258 lines
22 KiB
HTML
258 lines
22 KiB
HTML
<!DOCTYPE html>
|
|
<html lang="zh" dir="ltr" class="client-nojs" xmlns="http://www.w3.org/1999/xhtml" xml:lang="zh">
|
|
<head><meta http-equiv="x-ua-compatible" content="ie=edge">
|
|
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
|
|
<title>std::adjacent_find</title>
|
|
<link rel="stylesheet" href="ext.css" />
|
|
<link rel="stylesheet" href="site_modules.css" />
|
|
</head>
|
|
<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_algorithm_adjacent_find skin-cppreference2 action-view cpp-navbar">
|
|
<div id="cpp-content-base">
|
|
<div id="content"><a id="top"></a>
|
|
<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::</span>adjacent_find</h1>
|
|
<div id="bodyContent">
|
|
<div id="contentSub"><span class="subpages">< <a href="cpp.html">cpp</a>‎ | <a href="cpp-algorithm.html">algorithm</a></span></div>
|
|
<div id="mw-content-text" lang="zh" dir="ltr" class="mw-content-ltr" xml:lang="zh">
|
|
<table class="t-dcl-begin">
|
|
<tbody>
|
|
<tr class="t-dsc-header">
|
|
<td>
|
|
<div>定义于头文件 <code><a href="cpp-header-algorithm.html"><algorithm></a></code></div>
|
|
</td>
|
|
<td></td>
|
|
<td></td>
|
|
</tr>
|
|
</tbody>
|
|
<tbody class="t-dcl-rev t-dcl-rev-num">
|
|
<tr class="t-dcl-rev-aux">
|
|
<td></td>
|
|
<td rowspan="142">(1)</td>
|
|
<td></td>
|
|
</tr>
|
|
<tr class="t-dcl t-until-cxx20">
|
|
<td>
|
|
<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 />
|
|
ForwardIt adjacent_find<span class="br0">(</span> ForwardIt first, ForwardIt last <span class="br0">)</span><span class="sy4">;</span></span></div>
|
|
</td>
|
|
<td class="t-dcl-nopad"></td>
|
|
<td><span class="t-mark-rev t-until-cxx20">(C++20 前)</span></td>
|
|
</tr>
|
|
<tr class="t-dcl t-since-cxx20">
|
|
<td>
|
|
<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 class="kw4">constexpr</span> ForwardIt adjacent_find<span class="br0">(</span> ForwardIt first, ForwardIt last <span class="br0">)</span><span class="sy4">;</span></span></div>
|
|
</td>
|
|
<td class="t-dcl-nopad"></td>
|
|
<td><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></td>
|
|
</tr>
|
|
</tbody>
|
|
<tbody>
|
|
<tr class="t-dcl t-since-cxx17">
|
|
<td>
|
|
<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>
|
|
<p>ForwardIt adjacent_find<span class="br0">(</span> ExecutionPolicy<span class="sy3">&&</span> policy,<br /></p>
|
|
ForwardIt first, ForwardIt last <span class="br0">)</span><span class="sy4">;</span></div>
|
|
</td>
|
|
<td>(2)</td>
|
|
<td><span class="t-mark-rev t-since-cxx17">(C++17 起)</span></td>
|
|
</tr>
|
|
</tbody>
|
|
<tbody class="t-dcl-rev t-dcl-rev-num">
|
|
<tr class="t-dcl-rev-aux">
|
|
<td></td>
|
|
<td rowspan="142">(3)</td>
|
|
<td></td>
|
|
</tr>
|
|
<tr class="t-dcl t-until-cxx20">
|
|
<td>
|
|
<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="kw1">class</span> BinaryPredicate<span class="sy1">></span><br />
|
|
ForwardIt adjacent_find<span class="br0">(</span> ForwardIt first, ForwardIt last, BinaryPredicate p <span class="br0">)</span><span class="sy4">;</span></span></div>
|
|
</td>
|
|
<td class="t-dcl-nopad"></td>
|
|
<td><span class="t-mark-rev t-until-cxx20">(C++20 前)</span></td>
|
|
</tr>
|
|
<tr class="t-dcl t-since-cxx20">
|
|
<td>
|
|
<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="kw1">class</span> BinaryPredicate<span class="sy1">></span><br />
|
|
<span class="kw4">constexpr</span> ForwardIt adjacent_find<span class="br0">(</span> ForwardIt first, ForwardIt last, BinaryPredicate p <span class="br0">)</span><span class="sy4">;</span></span></div>
|
|
</td>
|
|
<td class="t-dcl-nopad"></td>
|
|
<td><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></td>
|
|
</tr>
|
|
</tbody>
|
|
<tbody>
|
|
<tr class="t-dcl t-since-cxx17">
|
|
<td>
|
|
<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="kw1">class</span> BinaryPredicate<span class="sy1">></span><br /></span>
|
|
<p>ForwardIt adjacent_find<span class="br0">(</span> ExecutionPolicy<span class="sy3">&&</span> policy,<br /></p>
|
|
ForwardIt first, ForwardIt last, BinaryPredicate p <span class="br0">)</span><span class="sy4">;</span></div>
|
|
</td>
|
|
<td>(4)</td>
|
|
<td><span class="t-mark-rev t-since-cxx17">(C++17 起)</span></td>
|
|
</tr>
|
|
<tr class="t-dcl-sep">
|
|
<td></td>
|
|
<td></td>
|
|
<td></td>
|
|
</tr>
|
|
</tbody>
|
|
</table>
|
|
<p>在范围 <code>[first, last)</code> 中搜索二个相继的相等元素。</p>
|
|
<div class="t-li1"><span class="t-li">1)</span> 用 <code>operator==</code> 比较元素。</div>
|
|
<div class="t-li1"><span class="t-li">3)</span> 用给定的二元谓词 <code>p</code> 比较元素。</div>
|
|
<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>
|
|
<h3><span class="mw-headline" id=".E5.8F.82.E6.95.B0">参数</span></h3>
|
|
<table class="t-par-begin">
|
|
<tr class="t-par">
|
|
<td>first, last</td>
|
|
<td>-</td>
|
|
<td>要检验的元素范围</td>
|
|
</tr>
|
|
<tr class="t-par">
|
|
<td>policy</td>
|
|
<td>-</td>
|
|
<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>
|
|
</tr>
|
|
<tr class="t-par">
|
|
<td>p</td>
|
|
<td>-</td>
|
|
<td>若元素应被当做相等则返回 ​<span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">true</span></span></span> 的二元谓词。<br />
|
|
<p>谓词函数的签名应等价于如下：</p>
|
|
<p><span class="t-cc"><span class="mw-geshi cpp source-cpp"> <span class="kw4">bool</span> pred<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>
|
|
<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 />
|
|
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">ForwardIt</span></span> 类型的对象能在解引用后隐式转换到这两个类型。 ​</p>
|
|
</td>
|
|
</tr>
|
|
<tr class="t-par-hitem">
|
|
<td colspan="3">类型要求</td>
|
|
</tr>
|
|
<tr class="t-par-req">
|
|
<td colspan="3">-
|
|
<div class="spacer"></div>
|
|
<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>
|
|
</tr>
|
|
</table>
|
|
<h3><span class="mw-headline" id=".E8.BF.94.E5.9B.9E.E5.80.BC">返回值</span></h3>
|
|
<p>指向首对等同元素的首个元素的迭代器，即首个满足 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">*</span>it <span class="sy1">==</span> <span class="sy2">*</span><span class="br0">(</span>it<span class="sy2">+</span><span class="nu0">1</span><span class="br0">)</span></span></span> （第一版本）或 <span class="t-c"><span class="mw-geshi cpp source-cpp">p<span class="br0">(</span><span class="sy2">*</span>it, <span class="sy2">*</span><span class="br0">(</span>it <span class="sy2">+</span> <span class="nu0">1</span><span class="br0">)</span><span class="br0">)</span> <span class="sy3">!</span><span class="sy1">=</span> <span class="kw2">false</span></span></span>（第二版本） 的迭代器 <code>it</code> 。</p>
|
|
<p>若找不到这种元素，则返回 <code>last</code> 。</p>
|
|
<h3><span class="mw-headline" id=".E5.A4.8D.E6.9D.82.E5.BA.A6">复杂度</span></h3>
|
|
<div class="t-li1"><span class="t-li">1,3)</span> 准确应用 <code>min((result-first)+1, (last-first)-1)</code> 次谓词，其中 <code>result</code> 是返回值。</div>
|
|
<div class="t-li1"><span class="t-li">2,4)</span> 应用 <code>O(last-first)</code> 次对应的谓词。</div>
|
|
<h3><span class="mw-headline" id=".E5.BC.82.E5.B8.B8">异常</span></h3>
|
|
<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>
|
|
<ul>
|
|
<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>
|
|
<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>
|
|
</ul>
|
|
<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>
|
|
<table class="eq-fun-cpp-table">
|
|
<tr>
|
|
<th>版本一</th>
|
|
</tr>
|
|
<tr>
|
|
<td>
|
|
<div dir="ltr" class="mw-geshi" style="text-align: left;">
|
|
<div class="cpp source-cpp">
|
|
<pre class="de1"><span class="kw1">template</span><span class="sy1"><</span><span class="kw1">class</span> ForwardIt<span class="sy1">></span>
|
|
ForwardIt adjacent_find<span class="br0">(</span>ForwardIt first, ForwardIt last<span class="br0">)</span>
|
|
<span class="br0">{</span>
|
|
<span class="kw1">if</span> <span class="br0">(</span>first <span class="sy1">==</span> last<span class="br0">)</span> <span class="br0">{</span>
|
|
<span class="kw1">return</span> last<span class="sy4">;</span>
|
|
<span class="br0">}</span>
|
|
ForwardIt next <span class="sy1">=</span> first<span class="sy4">;</span>
|
|
<span class="sy2">++</span>next<span class="sy4">;</span>
|
|
<span class="kw1">for</span> <span class="br0">(</span><span class="sy4">;</span> next <span class="sy3">!</span><span class="sy1">=</span> last<span class="sy4">;</span> <span class="sy2">++</span>next, <span class="sy2">++</span>first<span class="br0">)</span> <span class="br0">{</span>
|
|
<span class="kw1">if</span> <span class="br0">(</span><span class="sy2">*</span>first <span class="sy1">==</span> <span class="sy2">*</span>next<span class="br0">)</span> <span class="br0">{</span>
|
|
<span class="kw1">return</span> first<span class="sy4">;</span>
|
|
<span class="br0">}</span>
|
|
<span class="br0">}</span>
|
|
<span class="kw1">return</span> last<span class="sy4">;</span>
|
|
<span class="br0">}</span></pre></div>
|
|
</div>
|
|
</td>
|
|
</tr>
|
|
<tr>
|
|
<th>版本二</th>
|
|
</tr>
|
|
<tr>
|
|
<td>
|
|
<div dir="ltr" class="mw-geshi" style="text-align: left;">
|
|
<div class="cpp source-cpp">
|
|
<pre class="de1"><span class="kw1">template</span><span class="sy1"><</span><span class="kw1">class</span> ForwardIt, <span class="kw1">class</span> BinaryPredicate<span class="sy1">></span>
|
|
ForwardIt adjacent_find<span class="br0">(</span>ForwardIt first, ForwardIt last,
|
|
BinaryPredicate p<span class="br0">)</span>
|
|
<span class="br0">{</span>
|
|
<span class="kw1">if</span> <span class="br0">(</span>first <span class="sy1">==</span> last<span class="br0">)</span> <span class="br0">{</span>
|
|
<span class="kw1">return</span> last<span class="sy4">;</span>
|
|
<span class="br0">}</span>
|
|
ForwardIt next <span class="sy1">=</span> first<span class="sy4">;</span>
|
|
<span class="sy2">++</span>next<span class="sy4">;</span>
|
|
<span class="kw1">for</span> <span class="br0">(</span><span class="sy4">;</span> next <span class="sy3">!</span><span class="sy1">=</span> last<span class="sy4">;</span> <span class="sy2">++</span>next, <span class="sy2">++</span>first<span class="br0">)</span> <span class="br0">{</span>
|
|
<span class="kw1">if</span> <span class="br0">(</span>p<span class="br0">(</span><span class="sy2">*</span>first, <span class="sy2">*</span>next<span class="br0">)</span><span class="br0">)</span> <span class="br0">{</span>
|
|
<span class="kw1">return</span> first<span class="sy4">;</span>
|
|
<span class="br0">}</span>
|
|
<span class="br0">}</span>
|
|
<span class="kw1">return</span> last<span class="sy4">;</span>
|
|
<span class="br0">}</span></pre></div>
|
|
</div>
|
|
</td>
|
|
</tr>
|
|
</table>
|
|
<h3><span class="mw-headline" id=".E7.A4.BA.E4.BE.8B">示例</span></h3>
|
|
<div class="t-example">
|
|
<div class="t-example-live-link"></div>
|
|
<div dir="ltr" class="mw-geshi" style="text-align: left;">
|
|
<div class="cpp source-cpp">
|
|
<pre class="de1"><span class="co2">#include <algorithm></span>
|
|
<span class="co2">#include <iostream></span>
|
|
<span class="co2">#include <vector></span>
|
|
|
|
<span class="kw4">int</span> main<span class="br0">(</span><span class="br0">)</span>
|
|
<span class="br0">{</span>
|
|
<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> v1<span class="br0">{</span><span class="nu0">0</span>, <span class="nu0">1</span>, <span class="nu0">2</span>, <span class="nu0">3</span>, <span class="nu0">40</span>, <span class="nu0">40</span>, <span class="nu0">41</span>, <span class="nu0">41</span>, <span class="nu0">5</span><span class="br0">}</span><span class="sy4">;</span>
|
|
|
|
<span class="kw4">auto</span> i1 <span class="sy1">=</span> std<span class="sy4">::</span><span class="me2">adjacent_find</span><span class="br0">(</span>v1.<span class="me1">begin</span><span class="br0">(</span><span class="br0">)</span>, v1.<span class="me1">end</span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
|
|
|
|
<span class="kw1">if</span> <span class="br0">(</span>i1 <span class="sy1">==</span> v1.<span class="me1">end</span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span> <span class="br0">{</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">"no matching adjacent elements<span class="es1">\n</span>"</span><span class="sy4">;</span>
|
|
<span class="br0">}</span> <span class="kw1">else</span> <span class="br0">{</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">"the first adjacent pair of equal elements at: "</span>
|
|
<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>v1.<span class="me1">begin</span><span class="br0">(</span><span class="br0">)</span>, i1<span class="br0">)</span> <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
|
|
<span class="br0">}</span>
|
|
|
|
<span class="kw4">auto</span> i2 <span class="sy1">=</span> std<span class="sy4">::</span><span class="me2">adjacent_find</span><span class="br0">(</span>v1.<span class="me1">begin</span><span class="br0">(</span><span class="br0">)</span>, v1.<span class="me1">end</span><span class="br0">(</span><span class="br0">)</span>, <a href="cpp-utility-functional-greater.html"><span class="kw1037">std::<span class="me2">greater</span></span></a><span class="sy1"><</span><span class="kw4">int</span><span class="sy1">></span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
|
|
<span class="kw1">if</span> <span class="br0">(</span>i2 <span class="sy1">==</span> v1.<span class="me1">end</span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span> <span class="br0">{</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">"The entire vector is sorted in ascending order<span class="es1">\n</span>"</span><span class="sy4">;</span>
|
|
<span class="br0">}</span> <span class="kw1">else</span> <span class="br0">{</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">"The last element in the non-decreasing subsequence is at: "</span>
|
|
<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>v1.<span class="me1">begin</span><span class="br0">(</span><span class="br0">)</span>, i2<span class="br0">)</span> <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
|
|
<span class="br0">}</span>
|
|
<span class="br0">}</span></pre></div>
|
|
</div>
|
|
<p>输出：</p>
|
|
<div dir="ltr" class="mw-geshi" style="text-align: left;">
|
|
<div class="text source-text">
|
|
<pre class="de1">The first adjacent pair of equal elements at: 4
|
|
The last element in the non-decreasing subsequence is at: 7</pre></div>
|
|
</div>
|
|
</div>
|
|
<h3><span class="mw-headline" id=".E5.8F.82.E9.98.85">参阅</span></h3>
|
|
<table class="t-dsc-begin">
|
|
<tr class="t-dsc">
|
|
<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="cpp-algorithm-unique.html"><span class="t-lines"><span>unique</span></span></a></div>
|
|
</div>
|
|
</td>
|
|
<td>移除范围内的连续重复元素<br />
|
|
<span class="t-mark">(函数模板)</span></td>
|
|
</tr>
|
|
</table>
|
|
</div>
|
|
<div class="visualClear"></div>
|
|
</div>
|
|
</div>
|
|
</div>
|
|
</body>
|
|
</html>
|