82 lines
6.4 KiB
HTML
82 lines
6.4 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>C++ 具名要求：可复制构造 (CopyConstructible)</title>
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<link rel="stylesheet" href="ext.css" />
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_named_req_CopyConstructible skin-cppreference2 action-view 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%">C++ 具名要求：</span><span style="font-style:italic">可复制构造</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(CopyConstructible)</span></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-named_req.html">named req</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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<p>指定该类型的实例可以从<a href="cpp-language-value_category.html">左值表达式</a>进行复制构造。</p>
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<h3><span class="mw-headline" id=".E8.A6.81.E6.B1.82">要求</span></h3>
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<p>以下情况下，类型 <code>T</code> 满足<span style="font-style:italic">可复制构造</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(CopyConstructible)</span> ：</p>
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<ul>
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<li>类型 <code>T</code> 满足<a href="cpp-named_req-MoveConstructible.html"><span style="font-style:italic">可移动构造</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(MoveConstructible)</span></a> ，且</li>
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</ul>
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<p>给定</p>
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<ul>
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<li><code>v</code>，为 <code>T</code> 或 <code>const T</code> 类型的<a href="cpp-language-value_category.html">左值</a>表达式或 <code>const T</code> 类型的<a href="cpp-language-value_category.html">右值</a>表达式</li>
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<li>任意标识符 <code>u</code></li>
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</ul>
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<p>下列表达式必须合法且拥有其指定的效果</p>
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<table class="wikitable">
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<tr>
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<th>表达式</th>
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<th>后条件</th>
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</tr>
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<tr>
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<td><span class="t-c"><span class="mw-geshi cpp source-cpp">T u <span class="sy1">=</span> v<span class="sy4">;</span></span></span></td>
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<td><code>u</code> 的值等价于 <code>v</code> 的值。不更改 <code>v</code> 的值。</td>
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</tr>
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<tr>
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<td><span class="t-c"><span class="mw-geshi cpp source-cpp">T<span class="br0">(</span>v<span class="br0">)</span></span></span></td>
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<td><code>T(v)</code> 的值等价于 <code>v</code> 的值。不更改 <code>v</code> 的值。</td>
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</tr>
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</table>
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<table class="t-rev-begin">
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<tr class="t-rev t-until-cxx11">
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<td>
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<p>表达式 <span class="t-c"><span class="mw-geshi cpp source-cpp">v.~T<span class="br0">(</span><span class="br0">)</span></span></span> 亦必须合法，且对于左值 <code>v</code>，表达式 <code>&v</code> 必须具有 <span class="t-c"><span class="mw-geshi cpp source-cpp">T<span class="sy2">*</span></span></span> 或 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">const</span> T<span class="sy2">*</span></span></span> 类型，且必须求值为 <code>v</code> 的地址。</p>
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</td>
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<td><span class="t-mark-rev t-until-cxx11">(C++11 前)</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>C++11 前，重载了 <code>operator&</code> 的类并非<span style="font-style:italic">可复制构造</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(CopyConstructible)</span> ，从而不可用于标准库容器。C++11 开始，标准库在凡是需要对象地址时都使用 <span class="t-lc"><a href="cpp-memory-addressof.html">std::addressof</a></span>。</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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<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-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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</div>
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</td>
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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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</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-concepts-copy_constructible.html"><span class="t-lines"><span>copy_constructible</span></span></a></div>
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<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx20">(C++20)</span></span></span></div>
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</div>
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</td>
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<td>指定能复制构造和移动构造一个类型的对象<br />
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<span class="t-mark">(概念)</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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</body>
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