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<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=description content="JSON for Modern C++ is a header-only C++11 library that makes JSON a first-class data type."><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json_view/get_string/" rel="canonical"><link href=../get/ rel=prev><link href=../get_to/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.8.0"><title>get_string - 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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<!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_view/get_string/" rel="canonical"><link href=../get/ rel=prev><link href=../get_to/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.8.0"><title>get_string - 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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content </a> </div> <div data-md-component=announce> </div> <header class=md-header data-md-component=header> <nav class="md-header__inner md-grid" aria-label=Header> <a href=../../.. title="JSON for Modern C++" class="md-header__button md-logo" aria-label="JSON for Modern C++" data-md-component=logo> <img src=../../../images/wordmark-header.svg alt=logo> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> get_string </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" 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</code></pre></div> <p>Returns the string value as a <a href=../#member-types><code>string_view_t</code></a>, without copying it.</p> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">¶</a></h2> <p>The string, as a <a href=../#member-types><code>string_view_t</code></a> that points either into the document's <a href=../../basic_json_document/source/ ><code>source()</code></a> text (a string with no escape sequences), or into the document's own buffer of decoded strings (a string that contains escape sequences, such as <code class=highlight><span class=s2>"\n"</span></code> or <code class=highlight><span class=s2>"\u00e9"</span></code>, which had to be decoded once when the document was parsed).</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">¶</a></h2> <p>Strong guarantee: there are no changes to the view or the document it refers to.</p> <h2 id=exceptions>Exceptions<a class=headerlink href=#exceptions title="Permanent link">¶</a></h2> <p>Throws <a href=../../../home/exceptions/#jsonexceptiontype_error302><code>type_error.302</code></a> if the value is not a string; example: <code>"type must be string, but is array"</code>.</p> <p>As for <code>BasicJsonType</code>, with <a href=../../macros/json_diagnostics/ ><code>JSON_DIAGNOSTICS</code></a> the exception names the <abbr title="JavaScript Object Notation">JSON</abbr> Pointer path of the value within the document, and with <a href=../../macros/json_diagnostic_positions/ ><code>JSON_DIAGNOSTIC_POSITIONS</code></a> its bytes in the source text (when <a href=../materialize/ ><code>materialize()</code></a> sets them).</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">¶</a></h2> <p>Constant.</p> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">¶</a></h2> <p><code>basic_json_view</code> has no <code>BasicJsonType</code> value stored anywhere, so unlike <code>BasicJsonType</code>, it has no <code>get_ref()</code> to hand out a reference to a stored <code>string_t</code>. <code>get_string()</code> (equivalently, <a href=../get/ ><code>get<string_view_t>()</code></a>) is the zero-copy alternative: <a href=../../basic_json/get_ref/ ><code>BasicJsonType::get_ref<const string_t&>()</code></a> is its closest counterpart, except that it returns a view instead of a reference to a value that must already exist.</p> <p><code>get_string()</code> borrows the string: nothing is copied, whereas <a href=../get/ ><code>get<std::string>()</code></a> copies it. For a borrowed document, the returned <a href=../#member-types><code>string_view_t</code></a> is valid as long as the caller's buffer; for an owned one, as long as the document.</p> <p>The returned <a href=../#member-types><code>string_view_t</code></a> is valid exactly as long as the view that produced it — see the <a href=../ >validity rules</a> of <code>basic_json_view</code> — and, for a string with no escapes, for as long as the document's source text, which for a borrowed document must remain valid <strong>and unmodified</strong> for as long as the document exists, since floating-point values and unescaped strings are read from the source lazily.</p> <p>A string with escapes, a string of a document that owns its text, and an edited string must not be passed to <a href=../../basic_json_document/read/ ><code>read()</code></a> of the document it came from: <code>read()</code> releases them before it parses its input. Copy the string first. (A string read unchanged from a borrowed text is not affected.)</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">¶</a></h2> <details class=example> <summary>Example</summary> <p>The example below pulls one field out of a <abbr title="JavaScript Object Notation">JSON</abbr> text that stands in for a large <abbr title="Application Programming Interface">API</abbr> response, and shows that no <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>string</span></code> was allocated for it: the returned view still points inside the original buffer. A field that contains an escape sequence cannot point into the original text — it was decoded once into the document's own buffer instead — but still avoids a per-field allocation.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf><iostream></span>
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<span class=cp>#include</span><span class=w> </span><span class=cpf><nlohmann/json_view.hpp></span>
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<span class=cp>#include</span><span class=w> </span><span class=cpf><string></span>
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