220 lines
23 KiB
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220 lines
23 KiB
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<title>std::shift_left, std::shift_right</title>
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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::</span>shift_left, <span style="font-size:0.7em; line-height:130%">std::</span>shift_right</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></span></div>
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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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<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> <span class="kw1">class</span> ForwardIt <span class="sy1">></span><br /></span>
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<p><span class="kw4">constexpr</span> ForwardIt shift_left<span class="br0">(</span> ForwardIt first, ForwardIt last,<br /></p>
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<span class="kw1">typename</span> <a href="cpp-iterator-iterator_traits.html"><span class="kw651">std::<span class="me2">iterator_traits</span></span></a><span class="sy1"><</span>ForwardIt<span class="sy1">></span><span class="sy4">::</span><span class="me2">difference_type</span> n <span class="br0">)</span><span class="sy4">;</span></div>
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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">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 shift_left<span class="br0">(</span> ExecutionPolicy<span class="sy3">&&</span> policy, ForwardIt first, ForwardIt last,<br /></p>
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<span class="kw1">typename</span> <a href="cpp-iterator-iterator_traits.html"><span class="kw651">std::<span class="me2">iterator_traits</span></span></a><span class="sy1"><</span>ForwardIt<span class="sy1">></span><span class="sy4">::</span><span class="me2">difference_type</span> n <span class="br0">)</span><span class="sy4">;</span></div>
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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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<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 /></span>
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<p><span class="kw4">constexpr</span> ForwardIt shift_right<span class="br0">(</span> ForwardIt first, ForwardIt last,<br /></p>
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<span class="kw1">typename</span> <a href="cpp-iterator-iterator_traits.html"><span class="kw651">std::<span class="me2">iterator_traits</span></span></a><span class="sy1"><</span>ForwardIt<span class="sy1">></span><span class="sy4">::</span><span class="me2">difference_type</span> n <span class="br0">)</span><span class="sy4">;</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 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> <span class="kw1">class</span> ExecutionPolicy, <span class="kw1">class</span> ForwardIt <span class="sy1">></span><br /></span>
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<p>ForwardIt shift_right<span class="br0">(</span> ExecutionPolicy<span class="sy3">&&</span> policy, ForwardIt first, ForwardIt last,<br /></p>
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<span class="kw1">typename</span> <a href="cpp-iterator-iterator_traits.html"><span class="kw651">std::<span class="me2">iterator_traits</span></span></a><span class="sy1"><</span>ForwardIt<span class="sy1">></span><span class="sy4">::</span><span class="me2">difference_type</span> n <span class="br0">)</span><span class="sy4">;</span></div>
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<td>(4)</td>
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<td><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></td>
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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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<p>将范围 <code>[first, last)</code> 中的元素迁移 <code>n</code> 个位置。</p>
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<div class="t-li1"><span class="t-li">1)</span> 向范围开端迁移元素。若 <span class="t-c"><span class="mw-geshi cpp source-cpp">n <span class="sy1"><=</span> <span class="nu0">0</span> <span class="sy3">||</span> n <span class="sy1">>=</span> last <span class="sy2">-</span> first</span></span> 则无效果。若 <span class="t-c"><span class="mw-geshi cpp source-cpp">n <span class="sy1"><</span> <span class="nu0">0</span></span></span> 则行为未定义。否则，对于每个 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="br0">[</span><span class="nu0">0</span>, last <span class="sy2">-</span> first <span class="sy2">-</span> n<span class="br0">)</span></span></span> 中的整数 <code>i</code> ，移动原于位置 <span class="t-c"><span class="mw-geshi cpp source-cpp">first <span class="sy2">+</span> n <span class="sy2">+</span> i</span></span> 的元素到位置 <span class="t-c"><span class="mw-geshi cpp source-cpp">first <span class="sy2">+</span> i</span></span> 。以 <code>i</code> 从 <span class="t-c"><span class="mw-geshi cpp source-cpp">​<span class="nu0">0</span>​</span></span> 开始递增的顺序进行移动。</div>
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<div class="t-li1"><span class="t-li">3)</span> 向范围结尾迁移元素。若 <span class="t-c"><span class="mw-geshi cpp source-cpp">n <span class="sy1"><=</span> <span class="nu0">0</span> <span class="sy3">||</span> n <span class="sy1">>=</span> last <span class="sy2">-</span> first</span></span> 则无效果。若 <span class="t-c"><span class="mw-geshi cpp source-cpp">n <span class="sy1"><</span> <span class="nu0">0</span></span></span> 则行为未定义。否则对于每个 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="br0">[</span><span class="nu0">0</span>, last <span class="sy2">-</span> first <span class="sy2">-</span> n<span class="br0">)</span></span></span> 中的整数 <code>i</code> ，移动原于位置 <span class="t-c"><span class="mw-geshi cpp source-cpp">first <span class="sy2">+</span> i</span></span> 的元素到位置 <span class="t-c"><span class="mw-geshi cpp source-cpp">first <span class="sy2">+</span> n <span class="sy2">+</span> i</span></span> 。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> 的要求，则以 <code>i</code> 从 <span class="t-c"><span class="mw-geshi cpp source-cpp">last <span class="sy2">-</span> first <span class="sy2">-</span> n <span class="sy2">-</span> <span class="nu0">1</span></span></span> 开始递减的顺序进行移动。</div>
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<div class="t-li1"><span class="t-li">2,4)</span> 分别同 <span class="t-v">(1)</span> 与 <span class="t-v">(3)</span> ，但按照 <code>policy</code> 执行并可能以任何顺序进行移动。这些重载仅若 <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> 为 true 才参与重载决议。</div>
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<p>在原范围但不在新范围中的元素被置于合法但未指定的状态。</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</td>
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<td>-</td>
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<td>原范围的开端</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>n</td>
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<td>-</td>
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<td>要迁移的位置数</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-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>
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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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对于重载 <span class="t-v">(3-4)</span> <code>ForwardIt</code> 必须满足<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> 的要求或<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> 的要求。</td>
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</tr>
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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> 的要求。</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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<div class="t-li1"><span class="t-li">1-2)</span> 结果范围的结尾。若 <code>n</code> 小于 <code>last - first</code> ，则返回 <code>first + (last - first - n)</code> 。否则返回 <code>first</code> 。</div>
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<div class="t-li1"><span class="t-li">3-4)</span> 结果范围的开始。若 <code>n</code> 小于 <code>last - first</code> ，则返回 <code>first + n</code> 。否则返回 <code>last</code> 。</div>
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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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<div class="t-li1"><span class="t-li">1-2)</span> 至多 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-iterator-distance.html"><span class="kw673">std::<span class="me2">distance</span></span></a><span class="br0">(</span>first, last<span class="br0">)</span> <span class="sy2">-</span> n</span></span> 次赋值。</div>
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<div class="t-li1"><span class="t-li">3-4)</span> 至多 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-iterator-distance.html"><span class="kw673">std::<span class="me2">distance</span></span></a><span class="br0">(</span>first, last<span class="br0">)</span> <span class="sy2">-</span> n</span></span> 次赋值或交换。</div>
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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=".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 <iostream></span>
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<span class="co2">#include <algorithm></span>
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<span class="co2">#include <vector></span>
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<span class="kw1">struct</span> S <span class="br0">{</span>
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<span class="kw4">int</span> value<span class="br0">{</span><span class="nu0">0</span><span class="br0">}</span><span class="sy4">;</span>
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<span class="kw4">bool</span> specified_state<span class="br0">{</span><span class="kw2">true</span><span class="br0">}</span><span class="sy4">;</span>
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S<span class="br0">(</span><span class="kw4">int</span> v <span class="sy1">=</span> <span class="nu0">0</span><span class="br0">)</span> <span class="sy4">:</span> value<span class="br0">{</span>v<span class="br0">}</span> <span class="br0">{</span><span class="br0">}</span>
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S<span class="br0">(</span>S <span class="kw4">const</span><span class="sy3">&</span> rhs<span class="br0">)</span> <span class="sy1">=</span> <span class="kw1">default</span><span class="sy4">;</span>
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S<span class="br0">(</span>S<span class="sy3">&&</span> rhs<span class="br0">)</span> <span class="br0">{</span> <span class="sy2">*</span>this <span class="sy1">=</span> std<span class="sy4">::</span><span class="me2">move</span><span class="br0">(</span>rhs<span class="br0">)</span><span class="sy4">;</span> <span class="br0">}</span>
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S<span class="sy3">&</span> operator<span class="sy1">=</span><span class="br0">(</span>S <span class="kw4">const</span><span class="sy3">&</span> rhs<span class="br0">)</span> <span class="sy1">=</span> <span class="kw1">default</span><span class="sy4">;</span>
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S<span class="sy3">&</span> operator<span class="sy1">=</span><span class="br0">(</span>S<span class="sy3">&&</span> rhs<span class="br0">)</span> <span class="br0">{</span>
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<span class="kw1">if</span> <span class="br0">(</span>this <span class="sy3">!</span><span class="sy1">=</span> <span class="sy3">&</span>rhs<span class="br0">)</span> <span class="br0">{</span>
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value <span class="sy1">=</span> rhs.<span class="me1">value</span><span class="sy4">;</span>
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specified_state <span class="sy1">=</span> rhs.<span class="me1">specified_state</span><span class="sy4">;</span>
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rhs.<span class="me1">specified_state</span> <span class="sy1">=</span> <span class="kw2">false</span><span class="sy4">;</span>
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<span class="br0">}</span>
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<span class="kw1">return</span> <span class="sy2">*</span>this<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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<a href="cpp-io-basic_ostream.html"><span class="kw1729">std::<span class="me2">ostream</span></span></a><span class="sy3">&</span> operator<span class="sy1"><<</span> <span class="br0">(</span><a href="cpp-io-basic_ostream.html"><span class="kw1729">std::<span class="me2">ostream</span></span></a><span class="sy3">&</span> os, <a href="cpp-container-vector.html"><span class="kw1269">std::<span class="me2">vector</span></span></a><span class="sy1"><</span>S<span class="sy1">></span> <span class="kw4">const</span><span class="sy3">&</span> v<span class="br0">)</span> <span class="br0">{</span>
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<span class="kw1">for</span> <span class="br0">(</span><span class="kw4">const</span> <span class="kw4">auto</span><span class="sy3">&</span> s <span class="sy4">:</span> v<span class="br0">)</span>
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s.<span class="me1">specified_state</span> <span class="sy4">?</span> os <span class="sy1"><<</span> s.<span class="me1">value</span> <span class="sy1"><<</span> <span class="st0">' '</span> <span class="sy4">:</span> os <span class="sy1"><<</span> <span class="st0">"? "</span><span class="sy4">;</span>
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<span class="kw1">return</span> os <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
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<span class="br0">}</span>
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<span class="kw4">int</span> main<span class="br0">(</span><span class="br0">)</span>
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<span class="br0">{</span>
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<a href="cpp-container-vector.html"><span class="kw1269">std::<span class="me2">vector</span></span></a><span class="sy1"><</span>S<span class="sy1">></span> v<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="nu0">6</span>,<span class="nu0">7</span><span class="br0">}</span><span class="sy4">;</span>
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std<span class="sy4">::</span><span class="me2">shift_left</span><span class="br0">(</span>v.<span class="me1">begin</span><span class="br0">(</span><span class="br0">)</span>, v.<span class="me1">end</span><span class="br0">(</span><span class="br0">)</span>, <span class="nu0">8</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 无效果： n >= last - first</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> v<span class="sy4">;</span>
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<span class="co1">// std::shift_left(v.begin(), v.end(), -3); // UB ：例如分段错误。</span>
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std<span class="sy4">::</span><span class="me2">shift_left</span><span class="br0">(</span>v.<span class="me1">begin</span><span class="br0">(</span><span class="br0">)</span>, v.<span class="me1">end</span><span class="br0">(</span><span class="br0">)</span>, <span class="sy2">+</span><span class="nu0">3</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// OK</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> v<span class="sy4">;</span>
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std<span class="sy4">::</span><span class="me2">shift_right</span><span class="br0">(</span>v.<span class="me1">begin</span><span class="br0">(</span><span class="br0">)</span>, v.<span class="me1">end</span><span class="br0">(</span><span class="br0">)</span>, <span class="nu0">2</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// OK</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> v<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">1 2 3 4 5 6 7
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4 5 6 7 ? ? ?
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? ? 4 5 6 7 ?</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-move.html"><span class="t-lines"><span>move</span></span></a></div>
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<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div>
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</div>
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</td>
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<td>将某一范围的元素移动到一个新的位置<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-move_backward.html"><span class="t-lines"><span>move_backward</span></span></a></div>
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<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div>
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</div>
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</td>
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<td>按从后往前的顺序移动某一范围的元素到新的位置<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-rotate.html"><span class="t-lines"><span>rotate</span></span></a></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">(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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