252 lines
22 KiB
HTML
252 lines
22 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::rotate</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_algorithm_rotate skin-cppreference2 action-view cpp-navbar">
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<div id="cpp-content-base">
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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::</span>rotate</h1>
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<div id="contentSub"><span class="subpages">< <a href="cpp.html">cpp</a>‎ | <a href="cpp-algorithm.html">algorithm</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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<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></td>
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<td></td>
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<td rowspan="142">(1)</td>
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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> ForwardIt <span class="sy1">></span><br />
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<span class="kw4">void</span> rotate<span class="br0">(</span> ForwardIt first, ForwardIt n_first, ForwardIt last <span class="br0">)</span><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><span class="t-mark-rev t-until-cxx11">(C++11 前)</span></td>
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<tr class="t-dcl t-since-cxx11 t-until-cxx20">
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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> ForwardIt <span class="sy1">></span><br />
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ForwardIt rotate<span class="br0">(</span> ForwardIt first, ForwardIt n_first, ForwardIt last <span class="br0">)</span><span class="sy4">;</span></span></div>
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<td class="t-dcl-nopad"></td>
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<td><span class="t-mark-rev t-since-cxx11">(C++11 起)</span><br />
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<span class="t-mark-rev t-until-cxx20">(C++20 前)</span></td>
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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> ForwardIt <span class="sy1">></span><br />
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<span class="kw4">constexpr</span> ForwardIt rotate<span class="br0">(</span> ForwardIt first, ForwardIt n_first, ForwardIt last <span class="br0">)</span><span class="sy4">;</span></span></div>
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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">template</span><span class="sy1"><</span> <span class="kw1">class</span> ExecutionPolicy, <span class="kw1">class</span> ForwardIt <span class="sy1">></span><br /></span>
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<p>ForwardIt rotate<span class="br0">(</span> ExecutionPolicy<span class="sy3">&&</span> policy,<br /></p>
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ForwardIt first, ForwardIt n_first, ForwardIt last <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-cxx17">(C++17 起)</span></td>
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<div class="t-li1"><span class="t-li">1)</span> 进行元素范围上的左旋转。</div>
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<div class="t-li1"><span class="t-li"></span> 具体而言， <code>std::rotate</code> 交换范围 <code>[first, last)</code> 中的元素，方式满足元素 <code>n_first</code> 成为新范围的首个元素，而 <code>n_first - 1</code> 成为最后元素。</div>
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<div class="t-li1"><span class="t-li"></span> 此函数的前提条件是 <code>[first, n_first)</code> 和 <code>[n_first, last)</code> 为合法范围。</div>
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<div class="t-li1"><span class="t-li">2)</span> 同 <span class="t-v">(1)</span> ，但按照 <code>policy</code> 执行。此重载仅若 <span class="t-rev-inl t-until-cxx20"><span><span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-algorithm-is_execution_policy.html"><span class="kw1564">std::<span class="me2">is_execution_policy_v</span></span></a><span class="sy1"><</span><a href="cpp-types-decay.html"><span class="kw629">std::<span class="me2">decay_t</span></span></a><span class="sy1"><</span>ExecutionPolicy<span class="sy1">>></span></span></span></span> <span><span class="t-mark-rev t-until-cxx20">(C++20 前)</span></span></span><span class="t-rev-inl t-since-cxx20"><span><span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-algorithm-is_execution_policy.html"><span class="kw1564">std::<span class="me2">is_execution_policy_v</span></span></a><span class="sy1"><</span>std<span class="sy4">::</span><span class="me2">remove_cvref_t</span><span class="sy1"><</span>ExecutionPolicy<span class="sy1">>></span></span></span></span> <span><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></span></span> 为 true 才参与重载决议。</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>first</td>
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<td>-</td>
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<td>原范围的起始</td>
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</tr>
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<tr class="t-par">
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<td>n_first</td>
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<td>-</td>
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<td>应出现在旋转后范围起始的元素</td>
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</tr>
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<tr class="t-par">
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<td>last</td>
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<td>-</td>
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<td>原范围的结尾</td>
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</tr>
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<tr class="t-par">
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<td>policy</td>
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<td>-</td>
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<td>所用的执行策略。细节见<a href="cpp-algorithm-execution_policy_tag_t.html">执行策略</a>。</td>
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<tr class="t-par-hitem">
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<td colspan="3">类型要求</td>
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<tr class="t-par-req">
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<td colspan="3">-
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<div class="spacer"></div>
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<code>ForwardIt</code> 必须满足<a href="cpp-named_req-ValueSwappable.html"><span style="font-style:italic">值可交换</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(ValueSwappable)</span></a> 和 <a href="cpp-named_req-ForwardIterator.html"><span style="font-style:italic">老式向前迭代器</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(LegacyForwardIterator)</span></a> 的要求。</td>
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<tr class="t-par-req">
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<td colspan="3">-
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<div class="spacer"></div>
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解引用 <code>ForwardIt</code> 结果的类型必须满足<a href="cpp-named_req-MoveAssignable.html"><span style="font-style:italic">可移动赋值</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(MoveAssignable)</span></a> 和<a href="cpp-named_req-MoveConstructible.html"><span style="font-style:italic">可移动构造</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(MoveConstructible)</span></a> 的要求。</td>
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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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<table class="t-rev-begin">
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<tr class="t-rev t-until-cxx11">
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<td>
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<p>（无）</p>
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</td>
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<td><span class="t-mark-rev t-until-cxx11">(C++11 前)</span></td>
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</tr>
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<tr class="t-rev t-since-cxx11">
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<td>
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<p>指向 <code>first</code> 指向的元素所在的新位置的迭代器。等于 <code>first + (last - n_first)</code> 。</p>
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</td>
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<td><span class="t-mark-rev t-since-cxx11">(C++11 起)</span></td>
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</table>
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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>与 <code>first</code> 和 <code>last</code> 间的距离成线性。</p>
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<h3><span class="mw-headline" id=".E5.BC.82.E5.B8.B8">异常</span></h3>
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<p>拥有名为 <code>ExecutionPolicy</code> 的模板形参的重载按下列方式报告错误：</p>
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<ul>
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<li>若作为算法一部分调用的函数的执行抛出异常，且 <code>ExecutionPolicy</code> 为<a href="cpp-algorithm-execution_policy_tag_t.html">标准策略</a>之一，则调用 <span class="t-lc"><a href="cpp-error-terminate.html">std::terminate</a></span> 。对于任何其他 <code>ExecutionPolicy</code> ，行为是实现定义的。</li>
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<li>若算法无法分配内存，则抛出 <span class="t-lc"><a href="cpp-memory-new-bad_alloc.html">std::bad_alloc</a></span> 。</li>
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</ul>
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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>在常见实现上，若 <code>ForwardIt</code> 满足<a href="cpp-named_req-BidirectionalIterator.html"><span style="font-style:italic">老式双向迭代器</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(LegacyBidirectionalIterator)</span></a> 或（更好的）<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> 则 <code>ranges::rotate</code> 有更高的效率。</p>
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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> ）可能在迭代器类型满足<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> ，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/stl_algo.h#L1213-L1416">libstdc++</a>、 <a rel="nofollow" class="external text" href="https://github.com/llvm/llvm-project/tree/6adbc83ee9e46b476e0f75d5671c3a21f675a936/libcxx/include/__algorithm/rotate.h">libc++</a> 和 <a rel="nofollow" class="external text" href="https://github.com/microsoft/STL/blob/472161105d596192194d4715ccad307c6c163b4a/stl/inc/xutility#L5392-L5446">MSVC STL</a> 中的实现。</p>
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<table class="eq-fun-cpp-table">
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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">template</span><span class="sy1"><</span><span class="kw1">class</span> ForwardIt<span class="sy1">></span>
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<span class="kw4">constexpr</span> <span class="co1">// C++20 起</span>
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ForwardIt <span class="co1">// C++11 前为 void</span>
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rotate<span class="br0">(</span>ForwardIt first, ForwardIt n_first, ForwardIt last<span class="br0">)</span>
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<span class="br0">{</span>
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<span class="kw1">if</span><span class="br0">(</span>first <span class="sy1">==</span> n_first<span class="br0">)</span> <span class="kw1">return</span> last<span class="sy4">;</span>
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<span class="kw1">if</span><span class="br0">(</span>n_first <span class="sy1">==</span> last<span class="br0">)</span> <span class="kw1">return</span> first<span class="sy4">;</span>
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<span class="kw4">auto</span> read <span class="sy1">=</span> n_first<span class="sy4">;</span>
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<span class="kw4">auto</span> write <span class="sy1">=</span> first<span class="sy4">;</span>
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<span class="kw4">auto</span> next_read <span class="sy1">=</span> first<span class="sy4">;</span> <span class="co1">// "read" 撞击 "last" 时的读取位置</span>
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<span class="kw1">while</span><span class="br0">(</span>read <span class="sy3">!</span><span class="sy1">=</span> last<span class="br0">)</span> <span class="br0">{</span>
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<span class="kw1">if</span><span class="br0">(</span>write <span class="sy1">==</span> next_read<span class="br0">)</span> next_read <span class="sy1">=</span> read<span class="sy4">;</span> <span class="co1">// 跟踪 "first" 所至</span>
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<a href="cpp-algorithm-iter_swap.html"><span class="kw1601">std::<span class="me2">iter_swap</span></span></a><span class="br0">(</span>write<span class="sy2">++</span>, read<span class="sy2">++</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="br0">}</span>
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<span class="co1">// 旋转剩余序列到位置中</span>
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<span class="br0">(</span>rotate<span class="br0">)</span><span class="br0">(</span>write, next_read, last<span class="br0">)</span><span class="sy4">;</span>
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<span class="kw1">return</span> write<span class="sy4">;</span>
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<span class="br0">}</span></pre></div>
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</div>
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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 t-example-std-c++14">
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<p><code>std::rotate</code> 是许多算法中的公共构建块。此示例演示<a href="https://en.wikipedia.org/wiki/insertion_sort" class="extiw" title="enwiki:insertion sort">插入排序</a>。</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 <vector></span>
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<span class="co2">#include <iostream></span>
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<span class="co2">#include <algorithm></span>
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<span class="kw4">auto</span> print <span class="sy1">=</span> <span class="br0">[</span><span class="br0">]</span><span class="br0">(</span><span class="kw4">auto</span> <span class="kw4">const</span><span class="sy3">&</span> remark, <span class="kw4">auto</span> <span class="kw4">const</span><span class="sy3">&</span> v<span class="br0">)</span> <span class="br0">{</span>
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<a href="cpp-io-cout.html"><span class="kw1757">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> remark<span class="sy4">;</span>
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<span class="kw1">for</span> <span class="br0">(</span><span class="kw4">int</span> n<span class="sy4">:</span> v<span class="br0">)</span>
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<a href="cpp-io-cout.html"><span class="kw1757">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> n <span class="sy1"><<</span> <span class="st0">' '</span><span class="sy4">;</span>
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<a href="cpp-io-cout.html"><span class="kw1757">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><span class="sy4">;</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-container-vector.html"><span class="kw1269">std::<span class="me2">vector</span></span></a><span class="sy1"><</span><span class="kw4">int</span><span class="sy1">></span> v<span class="br0">{</span><span class="nu0">2</span>, <span class="nu0">4</span>, <span class="nu0">2</span>, <span class="nu0">0</span>, <span class="nu0">5</span>, <span class="nu0">10</span>, <span class="nu0">7</span>, <span class="nu0">3</span>, <span class="nu0">7</span>, <span class="nu0">1</span><span class="br0">}</span><span class="sy4">;</span>
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print<span class="br0">(</span><span class="st0">"before sort:<span class="es1">\t</span><span class="es1">\t</span>"</span>, v<span class="br0">)</span><span class="sy4">;</span>
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<span class="co1">// 插入排序</span>
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<span class="kw1">for</span> <span class="br0">(</span><span class="kw4">auto</span> i <span class="sy1">=</span> v.<span class="me1">begin</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span> i <span class="sy3">!</span><span class="sy1">=</span> v.<span class="me1">end</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span> <span class="sy2">++</span>i<span class="br0">)</span> <span class="br0">{</span>
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std<span class="sy4">::</span><span class="me2">rotate</span><span class="br0">(</span><a href="cpp-algorithm-upper_bound.html"><span class="kw1623">std::<span class="me2">upper_bound</span></span></a><span class="br0">(</span>v.<span class="me1">begin</span><span class="br0">(</span><span class="br0">)</span>, i, <span class="sy2">*</span>i<span class="br0">)</span>, i, i<span class="sy2">+</span><span class="nu0">1</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="br0">}</span>
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print<span class="br0">(</span><span class="st0">"after sort:<span class="es1">\t</span><span class="es1">\t</span>"</span>, v<span class="br0">)</span><span class="sy4">;</span>
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<span class="co1">// 简单向左旋转</span>
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std<span class="sy4">::</span><span class="me2">rotate</span><span class="br0">(</span>v.<span class="me1">begin</span><span class="br0">(</span><span class="br0">)</span>, v.<span class="me1">begin</span><span class="br0">(</span><span class="br0">)</span> <span class="sy2">+</span> <span class="nu0">1</span>, v.<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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print<span class="br0">(</span><span class="st0">"simple rotate left:<span class="es1">\t</span>"</span>, v<span class="br0">)</span><span class="sy4">;</span>
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<span class="co1">// 简单向右旋转</span>
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std<span class="sy4">::</span><span class="me2">rotate</span><span class="br0">(</span>v.<span class="me1">rbegin</span><span class="br0">(</span><span class="br0">)</span>, v.<span class="me1">rbegin</span><span class="br0">(</span><span class="br0">)</span> <span class="sy2">+</span> <span class="nu0">1</span>, v.<span class="me1">rend</span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
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print<span class="br0">(</span><span class="st0">"simple rotate right:<span class="es1">\t</span>"</span>, v<span class="br0">)</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">before sort: 2 4 2 0 5 10 7 3 7 1
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after sort: 0 1 2 2 3 4 5 7 7 10
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simple rotate left: 1 2 2 3 4 5 7 7 10 0
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simple rotate right: 0 1 2 2 3 4 5 7 7 10</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-rotate_copy.html"><span class="t-lines"><span>rotate_copy</span></span></a></div>
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</div>
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</td>
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<td>复制并旋转元素范围<br />
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<span class="t-mark">(函数模板)</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-algorithm-ranges-rotate.html"><span class="t-lines"><span>ranges::rotate</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>旋转范围中的元素顺序<br />
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<span class="t-mark">(niebloid)</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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