68 lines
3.1 KiB
HTML
68 lines
3.1 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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<title>std::variant_npos</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_utility_variant_variant_npos 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>variant_npos</h1>
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<div id="contentSub"><span class="subpages">< <a href="cpp.html">cpp</a>‎ | <a href="cpp-utility.html">utility</a>‎ | <a href="cpp-utility-variant.html">variant</a></span></div>
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<div>定义于头文件 <code><a href="cpp-header-variant.html"><variant></a></code></div>
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<td></td>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">inline</span> <span class="kw4">constexpr</span> <a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a> variant_npos <span class="sy1">=</span> <span class="sy2">-</span><span class="nu0">1</span><span class="sy4">;</span></span></div>
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<td><span class="t-mark-rev t-since-cxx17">(C++17 起)</span></td>
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<p>这是一个等于类型 <code>std::size_t</code> 最大可表示值的特殊值，用作 <span class="t-lc">index()</span> 在 <span class="t-lc">valueless_by_exception()</span> 为 <code>true</code> 时的返回值指示。</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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<div class="t-dsc-member-div">
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<div><a href="cpp-utility-variant-index.html"><span class="t-lines"><span>index</span></span></a></div>
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</div>
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</td>
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<td>返回 <code>variant</code> 所保有可选项的零基下标<br />
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<span class="t-mark">(公开成员函数)</span></td>
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<div><a href="cpp-utility-variant-valueless_by_exception.html"><span class="t-lines"><span>valueless_by_exception</span></span></a></div>
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</div>
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</td>
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<td>检查 <code>variant</code> 是否在非法状态<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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<div class="visualClear"></div>
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</body>
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