62 lines
3.3 KiB
HTML
62 lines
3.3 KiB
HTML
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<title>std::optional 的推导指引</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_utility_optional_deduction_guides skin-cppreference2 action-view cpp-navbar">
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<h1 id="firstHeading" class="firstHeading"><code>std::optional</code> 的推导指引</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-optional.html">optional</a></span></div>
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<div>定义于头文件 <code><a href="cpp-header-optional.html"><optional></a></code></div>
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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="sy1">></span><br />
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optional<span class="br0">(</span>T<span class="br0">)</span> <span class="sy2">-</span><span class="sy1">></span> optional<span class="sy1"><</span>T<span class="sy1">></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>为 <span class="t-lc"><a href="cpp-utility-optional.html">std::optional</a></span> 提供一个<a href="cpp-language-class_template_argument_deduction.html">推导指引</a>以处理隐式推导指引所遗漏的极端情况，尤其是不可复制参数和数组到指针转换。</p>
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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="cpp source-cpp">
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<pre class="de1"><span class="co2">#include <optional></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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<span class="kw4">int</span> a<span class="br0">[</span><span class="nu0">2</span><span class="br0">]</span><span class="sy4">;</span>
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<a href="cpp-utility-optional.html"><span class="kw1075">std::<span class="me2">optional</span></span></a> oa<span class="br0">{</span>a<span class="br0">}</span><span class="sy4">;</span> <span class="co1">// 用于此情况的显式推导指引</span>
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<span class="br0">}</span></pre></div>
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