136 lines
9.0 KiB
HTML
136 lines
9.0 KiB
HTML
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<title>std::pointer_traits<Ptr>::pointer_to</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_memory_pointer_traits_pointer_to 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::pointer_traits<Ptr>::</span>pointer_to</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-pointer_traits.html">pointer traits</a></span></div>
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<table class="t-dcl-begin">
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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="kw4">static</span> pointer<br />
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pointer_to<span class="br0">(</span> element_type<span class="sy3">&</span> r <span class="br0">)</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><br />
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<span class="t-mark">(<code>pointer_traits<Ptr></code> 特化的成员)</span></td>
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</tbody>
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<tbody class="t-dcl-rev t-dcl-rev-num">
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<td rowspan="142">(2)</td>
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<td></td>
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<tr class="t-dcl t-since-cxx11 t-until-cxx20">
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<div><span class="mw-geshi cpp source-cpp"><span class="kw4">static</span> pointer<br />
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pointer_to<span class="br0">(</span> element_type<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 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><br />
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<span class="t-mark">(<code>pointer_traits<T*></code> 特化的成员)</span></td>
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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="kw4">static</span> <span class="kw4">constexpr</span> pointer<br />
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pointer_to<span class="br0">(</span> element_type<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 class="t-dcl-nopad"></td>
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<td><span class="t-mark-rev t-since-cxx20">(C++20 起)</span><br />
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<span class="t-mark">(<code>pointer_traits<T*></code> 特化的成员)</span></td>
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<p>构造一个指向其参数的可解引用指针或类指针对象（“缀饰指针”）。</p>
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<div class="t-li1"><span class="t-li">1)</span> 此函数于非特化 <span class="t-lc"><a href="cpp-memory-pointer_traits.html">std::pointer_traits</a></span> 模板的版本简单地调用 <span class="t-c"><span class="mw-geshi cpp source-cpp">Ptr<span class="sy4">::</span><span class="me2">pointer_to</span><span class="br0">(</span>r<span class="br0">)</span></span></span> ，且若 Ptr 不提供静态成员函数 <code>pointer_to</code> ，则此函数的实例化为编译时错误。</div>
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<div class="t-li1"><span class="t-li">2)</span> 此函数于 <span class="t-lc"><a href="cpp-memory-pointer_traits.html">std::pointer_traits</a></span> 为指针类型特化的版本返回 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-memory-addressof.html"><span class="kw757">std::<span class="me2">addressof</span></span></a><span class="br0">(</span>r<span class="br0">)</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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<td>r</td>
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<td>-</td>
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<td><span class="t-c"><span class="mw-geshi cpp source-cpp">element_type<span class="sy3">&</span></span></span> 类型的到对象引用，除非 element_type 为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">void</span></span></span> ，此情况下 <code>r</code> 的类型未指定</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>指向 <code>r</code> 的可解引用指针，拥有 pointer_traits<>::pointer 类型。</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">1)</span> 未指定（通常同 <span class="t-c"><span class="mw-geshi cpp source-cpp">Ptr<span class="sy4">::</span><span class="me2">pointer_to</span></span></span> ）</div>
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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>若 Ptr::pointer_to 不存在，则此函数的 <a rel="nofollow" class="external text" href="http://www.boost.org/doc/libs/release/doc/html/boost/intrusive/pointer_traits.html">Boost.Intrusive 库版本</a> 返回 <span class="t-c"><span class="mw-geshi cpp source-cpp">pointer<span class="br0">(</span><a href="cpp-memory-addressof.html"><span class="kw757">std::<span class="me2">addressof</span></span></a><span class="br0">(</span>r<span class="br0">)</span><span class="br0">)</span></span></span> 。</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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<td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-memory-addressof.html"><span class="t-lines"><span>addressof</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>获得对象的实际地址，即使其重载了 <i>&</i> 运算符<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-allocator-address.html"><span class="t-lines"><span>address</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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</div>
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</td>
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<td>获得对象的地址，即使重载了 <span class="t-c"><span class="mw-geshi cpp source-cpp">operator<span class="sy3">&</span></span></span><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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<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-pointer_traits-to_address.html"><span class="t-lines"><span>to_address</span></span></a></div>
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<div><span class="t-lines"><span><span class="t-cmark">[静态]</span> <span class="t-mark-rev t-since-cxx20">(C++20)</span><span class="t-mark">(可选)</span></span></span></div>
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</div>
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</td>
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<td>从缀饰指针获得裸指针（ <code>pointer_to</code> 的反函数）<br />
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<span class="t-mark">(公开静态成员函数)</span></td>
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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-to_address.html"><span class="t-lines"><span>to_address</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>从指针式类型获得裸指针<br />
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<span class="t-mark">(函数模板)</span></td>
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</tr>
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</table>
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<div class="visualClear"></div>
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