75 lines
5.9 KiB
HTML
75 lines
5.9 KiB
HTML
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_concepts_copy_constructible 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::</span>copy_constructible</h1>
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<div id="contentSub"><span class="subpages">< <a href="cpp.html">cpp</a>‎ | <a href="cpp-concepts.html">concepts</a></span></div>
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<div>定义于头文件 <code><a href="cpp-header-concepts.html"><concepts></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="sy1">></span><br /></span>
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<p>concept copy_constructible <span class="sy1">=</span><br />
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std<span class="sy4">::</span><span class="me2">move_constructible</span><span class="sy1"><</span>T<span class="sy1">></span> <span class="sy3">&&</span><br />
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std<span class="sy4">::</span><span class="me2">constructible_from</span><span class="sy1"><</span>T, T<span class="sy3">&</span><span class="sy1">></span> <span class="sy3">&&</span> std<span class="sy4">::</span><span class="me2">convertible_to</span><span class="sy1"><</span>T<span class="sy3">&</span>, T<span class="sy1">></span> <span class="sy3">&&</span><br />
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std<span class="sy4">::</span><span class="me2">constructible_from</span><span class="sy1"><</span>T, <span class="kw4">const</span> T<span class="sy3">&</span><span class="sy1">></span> <span class="sy3">&&</span> std<span class="sy4">::</span><span class="me2">convertible_to</span><span class="sy1"><</span><span class="kw4">const</span> T<span class="sy3">&</span>, T<span class="sy1">></span> <span class="sy3">&&</span><br /></p>
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std<span class="sy4">::</span><span class="me2">constructible_from</span><span class="sy1"><</span>T, <span class="kw4">const</span> T<span class="sy1">></span> <span class="sy3">&&</span> std<span class="sy4">::</span><span class="me2">convertible_to</span><span class="sy1"><</span><span class="kw4">const</span> T, T<span class="sy1">></span><span class="sy4">;</span></div>
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<td><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></td>
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<p>概念 <code>copy_constructible</code> 若符合这些条件则得到满足： <code>T</code> 为左值引用类型，或若它是 <a href="cpp-concepts-move_constructible.html"><code>move_constructible</code></a> 对象类型，而能从（可为 const 的）该类型左值或 const 右值，在直接和复制初始化语境中以通常语义构造该类型对象（构造副本而不更改源）。</p>
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<h3><span class="mw-headline" id=".E8.AF.AD.E4.B9.89.E8.A6.81.E6.B1.82">语义要求</span></h3>
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<p>若 <code>T</code> 为对象类型，则 <code>copy_constructible<T></code> 仅若符合下列条件才得到实现。给定</p>
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<ul>
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<li><code>v</code> ， <code>T</code> 类型左值（可为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">const</span></span></span> ）或为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">const</span> T</span></span> 类型右值，</li>
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<p>下列为真：</p>
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<li>定义 <span class="t-c"><span class="mw-geshi cpp source-cpp">T u <span class="sy1">=</span> v<span class="sy4">;</span></span></span> 后， <code>u</code> 等于 <code>v</code> 且 <code>v</code> 不被修改；</li>
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<li><code>T(v)</code> 等于 <code>v</code> 且不修改 <code>v</code> 。</li>
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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><a href="cpp-types-is_copy_constructible.html"><span class="t-lines"><span>is_copy_constructible</span><span>is_trivially_copy_constructible</span><span>is_nothrow_copy_constructible</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><span class="t-mark-rev t-since-cxx11">(C++11)</span></span><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div>
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<td>检查类型是否拥有复制构造函数<br />
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<span class="t-mark">(类模板)</span></td>
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