122 lines
8.0 KiB
HTML
122 lines
8.0 KiB
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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<title>std::allocator_traits<Alloc>::construct</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_memory_allocator_traits_construct 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::allocator_traits<Alloc>::</span>construct</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-allocator_traits.html">allocator traits</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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<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>... <span class="me1">Args</span> <span class="sy1">></span><br />
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<span class="kw4">static</span> <span class="kw4">void</span> construct<span class="br0">(</span> Alloc<span class="sy3">&</span> a, T<span class="sy2">*</span> p, Args<span class="sy3">&&</span>... <span class="me1">args</span> <span class="br0">)</span><span class="sy4">;</span></span></div>
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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><br />
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<span class="t-mark-rev t-until-cxx20">(C++20 前)</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>... <span class="me1">Args</span> <span class="sy1">></span><br />
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<span class="kw4">static</span> <span class="kw4">constexpr</span> <span class="kw4">void</span> construct<span class="br0">(</span> Alloc<span class="sy3">&</span> a, T<span class="sy2">*</span> p, Args<span class="sy3">&&</span>... <span class="me1">args</span> <span class="br0">)</span><span class="sy4">;</span></span></div>
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<td class="t-dcl-nopad"></td>
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<td><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></td>
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<td></td>
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<p>若可能，则在 <code>p</code> 所指向的分配的未初始化存储构造 <code>T</code> 类型对象，通过调用</p>
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<p><span class="t-c"><span class="mw-geshi cpp source-cpp">a.<span class="me1">construct</span><span class="br0">(</span>p, <a href="cpp-utility-forward.html"><span class="kw1117">std::<span class="me2">forward</span></span></a><span class="sy1"><</span>Args<span class="sy1">></span><span class="br0">(</span>args<span class="br0">)</span>...<span class="br0">)</span></span></span></p>
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<p>若以上不可行（例如 <code>Alloc</code> 无 <code>construct()</code> 成员函数），则调用</p>
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<p><span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy4">::</span><span class="me2">new</span> <span class="br0">(</span><span class="kw1">static_cast</span><span class="sy1"><</span><span class="kw4">void</span><span class="sy2">*</span><span class="sy1">></span><span class="br0">(</span>p<span class="br0">)</span><span class="br0">)</span> T<span class="br0">(</span><a href="cpp-utility-forward.html"><span class="kw1117">std::<span class="me2">forward</span></span></a><span class="sy1"><</span>Args<span class="sy1">></span><span class="br0">(</span>args<span class="br0">)</span>...<span class="br0">)</span></span></span></p>
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<td><span class="t-mark-rev t-until-cxx20">(C++20 前)</span></td>
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<p><span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">construct_at</span><span class="br0">(</span>p, <a href="cpp-utility-forward.html"><span class="kw1117">std::<span class="me2">forward</span></span></a><span class="sy1"><</span>Args<span class="sy1">></span><span class="br0">(</span>args<span class="br0">)</span>...<span class="br0">)</span></span></span></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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<h3><span class="mw-headline" id=".E5.8F.82.E6.95.B0">参数</span></h3>
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<td>a</td>
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<td>-</td>
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<td>用于构造的分配器</td>
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<tr class="t-par">
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<td>p</td>
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<td>-</td>
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<td>指向未初始化存储的指针，将在其上构造 <code>T</code> 对象</td>
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<td>args...</td>
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<td>-</td>
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<td>传递给 <code>a.construct()</code> 或<span class="t-rev-inl t-until-cxx20"><span>布置 new</span> <span><span class="t-mark-rev t-until-cxx20">(C++20 前)</span></span></span> <span class="t-rev-inl t-since-cxx20"><span><span class="t-lc">std::construct_at()</span></span> <span><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></span></span> 的参数</td>
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<h3><span class="mw-headline" id=".E8.BF.94.E5.9B.9E.E5.80.BC">返回值</span></h3>
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<p>（无）</p>
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<h3><span class="mw-headline" id=".E6.B3.A8.E8.A7.A3">注解</span></h3>
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<p>此函数为标准库容器在插入、复制或移动元素时所用。</p>
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<p>因为此函数提供到布置 new 的自动回落，故 C++11 起成员函数 <code>construct()</code> 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> 的可选要求。</p>
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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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<div class="t-dsc-member-div">
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<div><a href="cpp-memory-new-operator_new.html"><span class="t-lines"><span>operator new</span><span>operator new[]</span></span></a></div>
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<td>分配函数<br />
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<span class="t-mark">(函数)</span></td>
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<tr class="t-dsc">
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<div class="t-dsc-member-div">
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<div><a href="cpp-memory-allocator-construct.html"><span class="t-lines"><span>construct</span></span></a></div>
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<div><span class="t-lines"><span><span class="t-mark-rev t-deprecated-cxx17">(C++17 中弃用)</span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span></span></div>
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<td>在分配的存储构造对象<br />
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<span class="t-mark">(<code>std::allocator<T></code> 的公开成员函数)</span></td>
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</div>
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<div class="visualClear"></div>
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