88 lines
7.6 KiB
HTML
88 lines
7.6 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::ranges::join_view<V>::begin</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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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_ranges_join_view_begin 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::ranges::join_view<V>::</span>begin</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-ranges.html">ranges</a>‎ | <a href="cpp-ranges-join_view.html">join view</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="kw4">constexpr</span> <span class="kw4">auto</span> begin<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span></span></div>
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</td>
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<td>(1)</td>
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<td><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></td>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw4">constexpr</span> <span class="kw4">auto</span> begin<span class="br0">(</span><span class="br0">)</span> <span class="kw4">const</span><br /></span>
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<p> requires ranges<span class="sy4">::</span><span class="me2">input_range</span><span class="sy1"><</span><span class="kw4">const</span> V<span class="sy1">></span> <span class="sy3">&&</span><br /></p>
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<a href="cpp-types-is_reference.html"><span class="kw481">std::<span class="me2">is_reference_v</span></span></a><span class="sy1"><</span>ranges<span class="sy4">::</span><span class="me2">range_reference_t</span><span class="sy1"><</span><span class="kw4">const</span> V<span class="sy1">>></span><span class="sy4">;</span></div>
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</td>
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<td>(2)</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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</tbody>
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<p>返回指向 <code>join_view</code> 首元素的<a href="https://zh.cppreference.com/mwiki/index.php?title=cpp/ranges/join_view/iterator&action=edit&redlink=1" class="new" title="cpp/ranges/join view/iterator（页面不存在）">迭代器</a>。给定 <code>base_</code> 为底层视图，</p>
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<div class="t-li1"><span class="t-li">1)</span> 若 <span class="t-c"><span class="mw-geshi cpp source-cpp">__SimpleView<span class="sy1"><</span>V<span class="sy1">></span></span></span> 得到满足且 <span class="t-c"><span class="mw-geshi cpp source-cpp">ranges<span class="sy4">::</span><span class="me2">range_reference_t</span><span class="sy1"><</span>V<span class="sy1">></span></span></span> 为引用类型则等价于 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw1">return</span> <span class="coMULTI">/*iterator*/</span><span class="sy1"><</span><span class="kw2">true</span><span class="sy1">></span><span class="br0">{</span><span class="sy2">*</span>this, ranges<span class="sy4">::</span><span class="me2">begin</span><span class="br0">(</span>base_<span class="br0">)</span><span class="br0">}</span><span class="sy4">;</span></span></span> 。否则等价于 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw1">return</span> <span class="coMULTI">/*iterator*/</span><span class="sy1"><</span><span class="kw2">false</span><span class="sy1">></span><span class="br0">{</span><span class="sy2">*</span>this, ranges<span class="sy4">::</span><span class="me2">begin</span><span class="br0">(</span>base_<span class="br0">)</span><span class="br0">}</span><span class="sy4">;</span></span></span> 。</div>
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<div class="t-li1"><span class="t-li">2)</span> 等价于 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw1">return</span> <span class="coMULTI">/*iterator*/</span><span class="sy1"><</span><span class="kw2">true</span><span class="sy1">></span><span class="br0">{</span><span class="sy2">*</span>this, ranges<span class="sy4">::</span><span class="me2">begin</span><span class="br0">(</span>base_<span class="br0">)</span><span class="br0">}</span><span class="sy4">;</span></span></span> 。</div>
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<h3><span class="mw-headline" id=".E5.8F.82.E6.95.B0">参数</span></h3>
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<p>（无）</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>到首元素的引用。</p>
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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>在 <span class="t-c"><span class="mw-geshi cpp source-cpp">ranges<span class="sy4">::</span><span class="me2">range_reference_t</span><span class="sy1"><</span>V<span class="sy1">></span></span></span> 不是引用类型，即解引用 <code>V</code> 的迭代器返回纯右值临时量时， <code>join_view</code> 仅为 <a href="cpp-ranges-input_range.html"><code>input_range</code></a> ，此情况下仅支持单趟迭代，而重复调用 <code>begin()</code> 可能不给出有意义的结果。</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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<table class="metadata plainlinks ambox mbox-small-left ambox-notice" style="">
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<td class="mbox-empty-cell"></td>
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<td class="mbox-text" style="">本节未完成<br />
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原因：暂无示例</td>
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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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<div class="t-dsc-member-div">
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<div><a href="https://zh.cppreference.com/mwiki/index.php?title=cpp/ranges/join_view/end&action=edit&redlink=1" class="new" title="cpp/ranges/join view/end（页面不存在）"><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或哨位<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-ranges-begin.html"><span class="t-lines"><span>ranges::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>返回指向范围起始的迭代器<br />
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<span class="t-mark">(定制点对象)</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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