241 lines
27 KiB
HTML
241 lines
27 KiB
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<title>std::static_pointer_cast, std::dynamic_pointer_cast, std::const_pointer_cast, std::reinterpret_pointer_cast</title>
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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::</span>static_pointer_cast, <span style="font-size:0.7em; line-height:130%">std::</span>dynamic_pointer_cast, <span style="font-size:0.7em; line-height:130%">std::</span>const_pointer_cast, <span style="font-size:0.7em; line-height:130%">std::</span>reinterpret_pointer_cast</h1>
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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 id="mw-content-text" lang="zh" dir="ltr" class="mw-content-ltr" xml:lang="zh">
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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="kw1">class</span> U <span class="sy1">></span><br />
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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>T<span class="sy1">></span> static_pointer_cast<span class="br0">(</span> <span class="kw4">const</span> <a href="cpp-memory-shared_ptr.html"><span class="kw734">std::<span class="me2">shared_ptr</span></span></a><span class="sy1"><</span>U<span class="sy1">></span><span class="sy3">&</span> r <span class="br0">)</span> <span class="kw1">noexcept</span><span class="sy4">;</span></span></div>
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</td>
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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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</tr>
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<tr class="t-dcl t-since-cxx20">
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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="kw1">class</span> U <span class="sy1">></span><br />
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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>T<span class="sy1">></span> static_pointer_cast<span class="br0">(</span> <a href="cpp-memory-shared_ptr.html"><span class="kw734">std::<span class="me2">shared_ptr</span></span></a><span class="sy1"><</span>U<span class="sy1">></span><span class="sy3">&&</span> r <span class="br0">)</span> <span class="kw1">noexcept</span><span class="sy4">;</span></span></div>
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</td>
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<td>(2)</td>
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<td><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></td>
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</tr>
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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> T, <span class="kw1">class</span> U <span class="sy1">></span><br />
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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>T<span class="sy1">></span> dynamic_pointer_cast<span class="br0">(</span> <span class="kw4">const</span> <a href="cpp-memory-shared_ptr.html"><span class="kw734">std::<span class="me2">shared_ptr</span></span></a><span class="sy1"><</span>U<span class="sy1">></span><span class="sy3">&</span> r <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><span class="t-mark-rev t-since-cxx11">(C++11 起)</span></td>
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</tr>
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<tr class="t-dcl t-since-cxx20">
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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="kw1">class</span> U <span class="sy1">></span><br />
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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>T<span class="sy1">></span> dynamic_pointer_cast<span class="br0">(</span> <a href="cpp-memory-shared_ptr.html"><span class="kw734">std::<span class="me2">shared_ptr</span></span></a><span class="sy1"><</span>U<span class="sy1">></span><span class="sy3">&&</span> r <span class="br0">)</span> <span class="kw1">noexcept</span><span class="sy4">;</span></span></div>
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</td>
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<td>(4)</td>
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<td><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></td>
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</tr>
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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> T, <span class="kw1">class</span> U <span class="sy1">></span><br />
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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>T<span class="sy1">></span> const_pointer_cast<span class="br0">(</span> <span class="kw4">const</span> <a href="cpp-memory-shared_ptr.html"><span class="kw734">std::<span class="me2">shared_ptr</span></span></a><span class="sy1"><</span>U<span class="sy1">></span><span class="sy3">&</span> r <span class="br0">)</span> <span class="kw1">noexcept</span><span class="sy4">;</span></span></div>
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</td>
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<td>(5)</td>
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<td><span class="t-mark-rev t-since-cxx11">(C++11 起)</span></td>
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</tr>
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<tr class="t-dcl t-since-cxx20">
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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="kw1">class</span> U <span class="sy1">></span><br />
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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>T<span class="sy1">></span> const_pointer_cast<span class="br0">(</span> <a href="cpp-memory-shared_ptr.html"><span class="kw734">std::<span class="me2">shared_ptr</span></span></a><span class="sy1"><</span>U<span class="sy1">></span><span class="sy3">&&</span> r <span class="br0">)</span> <span class="kw1">noexcept</span><span class="sy4">;</span></span></div>
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</td>
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<td>(6)</td>
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<td><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></td>
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</tr>
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<tr class="t-dcl t-since-cxx17">
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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="kw1">class</span> U <span class="sy1">></span><br />
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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>T<span class="sy1">></span> reinterpret_pointer_cast<span class="br0">(</span> <span class="kw4">const</span> <a href="cpp-memory-shared_ptr.html"><span class="kw734">std::<span class="me2">shared_ptr</span></span></a><span class="sy1"><</span>U<span class="sy1">></span><span class="sy3">&</span> r <span class="br0">)</span> <span class="kw1">noexcept</span><span class="sy4">;</span></span></div>
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</td>
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<td>(7)</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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<tr class="t-dcl t-since-cxx20">
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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="kw1">class</span> U <span class="sy1">></span><br />
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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>T<span class="sy1">></span> reinterpret_pointer_cast<span class="br0">(</span> <a href="cpp-memory-shared_ptr.html"><span class="kw734">std::<span class="me2">shared_ptr</span></span></a><span class="sy1"><</span>U<span class="sy1">></span><span class="sy3">&&</span> r <span class="br0">)</span> <span class="kw1">noexcept</span><span class="sy4">;</span></span></div>
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</td>
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<td>(8)</td>
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<td><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></td>
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</tr>
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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>创建 <span class="t-lc"><a href="cpp-memory-shared_ptr.html">std::shared_ptr</a></span> 的新实例，其存储指针从 <code>r</code> 的存储指针用转型表达式获得。</p>
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<p>若 <code>r</code> 为空，则新的 <code>shared_ptr</code> 亦然（但其存储指针不必为空）。否则，新的 <code>shared_ptr</code> 将与 <code>r</code> 的初始值共享所有权，除了若 <code>dynamic_pointer_cast</code> 所进行的 <code>dynamic_cast</code> 返回空指针，则为它空。</p>
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<p>令 <code>Y</code> 为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw1">typename</span> <a href="cpp-memory-shared_ptr.html"><span class="kw734">std::<span class="me2">shared_ptr</span></span></a><span class="sy1"><</span>T<span class="sy1">></span><span class="sy4">::</span><span class="me2">element_type</span></span></span> ，则将分别通过求值下列表达式，获得生成 <span class="t-lc"><a href="cpp-memory-shared_ptr.html">std::shared_ptr</a></span> 的存储指针：</p>
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<div class="t-li1"><span class="t-li">1-2)</span> <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw1">static_cast</span><span class="sy1"><</span>Y<span class="sy2">*</span><span class="sy1">></span><span class="br0">(</span>r.<span class="me1">get</span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span></span></span> 。</div>
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<div class="t-li1"><span class="t-li">3-4)</span> <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw1">dynamic_cast</span><span class="sy1"><</span>Y<span class="sy2">*</span><span class="sy1">></span><span class="br0">(</span>r.<span class="me1">get</span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span></span></span> （若 <code>dynamic_cast</code> 的结果是空指针值，则返回的 <code>shared_ptr</code> 将为空）。</div>
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<div class="t-li1"><span class="t-li">5-6)</span> <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw1">const_cast</span><span class="sy1"><</span>Y<span class="sy2">*</span><span class="sy1">></span><span class="br0">(</span>r.<span class="me1">get</span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span></span></span> 。</div>
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<div class="t-li1"><span class="t-li">7-8)</span> <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw1">reinterpret_cast</span><span class="sy1"><</span>Y<span class="sy2">*</span><span class="sy1">></span><span class="br0">(</span>r.<span class="me1">get</span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span></span></span> 。</div>
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<p>这些函数的行为未定义，除非从 <code>U*</code> 到 <code>T*</code> 的对应转型为良式：</p>
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<div class="t-li1"><span class="t-li">1-2)</span> 行为未定义，除非 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw1">static_cast</span><span class="sy1"><</span>T<span class="sy2">*</span><span class="sy1">></span><span class="br0">(</span><span class="br0">(</span>U<span class="sy2">*</span><span class="br0">)</span>nullptr<span class="br0">)</span></span></span> 为良式。</div>
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<div class="t-li1"><span class="t-li">3-4)</span> 行为未定义，除非 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw1">dynamic_cast</span><span class="sy1"><</span>T<span class="sy2">*</span><span class="sy1">></span><span class="br0">(</span><span class="br0">(</span>U<span class="sy2">*</span><span class="br0">)</span>nullptr<span class="br0">)</span></span></span> 为良式。</div>
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<div class="t-li1"><span class="t-li">5-6)</span> 行为未定义，除非 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw1">const_cast</span><span class="sy1"><</span>T<span class="sy2">*</span><span class="sy1">></span><span class="br0">(</span><span class="br0">(</span>U<span class="sy2">*</span><span class="br0">)</span>nullptr<span class="br0">)</span></span></span> 为良式。</div>
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<div class="t-li1"><span class="t-li">7-8)</span> 行为未定义，除非 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw1">reinterpret_cast</span><span class="sy1"><</span>T<span class="sy2">*</span><span class="sy1">></span><span class="br0">(</span><span class="br0">(</span>U<span class="sy2">*</span><span class="br0">)</span>nullptr<span class="br0">)</span></span></span> 为良式。</div>
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<table class="t-rev-begin">
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<tr class="t-rev t-since-cxx20">
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<td>
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<p>调用右值重载 <span class="t-v">(2,4,6,8)</span> 后， <code>r</code> 为空且 <span class="t-c"><span class="mw-geshi cpp source-cpp">r.<span class="me1">get</span><span class="br0">(</span><span class="br0">)</span> <span class="sy1">==</span> nullptr</span></span> ，除了对于 <code>dynamic_pointer_cast</code> <span class="t-v">(4)</span> ，若 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw1">dynamic_cast</span></span></span> 失败则不修改 <code>r</code> 。</p>
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</td>
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<td><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></td>
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</tr>
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</table>
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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>r</td>
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<td>-</td>
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<td>要转换的指针</td>
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</tr>
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</table>
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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>表达式 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-memory-shared_ptr.html"><span class="kw734">std::<span class="me2">shared_ptr</span></span></a><span class="sy1"><</span>T<span class="sy1">></span><span class="br0">(</span><span class="kw1">static_cast</span><span class="sy1"><</span>T<span class="sy2">*</span><span class="sy1">></span><span class="br0">(</span>r.<span class="me1">get</span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span><span class="br0">)</span></span></span> 、 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-memory-shared_ptr.html"><span class="kw734">std::<span class="me2">shared_ptr</span></span></a><span class="sy1"><</span>T<span class="sy1">></span><span class="br0">(</span><span class="kw1">dynamic_cast</span><span class="sy1"><</span>T<span class="sy2">*</span><span class="sy1">></span><span class="br0">(</span>r.<span class="me1">get</span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span><span class="br0">)</span></span></span> 及 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-memory-shared_ptr.html"><span class="kw734">std::<span class="me2">shared_ptr</span></span></a><span class="sy1"><</span>T<span class="sy1">></span><span class="br0">(</span><span class="kw1">const_cast</span><span class="sy1"><</span>T<span class="sy2">*</span><span class="sy1">></span><span class="br0">(</span>r.<span class="me1">get</span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span><span class="br0">)</span></span></span> 看起来可能拥有相同效果，但它们全都很可能导致未定义行为，试图删除同一对象二次！</p>
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<h3><span class="mw-headline" id=".E5.8F.AF.E8.83.BD.E7.9A.84.E5.AE.9E.E7.8E.B0">可能的实现</span></h3>
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<table class="eq-fun-cpp-table">
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<tr>
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<th>版本一</th>
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</tr>
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<tr>
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<td>
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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="kw1">template</span><span class="sy1"><</span> <span class="kw1">class</span> T, <span class="kw1">class</span> U <span class="sy1">></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>T<span class="sy1">></span> static_pointer_cast<span class="br0">(</span> <span class="kw4">const</span> <a href="cpp-memory-shared_ptr.html"><span class="kw734">std::<span class="me2">shared_ptr</span></span></a><span class="sy1"><</span>U<span class="sy1">></span><span class="sy3">&</span> r <span class="br0">)</span> <span class="kw1">noexcept</span>
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<span class="br0">{</span>
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<span class="kw4">auto</span> p <span class="sy1">=</span> <span class="kw1">static_cast</span><span class="sy1"><</span><span class="kw1">typename</span> <a href="cpp-memory-shared_ptr.html"><span class="kw734">std::<span class="me2">shared_ptr</span></span></a><span class="sy1"><</span>T<span class="sy1">></span><span class="sy4">::</span><span class="me2">element_type</span><span class="sy2">*</span><span class="sy1">></span><span class="br0">(</span>r.<span class="me1">get</span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="kw1">return</span> <a href="cpp-memory-shared_ptr.html"><span class="kw734">std::<span class="me2">shared_ptr</span></span></a><span class="sy1"><</span>T<span class="sy1">></span><span class="br0">(</span>r, p<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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</td>
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<tr>
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<th>版本二</th>
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</tr>
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<tr>
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<td>
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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="kw1">template</span><span class="sy1"><</span> <span class="kw1">class</span> T, <span class="kw1">class</span> U <span class="sy1">></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>T<span class="sy1">></span> dynamic_pointer_cast<span class="br0">(</span> <span class="kw4">const</span> <a href="cpp-memory-shared_ptr.html"><span class="kw734">std::<span class="me2">shared_ptr</span></span></a><span class="sy1"><</span>U<span class="sy1">></span><span class="sy3">&</span> r <span class="br0">)</span> <span class="kw1">noexcept</span>
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<span class="br0">{</span>
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<span class="kw1">if</span> <span class="br0">(</span><span class="kw4">auto</span> p <span class="sy1">=</span> <span class="kw1">dynamic_cast</span><span class="sy1"><</span><span class="kw1">typename</span> <a href="cpp-memory-shared_ptr.html"><span class="kw734">std::<span class="me2">shared_ptr</span></span></a><span class="sy1"><</span>T<span class="sy1">></span><span class="sy4">::</span><span class="me2">element_type</span><span class="sy2">*</span><span class="sy1">></span><span class="br0">(</span>r.<span class="me1">get</span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span><span class="br0">)</span> <span class="br0">{</span>
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<span class="kw1">return</span> <a href="cpp-memory-shared_ptr.html"><span class="kw734">std::<span class="me2">shared_ptr</span></span></a><span class="sy1"><</span>T<span class="sy1">></span><span class="br0">(</span>r, p<span class="br0">)</span><span class="sy4">;</span>
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<span class="br0">}</span> <span class="kw1">else</span> <span class="br0">{</span>
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<span class="kw1">return</span> <a href="cpp-memory-shared_ptr.html"><span class="kw734">std::<span class="me2">shared_ptr</span></span></a><span class="sy1"><</span>T<span class="sy1">></span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="br0">}</span>
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<span class="br0">}</span></pre></div>
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</div>
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</td>
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</tr>
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<tr>
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<th>版本三</th>
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</tr>
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<tr>
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<td>
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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="kw1">template</span><span class="sy1"><</span> <span class="kw1">class</span> T, <span class="kw1">class</span> U <span class="sy1">></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>T<span class="sy1">></span> const_pointer_cast<span class="br0">(</span> <span class="kw4">const</span> <a href="cpp-memory-shared_ptr.html"><span class="kw734">std::<span class="me2">shared_ptr</span></span></a><span class="sy1"><</span>U<span class="sy1">></span><span class="sy3">&</span> r <span class="br0">)</span> <span class="kw1">noexcept</span>
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<span class="br0">{</span>
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<span class="kw4">auto</span> p <span class="sy1">=</span> <span class="kw1">const_cast</span><span class="sy1"><</span><span class="kw1">typename</span> <a href="cpp-memory-shared_ptr.html"><span class="kw734">std::<span class="me2">shared_ptr</span></span></a><span class="sy1"><</span>T<span class="sy1">></span><span class="sy4">::</span><span class="me2">element_type</span><span class="sy2">*</span><span class="sy1">></span><span class="br0">(</span>r.<span class="me1">get</span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="kw1">return</span> <a href="cpp-memory-shared_ptr.html"><span class="kw734">std::<span class="me2">shared_ptr</span></span></a><span class="sy1"><</span>T<span class="sy1">></span><span class="br0">(</span>r, p<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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</td>
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</tr>
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</table>
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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> BaseClass <span class="br0">{</span><span class="br0">}</span><span class="sy4">;</span>
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<span class="kw1">struct</span> DerivedClass <span class="sy4">:</span> BaseClass
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<span class="br0">{</span>
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<span class="kw4">void</span> f<span class="br0">(</span><span class="br0">)</span> <span class="kw4">const</span>
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<span class="br0">{</span>
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<a href="cpp-io-cout.html"><span class="kw1755">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"Hello World!<span class="es1">\n</span>"</span><span class="sy4">;</span>
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<span class="br0">}</span>
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~DerivedClass<span class="br0">(</span><span class="br0">)</span><span class="br0">{</span> <span class="co1">// 注意：它不是虚的</span>
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<a href="cpp-io-cout.html"><span class="kw1755">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"~DerivedClass<span class="es1">\n</span>"</span><span class="sy4">;</span>
|
|
<span class="br0">}</span>
|
|
<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>
|
|
<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>BaseClass<span class="sy1">></span> ptr_to_base<span class="br0">(</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>DerivedClass<span class="sy1">></span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
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|
<span class="co1">// ptr_to_base->f(); // 错误不会编译： BaseClass 无名为 'f' 的成员</span>
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|
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|
std<span class="sy4">::</span><span class="me2">static_pointer_cast</span><span class="sy1"><</span>DerivedClass<span class="sy1">></span><span class="br0">(</span>ptr_to_base<span class="br0">)</span><span class="sy2">-</span><span class="sy1">></span>f<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// OK</span>
|
|
<span class="co1">// （构造临时 shared_ptr ，然后调用 operator-> ）</span>
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|
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|
<span class="kw1">static_cast</span><span class="sy1"><</span>DerivedClass<span class="sy2">*</span><span class="sy1">></span><span class="br0">(</span>ptr_to_base.<span class="me1">get</span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span><span class="sy2">-</span><span class="sy1">></span>f<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 亦 OK</span>
|
|
<span class="co1">// （直接转型，不构造临时 shared_ptr ）</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">Hello World!
|
|
Hello World!
|
|
~DerivedClass</pre></div>
|
|
</div>
|
|
</div>
|
|
<h3><span class="mw-headline" id=".E5.8F.82.E9.98.85">参阅</span></h3>
|
|
<table class="t-dsc-begin">
|
|
<tr class="t-dsc">
|
|
<td>
|
|
<div class="t-dsc-member-div t-dsc-member-nobold-div">
|
|
<div><a href="cpp-memory-shared_ptr-shared_ptr.html"><span class="t-lines"><span>(构造函数)</span></span></a></div>
|
|
</div>
|
|
</td>
|
|
<td>构造新的 <code>shared_ptr</code><br />
|
|
<span class="t-mark">(公开成员函数)</span></td>
|
|
</tr>
|
|
</table>
|
|
</div>
|
|
<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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