196 lines
17 KiB
HTML
196 lines
17 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::reverse</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_algorithm_ranges_reverse 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::</span>reverse</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-algorithm.html">algorithm</a>‎ | <a href="cpp-algorithm-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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<tbody>
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<td>
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<div>定义于头文件 <code><a href="cpp-header-algorithm.html"><algorithm></a></code></div>
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</td>
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<td></td>
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<td></td>
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<div>调用签名</div>
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</td>
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<td></td>
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<td></td>
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<tr class="t-dcl t-since-cxx20">
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span><span class="sy1"><</span> std<span class="sy4">::</span><span class="me2">bidirectional_iterator</span> I, std<span class="sy4">::</span><span class="me2">sentinel_for</span><span class="sy1"><</span>I<span class="sy1">></span> S <span class="sy1">></span><br /></span>
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<p> requires std<span class="sy4">::</span><span class="me2">permutable</span><span class="sy1"><</span>I<span class="sy1">></span><br />
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<span class="kw4">constexpr</span> I<br /></p>
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reverse<span class="br0">(</span> I first, S last <span class="br0">)</span><span class="sy4">;</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="kw1">template</span><span class="sy1"><</span> ranges<span class="sy4">::</span><span class="me2">bidirectional_range</span> R <span class="sy1">></span><br /></span>
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<p> requires std<span class="sy4">::</span><span class="me2">permutable</span><span class="sy1"><</span>ranges<span class="sy4">::</span><span class="me2">iterator_t</span><span class="sy1"><</span>R<span class="sy1">>></span><br />
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<span class="kw4">constexpr</span> ranges<span class="sy4">::</span><span class="me2">borrowed_iterator_t</span><span class="sy1"><</span>R<span class="sy1">></span><br /></p>
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reverse<span class="br0">(</span> R<span class="sy3">&&</span> r <span class="br0">)</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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</table>
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<div class="t-li1"><span class="t-li">1)</span> 逆转范围 <code>[first, last)</code> 中的元素顺序。</div>
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<div class="t-li1"><span class="t-li"></span> 表现如同对每个 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="nu0">0</span> ≤ i <span class="sy1"><</span> <span class="br0">(</span>last<span class="sy2">-</span>first<span class="br0">)</span><span class="sy2">/</span><span class="nu0">2</span></span></span> 中的整数 <code>i</code> 应用 <span class="t-lc">ranges::iter_swap</span> 到每对迭代器 <code>first+i, last-i-1</code> 。</div>
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<div class="t-li1"><span class="t-li">2)</span> 同 <span class="t-v">(1)</span> ，但以 <code>r</code> 为源范围，如同以 <span class="t-c"><span class="mw-geshi cpp source-cpp">ranges<span class="sy4">::</span><span class="me2">begin</span><span class="br0">(</span>r<span class="br0">)</span></span></span> 为 <code>first</code> 并以 <span class="t-c"><span class="mw-geshi cpp source-cpp">ranges<span class="sy4">::</span><span class="me2">end</span><span class="br0">(</span>r<span class="br0">)</span></span></span> 为 <code>last</code> 。</div>
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<p>此页面上描述的仿函数实体是 <i>niebloid</i> ，即：</p>
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<ul>
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<li>调用它们中的任何一者时不可指定显式模板实参。</li>
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<li>它们无一对<a href="cpp-language-adl.html">实参依赖查找</a>可见。</li>
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<li>在<a href="cpp-language-unqualified_lookup.html">通常无限定查找</a>寻找函数调用运算符左侧的名称找到它们之一时，它禁止<a href="cpp-language-adl.html">实参依赖查找</a>。</li>
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</ul>
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<p>实际上，它们能以函数对象，或以某些特殊编译器扩展实现。</p>
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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>first, last</td>
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<td>-</td>
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<td>要逆转的元素范围</td>
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</tr>
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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>要逆转的元素范围</td>
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</tr>
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</table>
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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>等于 <code>last</code> 的迭代器。</p>
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<h3><span class="mw-headline" id=".E5.A4.8D.E6.9D.82.E5.BA.A6">复杂度</span></h3>
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<p>准确交换 <code>(last - first)/2</code> 次。</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>实现（例如 <a rel="nofollow" class="external text" href="https://github.com/microsoft/STL/blob/main/stl/src/vector_algorithms.cpp">MSVC STL</a> ）可能在迭代器类型实现 <a href="cpp-iterator-contiguous_iterator.html"><code>contiguous_iterator</code></a> ，并且交换其值类型不调用非平凡的特殊成员函数或 <a href="cpp-language-adl.html">ADL</a> 所找到的 <code>swap</code> 时启用向量化。</p>
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<h3><span class="mw-headline" id=".E5.8F.AF.E8.83.BD.E7.9A.84.E5.AE.9E.E7.8E.B0">可能的实现</span></h3>
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<p>参阅 <a rel="nofollow" class="external text" href="https://github.com/gcc-mirror/gcc/blob/14d8a5ae472ca5743016f37da2dd4770d83dea21/libstdc%2B%2B-v3/include/bits/ranges_algo.h#L1278-L1325">libstdc++</a> 与 <a rel="nofollow" class="external text" href="https://github.com/microsoft/STL/blob/472161105d596192194d4715ccad307c6c163b4a/stl/inc/algorithm#L4154-L4180">MSVC STL</a> 中的实现。</p>
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<table class="eq-fun-cpp-table">
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<tr>
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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="kw1">struct</span> reverse_fn <span class="br0">{</span>
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<span class="kw1">template</span><span class="sy1"><</span>std<span class="sy4">::</span><span class="me2">bidirectional_iterator</span> I, std<span class="sy4">::</span><span class="me2">sentinel_for</span><span class="sy1"><</span>I<span class="sy1">></span> S<span class="sy1">></span>
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requires std<span class="sy4">::</span><span class="me2">permutable</span><span class="sy1"><</span>I<span class="sy1">></span>
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<span class="kw4">constexpr</span> I operator<span class="br0">(</span><span class="br0">)</span><span class="br0">(</span> I first, S last <span class="br0">)</span> <span class="kw4">const</span> <span class="br0">{</span>
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<span class="kw4">auto</span> last2<span class="br0">{</span> ranges<span class="sy4">::</span><span class="me2">next</span><span class="br0">(</span>first, last<span class="br0">)</span> <span class="br0">}</span><span class="sy4">;</span>
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<span class="kw1">for</span> <span class="br0">(</span><span class="kw4">auto</span> tail<span class="br0">{</span> last2 <span class="br0">}</span><span class="sy4">;</span> <span class="sy3">!</span><span class="br0">(</span>first <span class="sy1">==</span> tail or first <span class="sy1">==</span> <span class="sy2">--</span>tail<span class="br0">)</span><span class="sy4">;</span> <span class="sy2">++</span>first<span class="br0">)</span> <span class="br0">{</span>
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ranges<span class="sy4">::</span><span class="me2">iter_swap</span><span class="br0">(</span>first, tail<span class="br0">)</span><span class="sy4">;</span>
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<span class="br0">}</span>
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<span class="kw1">return</span> last2<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>ranges<span class="sy4">::</span><span class="me2">bidirectional_range</span> R<span class="sy1">></span>
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requires std<span class="sy4">::</span><span class="me2">permutable</span><span class="sy1"><</span>ranges<span class="sy4">::</span><span class="me2">iterator_t</span><span class="sy1"><</span>R<span class="sy1">>></span>
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<span class="kw4">constexpr</span> ranges<span class="sy4">::</span><span class="me2">borrowed_iterator_t</span><span class="sy1"><</span>R<span class="sy1">></span>
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operator<span class="br0">(</span><span class="br0">)</span><span class="br0">(</span> R<span class="sy3">&&</span> r <span class="br0">)</span> <span class="kw4">const</span> <span class="br0">{</span>
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<span class="kw1">return</span> <span class="br0">(</span><span class="sy2">*</span>this<span class="br0">)</span><span class="br0">(</span>ranges<span class="sy4">::</span><span class="me2">begin</span><span class="br0">(</span>r<span class="br0">)</span>, ranges<span class="sy4">::</span><span class="me2">end</span><span class="br0">(</span>r<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="br0">}</span><span class="sy4">;</span>
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<span class="kw1">inline</span> <span class="kw4">constexpr</span> reverse_fn reverse<span class="br0">{</span><span class="br0">}</span><span class="sy4">;</span></pre></div>
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</div>
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</td>
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</table>
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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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<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 <array></span>
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<span class="co2">#include <iostream></span>
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<span class="co2">#include <string></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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<a href="cpp-string-basic_string.html"><span class="kw1230">std::<span class="me2">string</span></span></a> s<span class="br0">{</span><span class="st0">"ABCDEF"</span><span class="br0">}</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> s <span class="sy1"><<</span> <span class="st0">" → "</span><span class="sy4">;</span>
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std<span class="sy4">::</span><span class="me2">ranges</span><span class="sy4">::</span><span class="me2">reverse</span><span class="br0">(</span>s.<span class="me1">begin</span><span class="br0">(</span><span class="br0">)</span>, s.<span class="me1">end</span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</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> s <span class="sy1"><<</span> <span class="st0">" → "</span><span class="sy4">;</span>
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std<span class="sy4">::</span><span class="me2">ranges</span><span class="sy4">::</span><span class="me2">reverse</span><span class="br0">(</span>s<span class="br0">)</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> s <span class="sy1"><<</span> <span class="st0">" │ "</span><span class="sy4">;</span>
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<a href="cpp-container-array.html"><span class="kw1268">std::<span class="me2">array</span></span></a> a<span class="br0">{</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="br0">}</span><span class="sy4">;</span>
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<span class="kw1">for</span><span class="br0">(</span><span class="kw4">auto</span> e <span class="sy4">:</span> a<span class="br0">)</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> e <span class="sy1"><<</span> <span class="st0">' '</span><span class="sy4">;</span> <span class="br0">}</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><span class="sy4">;</span>
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std<span class="sy4">::</span><span class="me2">ranges</span><span class="sy4">::</span><span class="me2">reverse</span><span class="br0">(</span>a<span class="br0">)</span><span class="sy4">;</span>
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<span class="kw1">for</span><span class="br0">(</span><span class="kw4">auto</span> e <span class="sy4">:</span> a<span class="br0">)</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> e <span class="sy1"><<</span> <span class="st0">' '</span><span class="sy4">;</span> <span class="br0">}</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></pre></div>
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</div>
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<p>输出：</p>
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<div dir="ltr" class="mw-geshi" style="text-align: left;">
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<div class="text source-text">
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<pre class="de1">ABCDEF → FEDCBA → ABCDEF │ 1 2 3 4 5 → 5 4 3 2 1</pre></div>
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</div>
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</div>
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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-algorithm-ranges-reverse_copy.html"><span class="t-lines"><span>ranges::revserse_copy</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>创建一个范围的逆向副本<br />
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<span class="t-mark">(niebloid)</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-reverse_view.html"><span class="t-lines"><span>ranges::reverse_view</span><span>views::reverse</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>以逆序迭代另一双向视图上的元素的 <a href="cpp-ranges-view.html"><code>view</code></a><br />
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<span class="t-mark">(类模板)</span> <span class="t-mark">(范围适配器对象)</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-algorithm-reverse.html"><span class="t-lines"><span>reverse</span></span></a></div>
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</div>
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</td>
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<td>逆转范围中的元素顺序<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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</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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