202 lines
18 KiB
HTML
202 lines
18 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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<head><meta http-equiv="x-ua-compatible" content="ie=edge">
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
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<title>std::list<T,Allocator>::operator=</title>
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<link rel="stylesheet" href="ext.css" />
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<link rel="stylesheet" href="site_modules.css" />
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</head>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_container_list_operator skin-cppreference2 action-view cpp-page-template cpp-navbar">
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<div id="cpp-content-base">
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<div id="content"><a id="top"></a>
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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::list<T,Allocator>::</span>operator=</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-list.html">list</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-cxx98">
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<td>
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<div><span class="mw-geshi cpp source-cpp">list<span class="sy3">&</span> operator<span class="sy1">=</span><span class="br0">(</span> <span class="kw4">const</span> list<span class="sy3">&</span> other <span class="br0">)</span><span class="sy4">;</span></span></div>
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</td>
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<td>(1)</td>
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<td class="t-dcl-nopad"></td>
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</tr>
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</tbody>
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<tbody class="t-dcl-rev t-dcl-rev-num">
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<tr class="t-dcl-rev-aux">
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<td></td>
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<td rowspan="142">(2)</td>
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<td></td>
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</tr>
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<tr class="t-dcl t-since-cxx11 t-until-cxx17">
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<td>
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<div><span class="mw-geshi cpp source-cpp">list<span class="sy3">&</span> operator<span class="sy1">=</span><span class="br0">(</span> list<span class="sy3">&&</span> other <span class="br0">)</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><br />
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<span class="t-mark-rev t-until-cxx17">(C++17 前)</span></td>
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</tr>
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<tr class="t-dcl t-since-cxx17">
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<td>
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<div><span class="mw-geshi cpp source-cpp">list<span class="sy3">&</span> operator<span class="sy1">=</span><span class="br0">(</span> list<span class="sy3">&&</span> other <span class="br0">)</span> <span class="kw1">noexcept</span><span class="br0">(</span><span class="coMULTI">/* see below */</span><span class="br0">)</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-cxx17">(C++17 起)</span></td>
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</tr>
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</tbody>
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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">list<span class="sy3">&</span> operator<span class="sy1">=</span><span class="br0">(</span> <a href="cpp-utility-initializer_list.html"><span class="kw960">std::<span class="me2">initializer_list</span></span></a><span class="sy1"><</span>T<span class="sy1">></span> ilist <span class="br0">)</span><span class="sy4">;</span></span></div>
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</td>
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<td>(3)</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>替换容器内容。</p>
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<div class="t-li1"><span class="t-li">1)</span> 复制赋值运算符。以 <code>other</code> 的副本替换内容。
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<table class="t-rev-begin">
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<tr class="t-rev t-since-cxx11">
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<td>
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<p>若 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-memory-allocator_traits.html"><span class="kw701">std::<span class="me2">allocator_traits</span></span></a><span class="sy1"><</span>allocator_type<span class="sy1">></span><span class="sy4">::</span><span class="me2">propagate_on_container_copy_assignment</span><span class="sy4">::</span><span class="me2">value</span></span></span> 为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">true</span></span></span> ，则用 <code>other</code> 的分配器的副本替换 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">*</span>this</span></span> 的分配器。若 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">*</span>this</span></span> 的分配器在赋值后将与其旧值比较不相等，则用旧分配器解分配内存，然后在复制元素前用新分配器分配内存。否则，在可行时可能复用 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">*</span>this</span></span> 所拥有的内存。任何情况下，原属于 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">*</span>this</span></span> 的元素要么被销毁，要么被逐元素复制赋值替换。</p>
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</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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</table>
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</div>
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<div class="t-li1"><span class="t-li">2)</span> 移动赋值运算符。用移动语义以 <code>other</code> 的内容替换内容（即从 <code>other</code> 移动 <code>other</code> 中的数据到此容器中）。之后 <code>other</code> 在合法但未指定的状态。</div>
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<div class="t-li1"><span class="t-li"></span> 若 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-memory-allocator_traits.html"><span class="kw701">std::<span class="me2">allocator_traits</span></span></a><span class="sy1"><</span>allocator_type<span class="sy1">></span><span class="sy4">::</span><span class="me2">propagate_on_container_move_assignment</span><span class="sy4">::</span><span class="me2">value</span></span></span> 为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">true</span></span></span> ，则用 <code>other</code> 的分配器的副本替换 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">*</span>this</span></span> 的分配器。若它为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">false</span></span></span> 且 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">*</span>this</span></span> 与 <code>other</code> 的分配器不比较相等，则 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">*</span>this</span></span> 不能接管 <code>other</code> 所拥有的内存的所有权且必须单独地移动赋值每个元素，并用其自身的分配器按需分配额外内存。任何情况下，原属于 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">*</span>this</span></span> 的元素要么被销毁，要么被逐元素移动赋值替换。</div>
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<div class="t-li1"><span class="t-li">3)</span> 以 initializer_list <code>ilist</code> 所标识者替换内容。</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>other</td>
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<td>-</td>
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<td>用作数据源的另一容器</td>
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</tr>
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<tr class="t-par">
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<td>ilist</td>
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<td>-</td>
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<td>用作数据源的 initializer_list</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><span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">*</span>this</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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<div class="t-li1"><span class="t-li">1)</span> 与 <code>*this</code> 和 <code>other</code> 的大小成线性。</div>
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<div class="t-li1"><span class="t-li">2)</span> 与 <code>*this</code> 的大小成线性，除非分配器不比较相等且不传播，该情况下与 <code>*this</code> 和 <code>other</code> 的大小成线性。</div>
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<div class="t-li1"><span class="t-li">3)</span> 与 <code>*this</code> 和 <code>ilist</code> 的大小成线性。</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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<table class="t-rev-begin">
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<tr class="t-rev t-until-cxx17">
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<td>
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<p>可能抛出实现定义的异常。</p>
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</td>
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<td><span class="t-mark-rev t-until-cxx17">(C++17 前)</span></td>
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</tr>
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<tr class="t-rev t-since-cxx17">
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<td>
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<div class="t-li1"><span class="t-li">1,3)</span> 可能抛出实现定义的异常。</div>
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<div class="t-li1"><span class="t-li">2)</span>
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<div class="t-noexcept-full"><a href="cpp-language-noexcept_spec.html"><tt>noexcept</tt></a> 说明：
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<div class="t-noexcept-box"><span class="t-cc"><span class="mw-geshi cpp source-cpp"><span class="kw1">noexcept</span><span class="br0">(</span><a href="cpp-memory-allocator_traits.html"><span class="kw701">std::<span class="me2">allocator_traits</span></span></a><span class="sy1"><</span>Allocator<span class="sy1">></span><span class="sy4">::</span><span class="me2">is_always_equal</span><span class="sy4">::</span><span class="me2">value</span><span class="br0">)</span></span></span></div>
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</div>
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</div>
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</td>
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<td><span class="t-mark-rev t-since-cxx17">(C++17 起)</span></td>
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</tr>
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</table>
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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>在容器移动赋值（重载 <span class="t-v">(2)</span> ）后，除非不兼容的分配器强制逐元素移动赋值，指向 <code>other</code> 的引用及迭代器（除了尾迭代器）保持合法，但指代现于 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">*</span>this</span></span> 中的元素。当前标准由 <a rel="nofollow" class="external text" href="https://eel.is/c++draft/container.requirements.general#12">[container.requirements.general]/12</a> 中的总括陈述作出此保证，而 <a rel="nofollow" class="external text" href="https://cplusplus.github.io/LWG/issue2321">LWG 2321</a> 正在考虑更严格的保证。</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-template-editlink" style=""></div>
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<div class="t-example">
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<p>下列代码用 <code>operator=</code> 赋值一个 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-container-list.html"><span class="kw1275">std::<span class="me2">list</span></span></a></span></span> 给另一个：</p>
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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 <list></span>
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<span class="co2">#include <iostream></span>
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<span class="kw4">void</span> display_sizes<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">int</span><span class="sy1">></span><span class="sy3">&</span> nums1,
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<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">int</span><span class="sy1">></span><span class="sy3">&</span> nums2,
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<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">int</span><span class="sy1">></span><span class="sy3">&</span> nums3<span class="br0">)</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">"nums1: "</span> <span class="sy1"><<</span> nums1.<span class="me1">size</span><span class="br0">(</span><span class="br0">)</span>
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<span class="sy1"><<</span> <span class="st0">" nums2: "</span> <span class="sy1"><<</span> nums2.<span class="me1">size</span><span class="br0">(</span><span class="br0">)</span>
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<span class="sy1"><<</span> <span class="st0">" nums3: "</span> <span class="sy1"><<</span> nums3.<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>
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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">int</span><span class="sy1">></span> nums1 <span class="br0">{</span><span class="nu0">3</span>, <span class="nu0">1</span>, <span class="nu0">4</span>, <span class="nu0">6</span>, <span class="nu0">5</span>, <span class="nu0">9</span><span class="br0">}</span><span class="sy4">;</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">int</span><span class="sy1">></span> nums2<span class="sy4">;</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">int</span><span class="sy1">></span> nums3<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">"Initially:<span class="es1">\n</span>"</span><span class="sy4">;</span>
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display_sizes<span class="br0">(</span>nums1, nums2, nums3<span class="br0">)</span><span class="sy4">;</span>
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<span class="co1">// 复制赋值从 nums1 复制数据到 nums2</span>
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nums2 <span class="sy1">=</span> nums1<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 assigment:<span class="es1">\n</span>"</span><span class="sy4">;</span>
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display_sizes<span class="br0">(</span>nums1, nums2, nums3<span class="br0">)</span><span class="sy4">;</span>
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<span class="co1">// 移动赋值从 nums1 移动数据到 nums3,</span>
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<span class="co1">// 一同修改 nums1 和 nums3</span>
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nums3 <span class="sy1">=</span> std<span class="sy4">::</span><span class="me2">move</span><span class="br0">(</span>nums1<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 move assigment:<span class="es1">\n</span>"</span><span class="sy4">;</span>
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display_sizes<span class="br0">(</span>nums1, nums2, nums3<span class="br0">)</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">Initially:
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nums1: 6 nums2: 0 nums3: 0
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After assigment:
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nums1: 6 nums2: 6 nums3: 0
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After move assigment:
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nums1: 0 nums2: 6 nums3: 6</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 t-dsc-member-nobold-div">
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<div><a href="cpp-container-list-list.html"><span class="t-lines"><span>(构造函数)</span></span></a></div>
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</div>
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</td>
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<td>构造 <code>list</code><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-list-assign.html"><span class="t-lines"><span>assign</span></span></a></div>
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</div>
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</td>
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<td>将值赋给容器<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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</html>
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