501 lines
35 KiB
HTML
501 lines
35 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</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_container_span 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>span</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-container.html">container</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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<tbody>
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<tr class="t-dsc-header">
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<td>
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<div>定义于头文件 <code><a href="cpp-header-span.html"><span></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>
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<tr class="t-dcl t-since-cxx20">
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<td>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span><span class="sy1"><</span><br /></span>
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<p> <span class="kw1">class</span> T,<br />
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<a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a> Extent <span class="sy1">=</span> std<span class="sy4">::</span><span class="me2">dynamic_extent</span><br /></p>
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<span class="sy1">></span> <span class="kw1">class</span> span<span class="sy4">;</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-cxx20">(C++20 起)</span></td>
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</tr>
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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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</tr>
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</tbody>
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</table>
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<p>类模板 <code>span</code> 所描述的对象能指代对象的相接序列，序列的首元素在零位置。 <code>span</code> 能拥有<i>静态</i>长度，该情况下序列中的元素数已知并编码于类型中，或拥有<i>动态</i>长度。</p>
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<p>典型实现只保有两个成员：指向 <code>T</code> 的指针和大小。</p>
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<table class="t-rev-begin">
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<tr class="t-rev t-since-cxx23">
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<td>
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<p><code>std::span</code> 的每个特化均为<a href="cpp-named_req-TriviallyCopyable.html"><span style="font-style:italic">可平凡复制</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(TriviallyCopyable)</span></a> 类型。</p>
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</td>
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<td><span class="t-mark-rev t-since-cxx23">(C++23 起)</span></td>
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</tr>
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</table>
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<h3><span class="mw-headline" id=".E6.A8.A1.E6.9D.BF.E5.BD.A2.E5.8F.82">模板形参</span></h3>
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<table class="t-par-begin">
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<tr class="t-par">
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<td>T</td>
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<td>-</td>
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<td>元素类型；必须是完整对象类型且非抽象类</td>
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</tr>
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<tr class="t-par">
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<td>Extent</td>
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<td>-</td>
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<td>序列中的元素数，或若它为动态则为 <code>std::dynamic_extent</code></td>
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</tr>
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</table>
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<h3><span class="mw-headline" id=".E6.88.90.E5.91.98.E7.B1.BB.E5.9E.8B">成员类型</span></h3>
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<table class="t-dsc-begin">
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<tr class="t-dsc-hitem">
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<td>成员类型</td>
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<td>定义</td>
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</tr>
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<tr class="t-dsc">
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<td><code>element_type</code></td>
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<td><code>T</code></td>
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</tr>
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<tr class="t-dsc">
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<td><code>value_type</code></td>
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<td><span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-types-remove_cv.html"><span class="kw597">std::<span class="me2">remove_cv_t</span></span></a><span class="sy1"><</span>T<span class="sy1">></span></span></span></td>
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</tr>
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<tr class="t-dsc">
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<td><code>size_type</code></td>
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<td><span class="t-lc"><a href="cpp-types-size_t.html">std::size_t</a></span></td>
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</tr>
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<tr class="t-dsc">
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<td><code>difference_type</code></td>
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<td><span class="t-lc"><a href="cpp-types-ptrdiff_t.html">std::ptrdiff_t</a></span></td>
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</tr>
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<tr class="t-dsc">
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<td><code>pointer</code></td>
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<td><code>T*</code></td>
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</tr>
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<tr class="t-dsc">
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<td><code>const_pointer</code></td>
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<td><code>const T*</code></td>
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</tr>
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<tr class="t-dsc">
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<td><code>reference</code></td>
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<td><code>T&</code></td>
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</tr>
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<tr class="t-dsc">
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<td><code>const_reference</code></td>
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<td><code>const T&</code></td>
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</tr>
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<tr class="t-dsc">
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<td><code>iterator</code></td>
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<td>实现定义的<a href="cpp-named_req-RandomAccessIterator.html"><span style="font-style:italic">老式随机访问迭代器</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(LegacyRandomAccessIterator)</span></a> 、<a href="cpp-named_req-ConstexprIterator.html"><span style="font-style:italic">常量表达式迭代器</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(ConstexprIterator)</span></a> 兼<a href="cpp-named_req-ContiguousIterator.html"><span style="font-style:italic">老式连续迭代器</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(LegacyContiguousIterator)</span></a> ，其 <code>value_type</code> 为 <code>value_type</code></td>
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</tr>
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<tr class="t-dsc">
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<td><code>reverse_iterator</code></td>
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<td><span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-iterator-reverse_iterator.html"><span class="kw658">std::<span class="me2">reverse_iterator</span></span></a><span class="sy1"><</span>iterator<span class="sy1">></span></span></span></td>
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</tr>
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<tr class="t-dsc">
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<td><code>const_reverse_iterator</code></td>
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<td><span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-iterator-reverse_iterator.html"><span class="kw658">std::<span class="me2">reverse_iterator</span></span></a><span class="sy1"><</span>const_iterator<span class="sy1">></span></span></span></td>
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</tr>
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</table>
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<p>注意：若 <code>T</code> 无 const 限定则 <code>iterator</code> 为可变迭代器。</p>
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<p><a href="cpp-named_req-Container.html"><span style="font-style:italic">容器</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(Container)</span></a> 的迭代器类型上的所有要求亦应用于 <code>span</code> 的 <code>iterator</code> 类型。</p>
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<h3><span class="mw-headline" id=".E6.88.90.E5.91.98.E5.B8.B8.E9.87.8F">成员常量</span></h3>
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<table class="t-dcl-begin">
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<tbody>
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<tr class="t-dcl">
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<td class="t-dcl-nopad">
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<div><span class="mw-geshi cpp source-cpp"><span class="kw4">static</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> extent <span class="sy1">=</span> Extent<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 class="t-dcl-nopad"></td>
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</tr>
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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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</tr>
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</tbody>
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</table>
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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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<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-container-span-span.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>span</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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<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-container-span-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>span</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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<tr>
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<td colspan="2">
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<h5><span class="mw-headline" id=".E8.BF.AD.E4.BB.A3.E5.99.A8">迭代器</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-container-span-begin.html"><span class="t-lines"><span>begin</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>返回指向起始的迭代器<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-container-span-end.html"><span class="t-lines"><span>end</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>返回指向末尾的迭代器<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-container-span-rbegin.html"><span class="t-lines"><span>rbegin</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>返回指向起始的逆向迭代器<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-container-span-rend.html"><span class="t-lines"><span>rend</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>返回指向末尾的逆向迭代器<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=".E5.85.83.E7.B4.A0.E8.AE.BF.E9.97.AE">元素访问</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-container-span-front.html"><span class="t-lines"><span>front</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>访问第一个元素<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-container-span-back.html"><span class="t-lines"><span>back</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>访问最后一个元素<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-container-span-operator_at.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>访问序列的元素<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-container-span-data.html"><span class="t-lines"><span>data</span></span></a></div>
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</div>
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</td>
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<td>返回指向元素序列起始的指针<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-container-span-size.html"><span class="t-lines"><span>size</span></span></a></div>
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</div>
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</td>
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<td>返回序列中的元素数<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-container-span-size_bytes.html"><span class="t-lines"><span>size_bytes</span></span></a></div>
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</div>
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</td>
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<td>返回以字节表示的序列大小<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-container-span-empty.html"><span class="t-lines"><span>empty</span></span></a></div>
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</div>
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</td>
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<td>检查序列是否为空<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=".E5.AD.90.E8.A7.86.E5.9B.BE">子视图</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-container-span-first.html"><span class="t-lines"><span>first</span></span></a></div>
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</div>
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</td>
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<td>获得由序列首 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>
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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-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>
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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-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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<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-container-span-as_bytes.html"><span class="t-lines"><span>as_bytes</span><span>as_writable_bytes</span></span></a></div>
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</div>
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</td>
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<td>转换 <code>span</code> 为对其底层字节的视图<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=".E9.9D.9E.E6.88.90.E5.91.98.E5.B8.B8.E9.87.8F">非成员常量</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-container-span-dynamic_extent.html"><span class="t-lines"><span>dynamic_extent</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><code>size_t</code> 类型常量，指明 <code>span</code> 拥有动态长度<br />
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<span class="t-mark">(常量)</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.E6.A8.A1.E6.9D.BF">辅助模板</span></h3>
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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, <a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a> Extent<span class="sy1">></span><br />
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<span class="kw1">inline</span> <span class="kw4">constexpr</span> <span class="kw4">bool</span> ranges<span class="sy4">::</span><span class="me2">enable_borrowed_range</span><span class="sy1"><</span>std<span class="sy4">::</span><span class="me2">span</span><span class="sy1"><</span>T, Extent<span class="sy1">>></span> <span class="sy1">=</span> <span class="kw2">true</span><span class="sy4">;</span></span></div>
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<p><a href="cpp-ranges-borrowed_range.html"><tt>std::ranges::enable_borrowed_range</tt></a> 的此特化使得 <code>span</code> 满足 <a href="cpp-ranges-borrowed_range.html"><code>borrowed_range</code></a> 。</p>
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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><span class="kw1">class</span> T, <a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a> Extent<span class="sy1">></span><br />
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<span class="kw1">inline</span> <span class="kw4">constexpr</span> <span class="kw4">bool</span> ranges<span class="sy4">::</span><span class="me2">enable_view</span><span class="sy1"><</span>std<span class="sy4">::</span><span class="me2">span</span><span class="sy1"><</span>T, Extent<span class="sy1">>></span> <span class="sy1">=</span> <span class="kw2">true</span><span class="sy4">;</span></span></div>
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<td class="t-dcl-nopad"></td>
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<p><a href="cpp-ranges-view.html"><tt>std::ranges::enable_view</tt></a> 的此特化使零或动态长度的 <code>span</code> 满足 <a href="cpp-ranges-view.html"><code>view</code></a> 。</p>
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<h3><span class="mw-headline" id=".E6.8E.A8.E5.AF.BC.E6.8C.87.E5.BC.95"><a href="cpp-container-span-deduction_guides.html">推导指引</a></span></h3>
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<h3><span class="mw-headline" id=".E6.B3.A8.E8.A7.A3">注解</span></h3>
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<p>即使在 C++23 中引入的正式要求前，所有既存实现中 <code>std::span</code> 的特化已经为可平凡复制类型。</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="t-example">
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<p>示例用 <code>std::span</code> 实现连续范围上的算法。</p>
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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 <algorithm></span>
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<span class="co2">#include <cstddef></span>
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<span class="co2">#include <iostream></span>
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<span class="co2">#include <span></span>
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<span class="kw1">template</span><span class="sy1"><</span><span class="kw1">class</span> T, <a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a> N<span class="sy1">></span> <span class="br0">[</span><span class="br0">[</span>nodiscard<span class="br0">]</span><span class="br0">]</span>
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<span class="kw4">constexpr</span> <span class="kw4">auto</span> slide<span class="br0">(</span>std<span class="sy4">::</span><span class="me2">span</span><span class="sy1"><</span>T,N<span class="sy1">></span> s, <a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a> offset, <a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a> width<span class="br0">)</span> <span class="br0">{</span>
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<span class="kw1">return</span> s.<span class="me1">subspan</span><span class="br0">(</span>offset, offset <span class="sy2">+</span> width <span class="sy1"><=</span> s.<span class="me1">size</span><span class="br0">(</span><span class="br0">)</span> <span class="sy4">?</span> width <span class="sy4">:</span> 0U<span class="br0">)</span><span class="sy4">;</span>
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<span class="br0">}</span>
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<span class="kw1">template</span><span class="sy1"><</span><span class="kw1">class</span> T, <a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a> N, <a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a> M<span class="sy1">></span> <span class="br0">[</span><span class="br0">[</span>nodiscard<span class="br0">]</span><span class="br0">]</span>
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<span class="kw4">constexpr</span> <span class="kw4">bool</span> starts_with<span class="br0">(</span>std<span class="sy4">::</span><span class="me2">span</span><span class="sy1"><</span>T,N<span class="sy1">></span> data, std<span class="sy4">::</span><span class="me2">span</span><span class="sy1"><</span>T,M<span class="sy1">></span> prefix<span class="br0">)</span> <span class="br0">{</span>
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<span class="kw1">return</span> data.<span class="me1">size</span><span class="br0">(</span><span class="br0">)</span> <span class="sy1">>=</span> prefix.<span class="me1">size</span><span class="br0">(</span><span class="br0">)</span>
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<span class="sy3">&&</span> <a href="cpp-algorithm-equal.html"><span class="kw1573">std::<span class="me2">equal</span></span></a><span class="br0">(</span>prefix.<span class="me1">begin</span><span class="br0">(</span><span class="br0">)</span>, prefix.<span class="me1">end</span><span class="br0">(</span><span class="br0">)</span>, data.<span class="me1">begin</span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="br0">}</span>
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<span class="kw1">template</span><span class="sy1"><</span><span class="kw1">class</span> T, <a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a> N, <a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a> M<span class="sy1">></span> <span class="br0">[</span><span class="br0">[</span>nodiscard<span class="br0">]</span><span class="br0">]</span>
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<span class="kw4">constexpr</span> <span class="kw4">bool</span> ends_with<span class="br0">(</span>std<span class="sy4">::</span><span class="me2">span</span><span class="sy1"><</span>T,N<span class="sy1">></span> data, std<span class="sy4">::</span><span class="me2">span</span><span class="sy1"><</span>T,M<span class="sy1">></span> suffix<span class="br0">)</span> <span class="br0">{</span>
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<span class="kw1">return</span> data.<span class="me1">size</span><span class="br0">(</span><span class="br0">)</span> <span class="sy1">>=</span> suffix.<span class="me1">size</span><span class="br0">(</span><span class="br0">)</span>
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<span class="sy3">&&</span> <a href="cpp-algorithm-equal.html"><span class="kw1573">std::<span class="me2">equal</span></span></a><span class="br0">(</span>data.<span class="me1">end</span><span class="br0">(</span><span class="br0">)</span> <span class="sy2">-</span> suffix.<span class="me1">size</span><span class="br0">(</span><span class="br0">)</span>, data.<span class="me1">end</span><span class="br0">(</span><span class="br0">)</span>,
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suffix.<span class="me1">end</span><span class="br0">(</span><span class="br0">)</span> <span class="sy2">-</span> suffix.<span class="me1">size</span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="br0">}</span>
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<span class="kw1">template</span><span class="sy1"><</span><span class="kw1">class</span> T, <a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a> N, <a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a> M<span class="sy1">></span> <span class="br0">[</span><span class="br0">[</span>nodiscard<span class="br0">]</span><span class="br0">]</span>
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<span class="kw4">constexpr</span> <span class="kw4">bool</span> contains<span class="br0">(</span>std<span class="sy4">::</span><span class="me2">span</span><span class="sy1"><</span>T,N<span class="sy1">></span> span, std<span class="sy4">::</span><span class="me2">span</span><span class="sy1"><</span>T,M<span class="sy1">></span> sub<span class="br0">)</span> <span class="br0">{</span>
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<span class="kw1">return</span> <a href="cpp-algorithm-search.html"><span class="kw1580">std::<span class="me2">search</span></span></a><span class="br0">(</span>span.<span class="me1">begin</span><span class="br0">(</span><span class="br0">)</span>, span.<span class="me1">end</span><span class="br0">(</span><span class="br0">)</span>, sub.<span class="me1">begin</span><span class="br0">(</span><span class="br0">)</span>, sub.<span class="me1">end</span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span> <span class="sy3">!</span><span class="sy1">=</span> span.<span class="me1">end</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="co1">// return std::ranges::search(span, sub).begin() != span.end();</span>
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<span class="br0">}</span>
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<span class="kw4">void</span> print<span class="br0">(</span><span class="kw4">const</span> <span class="kw4">auto</span><span class="sy3">&</span> seq<span class="br0">)</span> <span class="br0">{</span>
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<span class="kw1">for</span> <span class="br0">(</span><span class="kw4">const</span> <span class="kw4">auto</span><span class="sy3">&</span> elem <span class="sy4">:</span> seq<span class="br0">)</span> <a href="cpp-io-cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> elem <span class="sy1"><<</span> <span class="st0">' '</span><span class="sy4">;</span>
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<a href="cpp-io-cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <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="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">constexpr</span> <span class="kw4">int</span> a<span class="br0">[</span><span class="br0">]</span> <span class="br0">{</span> <span class="nu0">0</span>, <span class="nu0">1</span>, <span class="nu0">2</span>, <span class="nu0">3</span>, <span class="nu0">4</span>, <span class="nu0">5</span>, <span class="nu0">6</span>, <span class="nu0">7</span>, <span class="nu0">8</span> <span class="br0">}</span><span class="sy4">;</span>
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<span class="kw4">constexpr</span> <span class="kw4">int</span> b<span class="br0">[</span><span class="br0">]</span> <span class="br0">{</span> <span class="nu0">8</span>, <span class="nu0">7</span>, <span class="nu0">6</span> <span class="br0">}</span><span class="sy4">;</span>
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<span class="kw1">for</span> <span class="br0">(</span><a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a> offset<span class="br0">{</span><span class="br0">}</span><span class="sy4">;</span> <span class="sy4">;</span> <span class="sy2">++</span>offset<span class="br0">)</span> <span class="br0">{</span>
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<span class="kw4">constexpr</span> <a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a> width<span class="br0">{</span><span class="nu0">6</span><span class="br0">}</span><span class="sy4">;</span>
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<span class="kw4">auto</span> s <span class="sy1">=</span> slide<span class="br0">(</span>std<span class="sy4">::</span><span class="me2">span</span><span class="br0">{</span>a<span class="br0">}</span>, offset, width<span class="br0">)</span><span class="sy4">;</span>
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<span class="kw1">if</span> <span class="br0">(</span>s.<span class="me1">empty</span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span>
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<span class="kw1">break</span><span class="sy4">;</span>
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print<span class="br0">(</span>s<span class="br0">)</span><span class="sy4">;</span>
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<span class="br0">}</span>
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static_assert<span class="br0">(</span>starts_with<span class="br0">(</span>std<span class="sy4">::</span><span class="me2">span</span><span class="br0">{</span>a<span class="br0">}</span>, std<span class="sy4">::</span><span class="me2">span</span><span class="br0">{</span>a,<span class="nu0">4</span><span class="br0">}</span><span class="br0">)</span>
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<span class="sy3">&&</span> starts_with<span class="br0">(</span>std<span class="sy4">::</span><span class="me2">span</span><span class="br0">{</span>a<span class="sy2">+</span><span class="nu0">1</span>, <span class="nu0">4</span><span class="br0">}</span>, std<span class="sy4">::</span><span class="me2">span</span><span class="br0">{</span>a<span class="sy2">+</span><span class="nu0">1</span>,<span class="nu0">3</span><span class="br0">}</span><span class="br0">)</span>
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<span class="sy3">&&</span> <span class="sy3">!</span>starts_with<span class="br0">(</span>std<span class="sy4">::</span><span class="me2">span</span><span class="br0">{</span>a<span class="br0">}</span>, std<span class="sy4">::</span><span class="me2">span</span><span class="br0">{</span>b<span class="br0">}</span><span class="br0">)</span>
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<span class="sy3">&&</span> <span class="sy3">!</span>starts_with<span class="br0">(</span>std<span class="sy4">::</span><span class="me2">span</span><span class="br0">{</span>a,<span class="nu0">8</span><span class="br0">}</span>, std<span class="sy4">::</span><span class="me2">span</span><span class="br0">{</span>a<span class="sy2">+</span><span class="nu0">1</span>,<span class="nu0">3</span><span class="br0">}</span><span class="br0">)</span>
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<span class="sy3">&&</span> ends_with<span class="br0">(</span>std<span class="sy4">::</span><span class="me2">span</span><span class="br0">{</span>a<span class="br0">}</span>, std<span class="sy4">::</span><span class="me2">span</span><span class="br0">{</span>a<span class="sy2">+</span><span class="nu0">6</span>,<span class="nu0">3</span><span class="br0">}</span><span class="br0">)</span>
|
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<span class="sy3">&&</span> <span class="sy3">!</span>ends_with<span class="br0">(</span>std<span class="sy4">::</span><span class="me2">span</span><span class="br0">{</span>a<span class="br0">}</span>, std<span class="sy4">::</span><span class="me2">span</span><span class="br0">{</span>a<span class="sy2">+</span><span class="nu0">6</span>,<span class="nu0">2</span><span class="br0">}</span><span class="br0">)</span>
|
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<span class="sy3">&&</span> contains<span class="br0">(</span>std<span class="sy4">::</span><span class="me2">span</span><span class="br0">{</span>a<span class="br0">}</span>, std<span class="sy4">::</span><span class="me2">span</span><span class="br0">{</span>a<span class="sy2">+</span><span class="nu0">1</span>,<span class="nu0">4</span><span class="br0">}</span><span class="br0">)</span>
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<span class="sy3">&&</span> <span class="sy3">!</span>contains<span class="br0">(</span>std<span class="sy4">::</span><span class="me2">span</span><span class="br0">{</span>a,<span class="nu0">8</span><span class="br0">}</span>, std<span class="sy4">::</span><span class="me2">span</span><span class="br0">{</span>a,<span class="nu0">9</span><span class="br0">}</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
|
|
<span class="br0">}</span></pre></div>
|
|
</div>
|
|
<p>输出：</p>
|
|
<div dir="ltr" class="mw-geshi" style="text-align: left;">
|
|
<div class="text source-text">
|
|
<pre class="de1">0 1 2 3 4 5
|
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1 2 3 4 5 6
|
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2 3 4 5 6 7
|
|
3 4 5 6 7 8</pre></div>
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</div>
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</div>
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<h3><span class="mw-headline" id=".E7.BC.BA.E9.99.B7.E6.8A.A5.E5.91.8A">缺陷报告</span></h3>
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<p>下列更改行为的缺陷报告追溯地应用于以前出版的 C++ 标准。</p>
|
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<table class="dsctable" style="font-size:0.8em">
|
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<tr>
|
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<th>DR</th>
|
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<th>应用于</th>
|
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<th>出版时的行为</th>
|
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<th>正确行为</th>
|
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</tr>
|
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<tr>
|
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<td><a rel="nofollow" class="external text" href="https://wg21.link/P2325R3">P2325R3</a></td>
|
|
<td>C++20</td>
|
|
<td>非零静态长度的 <code>span</code> 不是 <code>view</code></td>
|
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<td><code>view</code> 不要求 <a href="cpp-concepts-default_initializable.html"><code>default_initializable</code></a> 故它们是</td>
|
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</tr>
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</table>
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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-initializer_list.html"><span class="t-lines"><span>initializer_list</span></span></a></div>
|
|
<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div>
|
|
</div>
|
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</td>
|
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<td>在<a href="cpp-language-list_initialization.html">列表初始化</a>中创建临时数组然后引用它<br />
|
|
<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-string-basic_string_view.html"><span class="t-lines"><span>basic_string_view</span></span></a></div>
|
|
<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx17">(C++17)</span></span></span></div>
|
|
</div>
|
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</td>
|
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<td>只读的字符串视图<br />
|
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<span class="t-mark">(类模板)</span></td>
|
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</tr>
|
|
<tr class="t-dsc">
|
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<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="cpp-ranges-subrange.html"><span class="t-lines"><span>ranges::subrange</span></span></a></div>
|
|
<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx20">(C++20)</span></span></span></div>
|
|
</div>
|
|
</td>
|
|
<td>将迭代器/哨位对结合为一个 <a href="cpp-ranges-view.html"><code>view</code></a><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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