409 lines
35 KiB
HTML
409 lines
35 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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<title>std::shared_ptr</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_memory_shared_ptr skin-cppreference2 action-view cpp-navbar">
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<div id="cpp-content-base">
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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::</span>shared_ptr</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></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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<table class="t-dcl-begin">
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<td>
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<div>定义于头文件 <code><a href="cpp-header-memory.html"><memory></a></code></div>
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<td></td>
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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> T <span class="sy1">></span> <span class="kw1">class</span> shared_ptr<span class="sy4">;</span></span></div>
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</td>
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<td class="t-dcl-nopad"></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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<p><code>std::shared_ptr</code> 是通过指针保持对象共享所有权的智能指针。多个 <code>shared_ptr</code> 对象可占有同一对象。下列情况之一出现时销毁对象并解分配其内存：</p>
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<ul>
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<li>最后剩下的占有对象的 <code>shared_ptr</code> 被销毁；</li>
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<li>最后剩下的占有对象的 <code>shared_ptr</code> 被通过 <span class="t-lc"><a href="cpp-memory-shared_ptr-operator=.html">operator=</a></span> 或 <span class="t-lc"><a href="cpp-memory-shared_ptr-reset.html">reset()</a></span> 赋值为另一指针。</li>
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</ul>
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<p>用 <a href="cpp-language-delete.html"><code>delete</code> 表达式</a>或在构造期间提供给 <code>shared_ptr</code> 的定制删除器销毁对象。</p>
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<p><code>shared_ptr</code> 能在存储指向一个对象的指针时共享另一对象的所有权。此特性能用于在占有其所属对象时，指向成员对象。存储的指针为 <span class="t-c"><span class="mw-geshi cpp source-cpp">get<span class="br0">(</span><span class="br0">)</span></span></span> 、解引用及比较运算符所访问。被管理指针是在 use_count 抵达零时传递给删除器者。</p>
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<p><code>shared_ptr</code> 亦可不占有对象，该情况下称它为<i>空 (empty)</i> （空 shared_ptr 可拥有非空存储指针，若以别名使用构造函数创建它）。</p>
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<p><code>shared_ptr</code> 的所有特化满足<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> 、<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> 和<a href="cpp-named_req-LessThanComparable.html"><span style="font-style:italic">可小于比较</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(LessThanComparable)</span></a> 的要求并<a href="cpp-language-implicit_conversion.html">可按语境转换</a>为 <code>bool</code> 。</p>
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<p>多个线程能在 <code>shared_ptr</code> 的不同实例上调用所有成员函数（包含复制构造函数与复制赋值）而不附加同步，即使这些实例是副本，且共享同一对象的所有权。若多个执行线程访问同一 <code>shared_ptr</code> 而不同步，且任一线程使用 <code>shared_ptr</code> 的非 const 成员函数，则将出现数据竞争；<a href="cpp-memory-shared_ptr-atomic.html">原子函数的 shared_ptr 特化</a>能用于避免数据竞争。</p>
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<h3><span class="mw-headline" id=".E6.88.90.E5.91.98.E7.B1.BB.E5.9E.8B">成员类型</span></h3>
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<table class="t-dsc-begin">
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<tr class="t-dsc-hitem">
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<td>成员类型</td>
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<td>定义</td>
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</tr>
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<tr class="t-dsc">
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<td><span class="t-c"><span class="mw-geshi cpp source-cpp">element_type</span></span></td>
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<td>
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<table class="t-rev-begin">
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<tr class="t-rev t-until-cxx17">
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<td><span class="t-c"><span class="mw-geshi cpp source-cpp">T</span></span></td>
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<td><span class="t-mark-rev t-until-cxx17">(C++17 前)</span></td>
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</tr>
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<tr class="t-rev t-since-cxx17">
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<td><span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-types-remove_extent.html"><span class="kw621">std::<span class="me2">remove_extent_t</span></span></a><span class="sy1"><</span>T<span class="sy1">></span></span></span></td>
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<td><span class="t-mark-rev t-since-cxx17">(C++17 起)</span></td>
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</tr>
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</table>
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</td>
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</tr>
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<tr class="t-dsc">
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<td><span class="t-c"><span class="mw-geshi cpp source-cpp">weak_type</span></span> <span class="t-mark-rev t-since-cxx17">(C++17 起)</span></td>
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<td><span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-memory-weak_ptr.html"><span class="kw740">std::<span class="me2">weak_ptr</span></span></a><span class="sy1"><</span>T<span class="sy1">></span></span></span></td>
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</tr>
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</table>
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<h3><span class="mw-headline" id=".E6.88.90.E5.91.98.E5.87.BD.E6.95.B0">成员函数</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 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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<tr class="t-dsc">
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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>(析构函数)</span></span></a></div>
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</div>
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</td>
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<td>如果没有更多 <code>shared_ptr</code> 指向持有的对象，则析构对象<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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<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-memory-shared_ptr-operator=.html"><span class="t-lines"><span>operator=</span></span></a></div>
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</div>
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</td>
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<td>对 <code>shared_ptr</code> 赋值<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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<tr>
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<td colspan="2">
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<h5><span class="mw-headline" id=".E4.BF.AE.E6.94.B9.E5.99.A8">修改器</span></h5>
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</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-memory-shared_ptr-reset.html"><span class="t-lines"><span>reset</span></span></a></div>
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</div>
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</td>
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<td>替换所管理的对象<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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<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-memory-shared_ptr-swap.html"><span class="t-lines"><span>swap</span></span></a></div>
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</div>
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</td>
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<td>交换所管理的对象<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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<tr>
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<td colspan="2">
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<h5><span class="mw-headline" id=".E8.A7.82.E5.AF.9F.E5.99.A8">观察器</span></h5>
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</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-memory-shared_ptr-get.html"><span class="t-lines"><span>get</span></span></a></div>
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</div>
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</td>
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<td>返回存储的指针<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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<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-memory-shared_ptr-operator*.html"><span class="t-lines"><span>operator*</span><span>operator-></span></span></a></div>
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</div>
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</td>
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<td>解引用存储的指针<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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<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-memory-shared_ptr-operator_at.html"><span class="t-lines"><span>operator[]</span></span></a></div>
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<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx17">(C++17)</span></span></span></div>
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</div>
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</td>
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<td>提供到被存储数组的带下标访问<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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<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-memory-shared_ptr-use_count.html"><span class="t-lines"><span>use_count</span></span></a></div>
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</div>
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</td>
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<td>返回 <code>shared_ptr</code> 所指对象的引用计数<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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<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-memory-shared_ptr-unique.html"><span class="t-lines"><span>unique</span></span></a></div>
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<div><span class="t-lines"><span><span class="t-mark-rev t-until-cxx20">(C++20 前)</span></span></span></div>
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</div>
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</td>
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<td>检查所管理对象是否仅由当前 <code>shared_ptr</code> 的实例管理<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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<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-memory-shared_ptr-operator_bool.html"><span class="t-lines"><span>operator bool</span></span></a></div>
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</div>
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</td>
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<td>检查是否有关联的管理对象<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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<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-memory-shared_ptr-owner_before.html"><span class="t-lines"><span>owner_before</span></span></a></div>
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</div>
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</td>
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<td>提供基于拥有者的共享指针排序<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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<h3><span class="mw-headline" id=".E9.9D.9E.E6.88.90.E5.91.98.E5.87.BD.E6.95.B0">非成员函数</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-memory-shared_ptr-make_shared.html"><span class="t-lines"><span>make_shared</span><span>make_shared_for_overwrite</span></span></a></div>
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<div><span class="t-lines"><span></span><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>创建管理一个新对象的共享指针<br />
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<span class="t-mark">(函数模板)</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-memory-shared_ptr-allocate_shared.html"><span class="t-lines"><span>allocate_shared</span><span>allocate_shared_for_overwrite</span></span></a></div>
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<div><span class="t-lines"><span></span><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>创建管理一个用分配器分配的新对象的共享指针<br />
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<span class="t-mark">(函数模板)</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-memory-shared_ptr-pointer_cast.html"><span class="t-lines"><span>static_pointer_cast</span><span>dynamic_pointer_cast</span><span>const_pointer_cast</span><span>reinterpret_pointer_cast</span></span></a></div>
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<div><span class="t-lines"><span></span><span></span><span></span><span><span class="t-mark-rev t-since-cxx17">(C++17)</span></span></span></div>
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</div>
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</td>
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<td>应用 <a href="cpp-language-static_cast.html"><tt>static_cast</tt></a>、<a href="cpp-language-dynamic_cast.html"><tt>dynamic_cast</tt></a>、<a href="cpp-language-const_cast.html"><tt>const_cast</tt></a> 或 <a href="cpp-language-reinterpret_cast.html"><tt>reinterpret_cast</tt></a> 到被存储指针<br />
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<span class="t-mark">(函数模板)</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-memory-shared_ptr-get_deleter.html"><span class="t-lines"><span>get_deleter</span></span></a></div>
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</div>
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</td>
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<td>返回指定类型中的删除器，若其拥有<br />
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<span class="t-mark">(函数模板)</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-memory-shared_ptr-operator_cmp.html"><span class="t-lines"><span>operator==</span><span>operator!=</span><span>operator<</span><span>operator<=</span><span>operator></span><span>operator>=</span><span>operator<=></span></span></a></div>
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<div><span class="t-lines"><span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><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>与另一个 <code>shared_ptr</code> 或 <span class="t-c"><span class="mw-geshi cpp source-cpp">nullptr</span></span> 进行比较<br />
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<span class="t-mark">(函数模板)</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-memory-shared_ptr-operator_ltlt.html"><span class="t-lines"><span>operator<<</span></span></a></div>
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</div>
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</td>
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<td>将存储的指针的值输出到输出流<br />
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<span class="t-mark">(函数模板)</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-memory-shared_ptr-swap2.html"><span class="t-lines"><span>std::swap<span class="t-dsc-small">(std::shared_ptr)</span></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></div>
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</div>
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</td>
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<td>特化 <span class="t-lc"><a href="cpp-algorithm-swap.html">std::swap</a></span> 算法<br />
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<span class="t-mark">(函数模板)</span></td>
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</tr>
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</table>
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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-memory-shared_ptr-atomic.html"><span class="t-lines"><span>std::atomic_is_lock_free<span class="t-dsc-small">(std::shared_ptr)</span></span><span>std::atomic_load<span class="t-dsc-small">(std::shared_ptr)</span></span><span>std::atomic_load_explicit<span class="t-dsc-small">(std::shared_ptr)</span></span><span>std::atomic_store<span class="t-dsc-small">(std::shared_ptr)</span></span><span>std::atomic_store_explicit<span class="t-dsc-small">(std::shared_ptr)</span></span><span>std::atomic_exchange<span class="t-dsc-small">(std::shared_ptr)</span></span><span>std::atomic_exchange_explicit<span class="t-dsc-small">(std::shared_ptr)</span></span><span>std::atomic_compare_exchange_weak<span class="t-dsc-small">(std::shared_ptr)</span></span><span>std::atomic_compare_exchange_strong<span class="t-dsc-small">(std::shared_ptr)</span></span><span>std::atomic_compare_exchange_weak_explicit<span class="t-dsc-small">(std::shared_ptr)</span></span><span>std::atomic_compare_exchange_strong_explicit<span class="t-dsc-small">(std::shared_ptr)</span></span></span></a></div>
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<div><span class="t-lines"><span><span class="t-mark-rev t-deprecated-cxx20">(C++20 中弃用)</span></span></span></div>
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</div>
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</td>
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<td>特化的原子操作<br />
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<span class="t-mark">(函数模板)</span></td>
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</tr>
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</table>
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<h3><span class="mw-headline" id=".E8.BE.85.E5.8A.A9.E7.B1.BB">辅助类</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-memory-shared_ptr-hash.html"><span class="t-lines"><span>std::hash<span class="t-dsc-small"><std::shared_ptr></span></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></div>
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</div>
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</td>
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<td><span class="t-lc"><strong class="selflink">std::shared_ptr</strong></span> 的散列支持<br />
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<span class="t-mark">(类模板特化)</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-memory-shared_ptr-atomic2.html"><span class="t-lines"><span>std::atomic<span class="t-dsc-small"><std::shared_ptr></span></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>原子共享指针<br />
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<span class="t-mark">(类模板特化)</span></td>
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</tr>
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</table>
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<h3><span class="mw-headline" id=".E6.8E.A8.E5.AF.BC.E6.8C.87.E5.BC.95.28C.2B.2B17_.E8.B5.B7.29"><a href="cpp-memory-shared_ptr-deduction_guides.html">推导指引</a><span class="t-mark-rev t-since-cxx17">(C++17 起)</span></span></h3>
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<h3><span class="mw-headline" id=".E6.B3.A8.E6.84.8F">注意</span></h3>
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<p>只能通过复制构造或复制赋值其值给另一 <code>shared_ptr</code> ，将对象所有权与另一 <code>shared_ptr</code> 共享。用另一 <code>shared_ptr</code> 所占有的底层指针创建新的 <code>shared_ptr</code> 导致未定义行为。</p>
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<p><code>std::shared_ptr</code> 可以用于<a href="cpp-language-type.html#.E4.B8.8D.E5.AE.8C.E6.95.B4.E7.B1.BB.E5.9E.8B">不完整类型</a> <code>T</code> 。然而，参数为裸指针的构造函数（ <span class="t-c"><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> shared_ptr<span class="br0">(</span>Y<span class="sy2">*</span><span class="br0">)</span></span></span> ）和 <span class="t-c"><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> <span class="kw4">void</span> reset<span class="br0">(</span>Y<span class="sy2">*</span><span class="br0">)</span></span></span> 成员函数只可以用指向完整类型的指针调用（注意 <span class="t-lc"><a href="cpp-memory-unique_ptr.html">std::unique_ptr</a></span> 可以从指向不完整类型的裸指针构造）。</p>
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<h3><span class="mw-headline" id=".E5.AE.9E.E7.8E.B0.E8.AF.B4.E6.98.8E">实现说明</span></h3>
|
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<p>在典型的实现中， <span class="t-lc"><strong class="selflink">std::shared_ptr</strong></span> 只保有二个指针：</p>
|
|
<ul>
|
|
<li><a href="cpp-memory-shared_ptr-get.html"><code>get()</code></a> 所返回的指针</li>
|
|
<li>指向<i>控制块</i>的指针</li>
|
|
</ul>
|
|
<p>控制块是一个动态分配的对象，其中包含：</p>
|
|
<ul>
|
|
<li>指向被管理对象的指针或被管理对象本身</li>
|
|
<li>删除器（类型擦除）</li>
|
|
<li>分配器（类型擦除）</li>
|
|
<li>占有被管理对象的 <code>shared_ptr</code> 的数量</li>
|
|
<li>涉及被管理对象的 <code>weak_ptr</code> 的数量</li>
|
|
</ul>
|
|
<p>以调用 <span class="t-lc"><a href="cpp-memory-shared_ptr-make_shared.html">std::make_shared</a></span> 或 <span class="t-lc"><a href="cpp-memory-shared_ptr-allocate_shared.html">std::allocate_shared</a></span> 创建 <code>shared_ptr</code> 时，以单次分配创建控制块和被管理对象。被管理对象在控制块的数据成员中原位构造。通过 <code>shared_ptr</code> 构造函数之一创建 <code>shared_ptr</code> 时，被管理对象和控制块必须分离分配。此情况中，控制块存储指向被管理对象的指针。</p>
|
|
<p><code>shared_ptr</code> 持有的指针是通过 <a href="cpp-memory-shared_ptr-get.html"><code>get()</code></a> 返回的；而控制块所持有的指针/对象则是最终引用计数归零时会被删除的那个。两者并不一定相等。</p>
|
|
<p><code>shared_ptr</code> 的析构函数会将控制块中的 <code>shared_ptr</code> 计数器减一，如果减至零，控制块就会调用被管理对象的析构函数。但控制块本身直到 <span class="t-lc"><a href="cpp-memory-weak_ptr.html">std::weak_ptr</a></span> 计数器同样归零时才会释放。</p>
|
|
<p>既存实现中，若有共享指针指向同一控制块，则自增弱指针计数 (<a rel="nofollow" class="external autonumber" href="https://stackoverflow.com/questions/43297517/stdshared-ptr-internals-weak-count-more-than-expected">[1]</a>, <a rel="nofollow" class="external autonumber" href="https://www.reddit.com/r/cpp/comments/3eia29/stdshared_ptrs_secret_constructor/ctfeh1p">[2]</a>) 。</p>
|
|
<p>为满足线程安全要求，引用计数器典型地用等价于用 <span class="t-lc"><a href="cpp-atomic-memory_order.html">std::memory_order_relaxed</a></span> 的 <span class="t-lc"><a href="cpp-atomic-atomic-fetch_add.html">std::atomic::fetch_add</a></span> 自增（自减要求更强的顺序，以安全销毁控制块）。</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="co2">#include <thread></span>
|
|
<span class="co2">#include <chrono></span>
|
|
<span class="co2">#include <mutex></span>
|
|
|
|
<span class="kw1">struct</span> Base
|
|
<span class="br0">{</span>
|
|
Base<span class="br0">(</span><span class="br0">)</span> <span class="br0">{</span> <a href="cpp-io-cout.html"><span class="kw1757">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">" Base::Base()<span class="es1">\n</span>"</span><span class="sy4">;</span> <span class="br0">}</span>
|
|
<span class="co1">// 注意：此处非虚析构函数 OK</span>
|
|
~Base<span class="br0">(</span><span class="br0">)</span> <span class="br0">{</span> <a href="cpp-io-cout.html"><span class="kw1757">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">" Base::~Base()<span class="es1">\n</span>"</span><span class="sy4">;</span> <span class="br0">}</span>
|
|
<span class="br0">}</span><span class="sy4">;</span>
|
|
|
|
<span class="kw1">struct</span> Derived<span class="sy4">:</span> <span class="kw1">public</span> Base
|
|
<span class="br0">{</span>
|
|
Derived<span class="br0">(</span><span class="br0">)</span> <span class="br0">{</span> <a href="cpp-io-cout.html"><span class="kw1757">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">" Derived::Derived()<span class="es1">\n</span>"</span><span class="sy4">;</span> <span class="br0">}</span>
|
|
~Derived<span class="br0">(</span><span class="br0">)</span> <span class="br0">{</span> <a href="cpp-io-cout.html"><span class="kw1757">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">" Derived::~Derived()<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">void</span> thr<span class="br0">(</span>std<span class="sy4">::</span><span class="me2">shared_ptr</span><span class="sy1"><</span>Base<span class="sy1">></span> p<span class="br0">)</span>
|
|
<span class="br0">{</span>
|
|
<a href="cpp-thread-sleep_for.html"><span class="kw2148">std::<span class="me2">this_thread</span><span class="sy4">::</span><span class="me2">sleep_for</span></span></a><span class="br0">(</span><a href="cpp-chrono-duration.html"><span class="kw996">std::<span class="me2">chrono</span><span class="sy4">::</span><span class="me2">seconds</span></span></a><span class="br0">(</span><span class="nu0">1</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
|
|
std<span class="sy4">::</span><span class="me2">shared_ptr</span><span class="sy1"><</span>Base<span class="sy1">></span> lp <span class="sy1">=</span> p<span class="sy4">;</span> <span class="co1">// 线程安全，虽然自增共享的 use_count</span>
|
|
<span class="br0">{</span>
|
|
<span class="kw4">static</span> <a href="cpp-thread-mutex.html"><span class="kw2153">std::<span class="me2">mutex</span></span></a> io_mutex<span class="sy4">;</span>
|
|
<a href="cpp-thread-lock_guard.html"><span class="kw2165">std::<span class="me2">lock_guard</span></span></a><span class="sy1"><</span><a href="cpp-thread-mutex.html"><span class="kw2153">std::<span class="me2">mutex</span></span></a><span class="sy1">></span> lk<span class="br0">(</span>io_mutex<span class="br0">)</span><span class="sy4">;</span>
|
|
<a href="cpp-io-cout.html"><span class="kw1757">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"local pointer in a thread:<span class="es1">\n</span>"</span>
|
|
<span class="sy1"><<</span> <span class="st0">" lp.get() = "</span> <span class="sy1"><<</span> lp.<span class="me1">get</span><span class="br0">(</span><span class="br0">)</span>
|
|
<span class="sy1"><<</span> <span class="st0">", lp.use_count() = "</span> <span class="sy1"><<</span> lp.<span class="me1">use_count</span><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>
|
|
<span class="br0">}</span>
|
|
<span class="br0">}</span>
|
|
|
|
<span class="kw4">int</span> main<span class="br0">(</span><span class="br0">)</span>
|
|
<span class="br0">{</span>
|
|
std<span class="sy4">::</span><span class="me2">shared_ptr</span><span class="sy1"><</span>Base<span class="sy1">></span> p <span class="sy1">=</span> <a href="cpp-memory-shared_ptr-make_shared.html"><span class="kw735">std::<span class="me2">make_shared</span></span></a><span class="sy1"><</span>Derived<span class="sy1">></span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
|
|
|
|
<a href="cpp-io-cout.html"><span class="kw1757">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"Created a shared Derived (as a pointer to Base)<span class="es1">\n</span>"</span>
|
|
<span class="sy1"><<</span> <span class="st0">" p.get() = "</span> <span class="sy1"><<</span> p.<span class="me1">get</span><span class="br0">(</span><span class="br0">)</span>
|
|
<span class="sy1"><<</span> <span class="st0">", p.use_count() = "</span> <span class="sy1"><<</span> p.<span class="me1">use_count</span><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>
|
|
<a href="cpp-thread-thread.html"><span class="kw2145">std::<span class="me2">thread</span></span></a> t1<span class="br0">(</span>thr, p<span class="br0">)</span>, t2<span class="br0">(</span>thr, p<span class="br0">)</span>, t3<span class="br0">(</span>thr, p<span class="br0">)</span><span class="sy4">;</span>
|
|
p.<span class="me1">reset</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 从 main 释放所有权</span>
|
|
<a href="cpp-io-cout.html"><span class="kw1757">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"Shared ownership between 3 threads and released<span class="es1">\n</span>"</span>
|
|
<span class="sy1"><<</span> <span class="st0">"ownership from main:<span class="es1">\n</span>"</span>
|
|
<span class="sy1"><<</span> <span class="st0">" p.get() = "</span> <span class="sy1"><<</span> p.<span class="me1">get</span><span class="br0">(</span><span class="br0">)</span>
|
|
<span class="sy1"><<</span> <span class="st0">", p.use_count() = "</span> <span class="sy1"><<</span> p.<span class="me1">use_count</span><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>
|
|
t1.<span class="me1">join</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span> t2.<span class="me1">join</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span> t3.<span class="me1">join</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
|
|
<a href="cpp-io-cout.html"><span class="kw1757">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"All threads completed, the last one deleted Derived<span class="es1">\n</span>"</span><span class="sy4">;</span>
|
|
<span class="br0">}</span></pre></div>
|
|
</div>
|
|
<p>可能的输出：</p>
|
|
<div dir="ltr" class="mw-geshi" style="text-align: left;">
|
|
<div class="text source-text">
|
|
<pre class="de1">Base::Base()
|
|
Derived::Derived()
|
|
Created a shared Derived (as a pointer to Base)
|
|
p.get() = 0x2299b30, p.use_count() = 1
|
|
Shared ownership between 3 threads and released
|
|
ownership from main:
|
|
p.get() = 0, p.use_count() = 0
|
|
local pointer in a thread:
|
|
lp.get() = 0x2299b30, lp.use_count() = 5
|
|
local pointer in a thread:
|
|
lp.get() = 0x2299b30, lp.use_count() = 3
|
|
local pointer in a thread:
|
|
lp.get() = 0x2299b30, lp.use_count() = 2
|
|
Derived::~Derived()
|
|
Base::~Base()
|
|
All threads completed, the last one deleted Derived</pre></div>
|
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</div>
|
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</div>
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</div>
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<div class="visualClear"></div>
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</div>
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</div>
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</div>
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</body>
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</html>
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