71 lines
4.6 KiB
HTML
71 lines
4.6 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::span<T,Extent>::first</title>
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<link rel="stylesheet" href="ext.css" />
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</head>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_container_span_first 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<T,Extent>::</span>first</h1>
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<div id="contentSub"><span class="subpages">< <a href="cpp.html">cpp</a>‎ | <a href="cpp-container.html">container</a>‎ | <a href="cpp-container-span.html">span</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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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span><span class="sy1"><</span> <a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a> Count <span class="sy1">></span><br />
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<span class="kw4">constexpr</span> std<span class="sy4">::</span><span class="me2">span</span><span class="sy1"><</span>element_type, Count<span class="sy1">></span> first<span class="br0">(</span><span class="br0">)</span> <span class="kw4">const</span><span class="sy4">;</span></span></div>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw4">constexpr</span> std<span class="sy4">::</span><span class="me2">span</span><span class="sy1"><</span>element_type, std<span class="sy4">::</span><span class="me2">dynamic_extent</span><span class="sy1">></span> first<span class="br0">(</span> <a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a> Count <span class="br0">)</span> <span class="kw4">const</span><span class="sy4">;</span></span></div>
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<td class="t-dcl-nopad"></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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<p>获得 span ，其为此 span 的首 <code>Count</code> 个元素上的视图。若 <span class="t-c"><span class="mw-geshi cpp source-cpp">Count <span class="sy1">></span> Extent</span></span> 则程序非良构。若 <span class="t-c"><span class="mw-geshi cpp source-cpp">Count <span class="sy1">></span> size<span class="br0">(</span><span class="br0">)</span></span></span> 则行为未定义。</p>
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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>作为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">*</span>this</span></span> 的首 <code>Count</code> 个元素上的视图的 span <code>r</code> ，满足 <span class="t-c"><span class="mw-geshi cpp source-cpp">r.<span class="me1">data</span><span class="br0">(</span><span class="br0">)</span> <span class="sy1">==</span> this<span class="sy2">-</span><span class="sy1">></span>data<span class="br0">(</span><span class="br0">)</span> <span class="sy3">&&</span> r.<span class="me1">size</span><span class="br0">(</span><span class="br0">)</span> <span class="sy1">==</span> Count</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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<div class="t-dsc-member-div">
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<div><a href="cpp-container-span-last.html"><span class="t-lines"><span>last</span></span></a></div>
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</div>
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</td>
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<td>获得由序列末 N 个元素组成的子段<br />
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<span class="t-mark">(公开成员函数)</span></td>
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<tr class="t-dsc">
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<div class="t-dsc-member-div">
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<div><a href="cpp-container-span-subspan.html"><span class="t-lines"><span>subspan</span></span></a></div>
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</div>
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</td>
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<td>获得子段<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>
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<div class="visualClear"></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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