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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/" rel="canonical"><link href=../performance/ rel=prev><link href=json_lines/ rel=next><link rel=icon href=../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>Parsing - JSON for Modern C++</title><link rel=stylesheet href=../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../css/custom.css><script>__md_scope=new 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I["JSON input"] --&gt; P["parse()"]
I --&gt; S["sax_parse()"]
I --&gt; A["accept()"]
P --&gt;|"optional parser callback filters values"| D["basic_json value (DOM)"]
S --&gt; H["events delivered to a user SAX handler"]
A --&gt; V["bool: is the input valid JSON?"]</code></pre> <h2 id=input>Input<a class=headerlink href=#input title="Permanent link">&para;</a></h2> <p>The <a href=../../api/basic_json/parse/ ><code>parse</code></a> function reads a <abbr title="JavaScript Object Notation">JSON</abbr> value from an input. The input can be</p> <ul> <li>a string (<code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>string</span></code>, C string, or string literal),</li> <li>a <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>istream</span></code> (e.g., an <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>ifstream</span></code> reading from a file),</li> <li>a <code class=highlight><span class=kt>FILE</span><span class=o>*</span></code> pointer,</li> <li>a pair of iterators over a contiguous range (e.g., a <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>vector</span><span class=o>&lt;</span><span class=n>std</span><span class=o>::</span><span class=kt>uint8_t</span><span class=o>&gt;</span></code>), or</li> <li>a contiguous container.</li> </ul> <div class=highlight><pre><span></span><code><span class=c1>// parse from a string</span>
A --&gt; V["bool: is the input valid JSON?"]</code></pre> <h2 id=input>Input<a class=headerlink href=#input title="Permanent link">&para;</a></h2> <p>The <a href=../../api/basic_json/parse/ ><code>parse</code></a> function reads a <abbr title="JavaScript Object Notation">JSON</abbr> value from an input. The input can be</p> <ul> <li>a string (<code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>string</span></code>, C string, or string literal),</li> <li>a wide string (<code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>u16string</span></code>, <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>u32string</span></code>, or <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>wstring</span></code>, or a wide string literal),</li> <li>a <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>istream</span></code> (e.g., an <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>ifstream</span></code> reading from a file),</li> <li>a <code class=highlight><span class=kt>FILE</span><span class=o>*</span></code> pointer,</li> <li>a pair of iterators over a contiguous range (e.g., a <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>vector</span><span class=o>&lt;</span><span class=n>std</span><span class=o>::</span><span class=kt>uint8_t</span><span class=o>&gt;</span></code>), or</li> <li>a contiguous container.</li> </ul> <div class=highlight><pre><span></span><code><span class=c1>// parse from a string</span>
<span class=n>json</span><span class=w> </span><span class=n>j</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>json</span><span class=o>::</span><span class=n>parse</span><span class=p>(</span><span class=sa>R</span><span class=s>"</span><span class=dl>(</span><span class=s>{"happy": true, "pi": 3.141}</span><span class=dl>)</span><span class=s>"</span><span class=p>);</span>
<span class=c1>// parse from a file</span>
<span class=n>std</span><span class=o>::</span><span class=n>ifstream</span><span class=w> </span><span class=n>f</span><span class=p>(</span><span class=s>"example.json"</span><span class=p>);</span>
<span class=n>json</span><span class=w> </span><span class=n>data</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>json</span><span class=o>::</span><span class=n>parse</span><span class=p>(</span><span class=n>f</span><span class=p>);</span>
</code></pre></div> <p>The input must be encoded in <abbr title="Unicode Transformation Format">UTF</abbr>-8; other encodings are not supported. A single input may contain only one <abbr title="JavaScript Object Notation">JSON</abbr> value. Inputs consisting of multiple values separated by newlines are handled by the <a href=json_lines/ ><abbr title="JavaScript Object Notation">JSON</abbr> Lines</a> format.</p> <p>By default, the library rejects comments and trailing commas. Both can be enabled with parameters of the <code>parse</code> function — see <a href=../comments/ >comments</a> and <a href=../trailing_commas/ >trailing commas</a>.</p> <h2 id=strictness-and-trailing-data>Strictness and trailing data<a class=headerlink href=#strictness-and-trailing-data title="Permanent link">&para;</a></h2> <p><a href=../../api/basic_json/parse/ ><code>parse</code></a> reads a single <abbr title="JavaScript Object Notation">JSON</abbr> value and requires the whole input to be consumed: any non-whitespace data after the value is reported as a parse error. Use it when you want to guarantee that an input is exactly one complete <abbr title="JavaScript Object Notation">JSON</abbr> document.</p> <p><a href=../../api/operator_gtgt/ ><code>operator&gt;&gt;</code></a> follows relaxed <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>istream</span></code> semantics instead: it parses one <abbr title="JavaScript Object Notation">JSON</abbr> value and leaves the stream positioned right after it, without requiring the rest of the stream to be consumed. This is what makes it possible to read several concatenated values from the same stream, but it also means that "a valid document followed by trailing bytes" is accepted rather than rejected. If you are validating conformance, or need to reject any input that is not exactly one <abbr title="JavaScript Object Notation">JSON</abbr> document, prefer <code>parse</code>.</p> <p>When using <code>operator&gt;&gt;</code> to read several concatenated values this way, a value that is a number must be followed by whitespace, because <code>operator&gt;&gt;</code> consumes the character that terminates a number, unless <a href=../../api/macros/json_precise_stream_position/ ><code>JSON_PRECISE_STREAM_POSITION</code></a> is defined to <code>1</code> — see the <a href=../../api/operator_gtgt/#notes><code>operator&gt;&gt;</code> notes</a> for details and examples.</p> <h2 id=input-sources-and-performance>Input sources and performance<a class=headerlink href=#input-sources-and-performance title="Permanent link">&para;</a></h2> <p>All inputs produce the same values and the same exceptions, but they are read in different ways, which makes some of them faster than others:</p> <table> <thead> <tr> <th>input</th> <th>how it is read</th> </tr> </thead> <tbody> <tr> <td>strings, string views, string literals, contiguous containers, pointer or iterator ranges over contiguous memory</td> <td>the whole input is scanned in bulk: runs of string characters, numbers, and indentation are recognized several bytes at a time</td> </tr> <tr> <td><code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>istream</span></code> (<code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>ifstream</span></code>, <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>istringstream</span></code>, ...)</td> <td>the characters the stream buffer holds are scanned in bulk like a string; the stream buffer is asked for more when they are used up</td> </tr> <tr> <td><code class=highlight><span class=kt>FILE</span><span class=o>*</span></code></td> <td>one character at a time, with the file locked once for the whole parse</td> </tr> <tr> <td>other iterator ranges (e.g., <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>list</span><span class=o>&lt;</span><span class=kt>char</span><span class=o>&gt;</span></code>, <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>istreambuf_iterator</span><span class=o>&lt;</span><span class=kt>char</span><span class=o>&gt;</span></code>), wide strings</td> <td>one character at a time</td> </tr> </tbody> </table> <p>Parsing a file from a <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>ifstream</span></code> is therefore only about 10 to 20 % slower than reading the whole file into a <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>string</span></code> first and parsing that, and it needs no memory for a copy of the file. The stream is never read ahead: after parsing, it is positioned exactly as if every character had been read one at a time, so <a href=../../api/operator_gtgt/ ><code>operator&gt;&gt;</code></a> can still read several values from one stream (see also <a href=json_lines/ ><abbr title="JavaScript Object Notation">JSON</abbr> Lines</a>).</p> <Line truncated
</code></pre></div> <p>The input must be encoded in <abbr title="Unicode Transformation Format">UTF</abbr>-8; other encodings are not supported. The exception is wide-character input, which is read as <abbr title="Unicode Transformation Format">UTF</abbr>-16 or <abbr title="Unicode Transformation Format">UTF</abbr>-32 -- depending on the character type -- and converted to <abbr title="Unicode Transformation Format">UTF</abbr>-8; see the <a href=../../api/basic_json/parse/ ><code>parse</code></a> page for an example. A single input may contain only one <abbr title="JavaScript Object Notation">JSON</abbr> value. Inputs consisting of multiple values separated by newlines are handled by the <a href=json_lines/ ><abbr title="JavaScript Object Notation">JSON</abbr> Lines</a> format.</p> <p>By default, the library rejects comments and trailing commas. Both can be enabled with parameters of the <code>parse</code> function — see <a href=../comments/ >comments</a> and <a href=../trailing_commas/ >trailing commas</a>.</p> <p><a href=../../api/basic_json_document/parse/ ><code>basic_json_document::parse</code></a> accepts the same inputs with the same options, but keeps the result in a document rather than in a <code>basic_json</code> value; see <a href=#documents-and-views>Documents and views</a> below.</p> <h2 id=strictness-and-trailing-data>Strictness and trailing data<a class=headerlink href=#strictness-and-trailing-data title="Permanent link">&para;</a></h2> <p><a href=../../api/basic_json/parse/ ><code>parse</code></a> reads a single <abbr title="JavaScript Object Notation">JSON</abbr> value and requires the whole input to be consumed: any non-whitespace data after the value is reported as a parse error. Use it when you want to guarantee that an input is exactly one complete <abbr title="JavaScript Object Notation">JSON</abbr> document.</p> <p><a href=../../api/operator_gtgt/ ><code>operator&gt;&gt;</code></a> follows relaxed <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>istream</span></code> semantics instead: it parses one <abbr title="JavaScript Object Notation">JSON</abbr> value and leaves the stream positioned right after it, without requiring the rest of the stream to be consumed. This is what makes it possible to read several concatenated values from the same stream, but it also means that "a valid document followed by trailing bytes" is accepted rather than rejected. If you are validating conformance, or need to reject any input that is not exactly one <abbr title="JavaScript Object Notation">JSON</abbr> document, prefer <code>parse</code>.</p> <p>When using <code>operator&gt;&gt;</code> to read several concatenated values this way, a value that is a number must be followed by whitespace, because <code>operator&gt;&gt;</code> consumes the character that terminates a number, unless <a href=../../api/macros/json_precise_stream_position/ ><code>JSON_PRECISE_STREAM_POSITION</code></a> is defined to <code>1</code> — see the <a href=../../api/operator_gtgt/#notes><code>operator&gt;&gt;</code> notes</a> for details and examples.</p> <h2 id=input-sources-and-performance>Input sources and performance<a class=headerlink href=#input-sources-and-performance title="Permanent link">&para;</a></h2> <p>All inputs produce the same values and the same exceptions, but they are read in different ways, which makes some of them faster than others:</p> <table> <thead> <tr> <th>input</th> <th>how it is read</th> </tr> </thead> <tbody> <tr> <td>strings, string views, string literals, contiguous containers, pointer or iterator ranges over contiguous memory</td> <td>the whole input is scanned in bulk: runs of string characters, numbers, and indentation are recognized several bytes at a time</td> </tr> <tr> <td><code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>istream</span></code> (<code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>ifstream</span></code>, <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>istringstream</span></code>, ...)</td> <td>the characters the stream buffer holds are scanned in bulk like a string; the stream buffer is asked for more when they are used up</td> </tr> <tr> <td><code class=highlight><span class=kt>FILE</span><span class=o>*</span></code></td> <td>one character at a time, with the file locked once for the whole parse</td> </tr> <tr> <td>other iterator ranges (e.g., <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>list</span><span class=o>&lt;</span><span class=kt>char</span><span class=o>&gt;</span></code>, <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>istreambuf_iterator</span><span class=o>&lt;</span><span class=kt>char</span><span class=o>&gt;</span></code>), wide strings</td> <td>one character at a time</td> </tr> </tbody> </table> <p>Parsing a file from a <code class=highlight><span claLine truncated
<span class=n>json_document</span><span class=w> </span><span class=n>doc</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>json_document</span><span class=o>::</span><span class=n>parse</span><span class=p>(</span><span class=sa>R</span><span class=s>"</span><span class=dl>(</span><span class=s>{"happy": true, "pi": 3.141}</span><span class=dl>)</span><span class=s>"</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>doc</span><span class=p>.</span><span class=n>root</span><span class=p>()[</span><span class=s>"happy"</span><span class=p>].</span><span class=n>get</span><span class=o>&lt;</span><span class=kt>bool</span><span class=o>&gt;</span><span class=p>()</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=sc>'\n'</span><span class=p>;</span>
</code></pre></div> <p>See <a href=../json_view/ >Zero-copy <abbr title="JavaScript Object Notation">JSON</abbr> views</a> for the concept and the trade-offs.</p> <h2 id=exceptions>Exceptions<a class=headerlink href=#exceptions title="Permanent link">&para;</a></h2> <p>When the input is not valid <abbr title="JavaScript Object Notation">JSON</abbr>, the <code>parse</code> function throws an exception by default. If exceptions are undesired or unavailable, the parser can instead return a discarded value, or <a href=../../api/basic_json/accept/ ><code>accept</code></a> can be used to only check whether an input is valid <abbr title="JavaScript Object Notation">JSON</abbr>. See <a href=parse_exceptions/ >parsing and exceptions</a> for the available options.</p> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../../api/basic_json/parse/ ><code>parse</code></a> - deserialize from a compatible input</li> <li><a href=../../api/basic_json_document/parse/ ><code>basic_json_document::parse</code></a> - deserialize into a document instead of a value</li> <li><a href=../../api/basic_json/accept/ ><code>accept</code></a> - check if the input is valid <abbr title="JavaScript Object Notation">JSON</abbr></li> <li><a href=../../api/basic_json/sax_parse/ ><code>sax_parse</code></a> - generate <abbr title="Simple API for XML">SAX</abbr> events</li> <li><a href=json_lines/ ><abbr title="JavaScript Object Notation">JSON</abbr> Lines</a> - parse newline-delimited <abbr title="JavaScript Object Notation">JSON</abbr></li> <li><a href=parser_callbacks/ >parser callbacks</a> - influence the parsing by a callback function</li> <li><a href=sax_interface/ ><abbr title="Simple API for XML">SAX</abbr> interface</a> - implement a custom <abbr title="Simple API for XML">SAX</abbr> handler</li> <li><a href=parse_exceptions/ >parsing and exceptions</a> - control error handling</li> <li><a href=untrusted_input/ >parsing untrusted input</a> - what to consider when parsing input from untrusted sources</li> <li><a href=../json_view/ >Zero-copy <abbr title="JavaScript Object Notation">JSON</abbr> views</a> - parse into a document and read it through a view</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 25, 2026 05:18:07 UTC">October 25, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 2013-2026 Niels Lohmann </div> </div> <div class=md-social> <a href="https://github.com/nlohmann" target="_blank" rel="noopener" title="github.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 512 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M173.9 397.4c0 2-2.3 3.6-5.2 3.6-3.3.3-5.6-1.3-5.6-3.6 0-2 2.3-3.6 5.2-3.6 3-.3 5.6 1.3 5.6 3.6m-31.1-4.5c-.7 2 1.3 4.3 4.3 4.9 2.6 1 5.6 0 6.2-2s-1.3-4.3-4.3-5.2c-2.6-.7-5.5.3-6.2 2.3m44.2-1.7c-2.9.7-4.9 2.6-4.6 4.9.3 2 2.9 3.3 5.9 2.6 2.9-.7 4.9-2.6 4.6-4.6-.3-1.9-3-3.2-5.9-2.9M252.8 8C114.1 8 8 113.3 8 252c0 110.9 69.8 205.8 169.5 239.2 12.8 2.3 17.3-5.6 17.3-12.1 0-6.2-.3-40.4-.3-61.4 0 0-70 15-84.7-29.8 0 0-11.4-29.1-27.8-36.6 0 0-22.9-15.7 1.6-15.4 0 0 24.9 2 38.6 25.8 21.9 38.6 58.6 27.5 72.9 20.9 2.3-16 8.8-27.1 16-33.7-55.9-6.2-112.3-14.3-112.3-110.5 0-27.5 7.6-41.3 23.6-58.9-2Line truncated
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@@ -17,6 +17,7 @@ flowchart LR
The [`parse`](https://json.nlohmann.me/api/basic_json/parse/index.md) function reads a JSON value from an input. The input can be
- a string (`std::string`, C string, or string literal),
- a wide string (`std::u16string`, `std::u32string`, or `std::wstring`, or a wide string literal),
- a `std::istream` (e.g., an `std::ifstream` reading from a file),
- a `FILE*` pointer,
- a pair of iterators over a contiguous range (e.g., a `std::vector<std::uint8_t>`), or
@@ -31,10 +32,12 @@ std::ifstream f("example.json");
json data = json::parse(f);
```
The input must be encoded in UTF-8; other encodings are not supported. A single input may contain only one JSON value. Inputs consisting of multiple values separated by newlines are handled by the [JSON Lines](https://json.nlohmann.me/features/parsing/json_lines/index.md) format.
The input must be encoded in UTF-8; other encodings are not supported. The exception is wide-character input, which is read as UTF-16 or UTF-32 -- depending on the character type -- and converted to UTF-8; see the [`parse`](https://json.nlohmann.me/api/basic_json/parse/index.md) page for an example. A single input may contain only one JSON value. Inputs consisting of multiple values separated by newlines are handled by the [JSON Lines](https://json.nlohmann.me/features/parsing/json_lines/index.md) format.
By default, the library rejects comments and trailing commas. Both can be enabled with parameters of the `parse` function — see [comments](https://json.nlohmann.me/features/comments/index.md) and [trailing commas](https://json.nlohmann.me/features/trailing_commas/index.md).
[`basic_json_document::parse`](https://json.nlohmann.me/api/basic_json_document/parse/index.md) accepts the same inputs with the same options, but keeps the result in a document rather than in a `basic_json` value; see [Documents and views](#documents-and-views) below.
## Strictness and trailing data
[`parse`](https://json.nlohmann.me/api/basic_json/parse/index.md) reads a single JSON value and requires the whole input to be consumed: any non-whitespace data after the value is reported as a parse error. Use it when you want to guarantee that an input is exactly one complete JSON document.
@@ -69,6 +72,19 @@ The library offers two parsing models:
You can influence a DOM parse without switching to the SAX interface by passing a [parser callback](https://json.nlohmann.me/features/parsing/parser_callbacks/index.md), which is called during parsing and can, for example, discard parts of the input.
## Documents and views
A third model sits between DOM and SAX: [`basic_json_document::parse`](https://json.nlohmann.me/api/basic_json_document/parse/index.md) parses the input into a document that keeps the text and a flat index of the values in it, and [`basic_json_view`](https://json.nlohmann.me/api/basic_json_view/index.md) gives read-only access to the values through that index. The whole input is validated during parsing, but only integers and strings that contain escape sequences are converted right away (the strings into a buffer owned by the document). Floating-point numbers and all other strings stay in the source text and are only converted when they are read, which is faster and uses less memory than building a tree of `basic_json` values when only parts of the document are needed. A document can also be modified in place, and it can be saved and loaded again without parsing it.
```
#include <nlohmann/json_view.hpp>
json_document doc = json_document::parse(R"({"happy": true, "pi": 3.141})");
std::cout << doc.root()["happy"].get<bool>() << '\n';
```
See [Zero-copy JSON views](https://json.nlohmann.me/features/json_view/index.md) for the concept and the trade-offs.
## Exceptions
When the input is not valid JSON, the `parse` function throws an exception by default. If exceptions are undesired or unavailable, the parser can instead return a discarded value, or [`accept`](https://json.nlohmann.me/api/basic_json/accept/index.md) can be used to only check whether an input is valid JSON. See [parsing and exceptions](https://json.nlohmann.me/features/parsing/parse_exceptions/index.md) for the available options.
@@ -76,6 +92,7 @@ When the input is not valid JSON, the `parse` function throws an exception by de
## See also
- [`parse`](https://json.nlohmann.me/api/basic_json/parse/index.md) - deserialize from a compatible input
- [`basic_json_document::parse`](https://json.nlohmann.me/api/basic_json_document/parse/index.md) - deserialize into a document instead of a value
- [`accept`](https://json.nlohmann.me/api/basic_json/accept/index.md) - check if the input is valid JSON
- [`sax_parse`](https://json.nlohmann.me/api/basic_json/sax_parse/index.md) - generate SAX events
- [JSON Lines](https://json.nlohmann.me/features/parsing/json_lines/index.md) - parse newline-delimited JSON
@@ -83,3 +100,4 @@ When the input is not valid JSON, the `parse` function throws an exception by de
- [SAX interface](https://json.nlohmann.me/features/parsing/sax_interface/index.md) - implement a custom SAX handler
- [parsing and exceptions](https://json.nlohmann.me/features/parsing/parse_exceptions/index.md) - control error handling
- [parsing untrusted input](https://json.nlohmann.me/features/parsing/untrusted_input/index.md) - what to consider when parsing input from untrusted sources
- [Zero-copy JSON views](https://json.nlohmann.me/features/json_view/index.md) - parse into a document and read it through a view
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@@ -81,6 +81,9 @@ Invalid UTF-8 is rejected while parsing, not just while serializing:
- In JSON text, an ill-formed UTF-8 byte in a string is a
[`parse_error.101`](../../home/exceptions.md#jsonexceptionparse_error101) ("invalid string: ill-formed UTF-8 byte").
- In UTF-16 or UTF-32 input, an ill-formed sequence is a
[`parse_error.101`](../../home/exceptions.md#jsonexceptionparse_error101) as well: a lone surrogate, a high surrogate
that is not followed by its low surrogate, and a code point above `U+10FFFF` are all rejected.
- In a binary format, a string that is not valid UTF-8 is a
[`parse_error.113`](../../home/exceptions.md#jsonexceptionparse_error113).
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@@ -39,6 +39,7 @@ For the binary formats, an announced size is never trusted outright:
Invalid UTF-8 is rejected while parsing, not just while serializing:
- In JSON text, an ill-formed UTF-8 byte in a string is a [`parse_error.101`](https://json.nlohmann.me/home/exceptions/#jsonexceptionparse_error101) ("invalid string: ill-formed UTF-8 byte").
- In UTF-16 or UTF-32 input, an ill-formed sequence is a [`parse_error.101`](https://json.nlohmann.me/home/exceptions/#jsonexceptionparse_error101) as well: a lone surrogate, a high surrogate that is not followed by its low surrogate, and a code point above `U+10FFFF` are all rejected.
- In a binary format, a string that is not valid UTF-8 is a [`parse_error.113`](https://json.nlohmann.me/home/exceptions/#jsonexceptionparse_error113).
A `'\0'` (NUL) byte *inside* a quoted JSON string is always rejected (it must be escaped as `\u0000`). A NUL byte *outside* of a string is different: by default it is silently treated as the end of the input, so trailing bytes after it -- including further, otherwise well-formed JSON -- are silently ignored rather than rejected. Since untrusted input that happens to embed a NUL is a way to make part of it disappear without a parse error, see the [FAQ entry](https://json.nlohmann.me/home/faq/#nul-bytes-in-the-input) and consider defining [`JSON_STRICT_NUL_HANDLING`](https://json.nlohmann.me/api/macros/json_strict_nul_handling/index.md) to `1` to reject a NUL byte like any other unexpected byte instead.