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@@ -58,7 +58,9 @@ is not UTF-8 encoded and `error_handler` is set to `strict`
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## Complexity
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Linear.
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Linear in the size of the result. With an `indent`, every line starts with up to `indent` characters per nesting level,
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so the result can be larger than the value by a factor of its nesting depth (see
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[Parsing untrusted input](../../features/parsing/untrusted_input.md#nesting-depth)).
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## Notes
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@@ -2,7 +2,7 @@
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<span class=w> </span><span class=k>const</span><span class=w> </span><span class=kt>char</span><span class=w> </span><span class=n>indent_char</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=sc>' '</span><span class=p>,</span>
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<span class=w> </span><span class=k>const</span><span class=w> </span><span class=kt>bool</span><span class=w> </span><span class=n>ensure_ascii</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=nb>false</span><span class=p>,</span>
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<span class=w> </span><span class=k>const</span><span class=w> </span><span class=n>error_handler_t</span><span class=w> </span><span class=n>error_handler</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>error_handler_t</span><span class=o>::</span><span class=n>strict</span><span class=p>)</span><span class=w> </span><span class=k>const</span><span class=p>;</span>
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</code></pre></div> <p>Serialization function for <abbr title="JavaScript Object Notation">JSON</abbr> values. The function tries to mimic Python's <a href="https://docs.python.org/2/library/json.html#json.dump"><code>json.dumps()</code> function</a>, and currently supports its <code>indent</code> and <code>ensure_ascii</code> parameters.</p> <h2 id=parameters>Parameters<a class=headerlink href=#parameters title="Permanent link">¶</a></h2> <dl> <dt><code>indent</code> (in)</dt> <dd>If <code>indent</code> is nonnegative, then array elements and object members will be pretty-printed with that indent level. An indent level of <code>0</code> will only insert newlines. <code>-1</code> (the default) selects the most compact representation.</dd> <dt><code>indent_char</code> (in)</dt> <dd>The character to use for indentation if <code>indent</code> is greater than <code>0</code>. The default is <code></code> (space).</dd> <dt><code>ensure_ascii</code> (in)</dt> <dd>If <code>ensure_ascii</code> is true, all non-<abbr title="American Standard Code for Information Interchange">ASCII</abbr> characters in the output are escaped with <code>\uXXXX</code> sequences, and the result consists of <abbr title="American Standard Code for Information Interchange">ASCII</abbr> characters only.</dd> <dt><code>error_handler</code> (in)</dt> <dd>how to react on decoding errors; there are four possible values (see <a href=../error_handler_t/ ><code>error_handler_t</code></a>: <code>strict</code> (throws an exception in case a decoding error occurs; default), <code>replace</code> (replace invalid <abbr title="Unicode Transformation Format">UTF</abbr>-8 sequences with U+FFFD), <code>ignore</code> (ignore invalid <abbr title="Unicode Transformation Format">UTF</abbr>-8 sequences during serialization; all valid bytes are copied to the output unchanged, and invalid bytes are dropped), and <code>keep</code> (write the ill-formed bytes to the output as is, without escaping them, even if <code>ensure_ascii</code> is <code class=highlight><span class=nb>true</span></code>; the result is then not valid <abbr title="Unicode Transformation Format">UTF</abbr>-8, but equals the input bytes exactly, and well-formed characters around the ill-formed bytes are still escaped as usual)).</dd> </dl> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">¶</a></h2> <p>string containing the serialization of the <abbr title="JavaScript Object Notation">JSON</abbr> value</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">¶</a></h2> <p>Strong guarantee: if an exception is thrown, there are no changes to any <abbr title="JavaScript Object Notation">JSON</abbr> value.</p> <h2 id=exceptions>Exceptions<a class=headerlink href=#exceptions title="Permanent link">¶</a></h2> <p>Throws <a href=../../../home/exceptions/#jsonexceptiontype_error316><code>type_error.316</code></a> if a string stored inside the <abbr title="JavaScript Object Notation">JSON</abbr> value is not <abbr title="Unicode Transformation Format">UTF</abbr>-8 encoded and <code>error_handler</code> is set to <code>strict</code></p> <div class="admonition warning"> <p class=admonition-title>Serializing untrusted input</p> <p>When serializing values that may contain invalid or untrusted <abbr title="Unicode Transformation Format">UTF</abbr>-8 (e.g., bytes taken directly from network input), <code>dump()</code> throws <a href=../../../home/exceptions/#jsonexceptiontype_error316><code>type_error.316</code></a> in the default <code>strict</code> mode. To serialize such data without throwing, pass <a href=../error_handler_t/ ><code>error_handler_t::replace</code></a> (substitutes U+FFFD) or <a href=../error_handler_t/ ><code>error_handler_t::ignore</code></a>. Callers that serialize untrusted input on a crash-sensitive path should either choose a non-strict error handler or wrap <code>dump()</code> in a <code class=highlight><span class=k>try</span></code>/<code class=highlight><span class=k>catch</span></code>.</p> <p>See the <a href=../../../home/faq/#serializing-untrusted-or-invalid-utf-8><abbr title="Frequently Asked Questions">FAQ</abbr></a> for details.</p> </div> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">¶</a></h2> <p>Linear.</p> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">¶</a></h2> <p>Floating-point numbers are written with the fewest digits that read back as the same value (for <code class=highlight><span class=kt>double</span></code>; see <a href=../../../features/types/number_handling/#number-serialization>number handling</a>).</p> <p>Binary values are serialized as an object containing two keys:</p> <ul> <li>"bytes": an array of bytes as integers</li> <li>"subtype": the subtype as integer or <code class=highlight><span class=kc>null</span></code> if the binary has no subtype</li> </ul> <h2 id=exaLine truncated
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</code></pre></div> <p>Serialization function for <abbr title="JavaScript Object Notation">JSON</abbr> values. The function tries to mimic Python's <a href="https://docs.python.org/2/library/json.html#json.dump"><code>json.dumps()</code> function</a>, and currently supports its <code>indent</code> and <code>ensure_ascii</code> parameters.</p> <h2 id=parameters>Parameters<a class=headerlink href=#parameters title="Permanent link">¶</a></h2> <dl> <dt><code>indent</code> (in)</dt> <dd>If <code>indent</code> is nonnegative, then array elements and object members will be pretty-printed with that indent level. An indent level of <code>0</code> will only insert newlines. <code>-1</code> (the default) selects the most compact representation.</dd> <dt><code>indent_char</code> (in)</dt> <dd>The character to use for indentation if <code>indent</code> is greater than <code>0</code>. The default is <code></code> (space).</dd> <dt><code>ensure_ascii</code> (in)</dt> <dd>If <code>ensure_ascii</code> is true, all non-<abbr title="American Standard Code for Information Interchange">ASCII</abbr> characters in the output are escaped with <code>\uXXXX</code> sequences, and the result consists of <abbr title="American Standard Code for Information Interchange">ASCII</abbr> characters only.</dd> <dt><code>error_handler</code> (in)</dt> <dd>how to react on decoding errors; there are four possible values (see <a href=../error_handler_t/ ><code>error_handler_t</code></a>: <code>strict</code> (throws an exception in case a decoding error occurs; default), <code>replace</code> (replace invalid <abbr title="Unicode Transformation Format">UTF</abbr>-8 sequences with U+FFFD), <code>ignore</code> (ignore invalid <abbr title="Unicode Transformation Format">UTF</abbr>-8 sequences during serialization; all valid bytes are copied to the output unchanged, and invalid bytes are dropped), and <code>keep</code> (write the ill-formed bytes to the output as is, without escaping them, even if <code>ensure_ascii</code> is <code class=highlight><span class=nb>true</span></code>; the result is then not valid <abbr title="Unicode Transformation Format">UTF</abbr>-8, but equals the input bytes exactly, and well-formed characters around the ill-formed bytes are still escaped as usual)).</dd> </dl> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">¶</a></h2> <p>string containing the serialization of the <abbr title="JavaScript Object Notation">JSON</abbr> value</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">¶</a></h2> <p>Strong guarantee: if an exception is thrown, there are no changes to any <abbr title="JavaScript Object Notation">JSON</abbr> value.</p> <h2 id=exceptions>Exceptions<a class=headerlink href=#exceptions title="Permanent link">¶</a></h2> <p>Throws <a href=../../../home/exceptions/#jsonexceptiontype_error316><code>type_error.316</code></a> if a string stored inside the <abbr title="JavaScript Object Notation">JSON</abbr> value is not <abbr title="Unicode Transformation Format">UTF</abbr>-8 encoded and <code>error_handler</code> is set to <code>strict</code></p> <div class="admonition warning"> <p class=admonition-title>Serializing untrusted input</p> <p>When serializing values that may contain invalid or untrusted <abbr title="Unicode Transformation Format">UTF</abbr>-8 (e.g., bytes taken directly from network input), <code>dump()</code> throws <a href=../../../home/exceptions/#jsonexceptiontype_error316><code>type_error.316</code></a> in the default <code>strict</code> mode. To serialize such data without throwing, pass <a href=../error_handler_t/ ><code>error_handler_t::replace</code></a> (substitutes U+FFFD) or <a href=../error_handler_t/ ><code>error_handler_t::ignore</code></a>. Callers that serialize untrusted input on a crash-sensitive path should either choose a non-strict error handler or wrap <code>dump()</code> in a <code class=highlight><span class=k>try</span></code>/<code class=highlight><span class=k>catch</span></code>.</p> <p>See the <a href=../../../home/faq/#serializing-untrusted-or-invalid-utf-8><abbr title="Frequently Asked Questions">FAQ</abbr></a> for details.</p> </div> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">¶</a></h2> <p>Linear in the size of the result. With an <code>indent</code>, every line starts with up to <code>indent</code> characters per nesting level, so the result can be larger than the value by a factor of its nesting depth (see <a href=../../../features/parsing/untrusted_input/#nesting-depth>Parsing untrusted input</a>).</p> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">¶</a></h2> <p>Floating-point numbers are written with the fewest digits that read back as the same value (for <code class=highlight><span class=kt>double</span></code>; see <a href=../../../features/types/number_handling/#number-Line truncated
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<span class=cp>#include</span><span class=w> </span><span class=cpf><nlohmann/json.hpp></span>
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<span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
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@@ -105,4 +105,4 @@
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<span class=p>[</span><span class=err>jso</span><span class=kc>n</span><span class=err>.excep</span><span class=kc>t</span><span class=err>io</span><span class=kc>n</span><span class=err>.</span><span class=kc>t</span><span class=err>ype_error.</span><span class=mi>316</span><span class=p>]</span><span class=w> </span><span class=err>i</span><span class=kc>n</span><span class=err>valid</span><span class=w> </span><span class=err>UTF</span><span class=mi>-8</span><span class=w> </span><span class=err>by</span><span class=kc>te</span><span class=w> </span><span class=err>a</span><span class=kc>t</span><span class=w> </span><span class=err>i</span><span class=kc>n</span><span class=err>dex</span><span class=w> </span><span class=mi>2</span><span class=p>:</span><span class=w> </span><span class=mi>0</span><span class=err>xA</span><span class=mi>9</span>
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<span class=err>s</span><span class=kc>tr</span><span class=err>i</span><span class=kc>n</span><span class=err>g</span><span class=w> </span><span class=err>wi</span><span class=kc>t</span><span class=err>h</span><span class=w> </span><span class=err>replaced</span><span class=w> </span><span class=err>i</span><span class=kc>n</span><span class=err>valid</span><span class=w> </span><span class=err>charac</span><span class=kc>ters</span><span class=p>:</span><span class=w> </span><span class=s2>"ä�ü"</span>
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<span class=err>s</span><span class=kc>tr</span><span class=err>i</span><span class=kc>n</span><span class=err>g</span><span class=w> </span><span class=err>wi</span><span class=kc>t</span><span class=err>h</span><span class=w> </span><span class=err>ig</span><span class=kc>n</span><span class=err>ored</span><span class=w> </span><span class=err>i</span><span class=kc>n</span><span class=err>valid</span><span class=w> </span><span class=err>charac</span><span class=kc>ters</span><span class=p>:</span><span class=w> </span><span class=s2>"äü"</span>
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</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">¶</a></h2> <ul> <li><a href=../to_string/ ><code>to_string</code></a> - returns a string representation of a <abbr title="JavaScript Object Notation">JSON</abbr> value</li> <li><a href=../../operator_ltlt/ ><code>operator<<</code></a> - serialize to stream</li> <li><a href=../../basic_json_view/dump/ ><code>basic_json_view::dump</code></a> - the corresponding function of <code>basic_json_view</code>, serializing directly from a flat index without building a <code>basic_json</code> value</li> <li><a href=../../../features/serialization/ >Serialization</a> - the serialization article</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">¶</a></h2> <ul> <li>Added in version 1.0.0.</li> <li>Indentation character <code>indent_char</code>, option <code>ensure_ascii</code> and exceptions added in version 3.0.0.</li> <li>Error handlers added in version 3.4.0.</li> <li>Serialization of binary values added in version 3.8.0.</li> <li>Error handler <code>keep</code> added in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</li> <li>Doubles are written with the shortest digits (Żmij instead of Grisu2) since version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>; about 0.1% of doubles are written differently, most of them with fewer digits.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 27, 2026 06:41:42 UTC">October 27, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <nav class="md-footer__inner md-grid" aria-label=Footer> <a href=../diff/ class="md-footer__link md-footer__link--prev" aria-label="Previous: diff"> <div class="md-footer__button md-icon"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M20 11v2H8l5.5 5.5-1.42 1.42L4.16 12l7.92-7.92L13.5 5.5 8 11z"/></svg> </div> <div class=md-footer__title> <span class=md-footer__direction> Previous </span> <div class=md-ellipsis> diff </div> </div> </a> <a href=../emplace/ class="md-footer__link md-footer__link--next" aria-label="Next: emplace"> <div class=md-footer__title> <span class=md-footer__direction> Next </span> <div class=md-ellipsis> emplace </div> </div> <div class="md-footer__button md-icon"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M4 11v2h12l-5.5 5.5 1.42 1.42L19.84 12l-7.92-7.92L10.5 5.5 16 11z"/></svg> </div> </a> </nav> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright © 2013-2026 Niels Lohmann </div> </div> <div class=md-social> <a href="https://github.com/nlohmann" target="_blank" rel="noopener" title="github.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 512 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M173.9 397.4c0 2-2.3 3.6-5.2 3.6-3.3.3-5.6-1.3-5.6-3.6 0-2 2.3-3.6 5.2-3.6 3-.3 5.6 1.3 5.6 3.6m-31.1-4.5c-.7 2 1.3 4.3 4.3 4.9 2.6 1 5.6 0 6.2-2s-1.3-4.3-4.3-5.2c-2.6-.7-5.5.3-6.2 2.3m44.2-1.7c-2.9.7-4.9 2.6-4.6 4.9.3 2 2.9 3.3 5.9 2.6 2.9-.7 4.9-2.6 4.6-4.6-.3-1.9-3-3.2-5.9-2.9M252.8 8C114.1 8 8 113.3 8 252c0 110.9 69.8 205.8 169.5 239.2 12.Line truncated
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</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">¶</a></h2> <ul> <li><a href=../to_string/ ><code>to_string</code></a> - returns a string representation of a <abbr title="JavaScript Object Notation">JSON</abbr> value</li> <li><a href=../../operator_ltlt/ ><code>operator<<</code></a> - serialize to stream</li> <li><a href=../../basic_json_view/dump/ ><code>basic_json_view::dump</code></a> - the corresponding function of <code>basic_json_view</code>, serializing directly from a flat index without building a <code>basic_json</code> value</li> <li><a href=../../../features/serialization/ >Serialization</a> - the serialization article</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">¶</a></h2> <ul> <li>Added in version 1.0.0.</li> <li>Indentation character <code>indent_char</code>, option <code>ensure_ascii</code> and exceptions added in version 3.0.0.</li> <li>Error handlers added in version 3.4.0.</li> <li>Serialization of binary values added in version 3.8.0.</li> <li>Error handler <code>keep</code> added in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</li> <li>Doubles are written with the shortest digits (Żmij instead of Grisu2) since version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>; about 0.1% of doubles are written differently, most of them with fewer digits.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="November 13, 2026 16:54:22 UTC">November 13, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <nav class="md-footer__inner md-grid" aria-label=Footer> <a href=../diff/ class="md-footer__link md-footer__link--prev" aria-label="Previous: diff"> <div class="md-footer__button md-icon"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M20 11v2H8l5.5 5.5-1.42 1.42L4.16 12l7.92-7.92L13.5 5.5 8 11z"/></svg> </div> <div class=md-footer__title> <span class=md-footer__direction> Previous </span> <div class=md-ellipsis> diff </div> </div> </a> <a href=../emplace/ class="md-footer__link md-footer__link--next" aria-label="Next: emplace"> <div class=md-footer__title> <span class=md-footer__direction> Next </span> <div class=md-ellipsis> emplace </div> </div> <div class="md-footer__button md-icon"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M4 11v2h12l-5.5 5.5 1.42 1.42L19.84 12l-7.92-7.92L10.5 5.5 16 11z"/></svg> </div> </a> </nav> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright © 2013-2026 Niels Lohmann </div> </div> <div class=md-social> <a href="https://github.com/nlohmann" target="_blank" rel="noopener" title="github.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 512 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M173.9 397.4c0 2-2.3 3.6-5.2 3.6-3.3.3-5.6-1.3-5.6-3.6 0-2 2.3-3.6 5.2-3.6 3-.3 5.6 1.3 5.6 3.6m-31.1-4.5c-.7 2 1.3 4.3 4.3 4.9 2.6 1 5.6 0 6.2-2s-1.3-4.3-4.3-5.2c-2.6-.7-5.5.3-6.2 2.3m44.2-1.7c-2.9.7-4.9 2.6-4.6 4.9.3 2 2.9 3.3 5.9 2.6 2.9-.7 4.9-2.6 4.6-4.6-.3-1.9-3-3.2-5.9-2.9M252.8 8C114.1 8 8 113.3 8 252c0 110.9 69.8 205.8 169.5 239.2 1Line truncated
|
||||
@@ -39,7 +39,7 @@ See the [FAQ](https://json.nlohmann.me/home/faq/#serializing-untrusted-or-invali
|
||||
|
||||
## Complexity
|
||||
|
||||
Linear.
|
||||
Linear in the size of the result. With an `indent`, every line starts with up to `indent` characters per nesting level, so the result can be larger than the value by a factor of its nesting depth (see [Parsing untrusted input](https://json.nlohmann.me/features/parsing/untrusted_input/#nesting-depth)).
|
||||
|
||||
## Notes
|
||||
|
||||
|
||||
@@ -18,7 +18,8 @@ Strong exception safety: if an exception occurs, the original value stays intact
|
||||
|
||||
## Complexity
|
||||
|
||||
Linear in the size of the JSON value.
|
||||
Linear in the size of the result. Every key repeats the path of its value, so the keys can be larger than the value by a
|
||||
factor of its nesting depth (see [Parsing untrusted input](../../features/parsing/untrusted_input.md#nesting-depth)).
|
||||
|
||||
## Notes
|
||||
|
||||
|
||||
@@ -1,5 +1,5 @@
|
||||
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=description content="JSON for Modern C++ is a header-only C++11 library that makes JSON a first-class data type."><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/flatten/" rel="canonical"><link href=../find/ rel=prev><link href=../format_as/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.8.0"><title>flatten - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.57a0d79d.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.fb2fffe2.min.css><link rel=stylesheet href=../../../css/custom.css><link rel=stylesheet href=../../../css/brand.css><link rel=stylesheet href=../../../css/fig-sax.css><link rel=stylesheet href=../../../css/fig-jsonview.css><link rel=stylesheet 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</div> <div data-md-component=announce> </div> <header class=md-header data-md-component=header> <nav class="md-header__inner md-grid" aria-label=Header> <a href=../../.. title="JSON for Modern C++" class="md-header__button md-logo" aria-label="JSON for Modern C++" data-md-component=logo> <img src=../../../images/wordmark-header.svg alt=logo> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> flatten </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default 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0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16Line truncated
|
||||
</code></pre></div> <p>The function creates a <abbr title="JavaScript Object Notation">JSON</abbr> object whose keys are <abbr title="JavaScript Object Notation">JSON</abbr> pointers (see <a href="https://tools.ietf.org/html/rfc6901"><abbr title="Request for Comments">RFC</abbr> 6901</a>) and whose values are all primitive (see <a href=../is_primitive/ ><code>is_primitive()</code></a> for more information). The original <abbr title="JavaScript Object Notation">JSON</abbr> value can be restored using the <a href=../unflatten/ ><code>unflatten()</code></a> function.</p> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">¶</a></h2> <p>an object that maps <abbr title="JavaScript Object Notation">JSON</abbr> pointers to primitive values</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">¶</a></h2> <p>Strong exception safety: if an exception occurs, the original value stays intact.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">¶</a></h2> <p>Linear in the size of the <abbr title="JavaScript Object Notation">JSON</abbr> value.</p> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">¶</a></h2> <p>Empty objects and arrays are flattened to <code class=highlight><span class=kc>null</span></code> and will not be reconstructed correctly by the <a href=../unflatten/ ><code>unflatten()</code></a> function.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">¶</a></h2> <details class=example> <summary>Example: flatten a <abbr title="JavaScript Object Notation">JSON</abbr> object</summary> <p>The following code shows how a <abbr title="JavaScript Object Notation">JSON</abbr> object is flattened to an object whose keys consist of <abbr title="JavaScript Object Notation">JSON</abbr> pointers.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf><iostream></span>
|
||||
</code></pre></div> <p>The function creates a <abbr title="JavaScript Object Notation">JSON</abbr> object whose keys are <abbr title="JavaScript Object Notation">JSON</abbr> pointers (see <a href="https://tools.ietf.org/html/rfc6901"><abbr title="Request for Comments">RFC</abbr> 6901</a>) and whose values are all primitive (see <a href=../is_primitive/ ><code>is_primitive()</code></a> for more information). The original <abbr title="JavaScript Object Notation">JSON</abbr> value can be restored using the <a href=../unflatten/ ><code>unflatten()</code></a> function.</p> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">¶</a></h2> <p>an object that maps <abbr title="JavaScript Object Notation">JSON</abbr> pointers to primitive values</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">¶</a></h2> <p>Strong exception safety: if an exception occurs, the original value stays intact.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">¶</a></h2> <p>Linear in the size of the result. Every key repeats the path of its value, so the keys can be larger than the value by a factor of its nesting depth (see <a href=../../../features/parsing/untrusted_input/#nesting-depth>Parsing untrusted input</a>).</p> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">¶</a></h2> <p>Empty objects and arrays are flattened to <code class=highlight><span class=kc>null</span></code> and will not be reconstructed correctly by the <a href=../unflatten/ ><code>unflatten()</code></a> function.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">¶</a></h2> <details class=example> <summary>Example: flatten a <abbr title="JavaScript Object Notation">JSON</abbr> object</summary> <p>The following code shows how a <abbr title="JavaScript Object Notation">JSON</abbr> object is flattened to an object whose keys consist of <abbr title="JavaScript Object Notation">JSON</abbr> pointers.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf><iostream></span>
|
||||
<span class=cp>#include</span><span class=w> </span><span class=cpf><iomanip></span>
|
||||
<span class=cp>#include</span><span class=w> </span><span class=cpf><nlohmann/json.hpp></span>
|
||||
|
||||
@@ -77,4 +77,4 @@
|
||||
<span class=w> </span><span class=nt>"empty_object"</span><span class=p>:</span><span class=w> </span><span class=kc>null</span><span class=p>,</span>
|
||||
<span class=w> </span><span class=nt>"name"</span><span class=p>:</span><span class=w> </span><span class=s2>"Niels"</span>
|
||||
<span class=p>}</span>
|
||||
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">¶</a></h2> <ul> <li><a href=../unflatten/ ><code>unflatten</code></a> - the reverse function</li> <li><a href=../../../features/json_pointer/#flatten-unflatten><abbr title="JavaScript Object Notation">JSON</abbr> Pointer</a> - the article on <abbr title="JavaScript Object Notation">JSON</abbr> Pointer and flattening</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">¶</a></h2> <ul> <li>Added in version 2.0.0.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 27, 2026 06:41:42 UTC">October 27, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <nav class="md-footer__inner md-grid" aria-label=Footer> <a href=../find/ class="md-footer__link md-footer__link--prev" aria-label="Previous: find"> <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> find </div> </div> </a> <a href=../format_as/ class="md-footer__link md-footer__link--next" aria-label="Next: format_as"> <div class=md-footer__title> <span class=md-footer__direction> Next </span> <div class=md-ellipsis> format_as </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 © 2013-2026 Niels Lohmann </div> </div> <div class=md-social> <a href="https://github.com/nlohmann" target="_blank" rel="noopener" title="github.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 512 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M173.9 397.4c0 2-2.3 3.6-5.2 3.6-3.3.3-5.6-1.3-5.6-3.6 0-2 2.3-3.6 5.2-3.6 3-.3 5.6 1.3 5.6 3.6m-31.1-4.5c-.7 2 1.3 4.3 4.3 4.9 2.6 1 5.6 0 6.2-2s-1.3-4.3-4.3-5.2c-2.6-.7-5.5.3-6.2 2.3m44.2-1.7c-2.9.7-4.9 2.6-4.6 4.9.3 2 2.9 3.3 5.9 2.6 2.9-.7 4.9-2.6 4.6-4.6-.3-1.9-3-3.2-5.9-2.9M252.8 8C114.1 8 8 113.3 8 252c0 110.9 69.8 205.8 169.5 239.2 12.8 2.3 17.3-5.6 17.3-12.1 0-6.2-.3-40.4-.3-61.4 0 0-70 15-84.7-29.8 0 0-11.4-29.1-27.8-36.6 0 0-22.9-15.7 1.6-15.4 0 0 24.9 2 38.6 25.8 21.9 38.6 58.6 27.5 72.9 20.9 2.3-16 8.8-27.1 16-33.7-55.9-6.2-112.3-14.3-112.3-110.5 0-27.5 7.6-41.3 23.6-58.9-2.6-6.5-11.1-33.3 2.6-67.9 20.9-6.5 69 27 69 27 20-5.6 41.5-8.5 62.8-8.5s42.8 2.9 62.8 8.5c0 0 48.1-33.6 69-27 13.7 34.7 5.2 61.4 2.6 67.9 16 17.7 25.8 31.5 25.8 58.9 0 96.5-58.9 104.2-114.8 110.5 9.2 7.9 17 22.9 17 46.4 0 33.7-.3 75.4-.3 83.6 0 6.5 4.6 14.4 17.3 12.1C436.2 457.8 504 362.9 504 252 504 113.3 391.5 8 252.8 8M105.2 352.9c-1.3 1-1 3.3.7 5.2 1.6 1.6 3.9 2.3 5.2 1 1.3-1 1-3.3-.7-5.2-1.6-1.6-3.9-2.3-5.2-1m-10.8-8.1c-.7 1.3.3 2.9 2.3 3.9 1.6 1 3.6.7 4.3-.7.7-1.3-.3-2.9-2.3-3.9-2-.6-3.6-.3-4.3.7m32.4 35.6c-1.6 1.3-1 4.3 1.3 6.2 2.3 2.3 5.2 2.6 6.5 1 1.3-1.3.7-4.3-1.3-6.2-2.2-2.3-5.2-2.6-6.5-1m-11.4-14.7c-1.6 1-1.6 3.6 0 5.9s4.3 3.3 5.6 2.3c1.6-1.3 1.6-3.9 0-6.2-1.4-2.3-4-3.3-5.6-2"/></svg> </a> <a href="https://www.linkediLine truncated
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</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">¶</a></h2> <ul> <li><a href=../unflatten/ ><code>unflatten</code></a> - the reverse function</li> <li><a href=../../../features/json_pointer/#flatten-unflatten><abbr title="JavaScript Object Notation">JSON</abbr> Pointer</a> - the article on <abbr title="JavaScript Object Notation">JSON</abbr> Pointer and flattening</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">¶</a></h2> <ul> <li>Added in version 2.0.0.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="November 13, 2026 16:54:22 UTC">November 13, 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=../find/ class="md-footer__link md-footer__link--prev" aria-label="Previous: find"> <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> find </div> </div> </a> <a href=../format_as/ class="md-footer__link md-footer__link--next" aria-label="Next: format_as"> <div class=md-footer__title> <span class=md-footer__direction> Next </span> <div class=md-ellipsis> format_as </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 © 2013-2026 Niels Lohmann </div> </div> <div class=md-social> <a href="https://github.com/nlohmann" target="_blank" rel="noopener" title="github.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 512 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M173.9 397.4c0 2-2.3 3.6-5.2 3.6-3.3.3-5.6-1.3-5.6-3.6 0-2 2.3-3.6 5.2-3.6 3-.3 5.6 1.3 5.6 3.6m-31.1-4.5c-.7 2 1.3 4.3 4.3 4.9 2.6 1 5.6 0 6.2-2s-1.3-4.3-4.3-5.2c-2.6-.7-5.5.3-6.2 2.3m44.2-1.7c-2.9.7-4.9 2.6-4.6 4.9.3 2 2.9 3.3 5.9 2.6 2.9-.7 4.9-2.6 4.6-4.6-.3-1.9-3-3.2-5.9-2.9M252.8 8C114.1 8 8 113.3 8 252c0 110.9 69.8 205.8 169.5 239.2 12.8 2.3 17.3-5.6 17.3-12.1 0-6.2-.3-40.4-.3-61.4 0 0-70 15-84.7-29.8 0 0-11.4-29.1-27.8-36.6 0 0-22.9-15.7 1.6-15.4 0 0 24.9 2 38.6 25.8 21.9 38.6 58.6 27.5 72.9 20.9 2.3-16 8.8-27.1 16-33.7-55.9-6.2-112.3-14.3-112.3-110.5 0-27.5 7.6-41.3 23.6-58.9-2.6-6.5-11.1-33.3 2.6-67.9 20.9-6.5 69 27 69 27 20-5.6 41.5-8.5 62.8-8.5s42.8 2.9 62.8 8.5c0 0 48.1-33.6 69-27 13.7 34.7 5.2 61.4 2.6 67.9 16 17.7 25.8 31.5 25.8 58.9 0 96.5-58.9 104.2-114.8 110.5 9.2 7.9 17 22.9 17 46.4 0 33.7-.3 75.4-.3 83.6 0 6.5 4.6 14.4 17.3 12.1C436.2 457.8 504 362.9 504 252 504 113.3 391.5 8 252.8 8M105.2 352.9c-1.3 1-1 3.3.7 5.2 1.6 1.6 3.9 2.3 5.2 1 1.3-1 1-3.3-.7-5.2-1.6-1.6-3.9-2.3-5.2-1m-10.8-8.1c-.7 1.3.3 2.9 2.3 3.9 1.6 1 3.6.7 4.3-.7.7-1.3-.3-2.9-2.3-3.9-2-.6-3.6-.3-4.3.7m32.4 35.6c-1.6 1.3-1 4.3 1.3 6.2 2.3 2.3 5.2 2.6 6.5 1 1.3-1.3.7-4.3-1.3-6.2-2.2-2.3-5.2-2.6-6.5-1m-11.4-14.7c-1.6 1-1.6 3.6 0 5.9s4.3 3.3 5.6 2.3c1.6-1.3 1.6-3.9 0-6.2-1.4-2.3-4-3.3-5.6-2"/></svg> </a> <a href="https://www.linkeLine truncated
|
||||
@@ -16,7 +16,7 @@ Strong exception safety: if an exception occurs, the original value stays intact
|
||||
|
||||
## Complexity
|
||||
|
||||
Linear in the size of the JSON value.
|
||||
Linear in the size of the result. Every key repeats the path of its value, so the keys can be larger than the value by a factor of its nesting depth (see [Parsing untrusted input](https://json.nlohmann.me/features/parsing/untrusted_input/#nesting-depth)).
|
||||
|
||||
## Notes
|
||||
|
||||
|
||||
@@ -69,8 +69,10 @@ Strong guarantee: if an exception is thrown, there are no changes in the JSON va
|
||||
|
||||
## Exceptions
|
||||
|
||||
- Throws [parse_error.110](../../home/exceptions.md#jsonexceptionparse_error110) if the given input ends prematurely or
|
||||
the end of the file was not reached when `strict` was set to true
|
||||
- Throws [parse_error.110](../../home/exceptions.md#jsonexceptionparse_error110) if the given input ends prematurely,
|
||||
if the end of the file was not reached when `strict` was set to true, or if a string at the end of the value is not
|
||||
terminated by 0xFF although a byte follows it (also when `strict` is false: the byte that ends the string is
|
||||
taken from the input, so the next value would be lost)
|
||||
- Throws [parse_error.112](../../home/exceptions.md#jsonexceptionparse_error112) if a parse error occurs, for instance
|
||||
an invalid byte, a string that is not valid UTF-8, or an object key that is not a string
|
||||
|
||||
|
||||
@@ -8,7 +8,7 @@
|
||||
<span class=k>static</span><span class=w> </span><span class=n>basic_json</span><span class=w> </span><span class=n>from_bon8</span><span class=p>(</span><span class=n>IteratorType</span><span class=w> </span><span class=n>first</span><span class=p>,</span><span class=w> </span><span class=n>SentinelType</span><span class=w> </span><span class=n>last</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>strict</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=nb>true</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>allow_exceptions</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=nb>true</span><span class=p>);</span>
|
||||
</code></pre></div> <p>Deserializes a given input to a <abbr title="JavaScript Object Notation">JSON</abbr> value using the <abbr title="Binary Object Notation 8">BON8</abbr> (Binary Object Notation 8) serialization format.</p> <ol> <li>Reads from a compatible input.</li> <li>Reads from an iterator range, or an iterator and a sentinel of a different type (C++20 ranges support).</li> </ol> <p>The exact mapping and its limitations are described on a <a href=../../../features/binary_formats/bon8/ >dedicated page</a>.</p> <h2 id=template-parameters>Template parameters<a class=headerlink href=#template-parameters title="Permanent link">¶</a></h2> <dl> <dt><code>InputType</code></dt> <dd> <p>A compatible input, for instance:</p> <ul> <li>an <code>std::istream</code> object</li> <li>a <code>FILE</code> pointer</li> <li>a C-style array of characters</li> <li>a pointer to a null-terminated string of single byte characters</li> <li>a container <code>obj</code> for which <code>begin(obj)</code> and <code>end(obj)</code> produce a valid pair of iterators (as found via <abbr title="Argument-dependent lookup">ADL</abbr> or member functions, with semantics compatible to <code>std::begin</code> and <code>std::end</code>)</li> </ul> </dd> <dt><code>IteratorType</code></dt> <dd>a compatible iterator type</dd> <dt><code>SentinelType</code></dt> <dd> <p>defaults to <code>IteratorType</code>; may be a different type comparable to <code>IteratorType</code> via <code>operator!=</code>, for instance.</p> <ul> <li>a custom sentinel type for C++20 ranges</li> <li><code>std::default_sentinel_t</code>, when <code>IteratorType</code> is <code>std::counted_iterator</code></li> </ul> </dd> </dl> <h2 id=parameters>Parameters<a class=headerlink href=#parameters title="Permanent link">¶</a></h2> <dl> <dt><code>i</code> (in)</dt> <dd>an input in <abbr title="Binary Object Notation 8">BON8</abbr> format convertible to an input adapter</dd> <dt><code>first</code> (in)</dt> <dd>iterator to the start of the input</dd> <dt><code>last</code> (in)</dt> <dd>iterator to the end of the input, or a sentinel value that compares equal to the end iterator with <code>operator!=</code></dd> <dt><code>strict</code> (in)</dt> <dd>whether to expect the input to be consumed until <abbr title="End of File">EOF</abbr> (<code class=highlight><span class=nb>true</span></code> by default)</dd> <dt><code>allow_exceptions</code> (in)</dt> <dd>whether to throw exceptions in case of a parse error (optional, <code class=highlight><span class=nb>true</span></code> by default)</dd> </dl> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">¶</a></h2> <p>deserialized <abbr title="JavaScript Object Notation">JSON</abbr> value; in case of a parse error and <code>allow_exceptions</code> set to <code class=highlight><span class=nb>false</span></code>, the return value will be <code>value_t::discarded</code>. The latter can be checked with <a href=../is_discarded/ ><code>is_discarded</code></a>.</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">¶</a></h2> <p>Strong guarantee: if an exception is thrown, there are no changes in the <abbr title="JavaScript Object Notation">JSON</abbr> value.</p> <h2 id=exceptions>Exceptions<a class=headerlink href=#exceptions title="Permanent link">¶</a></h2> <ul> <li>Throws <a href=../../../home/exceptions/#jsonexceptionparse_error110>parse_error.110</a> if the given input ends prematurely or the end of the file was not reached when <code>strict</code> was set to true</li> <li>Throws <a href=../../../home/exceptions/#jsonexceptionparse_error112>parse_error.112</a> if a parse error occurs, for instance an invalid byte, a string that is not valid <abbr title="Unicode Transformation Format">UTF</abbr>-8, or an object key that is not a string</li> </ul> <p>The <abbr title="Unicode Transformation Format">UTF</abbr>-8 validity of strings is always checked, independent of <a href=../../macros/json_strict_binary_utf8/ ><code>JSON_STRICT_BINARY_UTF8</code></a>, because the end of a <abbr title="Binary Object Notation 8">BON8</abbr> string is determined from its encoding. Duplicate object keys are accepted; the last value wins (see <a href=../../../features/binary_formats/bon8/ ><abbr title="Binary Object Notation 8">BON8</abbr></a>).</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">¶</a></h2> <p>Linear in the size of the input.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">¶</a></h2> <details class=example> <summary>Example</summary> <p>The example shows the deserialization of a byte vector in <abbr title="Binary Object Notation 8">BON8</abbr> format to a <abbr title="JavaScript Object Notation">JSON</abbr> value.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf><iostreaLine truncated
|
||||
</code></pre></div> <p>Deserializes a given input to a <abbr title="JavaScript Object Notation">JSON</abbr> value using the <abbr title="Binary Object Notation 8">BON8</abbr> (Binary Object Notation 8) serialization format.</p> <ol> <li>Reads from a compatible input.</li> <li>Reads from an iterator range, or an iterator and a sentinel of a different type (C++20 ranges support).</li> </ol> <p>The exact mapping and its limitations are described on a <a href=../../../features/binary_formats/bon8/ >dedicated page</a>.</p> <h2 id=template-parameters>Template parameters<a class=headerlink href=#template-parameters title="Permanent link">¶</a></h2> <dl> <dt><code>InputType</code></dt> <dd> <p>A compatible input, for instance:</p> <ul> <li>an <code>std::istream</code> object</li> <li>a <code>FILE</code> pointer</li> <li>a C-style array of characters</li> <li>a pointer to a null-terminated string of single byte characters</li> <li>a container <code>obj</code> for which <code>begin(obj)</code> and <code>end(obj)</code> produce a valid pair of iterators (as found via <abbr title="Argument-dependent lookup">ADL</abbr> or member functions, with semantics compatible to <code>std::begin</code> and <code>std::end</code>)</li> </ul> </dd> <dt><code>IteratorType</code></dt> <dd>a compatible iterator type</dd> <dt><code>SentinelType</code></dt> <dd> <p>defaults to <code>IteratorType</code>; may be a different type comparable to <code>IteratorType</code> via <code>operator!=</code>, for instance.</p> <ul> <li>a custom sentinel type for C++20 ranges</li> <li><code>std::default_sentinel_t</code>, when <code>IteratorType</code> is <code>std::counted_iterator</code></li> </ul> </dd> </dl> <h2 id=parameters>Parameters<a class=headerlink href=#parameters title="Permanent link">¶</a></h2> <dl> <dt><code>i</code> (in)</dt> <dd>an input in <abbr title="Binary Object Notation 8">BON8</abbr> format convertible to an input adapter</dd> <dt><code>first</code> (in)</dt> <dd>iterator to the start of the input</dd> <dt><code>last</code> (in)</dt> <dd>iterator to the end of the input, or a sentinel value that compares equal to the end iterator with <code>operator!=</code></dd> <dt><code>strict</code> (in)</dt> <dd>whether to expect the input to be consumed until <abbr title="End of File">EOF</abbr> (<code class=highlight><span class=nb>true</span></code> by default)</dd> <dt><code>allow_exceptions</code> (in)</dt> <dd>whether to throw exceptions in case of a parse error (optional, <code class=highlight><span class=nb>true</span></code> by default)</dd> </dl> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">¶</a></h2> <p>deserialized <abbr title="JavaScript Object Notation">JSON</abbr> value; in case of a parse error and <code>allow_exceptions</code> set to <code class=highlight><span class=nb>false</span></code>, the return value will be <code>value_t::discarded</code>. The latter can be checked with <a href=../is_discarded/ ><code>is_discarded</code></a>.</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">¶</a></h2> <p>Strong guarantee: if an exception is thrown, there are no changes in the <abbr title="JavaScript Object Notation">JSON</abbr> value.</p> <h2 id=exceptions>Exceptions<a class=headerlink href=#exceptions title="Permanent link">¶</a></h2> <ul> <li>Throws <a href=../../../home/exceptions/#jsonexceptionparse_error110>parse_error.110</a> if the given input ends prematurely, if the end of the file was not reached when <code>strict</code> was set to true, or if a string at the end of the value is not terminated by 0xFF although a byte follows it (also when <code>strict</code> is false: the byte that ends the string is taken from the input, so the next value would be lost)</li> <li>Throws <a href=../../../home/exceptions/#jsonexceptionparse_error112>parse_error.112</a> if a parse error occurs, for instance an invalid byte, a string that is not valid <abbr title="Unicode Transformation Format">UTF</abbr>-8, or an object key that is not a string</li> </ul> <p>The <abbr title="Unicode Transformation Format">UTF</abbr>-8 validity of strings is always checked, independent of <a href=../../macros/json_strict_binary_utf8/ ><code>JSON_STRICT_BINARY_UTF8</code></a>, because the end of a <abbr title="Binary Object Notation 8">BON8</abbr> string is determined from its encoding. Duplicate object keys are accepted; the last value wins (see <a href=../../../features/binary_formats/bon8/ ><abbr title="Binary Object Notation 8">BON8</abbr></a>).</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">¶</a></h2> <p>Linear in the size of the input.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">¶</a></h2> <details class=example> <summary>Example</summary> <p>The example shows the deserialization of a byte vector in <abbr title="Binary Object NLine truncated
|
||||
<span class=cp>#include</span><span class=w> </span><span class=cpf><iomanip></span>
|
||||
<span class=cp>#include</span><span class=w> </span><span class=cpf><nlohmann/json.hpp></span>
|
||||
|
||||
@@ -34,4 +34,4 @@
|
||||
<span class=w> </span><span class=nt>"format"</span><span class=p>:</span><span class=w> </span><span class=s2>"BON8"</span><span class=p>,</span>
|
||||
<span class=w> </span><span class=nt>"schema"</span><span class=p>:</span><span class=w> </span><span class=mi>0</span>
|
||||
<span class=p>}</span>
|
||||
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">¶</a></h2> <ul> <li><a href=../../../features/binary_formats/bon8/ ><abbr title="Binary Object Notation 8">BON8</abbr></a> - the format, its byte layout and how values are mapped</li> <li><a href=../../../features/binary_formats/ >Binary formats</a> - overview and comparison of the supported binary formats</li> <li><a href=../../../features/parsing/untrusted_input/ >Parsing untrusted input</a> - limits and safe handling of hostile data</li> <li><a href=../to_bon8/ ><code>to_bon8</code></a> - create a <abbr title="Binary Object Notation 8">BON8</abbr> serialization of a <abbr title="JavaScript Object Notation">JSON</abbr> value</li> <li><a href=../from_cbor/ ><code>from_cbor</code></a> - create a <abbr title="JavaScript Object Notation">JSON</abbr> value from an input in <abbr title="Concise Binary Object Representation">CBOR</abbr> format</li> <li><a href=../from_msgpack/ ><code>from_msgpack</code></a> - create a <abbr title="JavaScript Object Notation">JSON</abbr> value from an input in MessagePack format</li> <li><a href=../from_bson/ ><code>from_bson</code></a> - create a <abbr title="JavaScript Object Notation">JSON</abbr> value from an input in <abbr title="Binary JSON">BSON</abbr> format</li> <li><a href=../from_ubjson/ ><code>from_ubjson</code></a> - create a <abbr title="JavaScript Object Notation">JSON</abbr> value from an input in <abbr title="Universal Binary JSON">UBJSON</abbr> format</li> <li><a href=../from_bjdata/ ><code>from_bjdata</code></a> - create a <abbr title="JavaScript Object Notation">JSON</abbr> value from an input in <abbr title="Binary JData">BJData</abbr> format</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">¶</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> <div class="admonition warning"> <p class=admonition-title>Deprecation</p> <ul> <li>Overload (2) replaces calls to <code>from_bon8</code> with a pointer and a length as first two parameters, which has been deprecated 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>. In version 4.0.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>, this overload will be deleted (<code>= delete</code>) rather than removed. Please replace all calls like <code class=highlight><span class=n>from_bon8</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><span class=w> </span><span class=p>...);</span></code> with <code class=highlight><span class=n>from_bon8</span><span class=p>(</span><span class=n>ptr</span><span class=p>,</span><span class=w> </span><span class=n>ptr</span><span class=o>+</span><span class=n>len</span><span class=p>,</span><span class=w> </span><span class=p>...);</span></code>.</li> </ul> <p>You should be warned by your compiler with a <code>-Wdeprecated-declarations</code> warning if you are using a deprecated function.</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" title="October 27, 2026 06:41:42 UTC">October 27, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <nav class="md-footer__inner md-grid" aria-label=Footer> <a href=../from_bjdata/ class="md-footer__link md-footer__link--prev" ariaLine truncated
|
||||
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">¶</a></h2> <ul> <li><a href=../../../features/binary_formats/bon8/ ><abbr title="Binary Object Notation 8">BON8</abbr></a> - the format, its byte layout and how values are mapped</li> <li><a href=../../../features/binary_formats/ >Binary formats</a> - overview and comparison of the supported binary formats</li> <li><a href=../../../features/parsing/untrusted_input/ >Parsing untrusted input</a> - limits and safe handling of hostile data</li> <li><a href=../to_bon8/ ><code>to_bon8</code></a> - create a <abbr title="Binary Object Notation 8">BON8</abbr> serialization of a <abbr title="JavaScript Object Notation">JSON</abbr> value</li> <li><a href=../from_cbor/ ><code>from_cbor</code></a> - create a <abbr title="JavaScript Object Notation">JSON</abbr> value from an input in <abbr title="Concise Binary Object Representation">CBOR</abbr> format</li> <li><a href=../from_msgpack/ ><code>from_msgpack</code></a> - create a <abbr title="JavaScript Object Notation">JSON</abbr> value from an input in MessagePack format</li> <li><a href=../from_bson/ ><code>from_bson</code></a> - create a <abbr title="JavaScript Object Notation">JSON</abbr> value from an input in <abbr title="Binary JSON">BSON</abbr> format</li> <li><a href=../from_ubjson/ ><code>from_ubjson</code></a> - create a <abbr title="JavaScript Object Notation">JSON</abbr> value from an input in <abbr title="Universal Binary JSON">UBJSON</abbr> format</li> <li><a href=../from_bjdata/ ><code>from_bjdata</code></a> - create a <abbr title="JavaScript Object Notation">JSON</abbr> value from an input in <abbr title="Binary JData">BJData</abbr> format</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">¶</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> <div class="admonition warning"> <p class=admonition-title>Deprecation</p> <ul> <li>Overload (2) replaces calls to <code>from_bon8</code> with a pointer and a length as first two parameters, which has been deprecated 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>. In version 4.0.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>, this overload will be deleted (<code>= delete</code>) rather than removed. Please replace all calls like <code class=highlight><span class=n>from_bon8</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><span class=w> </span><span class=p>...);</span></code> with <code class=highlight><span class=n>from_bon8</span><span class=p>(</span><span class=n>ptr</span><span class=p>,</span><span class=w> </span><span class=n>ptr</span><span class=o>+</span><span class=n>len</span><span class=p>,</span><span class=w> </span><span class=p>...);</span></code>.</li> </ul> <p>You should be warned by your compiler with a <code>-Wdeprecated-declarations</code> warning if you are using a deprecated function.</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" title="November 13, 2026 16:54:30 UTC">November 13, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <nav class="md-footer__inner md-grid" aria-label=Footer> <a href=../from_bjdata/ class="md-footer__link md-footer__link--prev" arLine truncated
|
||||
@@ -64,7 +64,7 @@ Strong guarantee: if an exception is thrown, there are no changes in the JSON va
|
||||
|
||||
## Exceptions
|
||||
|
||||
- Throws [parse_error.110](https://json.nlohmann.me/home/exceptions/#jsonexceptionparse_error110) if the given input ends prematurely or the end of the file was not reached when `strict` was set to true
|
||||
- Throws [parse_error.110](https://json.nlohmann.me/home/exceptions/#jsonexceptionparse_error110) if the given input ends prematurely, if the end of the file was not reached when `strict` was set to true, or if a string at the end of the value is not terminated by 0xFF although a byte follows it (also when `strict` is false: the byte that ends the string is taken from the input, so the next value would be lost)
|
||||
- Throws [parse_error.112](https://json.nlohmann.me/home/exceptions/#jsonexceptionparse_error112) if a parse error occurs, for instance an invalid byte, a string that is not valid UTF-8, or an object key that is not a string
|
||||
|
||||
The UTF-8 validity of strings is always checked, independent of [`JSON_STRICT_BINARY_UTF8`](https://json.nlohmann.me/api/macros/json_strict_binary_utf8/index.md), because the end of a BON8 string is determined from its encoding. Duplicate object keys are accepted; the last value wins (see [BON8](https://json.nlohmann.me/features/binary_formats/bon8/index.md)).
|
||||
|
||||
Reference in new issue
Block a user