195 lines
15 KiB
HTML
195 lines
15 KiB
HTML
<!DOCTYPE html>
|
|
<html lang="zh" dir="ltr" class="client-nojs" xmlns="http://www.w3.org/1999/xhtml" xml:lang="zh">
|
|
<head><meta http-equiv="x-ua-compatible" content="ie=edge">
|
|
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
|
|
<title>std::unique_ptr<T,Deleter>::operator=</title>
|
|
<link rel="stylesheet" href="ext.css" />
|
|
<link rel="stylesheet" href="site_modules.css" />
|
|
</head>
|
|
<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_memory_unique_ptr_operator skin-cppreference2 action-view cpp-navbar">
|
|
<div id="cpp-content-base">
|
|
<div id="content"><a id="top"></a>
|
|
<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::unique_ptr<T,Deleter>::</span>operator=</h1>
|
|
<div id="bodyContent">
|
|
<div id="contentSub"><span class="subpages">< <a href="cpp.html">cpp</a>‎ | <a href="cpp-memory.html">memory</a>‎ | <a href="cpp-memory-unique_ptr.html">unique ptr</a></span></div>
|
|
<div id="mw-content-text" lang="zh" dir="ltr" class="mw-content-ltr" xml:lang="zh">
|
|
<table class="t-dcl-begin">
|
|
<tbody>
|
|
<tr class="t-dcl-sep">
|
|
<td></td>
|
|
<td></td>
|
|
<td></td>
|
|
</tr>
|
|
<tr class="t-dcl-h">
|
|
<td>
|
|
<div>主模板 unique_ptr<T> 的成员</div>
|
|
</td>
|
|
<td></td>
|
|
<td></td>
|
|
</tr>
|
|
<tr class="t-dcl">
|
|
<td>
|
|
<div><span class="mw-geshi cpp source-cpp">unique_ptr<span class="sy3">&</span> operator<span class="sy1">=</span><span class="br0">(</span> unique_ptr<span class="sy3">&&</span> r <span class="br0">)</span> <span class="kw1">noexcept</span><span class="sy4">;</span></span></div>
|
|
</td>
|
|
<td>(1)</td>
|
|
<td class="t-dcl-nopad"></td>
|
|
</tr>
|
|
<tr class="t-dcl">
|
|
<td>
|
|
<div><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span><span class="sy1"><</span> <span class="kw1">class</span> U, <span class="kw1">class</span> E <span class="sy1">></span><br />
|
|
unique_ptr<span class="sy3">&</span> operator<span class="sy1">=</span><span class="br0">(</span> unique_ptr<span class="sy1"><</span>U,E<span class="sy1">></span><span class="sy3">&&</span> r <span class="br0">)</span> <span class="kw1">noexcept</span><span class="sy4">;</span></span></div>
|
|
</td>
|
|
<td>(2)</td>
|
|
<td class="t-dcl-nopad"></td>
|
|
</tr>
|
|
<tr class="t-dcl">
|
|
<td>
|
|
<div><span class="mw-geshi cpp source-cpp">unique_ptr<span class="sy3">&</span> operator<span class="sy1">=</span><span class="br0">(</span> <a href="cpp-types-nullptr_t.html"><span class="kw102">std::<span class="me2">nullptr_t</span></span></a> <span class="br0">)</span> <span class="kw1">noexcept</span><span class="sy4">;</span></span></div>
|
|
</td>
|
|
<td>(3)</td>
|
|
<td class="t-dcl-nopad"></td>
|
|
</tr>
|
|
<tr class="t-dcl-sep">
|
|
<td></td>
|
|
<td></td>
|
|
<td></td>
|
|
</tr>
|
|
<tr class="t-dcl-h">
|
|
<td>
|
|
<div>数组特化 unique_ptr<T[]> 的成员</div>
|
|
</td>
|
|
<td></td>
|
|
<td></td>
|
|
</tr>
|
|
<tr class="t-dcl">
|
|
<td>
|
|
<div><span class="mw-geshi cpp source-cpp">unique_ptr<span class="sy3">&</span> operator<span class="sy1">=</span><span class="br0">(</span> unique_ptr<span class="sy3">&&</span> r <span class="br0">)</span> <span class="kw1">noexcept</span><span class="sy4">;</span></span></div>
|
|
</td>
|
|
<td>(1)</td>
|
|
<td class="t-dcl-nopad"></td>
|
|
</tr>
|
|
<tr class="t-dcl">
|
|
<td>
|
|
<div><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span><span class="sy1"><</span> <span class="kw1">class</span> U, <span class="kw1">class</span> E <span class="sy1">></span><br />
|
|
unique_ptr<span class="sy3">&</span> operator<span class="sy1">=</span><span class="br0">(</span> unique_ptr<span class="sy1"><</span>U,E<span class="sy1">></span><span class="sy3">&&</span> r <span class="br0">)</span> <span class="kw1">noexcept</span><span class="sy4">;</span></span></div>
|
|
</td>
|
|
<td>(2)</td>
|
|
<td class="t-dcl-nopad"></td>
|
|
</tr>
|
|
<tr class="t-dcl">
|
|
<td>
|
|
<div><span class="mw-geshi cpp source-cpp">unique_ptr<span class="sy3">&</span> operator<span class="sy1">=</span><span class="br0">(</span> <a href="cpp-types-nullptr_t.html"><span class="kw102">std::<span class="me2">nullptr_t</span></span></a> <span class="br0">)</span> <span class="kw1">noexcept</span><span class="sy4">;</span></span></div>
|
|
</td>
|
|
<td>(3)</td>
|
|
<td class="t-dcl-nopad"></td>
|
|
</tr>
|
|
<tr class="t-dcl-sep">
|
|
<td></td>
|
|
<td></td>
|
|
<td></td>
|
|
</tr>
|
|
</tbody>
|
|
</table>
|
|
<div class="t-li1"><span class="t-li">1)</span> 移动赋值运算符。从 <code>r</code> 转移所有权到 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">*</span>this</span></span> ，如同以调用 <span class="t-c"><span class="mw-geshi cpp source-cpp">reset<span class="br0">(</span>r.<span class="me1">release</span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span></span></span> 后随从 <span class="t-lc"><a href="cpp-memory-unique_ptr-get_deleter.html">get_deleter()</a></span> 到 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-utility-forward.html"><span class="kw1117">std::<span class="me2">forward</span></span></a><span class="sy1"><</span>Deleter<span class="sy1">></span><span class="br0">(</span>r.<span class="me1">get_deleter</span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span></span></span> 的赋值。
|
|
<p>若 <code>Deleter</code> 不是引用类型，则要求它为不抛出<a href="cpp-named_req-MoveAssignable.html"><span style="font-style:italic">可移动赋值</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(MoveAssignable)</span></a> 。<br />
|
|
若 <code>Deleter</code> 是引用类型，则要求 <code>std::remove_reference<Deleter>::type</code> 为不抛出<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> 。<br /></p>
|
|
移动赋值运算符仅若 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-types-is_move_assignable.html"><span class="kw556">std::<span class="me2">is_move_assignable</span></span></a><span class="sy1"><</span>Deleter<span class="sy1">></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> 才参与重载决议。</div>
|
|
<div class="t-li1"><span class="t-li">2)</span> 转换赋值运算符。行为同 <span class="t-v">(1)</span> ，除了
|
|
<ul>
|
|
<li>主模板的此赋值运算符仅若 <code>U</code> 非数组类型且 <span class="t-c"><span class="mw-geshi cpp source-cpp">unique_ptr<span class="sy1"><</span>U,E<span class="sy1">></span><span class="sy4">::</span><span class="me2">pointer</span></span></span> 可隐式转换为 <code>pointer</code> 且 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-types-is_assignable.html"><span class="kw544">std::<span class="me2">is_assignable</span></span></a><span class="sy1"><</span>Deleter<span class="sy3">&</span>, E<span class="sy3">&&</span><span class="sy1">></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> 才参与重载决议。</li>
|
|
<li>数组特化 <code>std::unique_ptr<T[]></code> 的此赋值运算符的表现与主模板中的相同，除了仅若下列皆为真才参与重载决议：</li>
|
|
<li><code>U</code> 是数组类型</li>
|
|
<li><code>pointer</code> 与 <code>element_type*</code> 是同一类型</li>
|
|
<li><code>unique_ptr<U,E>::pointer</code> 与 <code>unique_ptr<U,E>::element_type*</code> 是同一类型</li>
|
|
<li><code>unique_ptr<U,E>::element_type(*)[]</code> 可转换为 <code>element_type(*)[]</code></li>
|
|
<li><span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-types-is_assignable.html"><span class="kw544">std::<span class="me2">is_assignable</span></span></a><span class="sy1"><</span>Deleter<span class="sy3">&</span>, E<span class="sy3">&&</span><span class="sy1">></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></li>
|
|
</ul>
|
|
</div>
|
|
<div class="t-li1"><span class="t-li">3)</span> 与调用 <span class="t-c"><span class="mw-geshi cpp source-cpp">reset<span class="br0">(</span><span class="br0">)</span></span></span> 等效。</div>
|
|
<p>注意 <code>unique_ptr</code> 的赋值运算符只接受典型地由 <span class="t-lc">std::move</span> 生成的<a href="cpp-language-value_category.html">右值</a>。（ <code>unique_ptr</code> 类显式删除其<a href="cpp-language-value_category.html">左值</a>复制构造函数和<a href="cpp-language-value_category.html">左值</a>赋值运算符。）</p>
|
|
<h3><span class="mw-headline" id=".E5.8F.82.E6.95.B0">参数</span></h3>
|
|
<table class="t-par-begin">
|
|
<tr class="t-par">
|
|
<td>r</td>
|
|
<td>-</td>
|
|
<td>所有权将被转移的智能指针</td>
|
|
</tr>
|
|
</table>
|
|
<h3><span class="mw-headline" id=".E8.BF.94.E5.9B.9E.E5.80.BC">返回值</span></h3>
|
|
<p><span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">*</span>this</span></span></p>
|
|
<h3><span class="mw-headline" id=".E7.A4.BA.E4.BE.8B">示例</span></h3>
|
|
<div class="t-example">
|
|
<div class="t-example-live-link"></div>
|
|
<div dir="ltr" class="mw-geshi" style="text-align: left;">
|
|
<div class="cpp source-cpp">
|
|
<pre class="de1"><span class="co2">#include <iostream></span>
|
|
<span class="co2">#include <memory></span>
|
|
|
|
<span class="kw1">struct</span> Foo <span class="br0">{</span>
|
|
Foo<span class="br0">(</span><span class="br0">)</span> <span class="br0">{</span> <a href="cpp-io-cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"Foo<span class="es1">\n</span>"</span><span class="sy4">;</span> <span class="br0">}</span>
|
|
~Foo<span class="br0">(</span><span class="br0">)</span> <span class="br0">{</span> <a href="cpp-io-cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"~Foo<span class="es1">\n</span>"</span><span class="sy4">;</span> <span class="br0">}</span>
|
|
<span class="br0">}</span><span class="sy4">;</span>
|
|
|
|
<span class="kw4">int</span> main<span class="br0">(</span><span class="br0">)</span>
|
|
<span class="br0">{</span>
|
|
<a href="cpp-memory-unique_ptr.html"><span class="kw733">std::<span class="me2">unique_ptr</span></span></a><span class="sy1"><</span>Foo<span class="sy1">></span> p1<span class="sy4">;</span>
|
|
|
|
<span class="br0">{</span>
|
|
<a href="cpp-io-cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"Creating new Foo...<span class="es1">\n</span>"</span><span class="sy4">;</span>
|
|
<a href="cpp-memory-unique_ptr.html"><span class="kw733">std::<span class="me2">unique_ptr</span></span></a><span class="sy1"><</span>Foo<span class="sy1">></span> p2<span class="br0">(</span> <a href="cpp-memory-unique_ptr-make_unique.html"><span class="kw735">std::<span class="me2">make_unique</span></span></a><span class="sy1"><</span>Foo<span class="sy1">></span><span class="br0">(</span><span class="br0">)</span> <span class="br0">)</span><span class="sy4">;</span>
|
|
<span class="co1">// p1 = p2; // 错误！不能复制 unique_ptr</span>
|
|
p1 <span class="sy1">=</span> std<span class="sy4">::</span><span class="me2">move</span><span class="br0">(</span>p2<span class="br0">)</span><span class="sy4">;</span>
|
|
<a href="cpp-io-cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"About to leave inner block...<span class="es1">\n</span>"</span><span class="sy4">;</span>
|
|
|
|
<span class="co1">// Foo 实例将继续生存，尽管 p2 离开作用域</span>
|
|
<span class="br0">}</span>
|
|
|
|
<a href="cpp-io-cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"About to leave program...<span class="es1">\n</span>"</span><span class="sy4">;</span>
|
|
<span class="br0">}</span></pre></div>
|
|
</div>
|
|
<p>输出：</p>
|
|
<div dir="ltr" class="mw-geshi" style="text-align: left;">
|
|
<div class="text source-text">
|
|
<pre class="de1">Creating new Foo...
|
|
Foo
|
|
About to leave inner block...
|
|
About to leave program...
|
|
~Foo</pre></div>
|
|
</div>
|
|
</div>
|
|
<h3><span class="mw-headline" id=".E7.BC.BA.E9.99.B7.E6.8A.A5.E5.91.8A">缺陷报告</span></h3>
|
|
<p>下列更改行为的缺陷报告追溯地应用于以前出版的 C++ 标准。</p>
|
|
<table class="dsctable" style="font-size:0.8em">
|
|
<tr>
|
|
<th>DR</th>
|
|
<th>应用于</th>
|
|
<th>出版时的行为</th>
|
|
<th>正确行为</th>
|
|
</tr>
|
|
<tr>
|
|
<td><a rel="nofollow" class="external text" href="https://cplusplus.github.io/LWG/issue2118">LWG 2118</a></td>
|
|
<td>C++11</td>
|
|
<td><code>unique_ptr<T[]>::operator=</code> 拒绝限定转换</td>
|
|
<td>接受</td>
|
|
</tr>
|
|
<tr>
|
|
<td><a rel="nofollow" class="external text" href="https://cplusplus.github.io/LWG/issue2228">LWG 2228</a></td>
|
|
<td>C++11</td>
|
|
<td>转换赋值运算符未受约束</td>
|
|
<td>已约束</td>
|
|
</tr>
|
|
<tr>
|
|
<td><a rel="nofollow" class="external text" href="https://cplusplus.github.io/LWG/issue2899">LWG 2899</a></td>
|
|
<td>C++11</td>
|
|
<td>移动赋值运算符未受约束</td>
|
|
<td>已约束</td>
|
|
</tr>
|
|
</table>
|
|
</div>
|
|
<div class="visualClear"></div>
|
|
</div>
|
|
</div>
|
|
</div>
|
|
</body>
|
|
</html>
|