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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/api/basic_json/find/" rel="canonical"><link href=../exception/ rel=prev><link href=../flatten/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>find - 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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<!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/api/basic_json/find/" rel="canonical"><link href=../exception/ rel=prev><link href=../flatten/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>find - 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 URL("../../..",location),__md_hash=e=>[...e].reduce(((e,_)=>(e<<5)-e+_.charCodeAt(0)),0),__md_get=(e,_=localStorage,t=__md_scope)=>JSON.parse(_.getItem(t.pathname+"."+e)),__md_set=(e,_,t=localStorage,a=__md_scope)=>{try{t.setItem(a.pathname+"."+e,JSON.stringify(_))}catch(e){}}</script></head> <body dir=ltr data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo> <input class=md-toggle data-md-toggle=drawer type=checkbox id=__drawer autocomplete=off> <input class=md-toggle data-md-toggle=search type=checkbox id=__search autocomplete=off> <label class=md-overlay for=__drawer></label> <div data-md-component=skip> <a href=#nlohmannbasic_jsonfind class=md-skip> Skip to 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> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> find </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark mode" 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<span class=n>iterator</span><span class=w> </span><span class=nf>find</span><span class=p>(</span><span class=k>const</span><span class=w> </span><span class=k>typename</span><span class=w> </span><span class=nc>object_t</span><span class=o>::</span><span class=n>key_type</span><span class=o>&amp;</span><span class=w> </span><span class=n>key</span><span class=p>);</span>
<span class=n>const_iterator</span><span class=w> </span><span class=nf>find</span><span class=p>(</span><span class=k>const</span><span class=w> </span><span class=k>typename</span><span class=w> </span><span class=nc>object_t</span><span class=o>::</span><span class=n>key_type</span><span class=o>&amp;</span><span class=w> </span><span class=n>key</span><span class=p>)</span><span class=w> </span><span class=k>const</span><span class=p>;</span>
@@ -16,7 +16,7 @@
</code></pre></div> <ol> <li>Finds an element in a <abbr title="JavaScript Object Notation">JSON</abbr> object with a key equivalent to <code>key</code>. If the element is not found or the <abbr title="JavaScript Object Notation">JSON</abbr> value is not an object, <code>end()</code> is returned.</li> <li>See 1. This overload is only available if <code>KeyType</code> is comparable with <code class=highlight><span class=k>typename</span><span class=w> </span><span class=nc>object_t</span><span class=o>::</span><span class=n>key_type</span></code> and <code class=highlight><span class=k>typename</span><span class=w> </span><span class=nc>object_comparator_t</span><span class=o>::</span><span class=n>is_transparent</span></code> denotes a type.</li> <li>Deleted: this overload is only available if <code>T</code> is an integral type and is declared as deleted, so that a call with an integer <code>key</code> (for example, <code class=highlight><span class=n>j</span><span class=p>.</span><span class=n>find</span><span class=p>(</span><span class=mi>0</span><span class=p>)</span></code>) fails to compile. Otherwise, the integer literal <code>0</code> would convert to a null <code class=highlight><span class=k>const</span><span class=w> </span><span class=kt>char</span><span class=o>*</span></code> and, from there, to the key type, causing undefined behavior at runtime.</li> </ol> <h2 id=template-parameters>Template parameters<a class=headerlink href=#template-parameters title="Permanent link">&para;</a></h2> <dl> <dt><code>KeyType</code></dt> <dd>A type for an object key other than <a href=../../json_pointer/ ><code>json_pointer</code></a> that is comparable with <a href=../string_t/ ><code>string_t</code></a> using <a href=../object_comparator_t/ ><code>object_comparator_t</code></a>. This can also be a string view (C++17).</dd> </dl> <h2 id=parameters>Parameters<a class=headerlink href=#parameters title="Permanent link">&para;</a></h2> <dl> <dt><code>key</code> (in)</dt> <dd>key value of the element to search for.</dd> </dl> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <p>Iterator to an element with a key equivalent to <code>key</code>. If no such element is found or the <abbr title="JavaScript Object Notation">JSON</abbr> value is not an object, a past-the-end iterator (see <code>end()</code>) is returned.</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">&para;</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">&para;</a></h2> <p>Logarithmic in the size of the <abbr title="JavaScript Object Notation">JSON</abbr> object.</p> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <ul> <li>This method always returns <code>end()</code> when executed on a <abbr title="JavaScript Object Notation">JSON</abbr> type that is not an object.</li> <li>Calling this function with an integer argument (for example, <code class=highlight><span class=n>find</span><span class=p>(</span><span class=mi>0</span><span class=p>)</span></code>) does not compile: such an argument would otherwise implicitly convert to a null <code class=highlight><span class=k>const</span><span class=w> </span><span class=kt>char</span><span class=o>*</span></code> and, from there, cause undefined behavior when constructing a <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>string</span></code> for the object key. To access an array element instead, use <a href=../at/ ><code>at</code></a>, <a href=../operator%5B%5D/ ><code>operator[]</code></a>, or compare against <a href=../size/ ><code>size</code></a>.</li> </ul> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example: (1) find object element by key</summary> <p>The example shows how <code>find()</code> is used.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<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>
<span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span>
<span class=p>{</span>
@@ -41,7 +41,7 @@
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=k>namespace</span><span class=w> </span><span class=nn>std</span><span class=o>::</span><span class=nn>string_view_literals</span><span class=p>;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<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>
<span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span>
<span class=p>{</span>
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@@ -57,7 +57,7 @@ The example shows how `find()` is used.
#include <iostream>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using nlohmann::json;
int main()
{
@@ -94,7 +94,7 @@ The example shows how `find()` is used.
#include <nlohmann/json.hpp>
using namespace std::string_view_literals;
using json = nlohmann::json;
using nlohmann::json;
int main()
{