206 lines
19 KiB
HTML
206 lines
19 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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<title>std::inplace_merge</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_algorithm_inplace_merge 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::</span>inplace_merge</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 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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<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><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span><span class="sy1"><</span> <span class="kw1">class</span> BidirIt <span class="sy1">></span><br />
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<span class="kw4">void</span> inplace_merge<span class="br0">(</span> BidirIt first, BidirIt middle, BidirIt last <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 class="t-dcl-nopad"></td>
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<tr class="t-dcl t-since-cxx17">
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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> BidirIt <span class="sy1">></span><br />
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<span class="kw4">void</span> inplace_merge<span class="br0">(</span> ExecutionPolicy<span class="sy3">&&</span> policy, BidirIt first, BidirIt middle, BidirIt last <span class="br0">)</span><span class="sy4">;</span></span></div>
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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><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span><span class="sy1"><</span> <span class="kw1">class</span> BidirIt, <span class="kw1">class</span> Compare<span class="sy1">></span><br />
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<span class="kw4">void</span> inplace_merge<span class="br0">(</span> BidirIt first, BidirIt middle, BidirIt last, Compare comp <span class="br0">)</span><span class="sy4">;</span></span></div>
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<td>(3)</td>
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<td class="t-dcl-nopad"></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> BidirIt, <span class="kw1">class</span> Compare<span class="sy1">></span><br />
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<span class="kw4">void</span> inplace_merge<span class="br0">(</span> ExecutionPolicy<span class="sy3">&&</span> policy, BidirIt first, BidirIt middle, BidirIt last, Compare comp <span class="br0">)</span><span class="sy4">;</span></span></div>
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<td>(4)</td>
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<td><span class="t-mark-rev t-since-cxx17">(C++17 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>归并二个相继的<i>已排序</i>范围 <code>[first, middle)</code> 及 <code>[middle, last)</code> 为一个<i>已排序</i>范围 <code>[first, last)</code> 。</p>
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<p>若对于任何指向序列的迭代器 <code>it</code> 与任何使得 <code>it + n</code> 为指向序列元素的合法迭代器的非负整数 <code>n</code> ， <span class="t-c"><span class="mw-geshi cpp source-cpp">comp<span class="br0">(</span><span class="sy2">*</span><span class="br0">(</span>it <span class="sy2">+</span> n<span class="br0">)</span>, <span class="sy2">*</span>it<span class="br0">)</span></span></span> 求值为 <code>false</code> ，则称序列 <code>[first, last)</code> 相对于 <code>comp</code> <i>已排序</i>。</p>
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<p>此归并是<i>稳定</i>的，意思是对于原先二个范围中的等价元素。来自第一范围的元素（保持其原顺序）先于来自第二范围的元素（保持其原顺序）。</p>
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<div class="t-li1"><span class="t-li">1)</span> 用 <code>operator<</code> 比较元素，且范围必须对于同关系已排序。</div>
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<div class="t-li1"><span class="t-li">3)</span> 用给定的二元比较函数 <code>comp</code> 比较元素，且范围必须对于同关系已排序。</div>
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<div class="t-li1"><span class="t-li">2,4)</span> 同 <span class="t-v">(1,3)</span> ，但按照 <code>policy</code> 执行。这些重载仅若 <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>第一个已排序范围的起始</td>
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</tr>
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<tr class="t-par">
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<td>middle</td>
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<td>-</td>
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<td>第一个已排序范围的结尾及第二个已排序范围的起始</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>第二个已排序范围的结尾</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>
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<tr class="t-par">
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<td>comp</td>
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<td>-</td>
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<td>比较函数对象（即满足<a href="cpp-named_req-Compare.html"><span style="font-style:italic">比较</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(Compare)</span></a> 概念的对象），若第一参数<i>小于</i>（即<i>先</i>序于）第二参数则返回 ​<span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">true</span></span></span> 。<br />
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<p>比较函数的签名应等价于如下：</p>
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<p><span class="t-cc"><span class="mw-geshi cpp source-cpp"> <span class="kw4">bool</span> cmp<span class="br0">(</span><span class="kw4">const</span> Type1 <span class="sy3">&</span>a, <span class="kw4">const</span> Type2 <span class="sy3">&</span>b<span class="br0">)</span><span class="sy4">;</span></span></span></p>
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<p>虽然签名不必有 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">const</span> <span class="sy3">&</span></span></span> ，函数也不能修改传递给它的对象，而且必须接受（可为 const 的）类型 <code>Type1</code> 与 <code>Type2</code> 的值，无关乎<a href="cpp-language-value_category.html">值类别</a>（从而不允许 <span class="t-c"><span class="mw-geshi cpp source-cpp">Type1 <span class="sy3">&</span></span></span> <span class="t-rev-inl t-since-cxx11"><span>，亦不允许 <span class="t-c"><span class="mw-geshi cpp source-cpp">Type1</span></span> ，除非 <code>Type1</code> 的移动等价于复制</span> <span><span class="t-mark-rev t-since-cxx11">(C++11 起)</span></span></span>）。<br />
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类型 <span class="t-c"><span class="mw-geshi cpp source-cpp">Type1</span></span> 与 <span class="t-c"><span class="mw-geshi cpp source-cpp">Type2</span></span> 必须使得 <span class="t-c"><span class="mw-geshi cpp source-cpp">BidirIt</span></span> 类型的对象能在解引用后隐式转换到这两个类型。 ​</p>
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</td>
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</tr>
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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>
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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>BidirIt</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-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。</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>BidirIt</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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</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>（无）</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>给定 <span class="t-c"><span class="mw-geshi cpp source-cpp">N <span class="sy1">=</span> <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></span>} ，</p>
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<div class="t-li1"><span class="t-li">1,3)</span> 若附加内存可用则准确为 <code>N-1</code> 次比较。若内存不足，则为 <code>O(N log N)</code> 次比较。</div>
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<div class="t-li1"><span class="t-li">2,4)</span> <code>O(N log N)</code> 次比较。</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=".E6.B3.A8.E8.A7.A3">注解</span></h3>
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<p>此函数试图分配临时缓冲区。若分配失败，则选择较低效的算法。</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/d9375e490072d1aae73a93949aa158fcd2a27018/libstdc%2B%2B-v3/include/bits/stl_algo.h#L2508">libstdc++</a> 与 <a rel="nofollow" class="external text" href="https://github.com/llvm-mirror/libcxx/blob/a12cb9d211019d99b5875b6d8034617cbc24c2cc/include/algorithm#L4452">libc++</a> 中的实现。</p>
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<h3><span class="mw-headline" id=".E7.A4.BA.E4.BE.8B">示例</span></h3>
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<div class="t-example">
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<p>下列代码为归并排序的一种实现。</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="kw1">template</span><span class="sy1"><</span><span class="kw1">class</span> Iter<span class="sy1">></span>
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<span class="kw4">void</span> merge_sort<span class="br0">(</span>Iter first, Iter 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>last <span class="sy2">-</span> first <span class="sy1">></span> <span class="nu0">1</span><span class="br0">)</span> <span class="br0">{</span>
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Iter middle <span class="sy1">=</span> first <span class="sy2">+</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 class="sy4">;</span>
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merge_sort<span class="br0">(</span>first, middle<span class="br0">)</span><span class="sy4">;</span>
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merge_sort<span class="br0">(</span>middle, last<span class="br0">)</span><span class="sy4">;</span>
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std<span class="sy4">::</span><span class="me2">inplace_merge</span><span class="br0">(</span>first, middle, last<span class="br0">)</span><span class="sy4">;</span>
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<span class="br0">}</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><span class="kw4">int</span><span class="sy1">></span> v<span class="br0">{</span><span class="nu0">8</span>, <span class="nu0">2</span>, <span class="sy2">-</span><span class="nu0">2</span>, <span class="nu0">0</span>, <span class="nu0">11</span>, <span class="nu0">11</span>, <span class="nu0">1</span>, <span class="nu0">7</span>, <span class="nu0">3</span><span class="br0">}</span><span class="sy4">;</span>
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merge_sort<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="br0">)</span><span class="sy4">;</span>
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<span class="kw1">for</span><span class="br0">(</span><span class="kw4">auto</span> n <span class="sy4">:</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> n <span class="sy1"><<</span> <span class="st0">' '</span><span class="sy4">;</span>
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<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> <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">-2 0 1 2 3 7 8 11 11</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-merge.html"><span class="t-lines"><span>merge</span></span></a></div>
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</div>
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</td>
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<td>归并两个已排序的范围<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-sort.html"><span class="t-lines"><span>sort</span></span></a></div>
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</div>
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</td>
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<td>将范围按升序排序<br />
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<span class="t-mark">(函数模板)</span></td>
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</tr>
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<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-stable_sort.html"><span class="t-lines"><span>stable_sort</span></span></a></div>
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</div>
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</td>
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<td>将范围内的元素排序，同时保持相等的元素之间的顺序<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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