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<span class=k>static</span><span class=w> </span><span class=kt>bool</span><span class=w> </span><span class=n>accept</span><span class=p>(</span><span class=n>InputType</span><span class=o>&amp;&amp;</span><span class=w> </span><span class=n>input</span><span class=p>,</span>
<span class=w> </span><span class=k>const</span><span class=w> </span><span class=kt>bool</span><span class=w> </span><span class=n>ignore_comments</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=nb>false</span><span class=p>,</span>
<span class=w> </span><span class=k>const</span><span class=w> </span><span class=kt>bool</span><span class=w> </span><span class=n>ignore_trailing_commas</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=nb>false</span><span class=p>);</span>
</code></pre></div> <p>Checks whether the input is valid <abbr title="JavaScript Object Notation">JSON</abbr>, accepting and rejecting exactly what <a href=../../basic_json/accept/ ><code>BasicJsonType::accept()</code></a> does, with the same options. Unlike <a href=../parse/ ><code>parse()</code></a>, this function never throws an exception for invalid input, and the returned <code class=highlight><span class=kt>bool</span></code> is the only result — no document is returned.</p> <p>The result is the same as that of <code>BasicJsonType::accept()</code> by design; the difference is how the check is made. This function runs the document's index builder (and discards the index), while <code>BasicJsonType::accept()</code> runs the <abbr title="Simple API for XML">SAX</abbr> parser with a handler that ignores every event. Use this one if you go on to parse the same input with <a href=../parse/ ><code>parse()</code></a> anyway, so that both use the same code; either is fine for a plain yes/no answer.</p> <h2 id=template-parameters>Template parameters<a class=headerlink href=#template-parameters title="Permanent link">&para;</a></h2> <dl> <dt><code>InputType</code></dt> <dd>A compatible input; see <a href=../parse/#template-parameters><code>parse</code></a>.</dd> </dl> <h2 id=parameters>Parameters<a class=headerlink href=#parameters title="Permanent link">&para;</a></h2> <dl> <dt><code>input</code> (in)</dt> <dd>Input to check.</dd> <dt><code>ignore_comments</code> (in)</dt> <dd>whether comments should be ignored and treated like whitespace (<code class=highlight><span class=nb>true</span></code>) or yield a parse error (<code class=highlight><span class=nb>false</span></code>); (optional, <code class=highlight><span class=nb>false</span></code> by default)</dd> <dt><code>ignore_trailing_commas</code> (in)</dt> <dd>whether trailing commas in arrays or objects should be ignored and treated like whitespace (<code class=highlight><span class=nb>true</span></code>) or yield a parse error (<code class=highlight><span class=nb>false</span></code>); (optional, <code class=highlight><span class=nb>false</span></code> by default)</dd> </dl> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <p>Whether the input is valid <abbr title="JavaScript Object Notation">JSON</abbr>.</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">&para;</a></h2> <p>Strong guarantee: this function itself never throws for an invalid input; it can only throw what allocating the input's own copy (for inputs that are always read into a buffer) throws.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">&para;</a></h2> <p>Linear in the length of the input.</p> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <p>An integer argument that is not a <code class=highlight><span class=kt>bool</span></code> where the flags are expected, such as <code class=highlight><span class=n>accept</span><span class=p>(</span><span class=n>ptr</span><span class=p>,</span><span class=w> </span><span class=n>len</span><span class=p>)</span></code>, does not compile; see <a href=../parse/#notes><code>parse</code></a>.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
</code></pre></div> <p>Checks whether the input is valid <abbr title="JavaScript Object Notation">JSON</abbr>, accepting and rejecting exactly what <a href=../../basic_json/accept/ ><code>BasicJsonType::accept()</code></a> does, with the same options. Unlike <a href=../parse/ ><code>parse()</code></a>, this function never throws an exception for invalid input, and the returned <code class=highlight><span class=kt>bool</span></code> is the only result — no document is returned.</p> <p>The result is the same as that of <code>BasicJsonType::accept()</code> by design; the difference is how the check is made. This function runs the document's builder, which checks the text as <a href=../parse/ ><code>parse()</code></a> does, while <code>BasicJsonType::accept()</code> runs the <abbr title="Simple API for XML">SAX</abbr> parser with a handler that ignores every event. Use this one if you go on to parse the same input with <a href=../parse/ ><code>parse()</code></a> anyway, so that both use the same code; either is fine for a plain yes/no answer.</p> <p>When both <code>ignore_comments</code> and <code>ignore_trailing_commas</code> are <code class=highlight><span class=nb>false</span></code> (the default), the builder writes no index. With either option set, it builds the index as <a href=../parse/ ><code>parse()</code></a> does and discards it: the result is the same, only the time differs. (Neither option needs the index; the variant that skips it exists only for the default options to keep the code size down.)</p> <h2 id=template-parameters>Template parameters<a class=headerlink href=#template-parameters title="Permanent link">&para;</a></h2> <dl> <dt><code>InputType</code></dt> <dd>A compatible input; see <a href=../parse/#template-parameters><code>parse</code></a>.</dd> </dl> <h2 id=parameters>Parameters<a class=headerlink href=#parameters title="Permanent link">&para;</a></h2> <dl> <dt><code>input</code> (in)</dt> <dd>Input to check.</dd> <dt><code>ignore_comments</code> (in)</dt> <dd>whether comments should be ignored and treated like whitespace (<code class=highlight><span class=nb>true</span></code>) or yield a parse error (<code class=highlight><span class=nb>false</span></code>); (optional, <code class=highlight><span class=nb>false</span></code> by default)</dd> <dt><code>ignore_trailing_commas</code> (in)</dt> <dd>whether trailing commas in arrays or objects should be ignored and treated like whitespace (<code class=highlight><span class=nb>true</span></code>) or yield a parse error (<code class=highlight><span class=nb>false</span></code>); (optional, <code class=highlight><span class=nb>false</span></code> by default)</dd> </dl> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <p>Whether the input is valid <abbr title="JavaScript Object Notation">JSON</abbr>.</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">&para;</a></h2> <p>Strong guarantee: this function itself never throws for an invalid input; it can only throw what allocating the input's own copy (for inputs that are always read into a buffer) throws.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">&para;</a></h2> <p>Linear in the length of the input.</p> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <p>An integer argument that is not a <code class=highlight><span class=kt>bool</span></code> where the flags are expected, such as <code class=highlight><span class=n>accept</span><span class=p>(</span><span class=n>ptr</span><span class=p>,</span><span class=w> </span><span class=n>len</span><span class=p>)</span></code>, does not compile; see <a href=../parse/#notes><code>parse</code></a>.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<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;nlohmann/json_view.hpp&gt;</span>
@@ -25,4 +25,4 @@
<span class=kc>false</span>
<span class=kc>true</span>
<span class=kc>true</span>
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../parse/ ><code>parse</code></a> - deserialize from a compatible input</li> <li><a href=../../basic_json/accept/ ><code>BasicJsonType::accept</code></a> - the corresponding function of <code>basic_json</code></li> <li><a href=../../../features/json_view/#what-is-the-same-as-parse>Zero-copy <abbr title="JavaScript Object Notation">JSON</abbr> views</a> - how parsing a document differs from, and matches, basic_json::parse</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ul> <li>Added in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 27, 2026 06:41:42 UTC">October 27, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <nav class="md-footer__inner md-grid" aria-label=Footer> <a href=../basic_json_document/ class="md-footer__link md-footer__link--prev" aria-label="Previous: (Constructor)"> <div class="md-footer__button md-icon"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M20 11v2H8l5.5 5.5-1.42 1.42L4.16 12l7.92-7.92L13.5 5.5 8 11z"/></svg> </div> <div class=md-footer__title> <span class=md-footer__direction> Previous </span> <div class=md-ellipsis> (Constructor) </div> </div> </a> <a href=../erase/ class="md-footer__link md-footer__link--next" aria-label="Next: erase"> <div class=md-footer__title> <span class=md-footer__direction> Next </span> <div class=md-ellipsis> erase </div> </div> <div class="md-footer__button md-icon"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M4 11v2h12l-5.5 5.5 1.42 1.42L19.84 12l-7.92-7.92L10.5 5.5 16 11z"/></svg> </div> </a> </nav> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 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</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../parse/ ><code>parse</code></a> - deserialize from a compatible input</li> <li><a href=../../basic_json/accept/ ><code>BasicJsonType::accept</code></a> - the corresponding function of <code>basic_json</code></li> <li><a href=../../../features/json_view/#what-is-the-same-as-parse>Zero-copy <abbr title="JavaScript Object Notation">JSON</abbr> views</a> - how parsing a document differs from, and matches, basic_json::parse</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ul> <li>Added in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="November 1, 2026 16:21:06 UTC">November 1, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <nav class="md-footer__inner md-grid" aria-label=Footer> <a href=../basic_json_document/ class="md-footer__link md-footer__link--prev" aria-label="Previous: (Constructor)"> <div class="md-footer__button md-icon"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M20 11v2H8l5.5 5.5-1.42 1.42L4.16 12l7.92-7.92L13.5 5.5 8 11z"/></svg> </div> <div class=md-footer__title> <span class=md-footer__direction> Previous </span> <div class=md-ellipsis> (Constructor) </div> </div> </a> <a href=../erase/ class="md-footer__link md-footer__link--next" aria-label="Next: erase"> <div class=md-footer__title> <span class=md-footer__direction> Next </span> <div class=md-ellipsis> erase </div> </div> <div class="md-footer__button md-icon"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M4 11v2h12l-5.5 5.5 1.42 1.42L19.84 12l-7.92-7.92L10.5 5.5 16 11z"/></svg> </div> </a> </nav> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 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