118 lines
9.0 KiB
HTML
118 lines
9.0 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::unordered_map<Key,T,Hash,KeyEqual,Allocator>::clear</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_container_unordered_map_clear 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::unordered_map<Key,T,Hash,KeyEqual,Allocator>::</span>clear</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-unordered_map.html">unordered 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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</div>
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<table class="t-dcl-begin">
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<tbody>
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<tr class="t-dcl t-since-cxx11">
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<td>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw4">void</span> clear<span class="br0">(</span><span class="br0">)</span> <span class="kw1">noexcept</span><span class="sy4">;</span></span></div>
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</td>
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<td class="t-dcl-nopad"></td>
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<td><span class="t-mark-rev t-since-cxx11">(C++11 起)</span></td>
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</tr>
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<tr class="t-dcl-sep">
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<td></td>
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<td></td>
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<td></td>
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</tr>
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</tbody>
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</table>
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<p>从容器擦除所有元素。此调用后 <span class="t-lc"><a href="cpp-container-unordered_map-size.html">size()</a></span> 返回零。</p>
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<p>非法化任何指代所含元素的引用、指针或迭代器。可能亦非法化尾后迭代器。</p>
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<h3><span class="mw-headline" id=".E5.8F.82.E6.95.B0">参数</span></h3>
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<p>（无）</p>
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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>（无）</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，即元素数成线性。</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 <algorithm></span>
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<span class="co2">#include <iostream></span>
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<span class="co2">#include <unordered_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-unordered_map.html"><span class="kw1293">std::<span class="me2">unordered_map</span></span></a><span class="sy1"><</span><span class="kw4">int</span>, <span class="kw4">char</span><span class="sy1">></span> container<span class="br0">{</span><span class="br0">{</span><span class="nu0">1</span>, <span class="st0">'x'</span><span class="br0">}</span>, <span class="br0">{</span><span class="nu0">2</span>, <span class="st0">'y'</span><span class="br0">}</span>, <span class="br0">{</span><span class="nu0">3</span>, <span class="st0">'z'</span><span class="br0">}</span><span class="br0">}</span><span class="sy4">;</span>
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<span class="kw4">auto</span> print <span class="sy1">=</span> <span class="br0">[</span><span class="br0">]</span><span class="br0">(</span><a href="cpp-utility-pair.html"><span class="kw1096">std::<span class="me2">pair</span></span></a><span class="sy1"><</span><span class="kw4">const</span> <span class="kw4">int</span>, <span class="kw4">char</span><span class="sy1">></span><span class="sy3">&</span> n<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> <span class="st0">" "</span> <span class="sy1"><<</span> n.<span class="me1">first</span> <span class="sy1"><<</span> <span class="st0">'('</span> <span class="sy1"><<</span> n.<span class="me1">second</span> <span class="sy1"><<</span> <span class="st0">')'</span><span class="sy4">;</span>
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<span class="br0">}</span><span class="sy4">;</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> <span class="st0">"Before clear:"</span><span class="sy4">;</span>
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<a href="cpp-algorithm-for_each.html"><span class="kw1568">std::<span class="me2">for_each</span></span></a><span class="br0">(</span>container.<span class="me1">begin</span><span class="br0">(</span><span class="br0">)</span>, container.<span class="me1">end</span><span class="br0">(</span><span class="br0">)</span>, print<span class="br0">)</span><span class="sy4">;</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> <span class="st0">"<span class="es1">\n</span>Size="</span> <span class="sy1"><<</span> container.<span class="me1">size</span><span class="br0">(</span><span class="br0">)</span> <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</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> <span class="st0">"Clear<span class="es1">\n</span>"</span><span class="sy4">;</span>
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container.<span class="me1">clear</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</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> <span class="st0">"After clear:"</span><span class="sy4">;</span>
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<a href="cpp-algorithm-for_each.html"><span class="kw1568">std::<span class="me2">for_each</span></span></a><span class="br0">(</span>container.<span class="me1">begin</span><span class="br0">(</span><span class="br0">)</span>, container.<span class="me1">end</span><span class="br0">(</span><span class="br0">)</span>, print<span class="br0">)</span><span class="sy4">;</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> <span class="st0">"<span class="es1">\n</span>Size="</span> <span class="sy1"><<</span> container.<span class="me1">size</span><span class="br0">(</span><span class="br0">)</span> <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
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<span class="br0">}</span></pre></div>
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</div>
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<p>可能的输出：</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">Before clear: 1(x) 2(y) 3(z)
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Size=3
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Clear
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After clear:
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Size=0</pre></div>
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</div>
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</div>
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<h3><span class="mw-headline" id=".E7.BC.BA.E9.99.B7.E6.8A.A5.E5.91.8A">缺陷报告</span></h3>
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<p>下列更改行为的缺陷报告追溯地应用于以前出版的 C++ 标准。</p>
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<table class="dsctable" style="font-size:0.8em">
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<tr>
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<th>DR</th>
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<th>应用于</th>
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<th>出版时的行为</th>
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<th>正确行为</th>
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</tr>
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<tr>
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<td><a rel="nofollow" class="external text" href="https://cplusplus.github.io/LWG/issue2550">LWG 2550</a></td>
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<td>C++11</td>
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<td>对于无序关联容器，不清楚复杂度是与元素数还是桶数成线性</td>
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<td>辨明它与元素数成线性</td>
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</tr>
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</table>
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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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<div class="t-dsc-member-div">
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<div><a href="cpp-container-unordered_map-erase.html"><span class="t-lines"><span>erase</span></span></a></div>
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<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div>
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</div>
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</td>
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<td>擦除元素<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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</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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</div>
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</body>
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