405 lines
25 KiB
HTML
405 lines
25 KiB
HTML
<!DOCTYPE html>
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<html lang="zh" dir="ltr" class="client-nojs" xmlns="http://www.w3.org/1999/xhtml" xml:lang="zh">
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<title>std::partial_ordering</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_utility_compare_partial_ordering 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>partial_ordering</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-utility.html">utility</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>定义于头文件 <code><a href="cpp-header-compare.html"><compare></a></code></div>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">class</span> partial_ordering<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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<p>类类型 <code>std::partial_ordering</code> 是这种<a href="cpp-language-operator_comparison.html#.E4.B8.89.E8.B7.AF.E6.AF.94.E8.BE.83">三路比较</a>的结果类型：</p>
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<ul>
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<li>接纳所有六个关系运算符（ == 、 != 、 < 、 <= 、 > 、 >= ）</li>
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</ul>
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<ul>
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<li>不隐含可替换性：若 a 等价于 b ，则 f(a) 可能不等价于 f(b) 。这里 f 所指代的函数仅可经由参数的公开 const 成员读取显著的比较状态。换言之，等价的值可能可区别。</li>
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<li>接纳不可比较值： a < b 、 a == b 和 a > b 可以均为 false</li>
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</ul>
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<h3><span class="mw-headline" id=".E5.B8.B8.E9.87.8F">常量</span></h3>
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<p>类型 <code>std::partial_ordering</code> 拥有四个合法值，实现为其类型的 const 静态数据成员：</p>
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<table class="t-dsc-begin">
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<td>成员常量</td>
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<td>定义</td>
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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><span class="t-lines"><span>less<span class="t-mark">(inline constexpr)</span></span></span></div>
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<div><span class="t-lines"><span><span class="t-cmark">[静态]</span></span></span></div>
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</div>
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</td>
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<td><code>std::partial_ordering</code> 类型合法值，指示小于（先序）关系<br />
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<span class="t-mark">(公开静态成员常量)</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><span class="t-lines"><span>equivalent<span class="t-mark">(inline constexpr)</span></span></span></div>
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<div><span class="t-lines"><span><span class="t-cmark">[静态]</span></span></span></div>
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</div>
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</td>
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<td><code>std::partial_ordering</code> 类型合法值，指示等价（既非先序亦非后序）<br />
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<span class="t-mark">(公开静态成员常量)</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><span class="t-lines"><span>greater<span class="t-mark">(inline constexpr)</span></span></span></div>
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<div><span class="t-lines"><span><span class="t-cmark">[静态]</span></span></span></div>
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</div>
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</td>
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<td><code>std::partial_ordering</code> 类型合法值，指示大于（后序）关系<br />
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<span class="t-mark">(公开静态成员常量)</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><span class="t-lines"><span>unordered<span class="t-mark">(inline constexpr)</span></span></span></div>
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<div><span class="t-lines"><span><span class="t-cmark">[静态]</span></span></span></div>
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</div>
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</td>
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<td><code>std::partial_ordering</code> 类型合法值，指示与不可比较值的关系<br />
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<span class="t-mark">(公开静态成员常量)</span></td>
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</tr>
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</table>
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<h3><span class="mw-headline" id=".E8.BD.AC.E6.8D.A2">转换</span></h3>
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<p><code>std::partial_ordering</code> 不可隐式转换其他比较类别类型，而 <span class="t-lc">std::strong_ordering</span> 和 <span class="t-lc">std::weak_ordering</span> 均可隐式转换为 <span class="t-lc">partial_ordering</span> 。</p>
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<h3><span class="mw-headline" id=".E6.AF.94.E8.BE.83">比较</span></h3>
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<p>比较运算符在此类型值和字面量 <span class="t-c"><span class="mw-geshi cpp source-cpp">​<span class="nu0">0</span>​</span></span> 间定义。这支持用表达式 <span class="t-c"><span class="mw-geshi cpp source-cpp">a <span class="sy1"><=></span> b <span class="sy1">==</span> <span class="nu0">0</span></span></span> 或 <span class="t-c"><span class="mw-geshi cpp source-cpp">a <span class="sy1"><=></span> b <span class="sy1"><</span> <span class="nu0">0</span></span></span> 转换三路比较的结果为布尔关系；见 <a href="cpp-utility-compare-named_comparison_functions.html"><tt>std::is_eq</tt></a> 、 <a href="cpp-utility-compare-named_comparison_functions.html"><tt>std::is_lt</tt></a> 等。</p>
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<p>这些函数对通常<a href="cpp-language-unqualified_lookup.html">无限定</a>或<a href="cpp-language-qualified_lookup.html">有限定查找</a>不可见，而只能在 <code>std::partial_ordering</code> 为参数的关联类时由<a href="cpp-language-adl.html">实参依赖查找</a>找到。</p>
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<p>若程序试图将 <code>partial_ordering</code> 与任何异于整数字面量 <span class="t-c"><span class="mw-geshi cpp source-cpp">​<span class="nu0">0</span>​</span></span> 的内容比较，则其行为未定义。</p>
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<table class="t-dsc-begin">
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<div class="t-dsc-member-div">
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<div><strong class="selflink"><span class="t-lines"><span>operator==</span><span>operator<</span><span>operator></span><span>operator<=</span><span>operator>=</span><span>operator<=></span></span></strong></div>
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</div>
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</td>
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<td>与零或 <code>partial_ordering</code> 比较<br />
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<span class="t-mark">(函数)</span></td>
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</table>
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<div class="t-member">
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<h2><span class="mw-headline" id="operator.3D.3D">operator==</span></h2>
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<table class="t-dcl-begin">
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">friend</span> <span class="kw4">constexpr</span> <span class="kw4">bool</span> operator<span class="sy1">==</span><span class="br0">(</span>partial_ordering v, <span class="coMULTI">/*unspecified*/</span> u<span class="br0">)</span> <span class="kw1">noexcept</span><span class="sy4">;</span></span></div>
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</td>
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<td>(1)</td>
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<td class="t-dcl-nopad"></td>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">friend</span> <span class="kw4">constexpr</span> <span class="kw4">bool</span><br />
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operator<span class="sy1">==</span><span class="br0">(</span>partial_ordering v, partial_ordering w<span class="br0">)</span> <span class="kw1">noexcept</span> <span class="sy1">=</span> <span class="kw1">default</span><span class="sy4">;</span></span></div>
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</td>
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<td>(2)</td>
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<td class="t-dcl-nopad"></td>
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<tr class="t-dcl-sep">
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<td></td>
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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>v, w</td>
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<td>-</td>
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<td>要检查的 <code>std::partial_ordering</code> 值</td>
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</tr>
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<tr class="t-par">
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<td>u</td>
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<td>-</td>
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<td>任何接受字面零实参的类型的不使用形参</td>
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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 <code>v</code> 为 <code>equivalent</code> 则为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">true</span></span></span> ，而若 <code>v</code> 为 <code>unordered</code> 、 <code>less</code> 或 <code>greater</code> 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> 若两个参数持有相同值则为 <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>
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<div class="t-member">
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<h2><span class="mw-headline" id="operator.3C">operator<</span></h2>
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<table class="t-dcl-begin">
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<td>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">friend</span> <span class="kw4">constexpr</span> <span class="kw4">bool</span> operator<span class="sy1"><</span><span class="br0">(</span>partial_ordering v, <span class="coMULTI">/*unspecified*/</span> u<span class="br0">)</span> <span class="kw1">noexcept</span><span class="sy4">;</span></span></div>
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</td>
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<td>(1)</td>
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<td class="t-dcl-nopad"></td>
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<tr class="t-dcl">
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<td>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">friend</span> <span class="kw4">constexpr</span> <span class="kw4">bool</span> operator<span class="sy1"><</span><span class="br0">(</span><span class="coMULTI">/*unspecified*/</span> u, partial_ordering v<span class="br0">)</span> <span class="kw1">noexcept</span><span class="sy4">;</span></span></div>
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</td>
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<td>(2)</td>
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<td class="t-dcl-nopad"></td>
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<h3><span class="mw-headline" id=".E5.8F.82.E6.95.B0_2">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>v</td>
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<td>-</td>
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<td>要检查的 <code>std::partial_ordering</code> 值</td>
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</tr>
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<tr class="t-par">
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<td>u</td>
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<td>-</td>
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<td>任何接受字面零实参的类型的不使用形参</td>
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</tr>
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<h3><span class="mw-headline" id=".E8.BF.94.E5.9B.9E.E5.80.BC_2">返回值</span></h3>
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<div class="t-li1"><span class="t-li">1)</span> 若 <code>v</code> 为 <code>less</code> 则为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">true</span></span></span> ，而若 <code>v</code> 为 <code>greater</code> 、 <code>equivalent</code> 或 <code>unordered</code> 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 <code>v</code> 为 <code>greater</code> 则为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">true</span></span></span> ，而若 <code>v</code> 为 <code>less</code> 、 <code>equivalent</code> 或 <code>unordered</code> 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>
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<div class="t-member">
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<h2><span class="mw-headline" id="operator.3C.3D">operator<=</span></h2>
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<table class="t-dcl-begin">
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">friend</span> <span class="kw4">constexpr</span> <span class="kw4">bool</span> operator<span class="sy1"><=</span><span class="br0">(</span>partial_ordering v, <span class="coMULTI">/*unspecified*/</span> u<span class="br0">)</span> <span class="kw1">noexcept</span><span class="sy4">;</span></span></div>
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</td>
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<td>(1)</td>
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<td class="t-dcl-nopad"></td>
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</tr>
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<tr class="t-dcl">
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<td>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">friend</span> <span class="kw4">constexpr</span> <span class="kw4">bool</span> operator<span class="sy1"><=</span><span class="br0">(</span><span class="coMULTI">/*unspecified*/</span> u, partial_ordering v<span class="br0">)</span> <span class="kw1">noexcept</span><span class="sy4">;</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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<h3><span class="mw-headline" id=".E5.8F.82.E6.95.B0_3">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>v</td>
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<td>-</td>
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<td>要检查的 <code>std::partial_ordering</code> 值</td>
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</tr>
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<tr class="t-par">
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<td>u</td>
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<td>-</td>
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<td>任何接受字面零实参的类型的不使用形参</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_3">返回值</span></h3>
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<div class="t-li1"><span class="t-li">1)</span> 若 <code>v</code> 为 <code>less</code> 或 <code>equivalent</code> 则为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">true</span></span></span> ，而若 <code>v</code> 为 <code>greater</code> 或 <code>unordered</code> 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 <code>v</code> 为 <code>greater</code> 或 <code>equivalent</code> 则为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">true</span></span></span> ，而若 <code>v</code> 为 <code>less</code> 或 <code>unordered</code> 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>
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<div class="t-member">
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<h2><span class="mw-headline" id="operator.3E">operator></span></h2>
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<table class="t-dcl-begin">
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<td>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">friend</span> <span class="kw4">constexpr</span> <span class="kw4">bool</span> operator<span class="sy1">></span><span class="br0">(</span>partial_ordering v, <span class="coMULTI">/*unspecified*/</span> u<span class="br0">)</span> <span class="kw1">noexcept</span><span class="sy4">;</span></span></div>
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</td>
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<td>(1)</td>
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<td class="t-dcl-nopad"></td>
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</tr>
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<tr class="t-dcl">
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<td>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">friend</span> <span class="kw4">constexpr</span> <span class="kw4">bool</span> operator<span class="sy1">></span><span class="br0">(</span><span class="coMULTI">/*unspecified*/</span> u, partial_ordering v<span class="br0">)</span> <span class="kw1">noexcept</span><span class="sy4">;</span></span></div>
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</td>
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<td>(2)</td>
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<td class="t-dcl-nopad"></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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</table>
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<h3><span class="mw-headline" id=".E5.8F.82.E6.95.B0_4">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>v</td>
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<td>-</td>
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<td>要检查的 <code>std::partial_ordering</code> 值</td>
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</tr>
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<tr class="t-par">
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<td>u</td>
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<td>-</td>
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<td>任何接受字面零实参的类型的不使用形参</td>
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</tr>
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<h3><span class="mw-headline" id=".E8.BF.94.E5.9B.9E.E5.80.BC_4">返回值</span></h3>
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<div class="t-li1"><span class="t-li">1)</span> 若 <code>v</code> 为 <code>greater</code> 则为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">true</span></span></span> ，而若 <code>v</code> 为 <code>less</code> 、 <code>equivalent</code> 或 <code>unordered</code> 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 <code>v</code> 为 <code>less</code> 则为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">true</span></span></span> ，而若 <code>v</code> 为 <code>greater</code> 、 <code>equivalent</code> 或 <code>unordered</code> 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>
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<div class="t-member">
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<h2><span class="mw-headline" id="operator.3E.3D">operator>=</span></h2>
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<table class="t-dcl-begin">
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<tbody>
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<tr class="t-dcl">
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<td>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">friend</span> <span class="kw4">constexpr</span> <span class="kw4">bool</span> operator<span class="sy1">>=</span><span class="br0">(</span>partial_ordering v, <span class="coMULTI">/*unspecified*/</span> u<span class="br0">)</span> <span class="kw1">noexcept</span><span class="sy4">;</span></span></div>
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</td>
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<td>(1)</td>
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<td class="t-dcl-nopad"></td>
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</tr>
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<tr class="t-dcl">
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<td>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">friend</span> <span class="kw4">constexpr</span> <span class="kw4">bool</span> operator<span class="sy1">>=</span><span class="br0">(</span><span class="coMULTI">/*unspecified*/</span> u, partial_ordering v<span class="br0">)</span> <span class="kw1">noexcept</span><span class="sy4">;</span></span></div>
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</td>
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<td>(2)</td>
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<td class="t-dcl-nopad"></td>
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</tr>
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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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<h3><span class="mw-headline" id=".E5.8F.82.E6.95.B0_5">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>v</td>
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<td>-</td>
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<td>要检查的 <code>std::partial_ordering</code> 值</td>
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</tr>
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<tr class="t-par">
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<td>u</td>
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<td>-</td>
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<td>任何接受字面零实参的类型的不使用形参</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_5">返回值</span></h3>
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<div class="t-li1"><span class="t-li">1)</span> 若 <code>v</code> 为 <code>greater</code> 或 <code>equivalent</code> 则为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">true</span></span></span> ，而若 <code>v</code> 为 <code>less</code> 或 <code>unordered</code> 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 <code>v</code> 为 <code>less</code> 或 <code>equivalent</code> 则为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">true</span></span></span> ，而若 <code>v</code> 为 <code>greater</code> 或 <code>unordered</code> 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>
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<div class="t-member">
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<h2><span class="mw-headline" id="operator.3C.3D.3E">operator<=></span></h2>
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<table class="t-dcl-begin">
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<tbody>
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<tr class="t-dcl">
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<td>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">friend</span> <span class="kw4">constexpr</span> partial_ordering operator<span class="sy1"><=></span><span class="br0">(</span>partial_ordering v, <span class="coMULTI">/*unspecified*/</span> u<span class="br0">)</span> <span class="kw1">noexcept</span><span class="sy4">;</span></span></div>
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</td>
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<td>(1)</td>
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<td class="t-dcl-nopad"></td>
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</tr>
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<tr class="t-dcl">
|
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<td>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">friend</span> <span class="kw4">constexpr</span> partial_ordering operator<span class="sy1"><=></span><span class="br0">(</span><span class="coMULTI">/*unspecified*/</span> u, partial_ordering v<span class="br0">)</span> <span class="kw1">noexcept</span><span class="sy4">;</span></span></div>
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</td>
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<td>(2)</td>
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<td class="t-dcl-nopad"></td>
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|
</tr>
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<tr class="t-dcl-sep">
|
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<td></td>
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<td></td>
|
|
<td></td>
|
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</tr>
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</tbody>
|
|
</table>
|
|
<h3><span class="mw-headline" id=".E5.8F.82.E6.95.B0_6">参数</span></h3>
|
|
<table class="t-par-begin">
|
|
<tr class="t-par">
|
|
<td>v</td>
|
|
<td>-</td>
|
|
<td>要检查的 <code>std::partial_ordering</code> 值</td>
|
|
</tr>
|
|
<tr class="t-par">
|
|
<td>u</td>
|
|
<td>-</td>
|
|
<td>任何接受字面零实参的类型的不使用形参</td>
|
|
</tr>
|
|
</table>
|
|
<h3><span class="mw-headline" id=".E8.BF.94.E5.9B.9E.E5.80.BC_6">返回值</span></h3>
|
|
<div class="t-li1"><span class="t-li">1)</span> <span class="t-c"><span class="mw-geshi cpp source-cpp">v</span></span> 。</div>
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<div class="t-li1"><span class="t-li">2)</span> 若 <code>v</code> 为 <code>less</code> 则为 <code>greater</code> ，若 <code>v</code> 为 <code>greater</code> 则为 <code>less</code> ，否则为 <code>v</code> 。</div>
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</div>
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<h3><span class="mw-headline" id=".E6.B3.A8.E6.84.8F">注意</span></h3>
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<p>浮点值之间的<a href="cpp-language-operator_comparison.html#.E4.B8.89.E8.B7.AF.E6.AF.94.E8.BE.83">内建运算符 <=></a> 使用此顺序：正零与负零比较为 <code>equivalent</code> ，但能辨别，而 NaN 值与任何其他值比较为 <code>unordered</code> 。</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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<table class="metadata plainlinks ambox mbox-small-left ambox-notice" style="">
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<tr>
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<td class="mbox-empty-cell"></td>
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<td class="mbox-text" style="">本节未完成<br />
|
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原因：暂无示例</td>
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</tr>
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</table>
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<h3><span class="mw-headline" id=".E5.8F.82.E9.98.85">参阅</span></h3>
|
|
<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-utility-compare-strong_ordering.html"><span class="t-lines"><span>strong_ordering</span></span></a></div>
|
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<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx20">(C++20)</span></span></span></div>
|
|
</div>
|
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</td>
|
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<td>三路比较的结果类型，支持所有 6 种运算符且可替换<br />
|
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<span class="t-mark">(类)</span></td>
|
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</tr>
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<tr class="t-dsc">
|
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<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="cpp-utility-compare-weak_ordering.html"><span class="t-lines"><span>weak_ordering</span></span></a></div>
|
|
<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx20">(C++20)</span></span></span></div>
|
|
</div>
|
|
</td>
|
|
<td>三路比较的结果类型，支持所有 6 种运算符且不可替换<br />
|
|
<span class="t-mark">(类)</span></td>
|
|
</tr>
|
|
</table>
|
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</div>
|
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<div class="visualClear"></div>
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</div>
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</div>
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</div>
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</body>
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</html>
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