373 lines
39 KiB
HTML
373 lines
39 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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<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
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<title>标准库头文件 <variant></title>
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<link rel="stylesheet" href="ext.css" />
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<link rel="stylesheet" href="site_modules.css" />
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</head>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_header_variant skin-cppreference2 action-view cpp-navbar">
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<div id="cpp-content-base">
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<div id="content"><a id="top"></a>
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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">标准库头文件</span> <variant></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-header.html">header</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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<p>此头文件是<a href="cpp-utility.html">通用工具</a>库的一部分。</p>
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<table class="t-dsc-begin">
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<tr>
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<td colspan="2">
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<h3><span class="mw-headline" id=".E5.8C.85.E5.90.AB">包含</span></h3>
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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-header-compare.html"><span class="t-lines"><span><compare></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><a href="cpp-language-operator_comparison.html#.E4.B8.89.E8.B7.AF.E6.AF.94.E8.BE.83">三路比较运算符</a>支持</td>
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</tr>
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<tr>
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<td colspan="2">
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<h3><span class="mw-headline" id=".E7.B1.BB">类</span></h3>
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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-utility-variant.html"><span class="t-lines"><span>variant</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>类型安全的可辨识联合体<br />
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<span class="t-mark">(类模板)</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-utility-variant-monostate.html"><span class="t-lines"><span>monostate</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>用作非可默认构造类型的 <code>variant</code> 的首个可选项的占位符类型<br />
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<span class="t-mark">(类)</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-utility-variant-bad_variant_access.html"><span class="t-lines"><span>bad_variant_access</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>非法地访问 <code>variant</code> 的值时抛出的异常<br />
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<span class="t-mark">(类)</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-utility-variant-variant_size.html"><span class="t-lines"><span>variant_size</span><span>variant_size_v</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>在编译时获得 <code>variant</code> 可选项列表的大小<br />
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<span class="t-mark">(类模板)</span> <span class="t-mark">(变量模板)</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-utility-variant-variant_alternative.html"><span class="t-lines"><span>variant_alternative</span><span>variant_alternative_t</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>在编译时获得以其下标指定的可选项的类型<br />
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<span class="t-mark">(类模板)</span> <span class="t-mark">(别名模板)</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-utility-variant-hash.html"><span class="t-lines"><span>std::hash<span class="t-dsc-small"><std::variant></span></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>特化 <span class="t-lc"><a href="cpp-utility-hash.html">std::hash</a></span> 算法<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>
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<td colspan="2">
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<h3><span class="mw-headline" id=".E5.B8.B8.E9.87.8F">常量</span></h3>
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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-utility-variant-variant_npos.html"><span class="t-lines"><span>variant_npos</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>非法状态的 <code>variant</code> 的下标<br />
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<span class="t-mark">(常量)</span></td>
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</tr>
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<tr>
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<td colspan="2">
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<h3><span class="mw-headline" id=".E5.87.BD.E6.95.B0">函数</span></h3>
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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-utility-variant-visit.html"><span class="t-lines"><span>visit</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>以一或多个 <code>variant</code> 所保有的各实参调用所提供的函数对象<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-utility-variant-holds_alternative.html"><span class="t-lines"><span>holds_alternative</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>检查某个 <code>variant</code> 是否当前持有某个给定类型<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-utility-variant-get.html"><span class="t-lines"><span>std::get<span class="t-dsc-small">(std::variant)</span></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>以给定索引或类型（若类型唯一）读取 <code>variant</code> 的值，错误时抛出异常<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-utility-variant-get_if.html"><span class="t-lines"><span>get_if</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>以给定索引或类型（若其唯一），获得指向被指向的 variant 的值的指针，错误时返回空指针<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-utility-variant-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 class="t-mark-rev t-since-cxx17">(C++17)</span></span><span><span class="t-mark-rev t-since-cxx17">(C++17)</span></span><span><span class="t-mark-rev t-since-cxx17">(C++17)</span></span><span><span class="t-mark-rev t-since-cxx17">(C++17)</span></span><span><span class="t-mark-rev t-since-cxx17">(C++17)</span></span><span><span class="t-mark-rev t-since-cxx17">(C++17)</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>以所含值比较 <code>variant</code> 对象<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-utility-variant-swap2.html"><span class="t-lines"><span>std::swap<span class="t-dsc-small">(std::variant)</span></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>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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<h3><span class="mw-headline" id=".E6.A6.82.E8.A6.81">概要</span></h3>
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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 <compare></span>
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<span class="kw1">namespace</span> std <span class="br0">{</span>
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<span class="co1">// 类模板 variant</span>
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<span class="kw1">template</span><span class="sy1"><</span><span class="kw1">class</span>... <span class="me1">Types</span><span class="sy1">></span>
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<span class="kw1">class</span> variant<span class="sy4">;</span>
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<span class="co1">// variant helper classes</span>
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<span class="kw1">template</span><span class="sy1"><</span><span class="kw1">class</span> T<span class="sy1">></span> <span class="kw1">struct</span> variant_size<span class="sy4">;</span> <span class="co1">// 不定义</span>
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<span class="kw1">template</span><span class="sy1"><</span><span class="kw1">class</span> T<span class="sy1">></span> <span class="kw1">struct</span> variant_size<span class="sy1"><</span><span class="kw4">const</span> T<span class="sy1">></span><span class="sy4">;</span>
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<span class="kw1">template</span><span class="sy1"><</span><span class="kw1">class</span> T<span class="sy1">></span>
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<span class="kw1">inline</span> <span class="kw4">constexpr</span> size_t variant_size_v <span class="sy1">=</span> variant_size<span class="sy1"><</span>T<span class="sy1">></span><span class="sy4">::</span><span class="me2">value</span><span class="sy4">;</span>
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<span class="kw1">template</span><span class="sy1"><</span><span class="kw1">class</span>... <span class="me1">Types</span><span class="sy1">></span>
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<span class="kw1">struct</span> variant_size<span class="sy1"><</span>variant<span class="sy1"><</span>Types...<span class="sy1">>></span><span class="sy4">;</span>
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<span class="kw1">template</span><span class="sy1"><</span>size_t I, <span class="kw1">class</span> T<span class="sy1">></span> <span class="kw1">struct</span> variant_alternative<span class="sy4">;</span> <span class="co1">// 不定义</span>
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<span class="kw1">template</span><span class="sy1"><</span>size_t I, <span class="kw1">class</span> T<span class="sy1">></span> <span class="kw1">struct</span> variant_alternative<span class="sy1"><</span>I, <span class="kw4">const</span> T<span class="sy1">></span><span class="sy4">;</span>
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<span class="kw1">template</span><span class="sy1"><</span>size_t I, <span class="kw1">class</span> T<span class="sy1">></span>
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<span class="kw1">using</span> variant_alternative_t <span class="sy1">=</span> <span class="kw1">typename</span> variant_alternative<span class="sy1"><</span>I, T<span class="sy1">></span><span class="sy4">::</span><span class="me2">type</span><span class="sy4">;</span>
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<span class="kw1">template</span><span class="sy1"><</span>size_t I, <span class="kw1">class</span>... <span class="me1">Types</span><span class="sy1">></span>
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<span class="kw1">struct</span> variant_alternative<span class="sy1"><</span>I, variant<span class="sy1"><</span>Types...<span class="sy1">>></span><span class="sy4">;</span>
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<span class="kw1">inline</span> <span class="kw4">constexpr</span> size_t variant_npos <span class="sy1">=</span> <span class="sy2">-</span><span class="nu0">1</span><span class="sy4">;</span>
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<span class="co1">// 值访问</span>
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<span class="kw1">template</span><span class="sy1"><</span><span class="kw1">class</span> T, <span class="kw1">class</span>... <span class="me1">Types</span><span class="sy1">></span>
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<span class="kw4">constexpr</span> <span class="kw4">bool</span> holds_alternative<span class="br0">(</span><span class="kw4">const</span> variant<span class="sy1"><</span>Types...<span class="sy1">></span><span class="sy3">&</span><span class="br0">)</span> <span class="kw1">noexcept</span><span class="sy4">;</span>
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<span class="kw1">template</span><span class="sy1"><</span>size_t I, <span class="kw1">class</span>... <span class="me1">Types</span><span class="sy1">></span>
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<span class="kw4">constexpr</span> variant_alternative_t<span class="sy1"><</span>I, variant<span class="sy1"><</span>Types...<span class="sy1">>></span><span class="sy3">&</span> get<span class="br0">(</span>variant<span class="sy1"><</span>Types...<span class="sy1">></span><span class="sy3">&</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="kw1">template</span><span class="sy1"><</span>size_t I, <span class="kw1">class</span>... <span class="me1">Types</span><span class="sy1">></span>
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<span class="kw4">constexpr</span> variant_alternative_t<span class="sy1"><</span>I, variant<span class="sy1"><</span>Types...<span class="sy1">>></span><span class="sy3">&&</span> get<span class="br0">(</span>variant<span class="sy1"><</span>Types...<span class="sy1">></span><span class="sy3">&&</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="kw1">template</span><span class="sy1"><</span>size_t I, <span class="kw1">class</span>... <span class="me1">Types</span><span class="sy1">></span>
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<span class="kw4">constexpr</span> <span class="kw4">const</span> variant_alternative_t<span class="sy1"><</span>I, variant<span class="sy1"><</span>Types...<span class="sy1">>></span><span class="sy3">&</span>
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get<span class="br0">(</span><span class="kw4">const</span> variant<span class="sy1"><</span>Types...<span class="sy1">></span><span class="sy3">&</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="kw1">template</span><span class="sy1"><</span>size_t I, <span class="kw1">class</span>... <span class="me1">Types</span><span class="sy1">></span>
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<span class="kw4">constexpr</span> <span class="kw4">const</span> variant_alternative_t<span class="sy1"><</span>I, variant<span class="sy1"><</span>Types...<span class="sy1">>></span><span class="sy3">&&</span>
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get<span class="br0">(</span><span class="kw4">const</span> variant<span class="sy1"><</span>Types...<span class="sy1">></span><span class="sy3">&&</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="kw1">template</span><span class="sy1"><</span><span class="kw1">class</span> T, <span class="kw1">class</span>... <span class="me1">Types</span><span class="sy1">></span>
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<span class="kw4">constexpr</span> T<span class="sy3">&</span> get<span class="br0">(</span>variant<span class="sy1"><</span>Types...<span class="sy1">></span><span class="sy3">&</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="kw1">template</span><span class="sy1"><</span><span class="kw1">class</span> T, <span class="kw1">class</span>... <span class="me1">Types</span><span class="sy1">></span>
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<span class="kw4">constexpr</span> T<span class="sy3">&&</span> get<span class="br0">(</span>variant<span class="sy1"><</span>Types...<span class="sy1">></span><span class="sy3">&&</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="kw1">template</span><span class="sy1"><</span><span class="kw1">class</span> T, <span class="kw1">class</span>... <span class="me1">Types</span><span class="sy1">></span>
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<span class="kw4">constexpr</span> <span class="kw4">const</span> T<span class="sy3">&</span> get<span class="br0">(</span><span class="kw4">const</span> variant<span class="sy1"><</span>Types...<span class="sy1">></span><span class="sy3">&</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="kw1">template</span><span class="sy1"><</span><span class="kw1">class</span> T, <span class="kw1">class</span>... <span class="me1">Types</span><span class="sy1">></span>
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<span class="kw4">constexpr</span> <span class="kw4">const</span> T<span class="sy3">&&</span> get<span class="br0">(</span><span class="kw4">const</span> variant<span class="sy1"><</span>Types...<span class="sy1">></span><span class="sy3">&&</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="kw1">template</span><span class="sy1"><</span>size_t I, <span class="kw1">class</span>... <span class="me1">Types</span><span class="sy1">></span>
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<span class="kw4">constexpr</span> add_pointer_t<span class="sy1"><</span>variant_alternative_t<span class="sy1"><</span>I, variant<span class="sy1"><</span>Types...<span class="sy1">>>></span>
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get_if<span class="br0">(</span>variant<span class="sy1"><</span>Types...<span class="sy1">></span><span class="sy2">*</span><span class="br0">)</span> <span class="kw1">noexcept</span><span class="sy4">;</span>
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<span class="kw1">template</span><span class="sy1"><</span>size_t I, <span class="kw1">class</span>... <span class="me1">Types</span><span class="sy1">></span>
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<span class="kw4">constexpr</span> add_pointer_t<span class="sy1"><</span><span class="kw4">const</span> variant_alternative_t<span class="sy1"><</span>I, variant<span class="sy1"><</span>Types...<span class="sy1">>>></span>
|
|
get_if<span class="br0">(</span><span class="kw4">const</span> variant<span class="sy1"><</span>Types...<span class="sy1">></span><span class="sy2">*</span><span class="br0">)</span> <span class="kw1">noexcept</span><span class="sy4">;</span>
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|
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<span class="kw1">template</span><span class="sy1"><</span><span class="kw1">class</span> T, <span class="kw1">class</span>... <span class="me1">Types</span><span class="sy1">></span>
|
|
<span class="kw4">constexpr</span> add_pointer_t<span class="sy1"><</span>T<span class="sy1">></span>
|
|
get_if<span class="br0">(</span>variant<span class="sy1"><</span>Types...<span class="sy1">></span><span class="sy2">*</span><span class="br0">)</span> <span class="kw1">noexcept</span><span class="sy4">;</span>
|
|
<span class="kw1">template</span><span class="sy1"><</span><span class="kw1">class</span> T, <span class="kw1">class</span>... <span class="me1">Types</span><span class="sy1">></span>
|
|
<span class="kw4">constexpr</span> add_pointer_t<span class="sy1"><</span><span class="kw4">const</span> T<span class="sy1">></span>
|
|
get_if<span class="br0">(</span><span class="kw4">const</span> variant<span class="sy1"><</span>Types...<span class="sy1">></span><span class="sy2">*</span><span class="br0">)</span> <span class="kw1">noexcept</span><span class="sy4">;</span>
|
|
|
|
<span class="co1">// 关系运算符</span>
|
|
<span class="kw1">template</span><span class="sy1"><</span><span class="kw1">class</span>... <span class="me1">Types</span><span class="sy1">></span>
|
|
<span class="kw4">constexpr</span> <span class="kw4">bool</span> operator<span class="sy1">==</span><span class="br0">(</span><span class="kw4">const</span> variant<span class="sy1"><</span>Types...<span class="sy1">></span><span class="sy3">&</span>, <span class="kw4">const</span> variant<span class="sy1"><</span>Types...<span class="sy1">></span><span class="sy3">&</span><span class="br0">)</span><span class="sy4">;</span>
|
|
<span class="kw1">template</span><span class="sy1"><</span><span class="kw1">class</span>... <span class="me1">Types</span><span class="sy1">></span>
|
|
<span class="kw4">constexpr</span> <span class="kw4">bool</span> operator<span class="sy3">!</span><span class="sy1">=</span><span class="br0">(</span><span class="kw4">const</span> variant<span class="sy1"><</span>Types...<span class="sy1">></span><span class="sy3">&</span>, <span class="kw4">const</span> variant<span class="sy1"><</span>Types...<span class="sy1">></span><span class="sy3">&</span><span class="br0">)</span><span class="sy4">;</span>
|
|
<span class="kw1">template</span><span class="sy1"><</span><span class="kw1">class</span>... <span class="me1">Types</span><span class="sy1">></span>
|
|
<span class="kw4">constexpr</span> <span class="kw4">bool</span> operator<span class="sy1"><</span><span class="br0">(</span><span class="kw4">const</span> variant<span class="sy1"><</span>Types...<span class="sy1">></span><span class="sy3">&</span>, <span class="kw4">const</span> variant<span class="sy1"><</span>Types...<span class="sy1">></span><span class="sy3">&</span><span class="br0">)</span><span class="sy4">;</span>
|
|
<span class="kw1">template</span><span class="sy1"><</span><span class="kw1">class</span>... <span class="me1">Types</span><span class="sy1">></span>
|
|
<span class="kw4">constexpr</span> <span class="kw4">bool</span> operator<span class="sy1">></span><span class="br0">(</span><span class="kw4">const</span> variant<span class="sy1"><</span>Types...<span class="sy1">></span><span class="sy3">&</span>, <span class="kw4">const</span> variant<span class="sy1"><</span>Types...<span class="sy1">></span><span class="sy3">&</span><span class="br0">)</span><span class="sy4">;</span>
|
|
<span class="kw1">template</span><span class="sy1"><</span><span class="kw1">class</span>... <span class="me1">Types</span><span class="sy1">></span>
|
|
<span class="kw4">constexpr</span> <span class="kw4">bool</span> operator<span class="sy1"><=</span><span class="br0">(</span><span class="kw4">const</span> variant<span class="sy1"><</span>Types...<span class="sy1">></span><span class="sy3">&</span>, <span class="kw4">const</span> variant<span class="sy1"><</span>Types...<span class="sy1">></span><span class="sy3">&</span><span class="br0">)</span><span class="sy4">;</span>
|
|
<span class="kw1">template</span><span class="sy1"><</span><span class="kw1">class</span>... <span class="me1">Types</span><span class="sy1">></span>
|
|
<span class="kw4">constexpr</span> <span class="kw4">bool</span> operator<span class="sy1">>=</span><span class="br0">(</span><span class="kw4">const</span> variant<span class="sy1"><</span>Types...<span class="sy1">></span><span class="sy3">&</span>, <span class="kw4">const</span> variant<span class="sy1"><</span>Types...<span class="sy1">></span><span class="sy3">&</span><span class="br0">)</span><span class="sy4">;</span>
|
|
<span class="kw1">template</span><span class="sy1"><</span><span class="kw1">class</span>... <span class="me1">Types</span><span class="sy1">></span> requires <span class="br0">(</span>three_way_comparable<span class="sy1"><</span>Types<span class="sy1">></span> <span class="sy3">&&</span> ...<span class="br0">)</span>
|
|
<span class="kw4">constexpr</span> common_comparison_category_t<span class="sy1"><</span>compare_three_way_result_t<span class="sy1"><</span>Types<span class="sy1">></span>...<span class="sy1">></span>
|
|
operator<span class="sy1"><=></span><span class="br0">(</span><span class="kw4">const</span> variant<span class="sy1"><</span>Types...<span class="sy1">></span><span class="sy3">&</span>, <span class="kw4">const</span> variant<span class="sy1"><</span>Types...<span class="sy1">></span><span class="sy3">&</span><span class="br0">)</span><span class="sy4">;</span>
|
|
|
|
<span class="co1">// 观览</span>
|
|
<span class="kw1">template</span><span class="sy1"><</span><span class="kw1">class</span> Visitor, <span class="kw1">class</span>... <span class="me1">Variants</span><span class="sy1">></span>
|
|
<span class="kw4">constexpr</span> <span class="coMULTI">/* 见描述 */</span> visit<span class="br0">(</span>Visitor<span class="sy3">&&</span>, Variants<span class="sy3">&&</span>...<span class="br0">)</span><span class="sy4">;</span>
|
|
<span class="kw1">template</span><span class="sy1"><</span><span class="kw1">class</span> R, <span class="kw1">class</span> Visitor, <span class="kw1">class</span>... <span class="me1">Variants</span><span class="sy1">></span>
|
|
<span class="kw4">constexpr</span> R visit<span class="br0">(</span>Visitor<span class="sy3">&&</span>, Variants<span class="sy3">&&</span>...<span class="br0">)</span><span class="sy4">;</span>
|
|
|
|
<span class="co1">// 类 monostate</span>
|
|
<span class="kw1">struct</span> monostate<span class="sy4">;</span>
|
|
|
|
<span class="co1">// monostate 关系运算符</span>
|
|
<span class="kw4">constexpr</span> <span class="kw4">bool</span> operator<span class="sy1">==</span><span class="br0">(</span>monostate, monostate<span class="br0">)</span> <span class="kw1">noexcept</span><span class="sy4">;</span>
|
|
<span class="kw4">constexpr</span> strong_ordering operator<span class="sy1"><=></span><span class="br0">(</span>monostate, monostate<span class="br0">)</span> <span class="kw1">noexcept</span><span class="sy4">;</span>
|
|
|
|
<span class="co1">// 特化的算法</span>
|
|
<span class="kw1">template</span><span class="sy1"><</span><span class="kw1">class</span>... <span class="me1">Types</span><span class="sy1">></span>
|
|
<span class="kw4">constexpr</span> <span class="kw4">void</span> swap<span class="br0">(</span>variant<span class="sy1"><</span>Types...<span class="sy1">></span><span class="sy3">&</span>,
|
|
variant<span class="sy1"><</span>Types...<span class="sy1">></span><span class="sy3">&</span><span class="br0">)</span> <span class="kw1">noexcept</span><span class="br0">(</span><span class="coMULTI">/* 见描述 */</span><span class="br0">)</span><span class="sy4">;</span>
|
|
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|
<span class="co1">// 类 bad_variant_access</span>
|
|
<span class="kw1">class</span> bad_variant_access<span class="sy4">;</span>
|
|
|
|
<span class="co1">// 散列支持</span>
|
|
<span class="kw1">template</span><span class="sy1"><</span><span class="kw1">class</span> T<span class="sy1">></span> <span class="kw1">struct</span> hash<span class="sy4">;</span>
|
|
<span class="kw1">template</span><span class="sy1"><</span><span class="kw1">class</span>... <span class="me1">Types</span><span class="sy1">></span> <span class="kw1">struct</span> hash<span class="sy1"><</span>variant<span class="sy1"><</span>Types...<span class="sy1">>></span><span class="sy4">;</span>
|
|
<span class="kw1">template</span><span class="sy1"><></span> <span class="kw1">struct</span> hash<span class="sy1"><</span>monostate<span class="sy1">></span><span class="sy4">;</span>
|
|
<span class="br0">}</span>
|
|
|
|
<span class="co1">// 弃用</span>
|
|
<span class="kw1">namespace</span> std <span class="br0">{</span>
|
|
<span class="kw1">template</span><span class="sy1"><</span><span class="kw1">class</span> T<span class="sy1">></span> <span class="kw1">struct</span> variant_size<span class="sy1"><</span><span class="kw4">volatile</span> T<span class="sy1">></span><span class="sy4">;</span>
|
|
<span class="kw1">template</span><span class="sy1"><</span><span class="kw1">class</span> T<span class="sy1">></span> <span class="kw1">struct</span> variant_size<span class="sy1"><</span><span class="kw4">const</span> <span class="kw4">volatile</span> T<span class="sy1">></span><span class="sy4">;</span>
|
|
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|
<span class="kw1">template</span><span class="sy1"><</span>size_t I, <span class="kw1">class</span> T<span class="sy1">></span> <span class="kw1">struct</span> variant_alternative<span class="sy1"><</span>I, <span class="kw4">volatile</span> T<span class="sy1">></span><span class="sy4">;</span>
|
|
<span class="kw1">template</span><span class="sy1"><</span>size_t I, <span class="kw1">class</span> T<span class="sy1">></span> <span class="kw1">struct</span> variant_alternative<span class="sy1"><</span>I, <span class="kw4">const</span> <span class="kw4">volatile</span> T<span class="sy1">></span><span class="sy4">;</span>
|
|
<span class="br0">}</span></pre></div>
|
|
</div>
|
|
<h4><span class="mw-headline" id=".E7.B1.BB.E6.A8.A1.E6.9D.BF_std::variant">类模板 <span class="t-lc"><a href="cpp-utility-variant.html">std::variant</a></span></span></h4>
|
|
<div dir="ltr" class="mw-geshi" style="text-align: left;">
|
|
<div class="cpp source-cpp">
|
|
<pre class="de1"><span class="kw1">namespace</span> std <span class="br0">{</span>
|
|
<span class="kw1">template</span><span class="sy1"><</span><span class="kw1">class</span>... <span class="me1">Types</span><span class="sy1">></span>
|
|
<span class="kw1">class</span> variant <span class="br0">{</span>
|
|
<span class="kw1">public</span><span class="sy4">:</span>
|
|
<span class="co1">// 构造函数</span>
|
|
<span class="kw4">constexpr</span> variant<span class="br0">(</span><span class="br0">)</span> <span class="kw1">noexcept</span><span class="br0">(</span><span class="coMULTI">/* 见描述 */</span><span class="br0">)</span><span class="sy4">;</span>
|
|
<span class="kw4">constexpr</span> variant<span class="br0">(</span><span class="kw4">const</span> variant<span class="sy3">&</span><span class="br0">)</span><span class="sy4">;</span>
|
|
<span class="kw4">constexpr</span> variant<span class="br0">(</span>variant<span class="sy3">&&</span><span class="br0">)</span> <span class="kw1">noexcept</span><span class="br0">(</span><span class="coMULTI">/* 见描述 */</span><span class="br0">)</span><span class="sy4">;</span>
|
|
|
|
<span class="kw1">template</span><span class="sy1"><</span><span class="kw1">class</span> T<span class="sy1">></span>
|
|
<span class="kw4">constexpr</span> variant<span class="br0">(</span>T<span class="sy3">&&</span><span class="br0">)</span> <span class="kw1">noexcept</span><span class="br0">(</span><span class="coMULTI">/* 见描述 */</span><span class="br0">)</span><span class="sy4">;</span>
|
|
|
|
<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>
|
|
<span class="kw4">constexpr</span> <span class="kw1">explicit</span> variant<span class="br0">(</span>in_place_type_t<span class="sy1"><</span>T<span class="sy1">></span>, Args<span class="sy3">&&</span>...<span class="br0">)</span><span class="sy4">;</span>
|
|
<span class="kw1">template</span><span class="sy1"><</span><span class="kw1">class</span> T, <span class="kw1">class</span> U, <span class="kw1">class</span>... <span class="me1">Args</span><span class="sy1">></span>
|
|
<span class="kw4">constexpr</span> <span class="kw1">explicit</span> variant<span class="br0">(</span>in_place_type_t<span class="sy1"><</span>T<span class="sy1">></span>, initializer_list<span class="sy1"><</span>U<span class="sy1">></span>, Args<span class="sy3">&&</span>...<span class="br0">)</span><span class="sy4">;</span>
|
|
|
|
<span class="kw1">template</span><span class="sy1"><</span>size_t I, <span class="kw1">class</span>... <span class="me1">Args</span><span class="sy1">></span>
|
|
<span class="kw4">constexpr</span> <span class="kw1">explicit</span> variant<span class="br0">(</span>in_place_index_t<span class="sy1"><</span>I<span class="sy1">></span>, Args<span class="sy3">&&</span>...<span class="br0">)</span><span class="sy4">;</span>
|
|
<span class="kw1">template</span><span class="sy1"><</span>size_t I, <span class="kw1">class</span> U, <span class="kw1">class</span>... <span class="me1">Args</span><span class="sy1">></span>
|
|
<span class="kw4">constexpr</span> <span class="kw1">explicit</span> variant<span class="br0">(</span>in_place_index_t<span class="sy1"><</span>I<span class="sy1">></span>, initializer_list<span class="sy1"><</span>U<span class="sy1">></span>, Args<span class="sy3">&&</span>...<span class="br0">)</span><span class="sy4">;</span>
|
|
|
|
<span class="co1">// 析构函数</span>
|
|
<span class="kw4">constexpr</span> ~variant<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
|
|
|
|
<span class="co1">// 赋值</span>
|
|
<span class="kw4">constexpr</span> variant<span class="sy3">&</span> operator<span class="sy1">=</span><span class="br0">(</span><span class="kw4">const</span> variant<span class="sy3">&</span><span class="br0">)</span><span class="sy4">;</span>
|
|
<span class="kw4">constexpr</span> variant<span class="sy3">&</span> operator<span class="sy1">=</span><span class="br0">(</span>variant<span class="sy3">&&</span><span class="br0">)</span> <span class="kw1">noexcept</span><span class="br0">(</span><span class="coMULTI">/* 见描述 */</span><span class="br0">)</span><span class="sy4">;</span>
|
|
|
|
<span class="kw1">template</span><span class="sy1"><</span><span class="kw1">class</span> T<span class="sy1">></span> <span class="kw4">constexpr</span> variant<span class="sy3">&</span> operator<span class="sy1">=</span><span class="br0">(</span>T<span class="sy3">&&</span><span class="br0">)</span> <span class="kw1">noexcept</span><span class="br0">(</span><span class="coMULTI">/* 见描述 */</span><span class="br0">)</span><span class="sy4">;</span>
|
|
|
|
<span class="co1">// 修改器</span>
|
|
<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>
|
|
<span class="kw4">constexpr</span> T<span class="sy3">&</span> emplace<span class="br0">(</span>Args<span class="sy3">&&</span>...<span class="br0">)</span><span class="sy4">;</span>
|
|
<span class="kw1">template</span><span class="sy1"><</span><span class="kw1">class</span> T, <span class="kw1">class</span> U, <span class="kw1">class</span>... <span class="me1">Args</span><span class="sy1">></span>
|
|
<span class="kw4">constexpr</span> T<span class="sy3">&</span> emplace<span class="br0">(</span>initializer_list<span class="sy1"><</span>U<span class="sy1">></span>, Args<span class="sy3">&&</span>...<span class="br0">)</span><span class="sy4">;</span>
|
|
<span class="kw1">template</span><span class="sy1"><</span>size_t I, <span class="kw1">class</span>... <span class="me1">Args</span><span class="sy1">></span>
|
|
<span class="kw4">constexpr</span> variant_alternative_t<span class="sy1"><</span>I, variant<span class="sy1"><</span>Types...<span class="sy1">>></span><span class="sy3">&</span> emplace<span class="br0">(</span>Args<span class="sy3">&&</span>...<span class="br0">)</span><span class="sy4">;</span>
|
|
<span class="kw1">template</span><span class="sy1"><</span>size_t I, <span class="kw1">class</span> U, <span class="kw1">class</span>... <span class="me1">Args</span><span class="sy1">></span>
|
|
<span class="kw4">constexpr</span> variant_alternative_t<span class="sy1"><</span>I, variant<span class="sy1"><</span>Types...<span class="sy1">>></span><span class="sy3">&</span>
|
|
emplace<span class="br0">(</span>initializer_list<span class="sy1"><</span>U<span class="sy1">></span>, Args<span class="sy3">&&</span>...<span class="br0">)</span><span class="sy4">;</span>
|
|
|
|
<span class="co1">// 值状态</span>
|
|
<span class="kw4">constexpr</span> <span class="kw4">bool</span> valueless_by_exception<span class="br0">(</span><span class="br0">)</span> <span class="kw4">const</span> <span class="kw1">noexcept</span><span class="sy4">;</span>
|
|
<span class="kw4">constexpr</span> size_t index<span class="br0">(</span><span class="br0">)</span> <span class="kw4">const</span> <span class="kw1">noexcept</span><span class="sy4">;</span>
|
|
|
|
<span class="co1">// 交换</span>
|
|
<span class="kw4">constexpr</span> <span class="kw4">void</span> swap<span class="br0">(</span>variant<span class="sy3">&</span><span class="br0">)</span> <span class="kw1">noexcept</span><span class="br0">(</span><span class="coMULTI">/* 见描述 */</span><span class="br0">)</span><span class="sy4">;</span>
|
|
<span class="br0">}</span><span class="sy4">;</span>
|
|
<span class="br0">}</span></pre></div>
|
|
</div>
|
|
<h4><span class="mw-headline" id=".E7.B1.BB_std::monostate">类 <span class="t-lc"><a href="cpp-utility-variant-monostate.html">std::monostate</a></span></span></h4>
|
|
<div dir="ltr" class="mw-geshi" style="text-align: left;">
|
|
<div class="cpp source-cpp">
|
|
<pre class="de1"><span class="kw1">struct</span> monostate<span class="br0">{</span><span class="br0">}</span><span class="sy4">;</span></pre></div>
|
|
</div>
|
|
<h4><span class="mw-headline" id=".E7.B1.BB_std::bad_variant_access">类 <span class="t-lc"><a href="cpp-utility-variant-bad_variant_access.html">std::bad_variant_access</a></span></span></h4>
|
|
<div dir="ltr" class="mw-geshi" style="text-align: left;">
|
|
<div class="cpp source-cpp">
|
|
<pre class="de1"><span class="kw1">class</span> bad_variant_access <span class="sy4">:</span> <span class="kw1">public</span> exception <span class="br0">{</span>
|
|
<span class="kw1">public</span><span class="sy4">:</span>
|
|
<span class="co1">// 特殊成员函数的规范见 [exception]</span>
|
|
<span class="kw4">const</span> <span class="kw4">char</span><span class="sy2">*</span> what<span class="br0">(</span><span class="br0">)</span> <span class="kw4">const</span> <span class="kw1">noexcept</span> override<span class="sy4">;</span>
|
|
<span class="br0">}</span><span class="sy4">;</span></pre></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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