81 lines
6.0 KiB
HTML
81 lines
6.0 KiB
HTML
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<title>std::basic_ostream<CharT,Traits>::operator=</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_io_basic_ostream_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::basic_ostream<CharT,Traits>::</span>operator=</h1>
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<div id="contentSub"><span class="subpages">< <a href="cpp.html">cpp</a>‎ | <a href="cpp-io.html">io</a>‎ | <a href="cpp-io-basic_ostream.html">basic ostream</a></span></div>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">protected</span><span class="sy4">:</span><br />
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basic_ostream<span class="sy3">&</span> operator<span class="sy1">=</span><span class="br0">(</span> <span class="kw4">const</span> basic_ostream<span class="sy3">&</span> rhs <span class="br0">)</span> <span class="sy1">=</span> delete<span class="sy4">;</span></span></div>
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<td>(1)</td>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">protected</span><span class="sy4">:</span><br />
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basic_ostream<span class="sy3">&</span> operator<span class="sy1">=</span><span class="br0">(</span> basic_ostream<span class="sy3">&&</span> rhs <span class="br0">)</span><span class="sy4">;</span></span></div>
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<td>(2)</td>
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<td><span class="t-mark-rev t-since-cxx11">(C++11 起)</span></td>
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<p>1) 复制赋值运算符为被保护，企鹅杯删除。输出流不<a href="cpp-named_req-CopyAssignable.html"><span style="font-style:italic">可复制赋值</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(CopyAssignable)</span></a> 。</p>
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<p>2) 移动赋值运算符如同以调用 <span class="t-c"><span class="mw-geshi cpp source-cpp">swap<span class="br0">(</span><span class="sy2">*</span>rhs<span class="br0">)</span></span></span> 与 <code>rhs</code> 交换基类的所有数据成员，除了 <code>rdbuf()</code> 。此移动赋值运算符为受保护：它只为导出可移动输出流类 <span class="t-lc"><a href="cpp-io-basic_ofstream.html">std::basic_ofstream</a></span> 和 <span class="t-lc"><a href="cpp-io-basic_ostringstream.html">std::basic_ostringstream</a></span> 的移动赋值运算符所调用，它们知道如何正确移动赋值关联的流缓冲。</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>rhs</td>
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<td>-</td>
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<td>要赋值给 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">*</span>this</span></span> 的 basic_ostream 对象</td>
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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="cpp source-cpp">
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<pre class="de1"><span class="co2">#include <sstream></span>
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<span class="co2">#include <utility></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-io-basic_ostringstream.html"><span class="kw1736">std::<span class="me2">ostringstream</span></span></a> s<span class="sy4">;</span>
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<span class="co1">// std::cout = s; // 错误：复制赋值运算符被删除</span>
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<span class="co1">// std::cout = std::move(s); // 错误：移动赋值运算符为受保护</span>
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s <span class="sy1">=</span> std<span class="sy4">::</span><span class="me2">move</span><span class="br0">(</span><a href="cpp-io-basic_ostringstream.html"><span class="kw1736">std::<span class="me2">ostringstream</span></span></a><span class="br0">(</span><span class="br0">)</span> <span class="sy1"><<</span> <span class="nu0">42</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// OK ：通过导出类移动</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> s.<span class="me1">str</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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<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">42</pre></div>
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