180 lines
12 KiB
HTML
180 lines
12 KiB
HTML
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<title>std::unique_ptr<T,Deleter>::reset</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_memory_unique_ptr_reset 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::unique_ptr<T,Deleter>::</span>reset</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-unique_ptr.html">unique ptr</a></span></div>
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<div>主模板 unique_ptr<T> 的成员</div>
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<td></td>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw4">void</span> reset<span class="br0">(</span> pointer ptr <span class="sy1">=</span> pointer<span class="br0">(</span><span class="br0">)</span> <span class="br0">)</span> <span class="kw1">noexcept</span><span class="sy4">;</span></span></div>
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<td>(1)</td>
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<div>特化 unique_ptr<T[]> 的成员</div>
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<td></td>
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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> U <span class="sy1">></span><br />
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<span class="kw4">void</span> reset<span class="br0">(</span> U <span class="br0">)</span> <span class="kw1">noexcept</span><span class="sy4">;</span></span></div>
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<td>(2)</td>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw4">void</span> reset<span class="br0">(</span> <a href="cpp-types-nullptr_t.html"><span class="kw102">std::<span class="me2">nullptr_t</span></span></a> p <span class="sy1">=</span> nullptr <span class="br0">)</span> <span class="kw1">noexcept</span><span class="sy4">;</span></span></div>
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<td>(3)</td>
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<td class="t-dcl-nopad"></td>
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<p>替换被管理对象。</p>
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<div class="t-li1"><span class="t-li">1)</span> 给定指向 <code>*this</code> 所管理对象的指针 <code>current_ptr</code> ，进行下列行动，以此顺序：
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<ol>
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<li>保存当前指针的副本 <span class="t-c"><span class="mw-geshi cpp source-cpp">old_ptr <span class="sy1">=</span> current_ptr</span></span></li>
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<li>以参数重写当前指针 <span class="t-c"><span class="mw-geshi cpp source-cpp">current_ptr <span class="sy1">=</span> ptr</span></span></li>
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<li>若旧指针非空，则删除先前管理的对象 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw1">if</span><span class="br0">(</span>old_ptr <span class="sy3">!</span><span class="sy1">=</span> nullptr<span class="br0">)</span> get_deleter<span class="br0">(</span><span class="br0">)</span><span class="br0">(</span>old_ptr<span class="br0">)</span></span></span> 。</li>
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</ol>
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</div>
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<div class="t-li1"><span class="t-li">2)</span> 表现同主模板的 reset 成员，除了它仅若满足下列任意条件才参与重载决议
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<ol>
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<li><code>U</code> 与 <code>pointer</code> 是同一类型，或</li>
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<li><code>pointer</code> 与 <code>element_type*</code> 是同一类型，且 <code>U</code> 为指针类型 <code>V*</code> ，并满足 <code>V(*)[]</code> 可隐式转换为 <code>element_type(*)[]</code> 。</li>
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</ol>
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</div>
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<div class="t-li1"><span class="t-li">3)</span> 等价于 <span class="t-c"><span class="mw-geshi cpp source-cpp">reset<span class="br0">(</span>pointer<span class="br0">(</span><span class="br0">)</span><span class="br0">)</span></span></span> 。</div>
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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>ptr</td>
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<td>-</td>
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<td>指向要管理的新对象的指针</td>
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</table>
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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>（无）</p>
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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>为在提供新删除器时替换被管理对象，可用移动赋值运算符。</p>
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<p>不进行自 reset 测试，即 <code>ptr</code> 是否指向已为 <code>*this</code> 管理的对象，除非作为编译器扩展，或调试断言提供。注意如 <span class="t-c"><span class="mw-geshi cpp source-cpp">p.<span class="me1">reset</span><span class="br0">(</span>p.<span class="me1">release</span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span></span></span> 的代码不涉及自重置，只有类似 <span class="t-c"><span class="mw-geshi cpp source-cpp">p.<span class="me1">reset</span><span class="br0">(</span>p.<span class="me1">get</span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span></span></span> 的代码会。</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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<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 <iostream></span>
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<span class="co2">#include <memory></span>
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<span class="kw1">struct</span> Foo <span class="br0">{</span>
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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>
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~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>
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<span class="br0">}</span><span class="sy4">;</span>
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<span class="kw1">struct</span> D <span class="br0">{</span>
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<span class="kw4">void</span> operator<span class="br0">(</span><span class="br0">)</span> <span class="br0">(</span>Foo<span class="sy2">*</span> p<span class="br0">)</span> <span class="br0">{</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> <span class="st0">"Calling delete for Foo object... <span class="es1">\n</span>"</span><span class="sy4">;</span>
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delete p<span class="sy4">;</span>
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<span class="br0">}</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>
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<span class="br0">{</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> <span class="st0">"Creating new Foo...<span class="es1">\n</span>"</span><span class="sy4">;</span>
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<a href="cpp-memory-unique_ptr.html"><span class="kw733">std::<span class="me2">unique_ptr</span></span></a><span class="sy1"><</span>Foo, D<span class="sy1">></span> up<span class="br0">(</span>new Foo<span class="br0">(</span><span class="br0">)</span>, D<span class="br0">(</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// up 占有 Foo 指针（删除器 D ）</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> <span class="st0">"Replace owned Foo with a new Foo...<span class="es1">\n</span>"</span><span class="sy4">;</span>
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up.<span class="me1">reset</span><span class="br0">(</span>new Foo<span class="br0">(</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 调用旧者的删除器</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> <span class="st0">"Release and delete the owned Foo...<span class="es1">\n</span>"</span><span class="sy4">;</span>
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up.<span class="me1">reset</span><span class="br0">(</span>nullptr<span class="br0">)</span><span class="sy4">;</span>
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<span class="br0">}</span></pre></div>
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</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">Creating new Foo...
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Foo...
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Replace owned Foo with a new Foo...
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Foo...
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Calling delete for Foo object...
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~Foo...
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Release and delete the owned Foo...
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Calling delete for Foo object...
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~Foo...</pre></div>
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</div>
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</div>
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<h3><span class="mw-headline" id=".E7.BC.BA.E9.99.B7.E6.8A.A5.E5.91.8A">缺陷报告</span></h3>
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<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>
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<table class="dsctable" style="font-size:0.8em">
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<tr>
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<th>DR</th>
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<th>应用于</th>
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<th>出版时的行为</th>
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<th>正确行为</th>
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</tr>
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<tr>
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<td><a rel="nofollow" class="external text" href="https://cplusplus.github.io/LWG/issue2118">LWG 2118</a></td>
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<td>C++11</td>
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<td><code>unique_ptr<T[]>::reset</code> 拒绝限定转换</td>
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<td>接受</td>
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</tr>
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</table>
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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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<td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-memory-unique_ptr-release.html"><span class="t-lines"><span>release</span></span></a></div>
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</div>
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</td>
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<td>返回一个指向被管理对象的指针，并释放所有权<br />
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<span class="t-mark">(公开成员函数)</span></td>
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