90 lines
9.4 KiB
HTML
90 lines
9.4 KiB
HTML
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<title>operator==,!=(std::unordered_set)</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_container_unordered_set_operator_cmp skin-cppreference2 action-view cpp-page-template cpp-navbar">
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<h1 id="firstHeading" class="firstHeading">operator==,!=<small>(std::unordered_set)</small></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-unordered_set.html">unordered set</a></span></div>
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<div class="t-page-template" style="">
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<p></p>
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<table class="t-dcl-begin">
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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> Key, <span class="kw1">class</span> Hash, <span class="kw1">class</span> KeyEqual, <span class="kw1">class</span> Allocator <span class="sy1">></span><br /></span>
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<p><span class="kw4">bool</span> operator<span class="sy1">==</span><span class="br0">(</span> <span class="kw4">const</span> <a href="cpp-container-unordered_set.html"><span class="kw1289">std::<span class="me2">unordered_set</span></span></a><span class="sy1"><</span>Key,Hash,KeyEqual,Allocator<span class="sy1">></span><span class="sy3">&</span> lhs,<br /></p>
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<span class="kw4">const</span> <a href="cpp-container-unordered_set.html"><span class="kw1289">std::<span class="me2">unordered_set</span></span></a><span class="sy1"><</span>Key,Hash,KeyEqual,Allocator<span class="sy1">></span><span class="sy3">&</span> rhs <span class="br0">)</span><span class="sy4">;</span></div>
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</td>
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<td>(1)</td>
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<tr class="t-dcl t-until-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> Key, <span class="kw1">class</span> Hash, <span class="kw1">class</span> KeyEqual, <span class="kw1">class</span> Allocator <span class="sy1">></span><br /></span>
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<p><span class="kw4">bool</span> operator<span class="sy3">!</span><span class="sy1">=</span><span class="br0">(</span> <span class="kw4">const</span> <a href="cpp-container-unordered_set.html"><span class="kw1289">std::<span class="me2">unordered_set</span></span></a><span class="sy1"><</span>Key,Hash,KeyEqual,Allocator<span class="sy1">></span><span class="sy3">&</span> lhs,<br /></p>
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<span class="kw4">const</span> <a href="cpp-container-unordered_set.html"><span class="kw1289">std::<span class="me2">unordered_set</span></span></a><span class="sy1"><</span>Key,Hash,KeyEqual,Allocator<span class="sy1">></span><span class="sy3">&</span> rhs <span class="br0">)</span><span class="sy4">;</span></div>
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</td>
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<td>(2)</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-dcl-sep">
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<td></td>
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<td></td>
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<td></td>
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</tr>
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</tbody>
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</table>
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<p>比较二个无序容器的内容。</p>
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<p>若下列条件成立则二个无序容器 <code>lhs</code> 与 <code>rhs</code> 相等：</p>
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<ul>
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<li><span class="t-c"><span class="mw-geshi cpp source-cpp">lhs.<span class="me1">size</span><span class="br0">(</span><span class="br0">)</span> <span class="sy1">==</span> rhs.<span class="me1">size</span><span class="br0">(</span><span class="br0">)</span></span></span></li>
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<li>从 <span class="t-c"><span class="mw-geshi cpp source-cpp">lhs.<span class="me1">equal_range</span><span class="br0">(</span>lhs_eq1<span class="br0">)</span></span></span> 获得的每组等价元素 <code>[lhs_eq1, lhs_eq2)</code> 拥有在另一容器中从 <span class="t-c"><span class="mw-geshi cpp source-cpp">rhs.<span class="me1">equal_range</span><span class="br0">(</span>rhs_eq1<span class="br0">)</span></span></span> 获得的对应等价元素组 <code>[rhs_eq1, rhs_eq2)</code> ，且它们拥有下列属性：</li>
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</ul>
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<dl>
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<dd>
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<ul>
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<li><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>lhs_eq1, lhs_eq2<span class="br0">)</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>rhs_eq1, rhs_eq2<span class="br0">)</span></span></span> 。</li>
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<li><span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-algorithm-is_permutation.html"><span class="kw1648">std::<span class="me2">is_permutation</span></span></a><span class="br0">(</span>lhs_eq1, lhs_eq2, rhs_eq1<span class="br0">)</span> <span class="sy1">==</span> <span class="kw2">true</span></span></span> 。</li>
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</ul>
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</dd>
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</dl>
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<p>若 <code>Key</code> 非<a href="cpp-named_req-EqualityComparable.html"><span style="font-style:italic">可相等比较</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(EqualityComparable)</span></a> 则行为未定义。</p>
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<p>若 <span class="t-rev-inl t-until-cxx20"><span><code>hash_function()</code> 和 <code>key_eq()</code></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><code>key_eq()</code></span> <span><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></span></span> 在 <code>lhs</code> 和 <code>rhs</code> 上拥有不相同的行为，或若 <code>Key</code> 的 <span class="t-c"><span class="mw-geshi cpp source-cpp">operator<span class="sy1">==</span></span></span> 不是对于 <code>key_eq()</code> 所引入的等价关键组的细分（即若用 <span class="t-c"><span class="mw-geshi cpp source-cpp">operator<span class="sy1">==</span></span></span> 比较相等的二个元素落入不同划分），则行为未定义。</p>
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<table class="t-rev-begin">
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<tr class="t-rev t-since-cxx20">
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<td>
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<p><code>!=</code> 运算符从 <code>operator==</code> <a href="cpp-language-operators.html#.E5.85.B3.E7.B3.BB.E8.BF.90.E7.AE.97.E7.AC.A6">合成</a>。</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=".E5.8F.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>lhs, rhs</td>
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<td>-</td>
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<td>要比较的无序容器</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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<div class="t-li1"><span class="t-li">1)</span> 若容器内容相等则为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">true</span></span></span> ，否则为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">false</span></span></span> 。</div>
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<div class="t-li1"><span class="t-li">2)</span> 若容器内容不相等则为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">true</span></span></span> ，否则为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">false</span></span></span> 。</div>
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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>调用 <code>value_type</code> 上的 <span class="t-c"><span class="mw-geshi cpp source-cpp">operator<span class="sy1">==</span></span></span> 、调用 <a href="cpp-container-unordered_set-key_eq.html">key_eq</a> 所返回的谓词，及调用 <a href="cpp-container-unordered_set-hash_function.html">hash_function</a> 所返回的哈希器的次数，平均情况下与 <i>N</i> 成正比，最坏情况下与 <i>N<sup>2</sup></i> 成正比，其中 <i>N</i> 是容器大小。</p>
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