160 lines
13 KiB
HTML
160 lines
13 KiB
HTML
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<title>std::qsort</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_algorithm_qsort skin-cppreference2 action-view cpp-navbar">
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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::</span>qsort</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-cstdlib.html"><cstdlib></a></code></div>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw4">void</span> qsort<span class="br0">(</span> <span class="kw4">void</span> <span class="sy2">*</span>ptr, <a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a> count, <a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a> size, <span class="coMULTI">/*compare-pred*/</span><span class="sy2">*</span> comp <span class="br0">)</span><span class="sy4">;</span><br />
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<span class="kw4">void</span> qsort<span class="br0">(</span> <span class="kw4">void</span> <span class="sy2">*</span>ptr, <a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a> count, <a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a> size, <span class="coMULTI">/*c-compare-pred*/</span><span class="sy2">*</span> comp <span class="br0">)</span><span class="sy4">;</span></span></div>
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<td>(1)</td>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw4">extern</span> <span class="st0">"C++"</span> <span class="kw1">using</span> <span class="coMULTI">/*compare-pred*/</span> <span class="sy1">=</span> <span class="kw4">int</span><span class="br0">(</span><span class="kw4">const</span> <span class="kw4">void</span><span class="sy2">*</span>, <span class="kw4">const</span> <span class="kw4">void</span><span class="sy2">*</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 仅用于阐释</span><br />
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<span class="kw4">extern</span> <span class="st0">"C"</span> <span class="kw1">using</span> <span class="coMULTI">/*c-compare-pred*/</span> <span class="sy1">=</span> <span class="kw4">int</span><span class="br0">(</span><span class="kw4">const</span> <span class="kw4">void</span><span class="sy2">*</span>, <span class="kw4">const</span> <span class="kw4">void</span><span class="sy2">*</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 仅用于阐释</span></span></div>
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<td>(2)</td>
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<td class="t-dcl-nopad"></td>
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<td></td>
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<p>以升序排序 <code>ptr</code> 所指向的给定数组。数组含 <code>count</code> 个 <code>size</code> 字节大小的元素。用 <code>comp</code> 所指向的函数比较对象。</p>
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<p>若 <code>comp</code> 指示二个元素等价，则其顺序未指定。</p>
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<p>若数组元素类型不是<span class="t-rev-inl t-until-cxx11"><span><a href="cpp-named_req-PODType.html"><span style="font-style:italic">简旧数据类型</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(PODType)</span></a></span> <span><span class="t-mark-rev t-until-cxx11">(C++11 前)</span></span></span><span class="t-rev-inl t-since-cxx11"><span><a href="cpp-named_req-TriviallyCopyable.html"><span style="font-style:italic">可平凡复制</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(TriviallyCopyable)</span></a> 类型</span> <span><span class="t-mark-rev t-since-cxx11">(C++11 起)</span></span></span>，则行为未定义。</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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<td>ptr</td>
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<td>-</td>
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<td>指向要排序的数组的指针</td>
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</tr>
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<td>count</td>
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<td>-</td>
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<td>数组元素数</td>
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<td>size</td>
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<td>-</td>
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<td>数组中元素的大小，以字节表示</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。若首个参数<i>小于</i>第二个，则返回负整数值，若首个参数<i>大于</i>第二个，则返回正整数值，若两参数等价，则返回零。<br />
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<p>比较函数的签名应等价于如下形式：</p>
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<p><span class="t-cc"><span class="mw-geshi cpp source-cpp"> <span class="kw4">int</span> cmp<span class="br0">(</span><span class="kw4">const</span> <span class="kw4">void</span> <span class="sy2">*</span>a, <span class="kw4">const</span> <span class="kw4">void</span> <span class="sy2">*</span>b<span class="br0">)</span><span class="sy4">;</span></span></span></p>
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<p>该函数必须不修改传递给它的对象，而且在调用比较相同对象时必须返回一致的结果，无关乎它们在数组中的位置。</p>
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<p>​</p>
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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=".E6.B3.A8.E8.A7.A3">注解</span></h3>
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<p>无关乎名称， C++、 C 及 POSIX 都不要求此函数用<a href="https://en.wikipedia.org/wiki/Quicksort" class="extiw" title="enwiki:Quicksort">快速排序</a>实现或作出任何复杂度和稳定性保证。</p>
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<p>C++ 标准库提供的二个重载不同，因为参数 <code>comp</code> 类型有别（<a href="cpp-language-language_linkage.html">语言链接</a>是类型的一部分）。</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>下列代码用 <code>qsort()</code> 排序整数数组。</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 <iostream></span>
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<span class="co2">#include <cstdlib></span>
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<span class="co2">#include <climits></span>
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<span class="co2">#include <compare></span>
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<span class="co2">#include <array></span>
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<span class="kw4">int</span> main<span class="br0">(</span><span class="br0">)</span> <span class="br0">{</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="sy2">-</span><span class="nu0">2</span>, <span class="nu0">99</span>, <span class="nu0">0</span>, <span class="sy2">-</span><span class="nu0">743</span>, <a href="cpp-types-climits.html"><span class="kw398">INT_MAX</span></a>, <span class="nu0">2</span>, <a href="cpp-types-climits.html"><span class="kw393">INT_MIN</span></a>, <span class="nu0">4</span> <span class="br0">}</span><span class="sy4">;</span>
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std<span class="sy4">::</span><span class="me2">qsort</span><span class="br0">(</span>
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a.<span class="me1">data</span><span class="br0">(</span><span class="br0">)</span>,
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a.<span class="me1">size</span><span class="br0">(</span><span class="br0">)</span>,
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sizeof<span class="br0">(</span>decltype<span class="br0">(</span>a<span class="br0">)</span><span class="sy4">::</span><span class="me2">value_type</span><span class="br0">)</span>,
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<span class="br0">[</span><span class="br0">]</span><span class="br0">(</span><span class="kw4">const</span> <span class="kw4">void</span><span class="sy2">*</span> x, <span class="kw4">const</span> <span class="kw4">void</span><span class="sy2">*</span> y<span class="br0">)</span> <span class="br0">{</span>
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<span class="kw4">const</span> <span class="kw4">int</span> arg1 <span class="sy1">=</span> <span class="sy2">*</span><span class="kw1">static_cast</span><span class="sy1"><</span><span class="kw4">const</span> <span class="kw4">int</span><span class="sy2">*</span><span class="sy1">></span><span class="br0">(</span>x<span class="br0">)</span><span class="sy4">;</span>
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<span class="kw4">const</span> <span class="kw4">int</span> arg2 <span class="sy1">=</span> <span class="sy2">*</span><span class="kw1">static_cast</span><span class="sy1"><</span><span class="kw4">const</span> <span class="kw4">int</span><span class="sy2">*</span><span class="sy1">></span><span class="br0">(</span>y<span class="br0">)</span><span class="sy4">;</span>
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<span class="kw4">const</span> <span class="kw4">auto</span> cmp <span class="sy1">=</span> arg1 <span class="sy1"><=></span> arg2<span class="sy4">;</span>
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<span class="kw1">if</span> <span class="br0">(</span>cmp <span class="sy1"><</span> <span class="nu0">0</span><span class="br0">)</span> <span class="kw1">return</span> <span class="sy2">-</span><span class="nu0">1</span><span class="sy4">;</span>
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<span class="kw1">if</span> <span class="br0">(</span>cmp <span class="sy1">></span> <span class="nu0">0</span><span class="br0">)</span> <span class="kw1">return</span> <span class="nu0">1</span><span class="sy4">;</span>
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<span class="kw1">return</span> <span class="nu0">0</span><span class="sy4">;</span>
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<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">int</span> ai <span class="sy4">:</span> a<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> ai <span class="sy1"><<</span> <span class="st0">' '</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">-2147483648 -743 -2 0 2 4 99</pre></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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<div class="t-dsc-member-div">
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<div><a href="cpp-algorithm-bsearch.html"><span class="t-lines"><span>bsearch</span></span></a></div>
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</div>
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</td>
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<td>在未指定类型的数组中搜索元素<br />
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<span class="t-mark">(函数)</span></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-types-is_trivial.html"><span class="t-lines"><span>is_trivial</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>检查类型是否平凡<br />
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<span class="t-mark">(类模板)</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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