156 lines
13 KiB
HTML
156 lines
13 KiB
HTML
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<title>std::erase, std::erase_if (std::list)</title>
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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::</span>erase, <span style="font-size:0.7em; line-height:130%">std::</span>erase_if <small>(std::list)</small></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-list.html">list</a></span></div>
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<p></p>
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<div>定义于头文件 <code><a href="cpp-header-list.html"><list></a></code></div>
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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> T, <span class="kw1">class</span> Alloc, <span class="kw1">class</span> U <span class="sy1">></span><br /></span>
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<p><span class="kw1">typename</span> <a href="cpp-container-list.html"><span class="kw1275">std::<span class="me2">list</span></span></a><span class="sy1"><</span>T,Alloc<span class="sy1">></span><span class="sy4">::</span><span class="me2">size_type</span><br /></p>
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erase<span class="br0">(</span><a href="cpp-container-list.html"><span class="kw1275">std::<span class="me2">list</span></span></a><span class="sy1"><</span>T,Alloc<span class="sy1">></span><span class="sy3">&</span> c, <span class="kw4">const</span> U<span class="sy3">&</span> value<span class="br0">)</span><span class="sy4">;</span></div>
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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> T, <span class="kw1">class</span> Alloc, <span class="kw1">class</span> Pred <span class="sy1">></span><br /></span>
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<p><span class="kw1">typename</span> <a href="cpp-container-list.html"><span class="kw1275">std::<span class="me2">list</span></span></a><span class="sy1"><</span>T,Alloc<span class="sy1">></span><span class="sy4">::</span><span class="me2">size_type</span><br /></p>
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erase_if<span class="br0">(</span><a href="cpp-container-list.html"><span class="kw1275">std::<span class="me2">list</span></span></a><span class="sy1"><</span>T,Alloc<span class="sy1">></span><span class="sy3">&</span> c, Pred pred<span class="br0">)</span><span class="sy4">;</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> 从容器中擦除所有比较等于 <code>value</code> 的元素。等价于 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw1">return</span> c.<span class="me1">remove_if</span><span class="br0">(</span><span class="br0">[</span><span class="sy3">&</span><span class="br0">]</span><span class="br0">(</span><span class="kw4">auto</span><span class="sy3">&</span> elem<span class="br0">)</span> <span class="br0">{</span> <span class="kw1">return</span> elem <span class="sy1">==</span> value<span class="sy4">;</span> <span class="br0">}</span><span class="br0">)</span><span class="sy4">;</span></span></span> 。</div>
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<div class="t-li1"><span class="t-li">2)</span> 从容器中擦除所有满足 <code>pred</code> 的元素。等价于 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw1">return</span> c.<span class="me1">remove_if</span><span class="br0">(</span>pred<span class="br0">)</span><span class="sy4">;</span></span></span> 。</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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<td>c</td>
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<td>-</td>
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<td>要从中擦除的容器</td>
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<tr class="t-par">
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<td>value</td>
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<td>-</td>
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<td>要擦除的值</td>
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<tr class="t-par">
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<td>pred</td>
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<td>-</td>
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<td>若应该擦除元素则返回 ​<span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">true</span></span></span> 的一元谓词。<br />
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<p>对每个（可为 const 的） <code>T</code> 类型参数 <code>v</code> ，表达式 <span class="t-c"><span class="mw-geshi cpp source-cpp">pred<span class="br0">(</span>v<span class="br0">)</span></span></span> 必须可转换为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">bool</span></span></span> ，无关乎<a href="cpp-language-value_category.html">值类别</a>，而且必须不修改 <code>v</code> 。从而不允许 <span class="t-c"><span class="mw-geshi cpp source-cpp">T<span class="sy3">&</span></span></span> 类型参数<span class="t-rev-inl t-since-cxx11"><span>，亦不允许 <span class="t-c"><span class="mw-geshi cpp source-cpp">T</span></span> ，除非对 <code>T</code> 而言移动等价于复制</span> <span><span class="t-mark-rev t-since-cxx11">(C++11 起)</span></span></span>。 ​</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>被擦除的元素数。</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>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 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 <numeric></span>
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<span class="co2">#include <list></span>
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<span class="kw4">void</span> print_container<span class="br0">(</span><span class="kw4">const</span> <a href="cpp-container-list.html"><span class="kw1275">std::<span class="me2">list</span></span></a><span class="sy1"><</span><span class="kw4">char</span><span class="sy1">></span><span class="sy3">&</span> c<span class="br0">)</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> x <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> x <span class="sy1"><<</span> <span class="st0">' '</span><span class="sy4">;</span>
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<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 class="es1">\n</span>'</span><span class="sy4">;</span>
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<span class="br0">}</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-list.html"><span class="kw1275">std::<span class="me2">list</span></span></a><span class="sy1"><</span><span class="kw4">char</span><span class="sy1">></span> cnt<span class="br0">(</span><span class="nu0">10</span><span class="br0">)</span><span class="sy4">;</span>
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<a href="cpp-algorithm-iota.html"><span class="kw1655">std::<span class="me2">iota</span></span></a><span class="br0">(</span>cnt.<span class="me1">begin</span><span class="br0">(</span><span class="br0">)</span>, cnt.<span class="me1">end</span><span class="br0">(</span><span class="br0">)</span>, <span class="st0">'0'</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">"Init:<span class="es1">\n</span>"</span><span class="sy4">;</span>
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print_container<span class="br0">(</span>cnt<span class="br0">)</span><span class="sy4">;</span>
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<span class="kw4">auto</span> erased <span class="sy1">=</span> std<span class="sy4">::</span><span class="me2">erase</span><span class="br0">(</span>cnt, <span class="st0">'3'</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">"Erase <span class="es1">\'</span>3<span class="es1">\'</span>:<span class="es1">\n</span>"</span><span class="sy4">;</span>
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print_container<span class="br0">(</span>cnt<span class="br0">)</span><span class="sy4">;</span>
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std<span class="sy4">::</span><span class="me2">erase_if</span><span class="br0">(</span>cnt, <span class="br0">[</span><span class="br0">]</span><span class="br0">(</span><span class="kw4">char</span> x<span class="br0">)</span> <span class="br0">{</span> <span class="kw1">return</span> <span class="br0">(</span>x <span class="sy2">-</span> <span class="st0">'0'</span><span class="br0">)</span> <span class="sy2">%</span> <span class="nu0">2</span> <span class="sy1">==</span> <span class="nu0">0</span><span class="sy4">;</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">"Erase all even numbers:<span class="es1">\n</span>"</span><span class="sy4">;</span>
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print_container<span class="br0">(</span>cnt<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">"In all "</span> <span class="sy1"><<</span> erased <span class="sy1"><<</span> <span class="st0">" even numbers were erased.<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>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">Init:
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0 1 2 3 4 5 6 7 8 9
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Erase '3':
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0 1 2 4 5 6 7 8 9
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Erase all even numbers:
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1 5 7 9
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In all 5 even numbers were erased.</pre></div>
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</div>
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</div>
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<h3><span class="mw-headline" id=".E6.B3.A8.E8.A7.A3">注解</span></h3>
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<p>不同于 <span class="t-lc"><a href="cpp-container-list-remove.html">std::list::remove</a></span> ， <code>erase</code> 接受异种类型并且不强制在调用 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy1">==</span></span></span> 运算符前转换到容器的值类型。</p>
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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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<div class="t-dsc-member-div">
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<div><a href="cpp-algorithm-remove.html"><span class="t-lines"><span>remove</span><span>remove_if</span></span></a></div>
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</div>
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</td>
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<td>移除满足特定判别标准的元素<br />
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<span class="t-mark">(函数模板)</span></td>
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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-list-remove.html"><span class="t-lines"><span>remove</span><span>remove_if</span></span></a></div>
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</div>
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</td>
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<td>移除满足特定标准的元素<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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</table>
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</div>
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<div class="visualClear"></div>
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</div>
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