p>The code above can be solved by explicitly checking the nature of the value with members such as <a href=../../../api/basic_json/is_number_integer/ ><code>is_number_integer()</code></a> or <a href=../../../api/basic_json/is_number_unsigned/ ><code>is_number_unsigned()</code></a>:</p> <div class=highlight><pre><span></span><code><span class=c1>// check if jd is really integer-valued</span>
<span class=hll><span class=k>if</span><span class=w> </span><span class=p>(</span><span class=n>jd</span><span class=p>.</span><span class=n>is_number_integer</span><span class=p>())</span>
</span><span class=p>{</span>
<span class=w> </span><span class=c1>// if so, do the conversion and use i</span>
@@ -52,6 +52,6 @@ val=nan
<span class=w> </span><span class=c1>// otherwise, take appropriate action</span>
<span class=w> </span><span class=c1>// ...</span>
<span class=p>}</span>
</code></pre></div> <p>Note this approach also has the advantage that it can react on non-numerical JSON value types such as strings.</p> <p>(Example taken from <a href=https://github.com/nlohmann/json/issues/777#issuecomment-459968458>#777</a>.)</p> </div> <h3 id=determine-number-types>Determine number types<a class=headerlink href=#determine-number-types title="Permanent link">&para;</a></h3> <p>As the example in <a href=#number-conversion>Number conversion</a> shows, there are different functions to determine the type of the stored number:</p> <ul> <li><a href=../../../api/basic_json/is_number/ ><code>is_number()</code></a> returns <code class=highlight><span class=nb>true</span></code> for any number type</li> <li><a href=../../../api/basic_json/is_number_integer/ ><code>is_number_integer()</code></a> returns <code class=highlight><span class=nb>true</span></code> for signed and unsigned integers</li> <li><a href=../../../api/basic_json/is_number_unsigned/ ><code>is_number_unsigned()</code></a> returns <code class=highlight><span class=nb>true</span></code> for unsigned integers only</li> <li><a href=../../../api/basic_json/is_number_float/ ><code>is_number_float()</code></a> returns <code class=highlight><span class=nb>true</span></code> for floating-point numbers</li> <li><a href=../../../api/basic_json/type_name/ ><code>type_name()</code></a> returns <code class=highlight><span class=s>&quot;number&quot;</span></code> for any number type</li> <li><a href=../../../api/basic_json/type/ ><code>type()</code></a> returns a different enumerator of <a href=../../../api/basic_json/value_t/ ><code>value_t</code></a> for all number types</li> </ul> <table> <thead> <tr> <th>function</th> <th>unsigned integer</th> <th>signed integer</th> <th>floating-point</th> <th>string</th> </tr> </thead> <tbody> <tr> <td><a href=../../../api/basic_json/is_number/ ><code>is_number()</code></a></td> <td><code class=highlight><span class=nb>true</span></code></td> <td><code class=highlight><span class=nb>true</span></code></td> <td><code class=highlight><span class=nb>true</span></code></td> <td><code class=highlight><span class=nb>false</span></code></td> </tr> <tr> <td><a href=../../../api/basic_json/is_number_integer/ ><code>is_number_integer()</code></a></td> <td><code class=highlight><span class=nb>true</span></code></td> <td><code class=highlight><span class=nb>true</span></code></td> <td><code class=highlight><span class=nb>false</span></code></td> <td><code class=highlight><span class=nb>false</span></code></td> </tr> <tr> <td><a href=../../../api/basic_json/is_number_unsigned/ ><code>is_number_unsigned()</code></a></td> <td><code class=highlight><span class=nb>true</span></code></td> <td><code class=highlight><span class=nb>false</span></code></td> <td><code class=highlight><span class=nb>false</span></code></td> <td><code class=highlight><span class=nb>false</span></code></td> </tr> <tr> <td><a href=../../../api/basic_json/is_number_float/ ><code>is_number_float()</code></a></td> <td><code class=highlight><span class=nb>false</span></code></td> <td><code class=highlight><span class=nb>false</span></code></td> <td><code class=highlight><span class=nb>true</span></code></td> <td><code class=highlight><span class=nb>false</span></code></td> </tr> <tr> <td><a href=../../../api/basic_json/type_name/ ><code>type_name()</code></a></td> <td><code class=highlight><span class=s>&quot;number&quot;</span></code></td> <td><code class=highlight><span class=s>&quot;number&quot;</span></code></td> <td><code class=highlight><span class=s>&quot;number&quot;</span></code></td> <td><code class=highlight><span class=s>&quot;string&quot;</span></code></td> </tr> <tr> <td><a href=../../../api/basic_json/type/ ><code>type()</code></a></td> <td><code>number_unsigned</code></td> <td><code>number_integer</code></td> <td><code>number_float</code></td> <td><code>string</code></td> </tr> </tbody> </table> <h3 id=template-number-types>Template number types<a class=headerlink href=#template-number-types title="Permanent link">&para;</a></h3> <p>The number types can be changed with template parameters.</p> <table> <thead> <tr> <th>position</th> <th>number type</th> <th>default type</th> <th>possible values</th> </tr> </thead> <tbody> <tr> <td>5</td> <td>signed integers</td> <td><code class=highlight><span class=n>std</span><span class=o>::</span><span class=kt>int64_t</span></code></td> <td><code class=highlight><span class=n>std</span><span class=o>::</span><span class=kt>int32_t</span></code>, <code class=highlight><span class=n>std</span><span class=o>::</span><span class=kt>int16_t</span></code>, etc.</td> </tr> <tr> <td>6</td> <td>unsigned integers</td> <td><code class=highlight><span class=n>std</span><span class=o>::</span><span class=kt>uint64_t</span></code></td> <td><code class=highlight><span class=n>std</span><span class=o>::</span><span class=kt>uint32_t</span></code>, <code class=highlight><span class=n>std</span><span class=o>::</spanLine truncated
</code></pre></div> <p>Note this approach also has the advantage that it can react on non-numerical <abbr title="JavaScript Object Notation">JSON</abbr> value types such as strings.</p> <p>(Example taken from <a href="https://github.com/nlohmann/json/issues/777#issuecomment-459968458">#777</a>.)</p> </div> <h3 id=determine-number-types>Determine number types<a class=headerlink href=#determine-number-types title="Permanent link">&para;</a></h3> <p>As the example in <a href=#number-conversion>Number conversion</a> shows, there are different functions to determine the type of the stored number:</p> <ul> <li><a href=../../../api/basic_json/is_number/ ><code>is_number()</code></a> returns <code class=highlight><span class=nb>true</span></code> for any number type</li> <li><a href=../../../api/basic_json/is_number_integer/ ><code>is_number_integer()</code></a> returns <code class=highlight><span class=nb>true</span></code> for signed and unsigned integers</li> <li><a href=../../../api/basic_json/is_number_unsigned/ ><code>is_number_unsigned()</code></a> returns <code class=highlight><span class=nb>true</span></code> for unsigned integers only</li> <li><a href=../../../api/basic_json/is_number_float/ ><code>is_number_float()</code></a> returns <code class=highlight><span class=nb>true</span></code> for floating-point numbers</li> <li><a href=../../../api/basic_json/type_name/ ><code>type_name()</code></a> returns <code class=highlight><span class=s>&quot;number&quot;</span></code> for any number type</li> <li><a href=../../../api/basic_json/type/ ><code>type()</code></a> returns a different enumerator of <a href=../../../api/basic_json/value_t/ ><code>value_t</code></a> for all number types</li> </ul> <table> <thead> <tr> <th>function</th> <th>unsigned integer</th> <th>signed integer</th> <th>floating-point</th> <th>string</th> </tr> </thead> <tbody> <tr> <td><a href=../../../api/basic_json/is_number/ ><code>is_number()</code></a></td> <td><code class=highlight><span class=nb>true</span></code></td> <td><code class=highlight><span class=nb>true</span></code></td> <td><code class=highlight><span class=nb>true</span></code></td> <td><code class=highlight><span class=nb>false</span></code></td> </tr> <tr> <td><a href=../../../api/basic_json/is_number_integer/ ><code>is_number_integer()</code></a></td> <td><code class=highlight><span class=nb>true</span></code></td> <td><code class=highlight><span class=nb>true</span></code></td> <td><code class=highlight><span class=nb>false</span></code></td> <td><code class=highlight><span class=nb>false</span></code></td> </tr> <tr> <td><a href=../../../api/basic_json/is_number_unsigned/ ><code>is_number_unsigned()</code></a></td> <td><code class=highlight><span class=nb>true</span></code></td> <td><code class=highlight><span class=nb>false</span></code></td> <td><code class=highlight><span class=nb>false</span></code></td> <td><code class=highlight><span class=nb>false</span></code></td> </tr> <tr> <td><a href=../../../api/basic_json/is_number_float/ ><code>is_number_float()</code></a></td> <td><code class=highlight><span class=nb>false</span></code></td> <td><code class=highlight><span class=nb>false</span></code></td> <td><code class=highlight><span class=nb>true</span></code></td> <td><code class=highlight><span class=nb>false</span></code></td> </tr> <tr> <td><a href=../../../api/basic_json/type_name/ ><code>type_name()</code></a></td> <td><code class=highlight><span class=s>&quot;number&quot;</span></code></td> <td><code class=highlight><span class=s>&quot;number&quot;</span></code></td> <td><code class=highlight><span class=s>&quot;number&quot;</span></code></td> <td><code class=highlight><span class=s>&quot;string&quot;</span></code></td> </tr> <tr> <td><a href=../../../api/basic_json/type/ ><code>type()</code></a></td> <td><code>number_unsigned</code></td> <td><code>number_integer</code></td> <td><code>number_float</code></td> <td><code>string</code></td> </tr> </tbody> </table> <h3 id=template-number-types>Template number types<a class=headerlink href=#template-number-types title="Permanent link">&para;</a></h3> <p>The number types can be changed with template parameters.</p> <table> <thead> <tr> <th>position</th> <th>number type</th> <th>default type</th> <th>possible values</th> </tr> </thead> <tbody> <tr> <td>5</td> <td>signed integers</td> <td><code class=highlight><span class=n>std</span><span class=o>::</span><span class=kt>int64_t</span></code></td> <td><code class=highlight><span class=n>std</span><span class=o>::</span><span class=kt>int32_t</span></code>, <code class=highlight><span class=n>std</span><span class=o>::</span><span class=kt>int16_t</span></code>, etc.</td> </tr> <tr> <td>6</td> <td>unsigned integers</td> <td><code class=highlight><span class=n>std</span><span class=o>::</span><span class=kt>uint64_t</span></code></td> <td><code class=highlight><span class=n>std</span><span class=o>::</span><span class=kt>uint32_t</span></code>, <code class=highliLine truncated
<span class=hll><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=kt>int64_t</span><span class=p>,</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=kt>uint64_t</span><span class=p>,</span><span class=w> </span><span class=kt>long</span><span class=w> </span><span class=kt>double</span><span class=o>&gt;</span><span class=p>;</span>
</span></code></pre></div> <p>Note values should then be parsed with <code>json_ld::parse</code> rather than <code>json::parse</code> as the latter would parse floating-point values to <code class=highlight><span class=kt>double</span></code> before then converting them to <code class=highlight><span class=kt>long</span><span class=w> </span><span class=kt>double</span></code>.</p> </div> <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">January 10, 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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</span></code></pre></div> <p>Note values should then be parsed with <code>json_ld::parse</code> rather than <code>json::parse</code> as the latter would parse floating-point values to <code class=highlight><span class=kt>double</span></code> before then converting them to <code class=highlight><span class=kt>long</span><span class=w> </span><span class=kt>double</span></code>.</p> </div> <!-- 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">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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