164 lines
15 KiB
HTML
164 lines
15 KiB
HTML
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<title>std::bsearch</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_algorithm_bsearch 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>bsearch</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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<td></td>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw4">void</span><span class="sy2">*</span> bsearch<span class="br0">(</span> <span class="kw4">const</span> <span class="kw4">void</span><span class="sy2">*</span> key, <span class="kw4">const</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,<br /></span>
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<p> <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><span class="sy2">*</span> bsearch<span class="br0">(</span> <span class="kw4">const</span> <span class="kw4">void</span><span class="sy2">*</span> key, <span class="kw4">const</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,<br /></p>
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<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></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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<p>在 <code>ptr</code> 所指向的数组中寻找等于 <code>key</code> 所指向的元素的元素。数组含有 <code>count</code> 个 <code>size</code> 字节的元素，且必须相对于 <code>key</code> 所指向的对象划分，即所有比较小于它的元素必须先出现于比较等于它的元素，而比较等于它者必须先出现于所有比较大于该关键对象的元素。完全排序的数组满足这些要求。用 <code>comp</code> 所指的函数比较数组元素。</p>
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<p>若数组未以按照 <code>comp</code> 所用的相同原则相对于 key 升序划分则行为未定义。</p>
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<p>若数组含有数个 <code>comp</code> 会指示等于被搜索元素的元素，则函数返回哪个元素是未指定的。</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>key</td>
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<td>-</td>
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<td>指向要搜索的元素的指针</td>
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</tr>
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<tr class="t-par">
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<td>ptr</td>
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<td>-</td>
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<td>指向要检验的数组的指针</td>
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</tr>
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<tr class="t-par">
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<td>count</td>
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<td>-</td>
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<td>数组中元素的数量</td>
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</tr>
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<tr class="t-par">
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<td>size</td>
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<td>-</td>
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<td>数组中每个元素的大小，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。作为首参数传递 <code>key</code> ，作为第二参数传递来自数组的元素。<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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</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>指向找到的元素的指针，或若找不到元素则为空指针。</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 或 POSIX 标准都不要求此函数用二分查找实现，或进行任何复杂度保证。</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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<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 <array></span>
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<span class="kw1">template</span> <span class="sy1"><</span><span class="kw1">typename</span> T<span class="sy1">></span>
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<span class="kw4">int</span> compare<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="br0">{</span>
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<span class="kw4">const</span> <span class="kw4">auto</span> <span class="sy3">&</span>arg1 <span class="sy1">=</span> <span class="sy2">*</span><span class="br0">(</span><span class="kw1">static_cast</span><span class="sy1"><</span><span class="kw4">const</span> T<span class="sy2">*</span><span class="sy1">></span><span class="br0">(</span>a<span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="kw4">const</span> <span class="kw4">auto</span> <span class="sy3">&</span>arg2 <span class="sy1">=</span> <span class="sy2">*</span><span class="br0">(</span><span class="kw1">static_cast</span><span class="sy1"><</span><span class="kw4">const</span> T<span class="sy2">*</span><span class="sy1">></span><span class="br0">(</span>b<span class="br0">)</span><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">return</span> cmp <span class="sy1"><</span> <span class="nu0">0</span> <span class="sy4">?</span> <span class="sy2">-</span><span class="nu0">1</span>
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<span class="sy4">:</span> cmp <span class="sy1">></span> <span class="nu0">0</span> <span class="sy4">?</span> <span class="sy2">+</span><span class="nu0">1</span>
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<span class="sy4">:</span> <span class="nu0">0</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> <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> arr <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="nu0">8</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">const</span> <span class="kw4">int</span> key <span class="sy4">:</span> <span class="br0">{</span> <span class="nu0">4</span>, <span class="nu0">8</span>, <span class="nu0">9</span> <span class="br0">}</span><span class="br0">)</span> <span class="br0">{</span>
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<span class="kw4">const</span> <span class="kw4">int</span><span class="sy2">*</span> p <span class="sy1">=</span> <span class="kw1">static_cast</span><span class="sy1"><</span><span class="kw4">int</span><span class="sy2">*</span><span class="sy1">></span><span class="br0">(</span>
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std<span class="sy4">::</span><span class="me2">bsearch</span><span class="br0">(</span><span class="sy3">&</span>key,
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arr.<span class="me1">data</span><span class="br0">(</span><span class="br0">)</span>,
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arr.<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>arr<span class="br0">)</span><span class="sy4">::</span><span class="me2">value_type</span><span class="br0">)</span>,
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compare<span class="sy1"><</span><span class="kw4">int</span><span class="sy1">></span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
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<a href="cpp-io-cout.html"><span class="kw1757">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"value "</span> <span class="sy1"><<</span> key<span class="sy4">;</span>
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<span class="br0">(</span>p<span class="br0">)</span> <span class="sy4">?</span> <a href="cpp-io-cout.html"><span class="kw1757">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">" found at position "</span> <span class="sy1"><<</span> <span class="br0">(</span>p <span class="sy2">-</span> arr.<span class="me1">data</span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span> <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span>
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<span class="sy4">:</span> <a href="cpp-io-cout.html"><span class="kw1757">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">" not found<span class="es1">\n</span>"</span><span class="sy4">;</span>
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<span class="br0">}</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">value 4 found at position 3
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value 8 found at position 7
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value 9 not found</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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<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-qsort.html"><span class="t-lines"><span>qsort</span></span></a></div>
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</div>
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</td>
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<td>对未指定类型的元素的一个范围进行排序<br />
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<span class="t-mark">(函数)</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-equal_range.html"><span class="t-lines"><span>equal_range</span></span></a></div>
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</div>
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</td>
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<td>返回匹配特定键值的元素范围<br />
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<span class="t-mark">(函数模板)</span></td>
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</tr>
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</table>
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</div>
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<div class="visualClear"></div>
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</div>
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