204 lines
14 KiB
HTML
204 lines
14 KiB
HTML
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<title>std::multimap<Key,T,Compare,Allocator>::erase</title>
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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::multimap<Key,T,Compare,Allocator>::</span>erase</h1>
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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-multimap.html">multimap</a></span></div>
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<p></p>
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<td rowspan="142">(1)</td>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw4">void</span> erase<span class="br0">(</span> iterator pos <span class="br0">)</span><span class="sy4">;</span></span></div>
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<td><span class="t-mark-rev t-until-cxx11">(C++11 前)</span></td>
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<div><span class="mw-geshi cpp source-cpp">iterator erase<span class="br0">(</span> iterator pos <span class="br0">)</span><span class="sy4">;</span></span></div>
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<td><span class="t-mark-rev t-since-cxx11">(C++11 起)</span></td>
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<div><span class="mw-geshi cpp source-cpp">iterator erase<span class="br0">(</span> const_iterator pos <span class="br0">)</span><span class="sy4">;</span></span></div>
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<td><span class="t-mark-rev t-since-cxx11">(C++11 起)</span></td>
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<td rowspan="142">(2)</td>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw4">void</span> erase<span class="br0">(</span> iterator first, iterator last <span class="br0">)</span><span class="sy4">;</span></span></div>
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<td><span class="t-mark-rev t-until-cxx11">(C++11 前)</span></td>
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<div><span class="mw-geshi cpp source-cpp">iterator erase<span class="br0">(</span> const_iterator first, const_iterator last <span class="br0">)</span><span class="sy4">;</span></span></div>
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<td><span class="t-mark-rev t-since-cxx11">(C++11 起)</span></td>
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<div><span class="mw-geshi cpp source-cpp">size_type erase<span class="br0">(</span> <span class="kw4">const</span> key_type<span class="sy3">&</span> key <span class="br0">)</span><span class="sy4">;</span></span></div>
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<td>(3)</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><br />
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size_type erase<span class="br0">(</span> K<span class="sy3">&&</span> x <span class="br0">)</span><span class="sy4">;</span></span></div>
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<td>(4)</td>
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<td><span class="t-mark-rev t-since-cxx23">(C++23 起)</span></td>
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<td></td>
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<p>从容器移除指定的元素。</p>
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<div class="t-li1"><span class="t-li">1)</span> 移除位于 <code>pos</code> 的元素。</div>
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<div class="t-li1"><span class="t-li">2)</span> 移除范围 <code>[first; last)</code> 中的元素，它必须是 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">*</span>this</span></span> 中的合法范围。</div>
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<div class="t-li1"><span class="t-li">3)</span> 移除键等价于 <code>key</code> 的所有元素。</div>
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<div class="t-li1"><span class="t-li">4)</span> 移除键比较<i>等价</i>于值 x 的所有元素。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，且 <code>iterator</code> 与 <code>const_iterator</code> 均不可从 <code>K</code> 隐式转换才参与重载决议。它允许无需构造 <code>Key</code> 的实例就调用此函数。</div>
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<p>指向被擦除元素的引用和迭代器被非法化。其他引用和迭代器不受影响。</p>
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<p>迭代器 <code>pos</code> 必须合法且可解引用。从而 <span class="t-lc"><a href="cpp-container-multimap-end.html">end()</a></span> 迭代器（合法，但不可解引用）不能用作 <code>pos</code> 所用的值。</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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<table class="t-par-begin">
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<td>pos</td>
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<td>-</td>
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<td>指向要移除的元素的迭代器</td>
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</tr>
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<tr class="t-par">
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<td>first, last</td>
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<td>-</td>
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<td>要移除的元素范围</td>
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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>要移除的元素键值</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>任何能与键通透比较的类型的值，指代要移除的元素</td>
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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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<div class="t-li1"><span class="t-li">1-2)</span> <span class="t-rev-inl t-until-cxx11"><span>（无）</span> <span><span class="t-mark-rev t-until-cxx11">(C++11 前)</span></span></span><span class="t-rev-inl t-since-cxx11"><span>后随最后被移除的元素的迭代器。</span> <span><span class="t-mark-rev t-since-cxx11">(C++11 起)</span></span></span></div>
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<div class="t-li1"><span class="t-li">3,4)</span> 被移除的元素数。</div>
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<h3><span class="mw-headline" id=".E5.BC.82.E5.B8.B8">异常</span></h3>
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<div class="t-li1"><span class="t-li">1,2)</span> 不抛出</div>
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<div class="t-li1"><span class="t-li">3,4)</span> 任何 <code>Compare</code> 对象所抛的异常</div>
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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>给定 <code>multimap</code> 的实例 <code>c</code> ：</p>
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<div class="t-li1"><span class="t-li">1)</span> 均摊常数</div>
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<div class="t-li1"><span class="t-li">2)</span> <span class="t-c"><span class="mw-geshi cpp source-cpp">log<span class="br0">(</span>c.<span class="me1">size</span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span> <span class="sy2">+</span> <a href="cpp-iterator-distance.html"><span class="kw673">std::<span class="me2">distance</span></span></a><span class="br0">(</span>first, last<span class="br0">)</span></span></span></div>
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<div class="t-li1"><span class="t-li">3)</span> <span class="t-c"><span class="mw-geshi cpp source-cpp">log<span class="br0">(</span>c.<span class="me1">size</span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span> <span class="sy2">+</span> c.<span class="me1">count</span><span class="br0">(</span>key<span class="br0">)</span></span></span></div>
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<div class="t-li1"><span class="t-li">4)</span> <span class="t-c"><span class="mw-geshi cpp source-cpp">log<span class="br0">(</span>c.<span class="me1">size</span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span> <span class="sy2">+</span> c.<span class="me1">count</span><span class="br0">(</span>x<span class="br0">)</span></span></span></div>
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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 <map></span>
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<span class="co2">#include <iostream></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-multimap.html"><span class="kw1285">std::<span class="me2">multimap</span></span></a><span class="sy1"><</span><span class="kw4">int</span>, <a href="cpp-string-basic_string.html"><span class="kw1230">std::<span class="me2">string</span></span></a><span class="sy1">></span> c <span class="sy1">=</span> <span class="br0">{</span>
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<span class="br0">{</span><span class="nu0">1</span>, <span class="st0">"one"</span> <span class="br0">}</span>, <span class="br0">{</span><span class="nu0">2</span>, <span class="st0">"two"</span> <span class="br0">}</span>, <span class="br0">{</span><span class="nu0">3</span>, <span class="st0">"three"</span><span class="br0">}</span>,
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<span class="br0">{</span><span class="nu0">4</span>, <span class="st0">"four"</span><span class="br0">}</span>, <span class="br0">{</span><span class="nu0">5</span>, <span class="st0">"five"</span><span class="br0">}</span>, <span class="br0">{</span><span class="nu0">6</span>, <span class="st0">"six"</span> <span class="br0">}</span>
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<span class="br0">}</span><span class="sy4">;</span>
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<span class="co1">// 从 c 擦除所有奇数</span>
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<span class="kw1">for</span><span class="br0">(</span><span class="kw4">auto</span> it <span class="sy1">=</span> c.<span class="me1">begin</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span> it <span class="sy3">!</span><span class="sy1">=</span> c.<span class="me1">end</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span> <span class="br0">)</span> <span class="br0">{</span>
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<span class="kw1">if</span><span class="br0">(</span>it<span class="sy2">-</span><span class="sy1">></span>first <span class="sy2">%</span> <span class="nu0">2</span> <span class="sy3">!</span><span class="sy1">=</span> <span class="nu0">0</span><span class="br0">)</span>
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it <span class="sy1">=</span> c.<span class="me1">erase</span><span class="br0">(</span>it<span class="br0">)</span><span class="sy4">;</span>
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<span class="kw1">else</span>
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<span class="sy2">++</span>it<span class="sy4">;</span>
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<span class="br0">}</span>
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<span class="kw1">for</span><span class="br0">(</span><span class="kw4">auto</span><span class="sy3">&</span> p <span class="sy4">:</span> c<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> p.<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>
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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">two four six</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/issue2059">LWG 2059</a></td>
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<td>C++11</td>
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<td>对一个 <code>const_iterator</code> 的重载引入了新的歧义</td>
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<td>添加了对 <code>iterator</code> 的重载</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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<td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-container-multimap-clear.html"><span class="t-lines"><span>clear</span></span></a></div>
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</div>
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</td>
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<td>清除内容<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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