148 lines
15 KiB
HTML
148 lines
15 KiB
HTML
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<title>std::shared_ptr<T>::reset</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_memory_shared_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::shared_ptr<T>::</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-shared_ptr.html">shared ptr</a></span></div>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw4">void</span> reset<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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<td><span class="t-mark-rev t-since-cxx11">(C++11 起)</span></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> Y <span class="sy1">></span><br />
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<span class="kw4">void</span> reset<span class="br0">(</span> Y<span class="sy2">*</span> ptr <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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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span><span class="sy1"><</span> <span class="kw1">class</span> Y, <span class="kw1">class</span> Deleter <span class="sy1">></span><br />
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<span class="kw4">void</span> reset<span class="br0">(</span> Y<span class="sy2">*</span> ptr, Deleter d <span class="br0">)</span><span class="sy4">;</span></span></div>
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<td>(3)</td>
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<td><span class="t-mark-rev t-since-cxx11">(C++11 起)</span></td>
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<tr class="t-dcl t-since-cxx11">
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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> Y, <span class="kw1">class</span> Deleter, <span class="kw1">class</span> Alloc <span class="sy1">></span><br />
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<span class="kw4">void</span> reset<span class="br0">(</span> Y<span class="sy2">*</span> ptr, Deleter d, Alloc alloc <span class="br0">)</span><span class="sy4">;</span></span></div>
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<td>(4)</td>
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<td><span class="t-mark-rev t-since-cxx11">(C++11 起)</span></td>
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<tr class="t-dcl-sep">
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<td></td>
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<td></td>
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<td></td>
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<p>以 <code>ptr</code> 所指向的对象替换被管理对象。能可选地提供删除器 <code>d</code> ，之后在无 <code>shared_ptr</code> 对象占有该对象时以之销毁新对象。默认以 <a href="cpp-language-delete.html"><tt>delete</tt></a> 表达式为删除器。始终选择对应提供类型的 <a href="cpp-language-delete.html"><tt>delete</tt></a> 表达式，这是函数以使用分离的形参 <code>Y</code> 的模板实现的理由。</p>
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<p>若 <code>*this</code> 已占有对象，且它是最后一个占有该对象的 <code>shared_ptr</code> ，则通过所占有的删除器销毁对象。</p>
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<p>若 <code>ptr</code> 所指向的对象已被占有，则函数通常会导致未定义行为。</p>
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<div class="t-li1"><span class="t-li">1)</span> 释放被管理对象的所有权，若存在。调用后， <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">*</span>this</span></span> 不管理对象。等价于 <span class="t-c"><span class="mw-geshi cpp source-cpp">shared_ptr<span class="br0">(</span><span class="br0">)</span>.<span class="me1">swap</span><span class="br0">(</span><span class="sy2">*</span>this<span class="br0">)</span><span class="sy4">;</span></span></span> 。</div>
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<div class="t-li1"><span class="t-li">2-4)</span> 以 <code>ptr</code> 所指向对象替换被管理对象。 <code>Y</code> 必须是完整类型且可隐式转换为 <code>T</code> 。另外：</div>
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<div class="t-li2"><span class="t-li">2)</span> 以 delete 表达式为删除器。合法的 delete 表达式必须可用，即 <span class="t-c"><span class="mw-geshi cpp source-cpp">delete ptr</span></span> 必须为良式，拥有良好定义行为且不抛任何异常。等价于 <span class="t-c"><span class="mw-geshi cpp source-cpp">shared_ptr<span class="sy1"><</span>T<span class="sy1">></span><span class="br0">(</span>ptr<span class="br0">)</span>.<span class="me1">swap</span><span class="br0">(</span><span class="sy2">*</span>this<span class="br0">)</span><span class="sy4">;</span></span></span> 。</div>
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<div class="t-li2"><span class="t-li">3)</span> 以指定的删除器 <code>d</code> 为删除器。 <code>Deleter</code> 必须对 <code>T</code> 类型可调用，即 <span class="t-c"><span class="mw-geshi cpp source-cpp">d<span class="br0">(</span>ptr<span class="br0">)</span></span></span>必须为良构，拥有良好定义行为且不抛任何异常。 <code>Deleter</code> 必须<a href="cpp-named_req-CopyConstructible.html"><span style="font-style:italic">可复制构造</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(CopyConstructible)</span></a> ，且其复制构造函数和析构函数必须不抛异常。等价于 <span class="t-c"><span class="mw-geshi cpp source-cpp">shared_ptr<span class="sy1"><</span>T<span class="sy1">></span><span class="br0">(</span>ptr, d<span class="br0">)</span>.<span class="me1">swap</span><span class="br0">(</span><span class="sy2">*</span>this<span class="br0">)</span><span class="sy4">;</span></span></span> 。</div>
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<div class="t-li2"><span class="t-li">4)</span> 同 <span class="t-v">(3)</span> ，但额外地用 <code>alloc</code> 的副本分配内部使用的数据。 <code>Alloc</code> 必须是<a href="cpp-named_req-Allocator.html"><span style="font-style:italic">分配器</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(Allocator)</span></a> 。复制构造函数和析构函数必须不抛异常。等价于 <span class="t-c"><span class="mw-geshi cpp source-cpp">shared_ptr<span class="sy1"><</span>T<span class="sy1">></span><span class="br0">(</span>ptr, d, alloc<span class="br0">)</span>.<span class="me1">swap</span><span class="br0">(</span><span class="sy2">*</span>this<span class="br0">)</span><span class="sy4">;</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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<tr class="t-par">
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<td>ptr</td>
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<td>-</td>
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<td>指向要取得所有权的对象的指针</td>
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<tr class="t-par">
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<td>d</td>
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<td>-</td>
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<td>为删除对象而存储的删除器</td>
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</tr>
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<tr class="t-par">
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<td>alloc</td>
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<td>-</td>
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<td>内部存储所用的分配器</td>
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</tr>
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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=".E5.BC.82.E5.B8.B8">异常</span></h3>
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<div class="t-li1"><span class="t-li">2)</span> 若无法获得要求的额外内存则为 <span class="t-lc"><a href="cpp-memory-new-bad_alloc.html">std::bad_alloc</a></span> 。可能因其他错误抛出实现定义的异常。若出现异常则调用 <span class="t-c"><span class="mw-geshi cpp source-cpp">delete ptr</span></span> 。</div>
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<div class="t-li1"><span class="t-li">3-4)</span> 若无法获得要求的额外内存则为 <span class="t-lc"><a href="cpp-memory-new-bad_alloc.html">std::bad_alloc</a></span> 。可能因其他错误抛出实现定义的异常。若出现异常则调用 <span class="t-c"><span class="mw-geshi cpp source-cpp">d<span class="br0">(</span>ptr<span class="br0">)</span></span></span> 。</div>
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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 <memory></span>
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<span class="co2">#include <iostream></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="kw4">int</span> n <span class="sy1">=</span> <span class="nu0">0</span><span class="br0">)</span> <span class="kw1">noexcept</span> <span class="sy4">:</span> bar<span class="br0">(</span>n<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">"Foo: constructor, bar = "</span> <span class="sy1"><<</span> bar <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>
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~Foo<span class="br0">(</span><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">"Foo: destructor, bar = "</span> <span class="sy1"><<</span> bar <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>
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<span class="kw4">int</span> getBar<span class="br0">(</span><span class="br0">)</span> <span class="kw4">const</span> <span class="kw1">noexcept</span> <span class="br0">{</span> <span class="kw1">return</span> bar<span class="sy4">;</span> <span class="br0">}</span>
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<span class="kw1">private</span><span class="sy4">:</span>
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<span class="kw4">int</span> bar<span class="sy4">;</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-memory-shared_ptr.html"><span class="kw734">std::<span class="me2">shared_ptr</span></span></a><span class="sy1"><</span>Foo<span class="sy1">></span> sptr <span class="sy1">=</span> <a href="cpp-memory-shared_ptr-make_shared.html"><span class="kw736">std::<span class="me2">make_shared</span></span></a><span class="sy1"><</span>Foo<span class="sy1">></span><span class="br0">(</span><span class="nu0">1</span><span class="br0">)</span><span class="sy4">;</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">"The first Foo's bar is "</span> <span class="sy1"><<</span> sptr<span class="sy2">-</span><span class="sy1">></span>getBar<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="co1">// 重置，交与新的 Foo 实例</span>
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<span class="co1">// （此调用后将销毁旧实例）</span>
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sptr.<span class="me1">reset</span><span class="br0">(</span>new Foo<span class="br0">)</span><span class="sy4">;</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">"The second Foo's bar is "</span> <span class="sy1"><<</span> sptr<span class="sy2">-</span><span class="sy1">></span>getBar<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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</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">Foo: constructor, bar = 1
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The first Foo's bar is 1
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Foo: constructor, bar = 0
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Foo: destructor, bar = 1
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The second Foo's bar is 0
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Foo: destructor, bar = 0</pre></div>
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</div>
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</div>
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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 t-dsc-member-nobold-div">
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<div><a href="cpp-memory-shared_ptr-shared_ptr.html"><span class="t-lines"><span>(构造函数)</span></span></a></div>
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</div>
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</td>
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<td>构造新的 <code>shared_ptr</code><br />
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<span class="t-mark">(公开成员函数)</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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</div>
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