126 lines
7.7 KiB
HTML
126 lines
7.7 KiB
HTML
<!DOCTYPE html>
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<html lang="zh" dir="ltr" class="client-nojs" xmlns="http://www.w3.org/1999/xhtml" xml:lang="zh">
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<title>std::map<Key,T,Compare,Allocator>::contains</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_container_map_contains skin-cppreference2 action-view cpp-page-template cpp-navbar">
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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::map<Key,T,Compare,Allocator>::</span>contains</h1>
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<div id="bodyContent">
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<div id="contentSub"><span class="subpages">< <a href="cpp.html">cpp</a>‎ | <a href="cpp-container.html">container</a>‎ | <a href="cpp-container-map.html">map</a></span></div>
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<div id="mw-content-text" lang="zh" dir="ltr" class="mw-content-ltr" xml:lang="zh">
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<div class="t-page-template" style="">
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<p></p>
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<table class="t-dcl-begin">
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<td>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw4">bool</span> contains<span class="br0">(</span> <span class="kw4">const</span> Key<span class="sy3">&</span> key <span class="br0">)</span> <span class="kw4">const</span><span class="sy4">;</span></span></div>
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</td>
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<td>(1)</td>
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<td><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></td>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span><span class="sy1"><</span> <span class="kw1">class</span> K <span class="sy1">></span> <span class="kw4">bool</span> contains<span class="br0">(</span> <span class="kw4">const</span> K<span class="sy3">&</span> x <span class="br0">)</span> <span class="kw4">const</span><span class="sy4">;</span></span></div>
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<td>(2)</td>
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<td><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></td>
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<div class="t-li1"><span class="t-li">1)</span> 检查容器中是否有键等价于 <code>key</code> 的元素。</div>
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<div class="t-li1"><span class="t-li">2)</span> 检查是否有键比较<i>等价</i>于值 <code>x</code> 的元素。此重载仅若有限定标识 <span class="t-c"><span class="mw-geshi cpp source-cpp">Compare<span class="sy4">::</span><span class="me2">is_transparent</span></span></span> 合法并指代类型才参与重载决议。它允许无需构造 <code>Key</code> 的实例就调用此函数。</div>
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<h3><span class="mw-headline" id=".E5.8F.82.E6.95.B0">参数</span></h3>
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<table class="t-par-begin">
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<tr class="t-par">
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<td>key</td>
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<td>-</td>
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<td>要搜索的元素键值</td>
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</tr>
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<tr class="t-par">
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<td>x</td>
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<td>-</td>
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<td>任何能通透地与键比较的类型的值</td>
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</tr>
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</table>
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<h3><span class="mw-headline" id=".E8.BF.94.E5.9B.9E.E5.80.BC">返回值</span></h3>
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<p>若有这种元素则为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">true</span></span></span> ，否则为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">false</span></span></span> 。</p>
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<h3><span class="mw-headline" id=".E5.A4.8D.E6.9D.82.E5.BA.A6">复杂度</span></h3>
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<p>与容器大小成对数。</p>
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<h3><span class="mw-headline" id=".E7.A4.BA.E4.BE.8B">示例</span></h3>
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<div class="t-example">
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<div class="t-example-live-link"></div>
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<div dir="ltr" class="mw-geshi" style="text-align: left;">
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<div class="cpp source-cpp">
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<pre class="de1"><span class="co2">#include <iostream></span>
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<span class="co2">#include <map></span>
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<span class="kw4">int</span> main<span class="br0">(</span><span class="br0">)</span>
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<span class="br0">{</span>
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<a href="cpp-container-map.html"><span class="kw1281">std::<span class="me2">map</span></span></a><span class="sy1"><</span><span class="kw4">int</span>,<span class="kw4">char</span><span class="sy1">></span> example <span class="sy1">=</span> <span class="br0">{</span><span class="br0">{</span><span class="nu0">1</span>,<span class="st0">'a'</span><span class="br0">}</span>,<span class="br0">{</span><span class="nu0">2</span>,<span class="st0">'b'</span><span class="br0">}</span><span class="br0">}</span><span class="sy4">;</span>
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<span class="kw1">for</span><span class="br0">(</span><span class="kw4">int</span> x<span class="sy4">:</span> <span class="br0">{</span><span class="nu0">2</span>, <span class="nu0">5</span><span class="br0">}</span><span class="br0">)</span> <span class="br0">{</span>
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<span class="kw1">if</span><span class="br0">(</span>example.<span class="me1">contains</span><span class="br0">(</span>x<span class="br0">)</span><span class="br0">)</span> <span class="br0">{</span>
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<a href="cpp-io-cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> x <span class="sy1"><<</span> <span class="st0">": Found<span class="es1">\n</span>"</span><span class="sy4">;</span>
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<span class="br0">}</span> <span class="kw1">else</span> <span class="br0">{</span>
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<a href="cpp-io-cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> x <span class="sy1"><<</span> <span class="st0">": Not found<span class="es1">\n</span>"</span><span class="sy4">;</span>
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<span class="br0">}</span>
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<span class="br0">}</span>
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<span class="br0">}</span></pre></div>
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</div>
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<p>输出：</p>
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<div dir="ltr" class="mw-geshi" style="text-align: left;">
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<div class="text source-text">
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<pre class="de1">2: Found
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5: Not found</pre></div>
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</div>
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</div>
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<h3><span class="mw-headline" id=".E5.8F.82.E9.98.85">参阅</span></h3>
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<table class="t-dsc-begin">
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<tr class="t-dsc">
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<td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-container-map-find.html"><span class="t-lines"><span>find</span></span></a></div>
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</div>
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</td>
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<td>寻找带有特定键的元素<br />
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<span class="t-mark">(公开成员函数)</span></td>
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</tr>
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<tr class="t-dsc">
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<td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-container-map-count.html"><span class="t-lines"><span>count</span></span></a></div>
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</div>
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</td>
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<td>返回匹配特定键的元素数量<br />
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<span class="t-mark">(公开成员函数)</span></td>
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</tr>
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<tr class="t-dsc">
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<td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-container-map-equal_range.html"><span class="t-lines"><span>equal_range</span></span></a></div>
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</div>
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</td>
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<td>返回匹配特定键的元素范围<br />
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<span class="t-mark">(公开成员函数)</span></td>
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</tr>
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</table>
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</div>
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<div class="visualClear"></div>
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</div>
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</div>
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</body>
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