72 lines
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HTML
72 lines
5.0 KiB
HTML
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<title>std::shared_ptr 的推导指引</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_memory_shared_ptr_deduction_guides skin-cppreference2 action-view cpp-navbar">
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<h1 id="firstHeading" class="firstHeading"><code>std::shared_ptr</code> 的推导指引</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>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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<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><br />
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shared_ptr<span class="br0">(</span><a href="cpp-memory-weak_ptr.html"><span class="kw741">std::<span class="me2">weak_ptr</span></span></a><span class="sy1"><</span>T<span class="sy1">></span><span class="br0">)</span> <span class="sy2">-</span><span class="sy1">></span> shared_ptr<span class="sy1"><</span>T<span class="sy1">></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-cxx17">(C++17 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> T, <span class="kw1">class</span> D<span class="sy1">></span><br />
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shared_ptr<span class="br0">(</span><a href="cpp-memory-unique_ptr.html"><span class="kw733">std::<span class="me2">unique_ptr</span></span></a><span class="sy1"><</span>T, D<span class="sy1">></span><span class="br0">)</span> <span class="sy2">-</span><span class="sy1">></span> shared_ptr<span class="sy1"><</span>T<span class="sy1">></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-cxx17">(C++17 起)</span></td>
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<p>为 <span class="t-lc"><a href="cpp-memory-shared_ptr.html">std::shared_ptr</a></span> 提供此<a href="cpp-language-class_template_argument_deduction.html">推导指引</a>，以囊括隐式推导指引所错失的极端情况。</p>
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<p>注意没有从指针类型的类模板实参推导，因为不可能辨别获得自 <code>new</code> 的数组和非数组形式的指针。</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="cpp source-cpp">
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<pre class="de1"><span class="co2">#include <memory></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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<span class="kw4">auto</span> p <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><span class="kw4">int</span><span class="sy1">></span><span class="br0">(</span><span class="nu0">42</span><span class="br0">)</span><span class="sy4">;</span>
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<a href="cpp-memory-weak_ptr.html"><span class="kw741">std::<span class="me2">weak_ptr</span></span></a> w<span class="br0">{</span>p<span class="br0">}</span><span class="sy4">;</span> <span class="co1">// 用于此情况的显式推导指引</span>
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<a href="cpp-memory-shared_ptr.html"><span class="kw734">std::<span class="me2">shared_ptr</span></span></a> p2<span class="br0">{</span>w<span class="br0">}</span><span class="sy4">;</span> <span class="co1">// 用于此情况的显式推导指引</span>
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<span class="br0">}</span></pre></div>
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