165 lines
12 KiB
HTML
165 lines
12 KiB
HTML
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<title>std::forward_list<T,Allocator>::unique</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_container_forward_list_unique skin-cppreference2 action-view cpp-page-template cpp-navbar">
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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::forward_list<T,Allocator>::</span>unique</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-container.html">container</a>‎ | <a href="cpp-container-forward_list.html">forward list</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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<div class="t-page-template" style="">
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<p></p>
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</div>
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<table class="t-dcl-begin">
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<tbody></tbody>
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<td></td>
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<td rowspan="142">(1)</td>
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<td></td>
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<tr class="t-dcl t-since-cxx11 t-until-cxx20">
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<td>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw4">void</span> unique<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span></span></div>
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<td class="t-dcl-nopad"></td>
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<td><span class="t-mark-rev t-since-cxx11">(C++11 起)</span><br />
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<span class="t-mark-rev t-until-cxx20">(C++20 前)</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">size_type unique<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span></span></div>
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<td class="t-dcl-nopad"></td>
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<td><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></td>
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<tbody></tbody>
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<tbody class="t-dcl-rev t-dcl-rev-num">
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<td rowspan="142">(2)</td>
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<td></td>
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<tr class="t-dcl t-since-cxx11 t-until-cxx20">
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<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> BinaryPredicate <span class="sy1">></span><br />
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<span class="kw4">void</span> unique<span class="br0">(</span> BinaryPredicate p <span class="br0">)</span><span class="sy4">;</span></span></div>
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<td class="t-dcl-nopad"></td>
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<td><span class="t-mark-rev t-since-cxx11">(C++11 起)</span><br />
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<span class="t-mark-rev t-until-cxx20">(C++20 前)</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> BinaryPredicate <span class="sy1">></span><br />
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size_type unique<span class="br0">(</span> BinaryPredicate p <span class="br0">)</span><span class="sy4">;</span></span></div>
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<td class="t-dcl-nopad"></td>
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<td><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></td>
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<td></td>
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<p>从容器移除所有<i>相继</i>的重复元素。只留下相等元素组中的第一个元素。若选择的比较器不建立等价关系则行为未定义。</p>
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<div class="t-li1"><span class="t-li">1)</span> 用 <span class="t-c"><span class="mw-geshi cpp source-cpp">operator<span class="sy1">==</span></span></span> 比较元素。</div>
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<div class="t-li1"><span class="t-li">2)</span> 用二元谓词 <code>p</code> 比较元素。</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>p</td>
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<td>-</td>
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<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 />
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<p>谓词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> 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>
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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">forward_list<span class="sy1"><</span>T,Allocator<span class="sy1">></span><span class="sy4">::</span><span class="me2">const_iterator</span></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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<h3><span class="mw-headline" id=".E8.BF.94.E5.9B.9E.E5.80.BC">返回值</span></h3>
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<table class="t-rev-begin">
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<td>
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<p>（无）</p>
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</td>
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<td><span class="t-mark-rev t-until-cxx20">(C++20 前)</span></td>
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<tr class="t-rev t-since-cxx20">
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<p>移除的元素数。</p>
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</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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</table>
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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>若容器非空则准确比较元素 <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>begin<span class="br0">(</span><span class="br0">)</span>, end<span class="br0">(</span><span class="br0">)</span><span class="br0">)</span> <span class="sy2">-</span> <span class="nu0">1</span></span></span> 次。否则不进行比较。</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 <forward_list></span>
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<span class="kw4">auto</span> print <span class="sy1">=</span> <span class="br0">[</span><span class="br0">]</span><span class="br0">(</span><span class="kw4">auto</span> remark, <span class="kw4">auto</span> <span class="kw4">const</span><span class="sy3">&</span> container<span class="br0">)</span> <span class="br0">{</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> remark<span class="sy4">;</span>
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<span class="kw1">for</span> <span class="br0">(</span><span class="kw4">auto</span> <span class="kw4">const</span><span class="sy3">&</span> val <span class="sy4">:</span> container<span class="br0">)</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> <span class="st0">' '</span> <span class="sy1"><<</span> val<span class="sy4">;</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> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
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<span class="br0">}</span><span class="sy4">;</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-forward_list.html"><span class="kw1273">std::<span class="me2">forward_list</span></span></a><span class="sy1"><</span><span class="kw4">int</span><span class="sy1">></span> c <span class="sy1">=</span> <span class="br0">{</span><span class="nu0">1</span>, <span class="nu0">2</span>, <span class="nu0">2</span>, <span class="nu0">3</span>, <span class="nu0">3</span>, <span class="nu0">2</span>, <span class="nu0">1</span>, <span class="nu0">1</span>, <span class="nu0">2</span><span class="br0">}</span><span class="sy4">;</span>
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print<span class="br0">(</span><span class="st0">"Before unique():"</span>, c<span class="br0">)</span><span class="sy4">;</span>
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c.<span class="me1">unique</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
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print<span class="br0">(</span><span class="st0">"After unique():"</span>, c<span class="br0">)</span><span class="sy4">;</span>
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c <span class="sy1">=</span> <span class="br0">{</span><span class="nu0">1</span>, <span class="nu0">2</span>, <span class="nu0">12</span>, <span class="nu0">23</span>, <span class="nu0">3</span>, <span class="nu0">2</span>, <span class="nu0">51</span>, <span class="nu0">1</span>, <span class="nu0">2</span><span class="br0">}</span><span class="sy4">;</span>
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print<span class="br0">(</span><span class="st0">"Before unique(pred):"</span>, c<span class="br0">)</span><span class="sy4">;</span>
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c.<span class="me1">unique</span><span class="br0">(</span><span class="br0">[</span>mod<span class="sy1">=</span><span class="nu0">10</span><span class="br0">]</span><span class="br0">(</span><span class="kw4">int</span> x, <span class="kw4">int</span> y<span class="br0">)</span> <span class="br0">{</span> <span class="kw1">return</span> <span class="br0">(</span>x <span class="sy2">%</span> mod<span class="br0">)</span> <span class="sy1">==</span> <span class="br0">(</span>y <span class="sy2">%</span> mod<span class="br0">)</span><span class="sy4">;</span> <span class="br0">}</span><span class="br0">)</span><span class="sy4">;</span>
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print<span class="br0">(</span><span class="st0">"After unique(pred):"</span>, c<span class="br0">)</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">Before unique(): 1 2 2 3 3 2 1 1 2
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After unique(): 1 2 3 2 1 2
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Before unique(pred): 1 2 12 23 3 2 51 1 2
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After unique(pred): 1 2 23 2 51 2</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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<td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-algorithm-unique.html"><span class="t-lines"><span>unique</span></span></a></div>
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</div>
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</td>
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<td>移除范围内的连续重复元素<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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</body>
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