106 lines
8.3 KiB
HTML
106 lines
8.3 KiB
HTML
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<title>std::enable_shared_from_this<T>::operator=</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_memory_enable_shared_from_this_operator skin-cppreference2 action-view cpp-navbar">
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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::enable_shared_from_this<T>::</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-memory.html">memory</a>‎ | <a href="cpp-memory-enable_shared_from_this.html">enable shared from this</a></span></div>
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<div><span class="mw-geshi cpp source-cpp">enable_shared_from_this<span class="sy1"><</span>T<span class="sy1">></span><span class="sy3">&</span> operator<span class="sy1">=</span><span class="br0">(</span> <span class="kw4">const</span> enable_shared_from_this<span class="sy1"><</span>T<span class="sy1">></span> <span class="sy3">&</span>obj <span class="br0">)</span> <span class="kw1">noexcept</span><span class="sy4">;</span></span></div>
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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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<td></td>
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<td></td>
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<td></td>
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<p>不做任何事；返回 <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=".E5.8F.82.E6.95.B0">参数</span></h3>
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<td>obj</td>
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<td>-</td>
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<td>赋值给 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">*</span>this</span></span> 的 <code>enable_shared_from_this</code></td>
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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=".E6.B3.A8.E6.84.8F">注意</span></h3>
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<p>私有的 <span class="t-lc">std::weak_ptr<T></span> 成员不受此赋值运算符影响。</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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<p>注意：定义 <span class="t-c"><span class="mw-geshi cpp source-cpp">enable_shared_from_this<span class="sy4">::</span><span class="me2">operator</span><span class="sy1">=</span></span></span> 为受保护以避免意外切片，但允许导出类拥有默认的赋值运算符。</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 <memory></span>
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<span class="co2">#include <iostream></span>
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<span class="kw1">class</span> SharedInt <span class="sy4">:</span> <span class="kw1">public</span> <a href="cpp-memory-enable_shared_from_this.html"><span class="kw744">std::<span class="me2">enable_shared_from_this</span></span></a><span class="sy1"><</span>SharedInt<span class="sy1">></span>
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<span class="br0">{</span>
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<span class="kw1">public</span><span class="sy4">:</span>
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<span class="kw1">explicit</span> SharedInt<span class="br0">(</span><span class="kw4">int</span> n<span class="br0">)</span> <span class="sy4">:</span> mNumber<span class="br0">(</span>n<span class="br0">)</span> <span class="br0">{</span><span class="br0">}</span>
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SharedInt<span class="br0">(</span><span class="kw4">const</span> SharedInt<span class="sy3">&</span><span class="br0">)</span> <span class="sy1">=</span> <span class="kw1">default</span><span class="sy4">;</span>
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SharedInt<span class="br0">(</span>SharedInt<span class="sy3">&&</span><span class="br0">)</span> <span class="sy1">=</span> <span class="kw1">default</span><span class="sy4">;</span>
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~SharedInt<span class="br0">(</span><span class="br0">)</span> <span class="sy1">=</span> <span class="kw1">default</span><span class="sy4">;</span>
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<span class="co1">// 两个赋值运算符都使用 enable_shared_from_this::operator=</span>
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SharedInt<span class="sy3">&</span> operator<span class="sy1">=</span><span class="br0">(</span><span class="kw4">const</span> SharedInt<span class="sy3">&</span><span class="br0">)</span> <span class="sy1">=</span> <span class="kw1">default</span><span class="sy4">;</span>
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SharedInt<span class="sy3">&</span> operator<span class="sy1">=</span><span class="br0">(</span>SharedInt<span class="sy3">&&</span><span class="br0">)</span> <span class="sy1">=</span> <span class="kw1">default</span><span class="sy4">;</span>
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<span class="kw4">int</span> number<span class="br0">(</span><span class="br0">)</span> <span class="kw4">const</span> <span class="br0">{</span> <span class="kw1">return</span> mNumber<span class="sy4">;</span> <span class="br0">}</span>
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<span class="kw1">private</span><span class="sy4">:</span>
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<span class="kw4">int</span> mNumber<span class="sy4">;</span>
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<span class="br0">}</span><span class="sy4">;</span>
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<span class="kw4">int</span> main<span class="br0">(</span><span class="br0">)</span> <span class="br0">{</span>
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<a href="cpp-memory-shared_ptr.html"><span class="kw734">std::<span class="me2">shared_ptr</span></span></a><span class="sy1"><</span>SharedInt<span class="sy1">></span> a <span class="sy1">=</span> <a href="cpp-memory-shared_ptr-make_shared.html"><span class="kw736">std::<span class="me2">make_shared</span></span></a><span class="sy1"><</span>SharedInt<span class="sy1">></span><span class="br0">(</span><span class="nu0">2</span><span class="br0">)</span><span class="sy4">;</span>
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<a href="cpp-memory-shared_ptr.html"><span class="kw734">std::<span class="me2">shared_ptr</span></span></a><span class="sy1"><</span>SharedInt<span class="sy1">></span> b <span class="sy1">=</span> <a href="cpp-memory-shared_ptr-make_shared.html"><span class="kw736">std::<span class="me2">make_shared</span></span></a><span class="sy1"><</span>SharedInt<span class="sy1">></span><span class="br0">(</span><span class="nu0">4</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="sy2">*</span>a <span class="sy1">=</span> <span class="sy2">*</span>b<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> a<span class="sy2">-</span><span class="sy1">></span>number<span class="br0">(</span><span class="br0">)</span> <span class="sy1"><<</span> <a href="cpp-io-manip-endl.html"><span class="kw1791">std::<span class="me2">endl</span></span></a><span class="sy4">;</span>
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<span class="br0">}</span></pre></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">4</pre></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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<div class="t-dsc-member-div">
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<div><a href="cpp-memory-shared_ptr.html"><span class="t-lines"><span>shared_ptr</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>拥有共享对象所有权语义的智能指针<br />
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<span class="t-mark">(类模板)</span></td>
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