466 lines
34 KiB
HTML
466 lines
34 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::ranges::views::reverse, std::ranges::reverse_view</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_ranges_reverse_view skin-cppreference2 action-view cpp-navbar">
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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::ranges::</span><span style="font-size:0.7em; line-height:130%">views::</span>reverse, <span style="font-size:0.7em; line-height:130%">std::ranges::</span>reverse_view</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></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>定义于头文件 <code><a href="cpp-header-ranges.html"><ranges></a></code></div>
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</td>
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<td></td>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span><span class="sy1"><</span> ranges<span class="sy4">::</span><span class="me2">view</span> V <span class="sy1">></span><br /></span>
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<p> requires ranges<span class="sy4">::</span><span class="me2">bidirectional_range</span><span class="sy1"><</span>V<span class="sy1">></span><br /></p>
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<span class="kw1">class</span> reverse_view <span class="sy4">:</span> <span class="kw1">public</span> ranges<span class="sy4">::</span><span class="me2">view_interface</span><span class="sy1"><</span>reverse_view<span class="sy1"><</span>V<span class="sy1">>></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="kw1">namespace</span> views <span class="br0">{</span><br /></span>
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<p> <span class="kw1">inline</span> <span class="kw4">constexpr</span> <span class="coMULTI">/*unspecified*/</span> reverse <span class="sy1">=</span> <span class="coMULTI">/*unspecified*/</span><span class="sy4">;</span><br /></p>
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<span class="br0">}</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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<div class="t-li1"><span class="t-li">1)</span> 代表有逆序的底层 <a href="cpp-ranges-view.html"><code>view</code></a> 的视图。</div>
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<div class="t-li1"><span class="t-li">2)</span> <a href="cpp-ranges.html#.E8.8C.83.E5.9B.B4.E9.80.82.E9.85.8D.E5.99.A8.E5.AF.B9.E8.B1.A1">范围适配器对象</a>。表达式 <span class="t-c"><span class="mw-geshi cpp source-cpp">views<span class="sy4">::</span><span class="me2">reverse</span><span class="br0">(</span>e<span class="br0">)</span></span></span> <i>表达式等价</i>于下列表达式之一，除了只求值 <code>E</code> 一次：
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<ul>
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<li><span class="t-c"><span class="mw-geshi cpp source-cpp">e.<span class="me1">base</span><span class="br0">(</span><span class="br0">)</span></span></span> ，若 <span class="t-c"><span class="mw-geshi cpp source-cpp">e</span></span> 的类型是（可有 cv 限定的） <code>reverse_view</code> 的特化；</li>
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<li>否则，若 <span class="t-c"><span class="mw-geshi cpp source-cpp">e</span></span> 的类型是（可有 cv 限定的）某迭代器类型 <code>I</code> 和 <code>ranges::subrange_kind</code> 类型值 <code>K</code> 的 <span class="t-c"><span class="mw-geshi cpp source-cpp">ranges<span class="sy4">::</span><span class="me2">subrange</span><span class="sy1"><</span><a href="cpp-iterator-reverse_iterator.html"><span class="kw658">std::<span class="me2">reverse_iterator</span></span></a><span class="sy1"><</span>I<span class="sy1">></span>, <a href="cpp-iterator-reverse_iterator.html"><span class="kw658">std::<span class="me2">reverse_iterator</span></span></a><span class="sy1"><</span>I<span class="sy1">></span>, K<span class="sy1">></span></span></span> ：</li>
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</ul>
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<dl>
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<dd>
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<ul>
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<li><span class="t-c"><span class="mw-geshi cpp source-cpp">ranges<span class="sy4">::</span><span class="me2">subrange</span><span class="sy1"><</span>I, I, K<span class="sy1">></span><span class="br0">(</span>e.<span class="me1">end</span><span class="br0">(</span><span class="br0">)</span>.<span class="me1">base</span><span class="br0">(</span><span class="br0">)</span>, e.<span class="me1">begin</span><span class="br0">(</span><span class="br0">)</span>.<span class="me1">base</span><span class="br0">(</span><span class="br0">)</span>, e.<span class="me1">size</span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span></span></span> ，若 <code>K</code> 为 <code>ranges::subrange_kind::sized</code>;</li>
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<li>否则为 <span class="t-c"><span class="mw-geshi cpp source-cpp">ranges<span class="sy4">::</span><span class="me2">subrange</span><span class="sy1"><</span>I, I, K<span class="sy1">></span><span class="br0">(</span>e.<span class="me1">end</span><span class="br0">(</span><span class="br0">)</span>.<span class="me1">base</span><span class="br0">(</span><span class="br0">)</span>, e.<span class="me1">begin</span><span class="br0">(</span><span class="br0">)</span>.<span class="me1">base</span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span></span></span> ；</li>
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</ul>
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</dd>
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</dl>
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<ul>
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<li>否则为 <span class="t-c"><span class="mw-geshi cpp source-cpp">ranges<span class="sy4">::</span><span class="me2">reverse_view</span><span class="br0">{</span>e<span class="br0">}</span></span></span> 。</li>
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</ul>
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换言之， <code>views::reverse</code> 尽可能解包逆转的视图。</div>
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<p><code>reverse_view</code> 始终实现 <a href="cpp-ranges-bidirectional_range.html"><code>bidirectional_range</code></a> 与 <a href="cpp-ranges-common_range.html"><code>common_range</code></a> ，而若底层视图类型 <code>V</code> 实现 <a href="cpp-ranges-borrowed_range.html"><code>borrowed_range</code></a>、 <a href="cpp-ranges-sized_range.html"><code>sized_range</code></a> 或 <a href="cpp-ranges-random_access_range.html"><code>random_access_range</code></a> 则它实现对应的概念。</p>
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<h3><span class="mw-headline" id=".E8.A1.A8.E8.BE.BE.E5.BC.8F.E7.AD.89.E4.BB.B7">表达式等价</span></h3>
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<p>表达式 <span class="t-c"><span class="mw-geshi cpp source-cpp">e</span></span> <i>表达式等价</i>于表达式 <span class="t-c"><span class="mw-geshi cpp source-cpp">f</span></span> ，若 <span class="t-c"><span class="mw-geshi cpp source-cpp">e</span></span> 与 <span class="t-c"><span class="mw-geshi cpp source-cpp">f</span></span> 拥有相同效果，均为<a href="cpp-language-noexcept_spec.html">潜在抛出</a>或均非潜在抛出（即 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw1">noexcept</span><span class="br0">(</span>e<span class="br0">)</span> <span class="sy1">==</span> <span class="kw1">noexcept</span><span class="br0">(</span>f<span class="br0">)</span></span></span> ），且均为<a href="cpp-language-constant_expression.html">常量子表达式</a>或均非常量子表达式。</p>
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<h3><span class="mw-headline" id=".E6.95.B0.E6.8D.AE.E6.88.90.E5.91.98">数据成员</span></h3>
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<p><code>reverse_view</code> 的典型实现仅保有一或二个成员对象：</p>
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<ul>
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<li><code>V</code> 类型的底层视图（此处示为 <code><i>base_</i></code> ，名称仅用于阐释），及</li>
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<li><span class="t-lc"><a href="cpp-utility-optional.html">std::optional</a></span> 式的缓存对象，不保有值或保有一个底层视图的尾迭代器/位置，仅若底层视图类型 <code>V</code> 不实现 <a href="cpp-ranges-common_range.html"><code>common_range</code></a> 才存在。</li>
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</ul>
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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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<div class="t-dsc-member-div t-dsc-member-nobold-div">
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<div><span class="t-lines"><span>(构造函数)</span></span></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>构造 <code>reverse_view</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><span class="t-lines"><span>base</span></span></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>返回底层视图 <code>V</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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<td>
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<div class="t-dsc-member-div">
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<div><span class="t-lines"><span>begin</span></span></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 <code>reverse_view</code> 的起始迭代器<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><span class="t-lines"><span>end</span></span></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 <code>reverse_view</code> 的尾迭代器<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><span class="t-lines"><span>size</span></span></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>若底层视图有界则返回其大小<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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<td colspan="2">
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<h5><span class="mw-headline" id=".E7.BB.A7.E6.89.BF.E8.87.AA_std::ranges::view_interface">继承自 <span class="t-lc">std::ranges::view_interface</span></span></h5>
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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-ranges-view_interface-empty.html"><span class="t-lines"><span>empty</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>返回视图是否为空。若视图满足 <a href="cpp-ranges-forward_range.html"><code>forward_range</code></a> 则提供。<br />
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<span class="t-mark">(<code>std::ranges::view_interface<D></code> 的公开成员函数)</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-view_interface-operator_bool.html"><span class="t-lines"><span>operator bool</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>返回派生视图是否为非空。若 <span class="t-lc">ranges::empty</span> 可应用于它则提供。<br />
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<span class="t-mark">(<code>std::ranges::view_interface<D></code> 的公开成员函数)</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-view_interface-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>返回派生视图中的首元素。若视图满足 <a href="cpp-ranges-forward_range.html"><code>forward_range</code></a> 则提供。<br />
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<span class="t-mark">(<code>std::ranges::view_interface<D></code> 的公开成员函数)</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-view_interface-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>返回派生视图中的末元素。若视图满足 <a href="cpp-ranges-bidirectional_range.html"><code>bidirectional_range</code></a> 与 <a href="cpp-ranges-common_range.html"><code>common_range</code></a> 则提供。<br />
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<span class="t-mark">(<code>std::ranges::view_interface<D></code> 的公开成员函数)</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-view_interface-operator_at.html"><span class="t-lines"><span>operator[]</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>返回派生视图中的第 n 个元素。若视图满足 <a href="cpp-ranges-random_access_range.html"><code>random_access_range</code></a> 则提供。<br />
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<span class="t-mark">(<code>std::ranges::view_interface<D></code> 的公开成员函数)</span></td>
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</tr>
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</table>
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<div class="t-member">
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<h2><span class="mw-headline" id="std::ranges::reverse_view::reverse_view"><span style="font-size:0.7em; line-height:130%">std::ranges::reverse_view::</span>reverse_view</span></h2>
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<table class="t-dcl-begin">
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<tbody>
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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">reverse_view<span class="br0">(</span><span class="br0">)</span> requires std<span class="sy4">::</span><span class="me2">default_initializable</span><span class="sy1"><</span>V<span class="sy1">></span> <span class="sy1">=</span> <span class="kw1">default</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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</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="kw4">constexpr</span> reverse_view<span class="br0">(</span>V r<span class="br0">)</span><span class="sy4">;</span></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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</tr>
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</tbody>
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</table>
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<div class="t-li1"><span class="t-li">1)</span> 经由其默认成员初始化器（ <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy1">=</span> V<span class="br0">(</span><span class="br0">)</span></span></span> ）值初始化 <code><i>base_</i></code> 。</div>
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<div class="t-li1"><span class="t-li">2)</span> 以 <span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">move</span><span class="br0">(</span>r<span class="br0">)</span></span></span> 初始化 <code><i>base_</i></code> 。</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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<table class="t-par-begin">
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<tr class="t-par">
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<td>r</td>
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<td>-</td>
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<td>要逆转的范围</td>
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</tr>
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</table>
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</div>
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<div class="t-member">
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<h2><span class="mw-headline" id="std::ranges::reverse_view::base"><span style="font-size:0.7em; line-height:130%">std::ranges::reverse_view::</span>base</span></h2>
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<table class="t-dcl-begin">
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<tbody>
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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="kw4">constexpr</span> V base<span class="br0">(</span><span class="br0">)</span> <span class="kw4">const</span><span class="sy3">&</span> requires std<span class="sy4">::</span><span class="me2">copy_constructible</span><span class="sy1"><</span>V<span class="sy1">></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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</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="kw4">constexpr</span> V base<span class="br0">(</span><span class="br0">)</span> <span class="sy3">&&</span><span class="sy4">;</span></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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</tr>
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</tbody>
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</table>
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<p>返回底层视图。</p>
|
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<div class="t-li1"><span class="t-li">1)</span> 从底层视图复制构造结果。等价于 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw1">return</span> base_<span class="sy4">;</span></span></span> 。</div>
|
|
<div class="t-li1"><span class="t-li">2)</span> 从底层视图移动构造结果。等价于 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw1">return</span> std<span class="sy4">::</span><span class="me2">move</span><span class="br0">(</span>base_<span class="br0">)</span><span class="sy4">;</span></span></span> 。</div>
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</div>
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<div class="t-member">
|
|
<h2><span class="mw-headline" id="std::ranges::reverse_view::begin"><span style="font-size:0.7em; line-height:130%">std::ranges::reverse_view::</span>begin</span></h2>
|
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<table class="t-dcl-begin">
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<tbody>
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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="kw4">constexpr</span> <a href="cpp-iterator-reverse_iterator.html"><span class="kw658">std::<span class="me2">reverse_iterator</span></span></a><span class="sy1"><</span>ranges<span class="sy4">::</span><span class="me2">iterator_t</span><span class="sy1"><</span>V<span class="sy1">>></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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</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="kw4">constexpr</span> <a href="cpp-iterator-reverse_iterator.html"><span class="kw658">std::<span class="me2">reverse_iterator</span></span></a><span class="sy1"><</span>ranges<span class="sy4">::</span><span class="me2">iterator_t</span><span class="sy1"><</span>V<span class="sy1">>></span> begin<span class="br0">(</span><span class="br0">)</span><br />
|
|
requires ranges<span class="sy4">::</span><span class="me2">common_range</span><span class="sy1"><</span>V<span class="sy1">></span><span class="sy4">;</span></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 t-since-cxx20">
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<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> requires ranges<span class="sy4">::</span><span class="me2">common_range</span><span class="sy1"><</span><span class="kw4">const</span> V<span class="sy1">></span><span class="sy4">;</span></span></div>
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</td>
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<td>(3)</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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<div class="t-li1"><span class="t-li">1)</span> 返回 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-iterator-make_reverse_iterator.html"><span class="kw663">std::<span class="me2">make_reverse_iterator</span></span></a><span class="br0">(</span>ranges<span class="sy4">::</span><span class="me2">next</span><span class="br0">(</span>ranges<span class="sy4">::</span><span class="me2">begin</span><span class="br0">(</span>base_<span class="br0">)</span>, ranges<span class="sy4">::</span><span class="me2">end</span><span class="br0">(</span>base_<span class="br0">)</span><span class="br0">)</span><span class="br0">)</span></span></span> 。为提供 <a href="cpp-ranges-range.html"><code>range</code></a> 概念所要求的的均摊常数时间复杂度，此函数在缓存对象内缓存结果，以供后继调用使用。</div>
|
|
<div class="t-li1"><span class="t-li">2-3)</span> 等价于 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw1">return</span> <a href="cpp-iterator-make_reverse_iterator.html"><span class="kw663">std::<span class="me2">make_reverse_iterator</span></span></a><span class="br0">(</span>ranges<span class="sy4">::</span><span class="me2">end</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>
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<div class="t-member">
|
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<h2><span class="mw-headline" id="std::ranges::reverse_view::end"><span style="font-size:0.7em; line-height:130%">std::ranges::reverse_view::</span>end</span></h2>
|
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<table class="t-dcl-begin">
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<tbody>
|
|
<tr class="t-dcl t-since-cxx20">
|
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<td>
|
|
<div><span class="mw-geshi cpp source-cpp"><span class="kw4">constexpr</span> <a href="cpp-iterator-reverse_iterator.html"><span class="kw658">std::<span class="me2">reverse_iterator</span></span></a><span class="sy1"><</span>ranges<span class="sy4">::</span><span class="me2">iterator_t</span><span class="sy1"><</span>V<span class="sy1">>></span> end<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span></span></div>
|
|
</td>
|
|
<td>(1)</td>
|
|
<td><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></td>
|
|
</tr>
|
|
<tr class="t-dcl t-since-cxx20">
|
|
<td>
|
|
<div><span class="mw-geshi cpp source-cpp"><span class="kw4">constexpr</span> <span class="kw4">auto</span> end<span class="br0">(</span><span class="br0">)</span> <span class="kw4">const</span> requires ranges<span class="sy4">::</span><span class="me2">common_range</span><span class="sy1"><</span><span class="kw4">const</span> V<span class="sy1">></span><span class="sy4">;</span></span></div>
|
|
</td>
|
|
<td>(2)</td>
|
|
<td><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></td>
|
|
</tr>
|
|
<tr class="t-dcl-sep">
|
|
<td></td>
|
|
<td></td>
|
|
<td></td>
|
|
</tr>
|
|
</tbody>
|
|
</table>
|
|
<p>等价于 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw1">return</span> <a href="cpp-iterator-make_reverse_iterator.html"><span class="kw663">std::<span class="me2">make_reverse_iterator</span></span></a><span class="br0">(</span>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> 。</p>
|
|
</div>
|
|
<div class="t-member">
|
|
<h2><span class="mw-headline" id="std::ranges::reverse_view::size"><span style="font-size:0.7em; line-height:130%">std::ranges::reverse_view::</span>size</span></h2>
|
|
<table class="t-dcl-begin">
|
|
<tbody>
|
|
<tr class="t-dcl t-since-cxx20">
|
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<td>
|
|
<div><span class="mw-geshi cpp source-cpp"><span class="kw4">constexpr</span> <span class="kw4">auto</span> size<span class="br0">(</span><span class="br0">)</span> requires ranges<span class="sy4">::</span><span class="me2">sized_range</span><span class="sy1"><</span>V<span class="sy1">></span> <span class="br0">{</span><br /></span>
|
|
<p> <span class="kw1">return</span> ranges<span class="sy4">::</span><span class="me2">size</span><span class="br0">(</span>base_<span class="br0">)</span><span class="sy4">;</span><br /></p>
|
|
<span class="br0">}</span></div>
|
|
</td>
|
|
<td>(1)</td>
|
|
<td><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></td>
|
|
</tr>
|
|
<tr class="t-dcl t-since-cxx20">
|
|
<td>
|
|
<div><span class="mw-geshi cpp source-cpp"><span class="kw4">constexpr</span> <span class="kw4">auto</span> size<span class="br0">(</span><span class="br0">)</span> <span class="kw4">const</span> requires ranges<span class="sy4">::</span><span class="me2">sized_range</span><span class="sy1"><</span><span class="kw4">const</span> V<span class="sy1">></span> <span class="br0">{</span><br /></span>
|
|
<p> <span class="kw1">return</span> ranges<span class="sy4">::</span><span class="me2">size</span><span class="br0">(</span>base_<span class="br0">)</span><span class="sy4">;</span><br /></p>
|
|
<span class="br0">}</span></div>
|
|
</td>
|
|
<td>(2)</td>
|
|
<td><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></td>
|
|
</tr>
|
|
<tr class="t-dcl-sep">
|
|
<td></td>
|
|
<td></td>
|
|
<td></td>
|
|
</tr>
|
|
</tbody>
|
|
</table>
|
|
<p>若视图有界则返回其大小。</p>
|
|
</div>
|
|
<h3><span class="mw-headline" id=".E6.8E.A8.E5.AF.BC.E6.8C.87.E5.BC.95">推导指引</span></h3>
|
|
<table class="t-dcl-begin">
|
|
<tbody>
|
|
<tr class="t-dcl t-since-cxx20">
|
|
<td>
|
|
<div><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span><span class="sy1"><</span><span class="kw1">class</span> R<span class="sy1">></span><br />
|
|
reverse_view<span class="br0">(</span>R<span class="sy3">&&</span><span class="br0">)</span> <span class="sy2">-</span><span class="sy1">></span> reverse_view<span class="sy1"><</span>views<span class="sy4">::</span><span class="me2">all_t</span><span class="sy1"><</span>R<span class="sy1">>></span><span class="sy4">;</span></span></div>
|
|
</td>
|
|
<td class="t-dcl-nopad"></td>
|
|
<td><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></td>
|
|
</tr>
|
|
<tr class="t-dcl-sep">
|
|
<td></td>
|
|
<td></td>
|
|
<td></td>
|
|
</tr>
|
|
</tbody>
|
|
</table>
|
|
<h3><span class="mw-headline" id=".E8.BE.85.E5.8A.A9.E6.A8.A1.E6.9D.BF">辅助模板</span></h3>
|
|
<table class="t-dcl-begin">
|
|
<tbody>
|
|
<tr class="t-dcl t-since-cxx20">
|
|
<td>
|
|
<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 /></span>
|
|
<p><span class="kw1">inline</span> <span class="kw4">constexpr</span> <span class="kw4">bool</span> enable_borrowed_range<span class="sy1"><</span>std<span class="sy4">::</span><span class="me2">ranges</span><span class="sy4">::</span><span class="me2">reverse_view</span><span class="sy1"><</span>T<span class="sy1">>></span> <span class="sy1">=</span><br /></p>
|
|
std<span class="sy4">::</span><span class="me2">ranges</span><span class="sy4">::</span><span class="me2">enable_borrowed_range</span><span class="sy1"><</span>T<span class="sy1">></span><span class="sy4">;</span></div>
|
|
</td>
|
|
<td class="t-dcl-nopad"></td>
|
|
<td><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></td>
|
|
</tr>
|
|
<tr class="t-dcl-sep">
|
|
<td></td>
|
|
<td></td>
|
|
<td></td>
|
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</tr>
|
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</tbody>
|
|
</table>
|
|
<p><a href="cpp-ranges-borrowed_range.html"><tt>std::ranges::enable_borrowed_range</tt></a> 的此特化使得 <code>reverse_view</code> 在底层视图满足 <a href="cpp-ranges-borrowed_range.html"><code>borrowed_range</code></a> 时满足它。</p>
|
|
<h3><span class="mw-headline" id=".E7.A4.BA.E4.BE.8B">示例</span></h3>
|
|
<div class="t-example">
|
|
<div class="t-example-live-link"></div>
|
|
<div dir="ltr" class="mw-geshi" style="text-align: left;">
|
|
<div class="cpp source-cpp">
|
|
<pre class="de1"><span class="co2">#include <ranges></span>
|
|
<span class="co2">#include <iostream></span>
|
|
|
|
<span class="kw4">int</span> main<span class="br0">(</span><span class="br0">)</span>
|
|
<span class="br0">{</span>
|
|
<span class="kw4">static</span> <span class="kw4">constexpr</span> <span class="kw4">auto</span> il <span class="sy1">=</span> <span class="br0">{</span><span class="nu0">3</span>, <span class="nu0">1</span>, <span class="nu0">4</span>, <span class="nu0">1</span>, <span class="nu0">5</span>, <span class="nu0">9</span><span class="br0">}</span><span class="sy4">;</span>
|
|
|
|
std<span class="sy4">::</span><span class="me2">ranges</span><span class="sy4">::</span><span class="me2">reverse_view</span> rv <span class="br0">{</span>il<span class="br0">}</span><span class="sy4">;</span>
|
|
<span class="kw1">for</span> <span class="br0">(</span><span class="kw4">int</span> i <span class="sy4">:</span> rv<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> i <span class="sy1"><<</span> <span class="st0">' '</span><span class="sy4">;</span>
|
|
|
|
<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>
|
|
|
|
<span class="kw1">for</span><span class="br0">(</span><span class="kw4">int</span> i <span class="sy4">:</span> il <span class="sy3">|</span> std<span class="sy4">::</span><span class="me2">views</span><span class="sy4">::</span><span class="me2">reverse</span><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> i <span class="sy1"><<</span> <span class="st0">' '</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">9 5 1 4 1 3
|
|
9 5 1 4 1 3</pre></div>
|
|
</div>
|
|
</div>
|
|
<h3><span class="mw-headline" id=".E7.BC.BA.E9.99.B7.E6.8A.A5.E5.91.8A">缺陷报告</span></h3>
|
|
<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>
|
|
<table class="dsctable" style="font-size:0.8em">
|
|
<tr>
|
|
<th>DR</th>
|
|
<th>应用于</th>
|
|
<th>出版时的行为</th>
|
|
<th>正确行为</th>
|
|
</tr>
|
|
<tr>
|
|
<td><a rel="nofollow" class="external text" href="https://cplusplus.github.io/LWG/issue3494">LWG 3494</a></td>
|
|
<td>C++20</td>
|
|
<td><code>reverse_view</code> 始终不是 <code>borrowed_range</code></td>
|
|
<td>若底层视图为 <code>borrowed_range</code> 则它是</td>
|
|
</tr>
|
|
</table>
|
|
<h3><span class="mw-headline" id=".E5.8F.82.E9.98.85">参阅</span></h3>
|
|
<table class="t-dsc-begin">
|
|
<tr class="t-dsc">
|
|
<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="cpp-iterator-reverse_iterator.html"><span class="t-lines"><span>reverse_iterator</span></span></a></div>
|
|
</div>
|
|
</td>
|
|
<td>逆序遍历的迭代器适配器<br />
|
|
<span class="t-mark">(类模板)</span></td>
|
|
</tr>
|
|
<tr class="t-dsc">
|
|
<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="cpp-algorithm-ranges-reverse.html"><span class="t-lines"><span>ranges::reverse</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>逆转范围中的元素顺序<br />
|
|
<span class="t-mark">(niebloid)</span></td>
|
|
</tr>
|
|
<tr class="t-dsc">
|
|
<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="cpp-algorithm-ranges-reverse_copy.html"><span class="t-lines"><span>ranges::revserse_copy</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>创建一个范围的逆向副本<br />
|
|
<span class="t-mark">(niebloid)</span></td>
|
|
</tr>
|
|
</table>
|
|
</div>
|
|
<div class="visualClear"></div>
|
|
</div>
|
|
</div>
|
|
</div>
|
|
</body>
|
|
</html>
|