267 lines
17 KiB
HTML
267 lines
17 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>std::any</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_utility_any 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%">std::</span>any</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-utility.html">utility</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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<table class="t-dcl-begin">
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<td>
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<div>定义于头文件 <code><a href="cpp-header-any.html"><any></a></code></div>
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</td>
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<td></td>
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<td></td>
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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">class</span> any<span class="sy4">;</span></span></div>
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</td>
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<td class="t-dcl-nopad"></td>
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<td><span class="t-mark-rev t-since-cxx17">(C++17 起)</span></td>
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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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</tbody>
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</table>
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<p>类 <code>any</code> 描述用于任何类型的单个值的类型安全容器。</p>
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<div class="t-li1"><span class="t-li">1)</span> 类 <code>any</code> 的对象存储任何满足构造函数要求的类型的一个实例或为空，而这被称为 <code>any</code> 类对象的<i>状态</i>。存储的实例被称作所含对象。若两个状态均为空，或均为非空且其所含对象等价，则两个状态等价。</div>
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<div class="t-li1"><span class="t-li">2)</span> 非成员 <code>any_cast</code> 函数提供对所含对象的类型安全访问。</div>
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<p>鼓励实现避免小对象的动态分配，但这种优化仅可以应用于 <span class="t-lc"><a href="cpp-types-is_move_constructible.html">std::is_nothrow_move_constructible</a></span> 对其返回 <code>true</code> 的类型。</p>
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<h3><span class="mw-headline" id=".E6.88.90.E5.91.98.E5.87.BD.E6.95.B0">成员函数</span></h3>
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<table class="t-dsc-begin">
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<div class="t-dsc-member-div t-dsc-member-nobold-div">
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<div><a href="cpp-utility-any-any.html"><span class="t-lines"><span>(构造函数)</span></span></a></div>
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</div>
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</td>
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<td>构造 <code>any</code> 对象<br />
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<span class="t-mark">(公开成员函数)</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-any-operator=.html"><span class="t-lines"><span>operator=</span></span></a></div>
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</div>
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</td>
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<td>赋值 <code>any</code> 对象<br />
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<span class="t-mark">(公开成员函数)</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 t-dsc-member-nobold-div">
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<div><a href="cpp-utility-any-~any.html"><span class="t-lines"><span>(析构函数)</span></span></a></div>
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</div>
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</td>
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<td>销毁 <code>any</code> 对象<br />
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<span class="t-mark">(公开成员函数)</span></td>
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</tr>
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<tr>
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<td colspan="2">
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<h5><span class="mw-headline" id=".E4.BF.AE.E6.94.B9.E5.99.A8">修改器</span></h5>
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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-any-emplace.html"><span class="t-lines"><span>emplace</span></span></a></div>
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</div>
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</td>
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<td>更改所含对象，直接构造新对象<br />
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<span class="t-mark">(公开成员函数)</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-any-reset.html"><span class="t-lines"><span>reset</span></span></a></div>
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</div>
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</td>
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<td>销毁所含对象<br />
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<span class="t-mark">(公开成员函数)</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-any-swap.html"><span class="t-lines"><span>swap</span></span></a></div>
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</div>
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</td>
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<td>交换二个 <code>any</code> 对象<br />
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<span class="t-mark">(公开成员函数)</span></td>
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</tr>
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<tr>
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<td colspan="2">
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<h5><span class="mw-headline" id=".E8.A7.82.E5.AF.9F.E5.99.A8">观察器</span></h5>
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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-any-has_value.html"><span class="t-lines"><span>has_value</span></span></a></div>
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</div>
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</td>
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<td>检查对象是否含有值<br />
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<span class="t-mark">(公开成员函数)</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-any-type.html"><span class="t-lines"><span>type</span></span></a></div>
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</div>
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</td>
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<td>返回所含值的 <code>typeid</code><br />
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<span class="t-mark">(公开成员函数)</span></td>
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</tr>
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</table>
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<h3><span class="mw-headline" id=".E9.9D.9E.E6.88.90.E5.91.98.E5.87.BD.E6.95.B0">非成员函数</span></h3>
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<table class="t-dsc-begin">
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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-any-swap2.html"><span class="t-lines"><span>std::swap<span class="t-dsc-small">(std::any)</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)</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-any-any_cast.html"><span class="t-lines"><span>any_cast</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>对被容纳对象的类型安全访问<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-any-make_any.html"><span class="t-lines"><span>make_any</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>创建 <code>any</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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</table>
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<h3><span class="mw-headline" id=".E8.BE.85.E5.8A.A9.E7.B1.BB">辅助类</span></h3>
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<table class="t-dsc-begin">
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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-any-bad_any_cast.html"><span class="t-lines"><span>bad_any_cast</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>当类型不匹配时按值返回形式的 <code>any_cast</code> 所抛出的异常<br />
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<span class="t-mark">(类)</span></td>
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</tr>
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</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 <any></span>
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<span class="co2">#include <iostream></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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<a href="cpp-io-cout.html"><span class="kw1757">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <a href="cpp-io-manip-boolalpha.html"><span class="kw1763">std::<span class="me2">boolalpha</span></span></a><span class="sy4">;</span>
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<span class="co1">// any 类型</span>
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std<span class="sy4">::</span><span class="me2">any</span> a <span class="sy1">=</span> <span class="nu0">1</span><span class="sy4">;</span>
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<a href="cpp-io-cout.html"><span class="kw1757">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> a.<span class="me1">type</span><span class="br0">(</span><span class="br0">)</span>.<span class="me1">name</span><span class="br0">(</span><span class="br0">)</span> <span class="sy1"><<</span> <span class="st0">": "</span> <span class="sy1"><<</span> <a href="cpp-utility-any-any_cast.html"><span class="kw1071">std::<span class="me2">any_cast</span></span></a><span class="sy1"><</span><span class="kw4">int</span><span class="sy1">></span><span class="br0">(</span>a<span class="br0">)</span> <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
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a <span class="sy1">=</span> <span class="nu16">3.14</span><span class="sy4">;</span>
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<a href="cpp-io-cout.html"><span class="kw1757">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> a.<span class="me1">type</span><span class="br0">(</span><span class="br0">)</span>.<span class="me1">name</span><span class="br0">(</span><span class="br0">)</span> <span class="sy1"><<</span> <span class="st0">": "</span> <span class="sy1"><<</span> <a href="cpp-utility-any-any_cast.html"><span class="kw1071">std::<span class="me2">any_cast</span></span></a><span class="sy1"><</span><span class="kw4">double</span><span class="sy1">></span><span class="br0">(</span>a<span class="br0">)</span> <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
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a <span class="sy1">=</span> <span class="kw2">true</span><span class="sy4">;</span>
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<a href="cpp-io-cout.html"><span class="kw1757">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> a.<span class="me1">type</span><span class="br0">(</span><span class="br0">)</span>.<span class="me1">name</span><span class="br0">(</span><span class="br0">)</span> <span class="sy1"><<</span> <span class="st0">": "</span> <span class="sy1"><<</span> <a href="cpp-utility-any-any_cast.html"><span class="kw1071">std::<span class="me2">any_cast</span></span></a><span class="sy1"><</span><span class="kw4">bool</span><span class="sy1">></span><span class="br0">(</span>a<span class="br0">)</span> <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
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<span class="co1">// 有误的转型</span>
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<span class="kw1">try</span>
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<span class="br0">{</span>
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a <span class="sy1">=</span> <span class="nu0">1</span><span class="sy4">;</span>
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<a href="cpp-io-cout.html"><span class="kw1757">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <a href="cpp-utility-any-any_cast.html"><span class="kw1071">std::<span class="me2">any_cast</span></span></a><span class="sy1"><</span><span class="kw4">float</span><span class="sy1">></span><span class="br0">(</span>a<span class="br0">)</span> <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
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<span class="br0">}</span>
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<span class="kw1">catch</span> <span class="br0">(</span><span class="kw4">const</span> <a href="cpp-utility-any-bad_any_cast.html"><span class="kw1073">std::<span class="me2">bad_any_cast</span></span></a><span class="sy3">&</span> e<span class="br0">)</span>
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<span class="br0">{</span>
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<a href="cpp-io-cout.html"><span class="kw1757">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> e.<span class="me1">what</span><span class="br0">(</span><span class="br0">)</span> <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
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<span class="br0">}</span>
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<span class="co1">// 拥有值</span>
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a <span class="sy1">=</span> <span class="nu0">1</span><span class="sy4">;</span>
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<span class="kw1">if</span> <span class="br0">(</span>a.<span class="me1">has_value</span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span>
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<span class="br0">{</span>
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<a href="cpp-io-cout.html"><span class="kw1757">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> a.<span class="me1">type</span><span class="br0">(</span><span class="br0">)</span>.<span class="me1">name</span><span class="br0">(</span><span class="br0">)</span> <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
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<span class="br0">}</span>
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<span class="co1">// 重置</span>
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a.<span class="me1">reset</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="kw1">if</span> <span class="br0">(</span><span class="sy3">!</span>a.<span class="me1">has_value</span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span>
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<span class="br0">{</span>
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<a href="cpp-io-cout.html"><span class="kw1757">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"no value<span class="es1">\n</span>"</span><span class="sy4">;</span>
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<span class="br0">}</span>
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<span class="co1">// 指向所含数据的指针</span>
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a <span class="sy1">=</span> <span class="nu0">1</span><span class="sy4">;</span>
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<span class="kw4">int</span><span class="sy2">*</span> i <span class="sy1">=</span> <a href="cpp-utility-any-any_cast.html"><span class="kw1071">std::<span class="me2">any_cast</span></span></a><span class="sy1"><</span><span class="kw4">int</span><span class="sy1">></span><span class="br0">(</span><span class="sy3">&</span>a<span class="br0">)</span><span class="sy4">;</span>
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<a href="cpp-io-cout.html"><span class="kw1757">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="sy2">*</span>i <span class="sy1"><<</span> <span class="st0">"<span class="es1">\n</span>"</span><span class="sy4">;</span>
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<span class="br0">}</span></pre></div>
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</div>
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<p>可能的输出：</p>
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<div dir="ltr" class="mw-geshi" style="text-align: left;">
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<div class="text source-text">
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<pre class="de1">i: 1
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d: 3.14
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b: true
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bad any_cast
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i
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no value
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1</pre></div>
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</div>
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</div>
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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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<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-functional-function.html"><span class="t-lines"><span>function</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>包装具有指定函数调用签名的任意可复制构造类型的可调用对象<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.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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</table>
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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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</html>
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