185 lines
12 KiB
HTML
185 lines
12 KiB
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::less_equal</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_utility_functional_less_equal 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>less_equal</h1>
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<div id="contentSub"><span class="subpages">< <a href="cpp.html">cpp</a>‎ | <a href="cpp-utility.html">utility</a>‎ | <a href="cpp-utility-functional.html">functional</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-functional.html"><functional></a></code></div>
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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> T <span class="sy1">></span><br />
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<span class="kw1">struct</span> less_equal<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-until-cxx14">(C++14 前)</span></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> T <span class="sy1">=</span> <span class="kw4">void</span> <span class="sy1">></span><br />
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<span class="kw1">struct</span> less_equal<span class="sy4">;</span></span></div>
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<td><span class="t-mark-rev t-since-cxx14">(C++14 起)</span></td>
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<p>进行比较的函数对象。调用类型 <code>T</code> 上的 <span class="t-c"><span class="mw-geshi cpp source-cpp">operator<span class="sy1"><=</span></span></span> ，除非特化。</p>
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<h3><span class="mw-headline" id=".E5.AE.9E.E7.8E.B0.E5.AE.9A.E4.B9.89.E7.9A.84.E6.8C.87.E9.92.88.E4.B8.8A.E7.9A.84.E4.B8.A5.E6.A0.BC.E5.85.A8.E5.BA.8F">实现定义的指针上的严格全序</span></h3>
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<p><code>std::less_equal</code> 对任何指针类型的特化产生实现定义的严格全序，即使内建的 <code><=</code> 运算符不如此。</p>
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<p>实现定义的严格全序与比较运算符（ <span class="t-rev-inl t-since-cxx20"><span><code><=></code>、</span> <span><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></span></span><code><</code>、 <code>></code>、 <code><=</code> 及 <code>>=</code> ）所施加的偏序一致，并在下列标准函数对象间一致：</p>
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<ul>
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<li><span class="t-lc"><a href="cpp-utility-functional-less.html">std::less</a></span>、 <span class="t-lc"><a href="cpp-utility-functional-greater.html">std::greater</a></span>、 <span class="t-lc"><strong class="selflink">std::less_equal</strong></span> 及 <span class="t-lc"><a href="cpp-utility-functional-greater_equal.html">std::greater_equal</a></span> ，当模板实参为指针类型<span class="t-rev-inl t-since-cxx14"><span>或 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">void</span></span></span></span> <span><span class="t-mark-rev t-since-cxx14">(C++14 起)</span></span></span>时</li>
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</ul>
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<tr class="t-rev t-since-cxx20">
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<ul>
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<li><a href="cpp-utility-functional-ranges-equal_to.html"><tt>std::ranges::equal_to</tt></a>、 <a href="cpp-utility-functional-ranges-not_equal_to.html"><tt>std::ranges::not_equal_to</tt></a>、 <a href="cpp-utility-functional-ranges-less.html"><tt>std::ranges::less</tt></a>、 <a href="cpp-utility-functional-ranges-greater.html"><tt>std::ranges::greater</tt></a>、 <a href="cpp-utility-functional-ranges-less_equal.html"><tt>std::ranges::less_equal</tt></a>、 <a href="cpp-utility-functional-ranges-greater_equal.html"><tt>std::ranges::greater_equal</tt></a> 及 <span class="t-lc">std::compare_three_way</span></li>
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</ul>
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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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<h3><span class="mw-headline" id=".E7.89.B9.E5.8C.96">特化</span></h3>
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<div class="t-dsc-member-div">
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<div><a href="cpp-utility-functional-less_equal_void.html"><span class="t-lines"><span>less_equal<span class="t-dsc-small"><void></span></span></span></a></div>
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<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx14">(C++14)</span></span></span></div>
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<td>实现 <span class="t-c"><span class="mw-geshi cpp source-cpp">x <span class="sy1"><=</span> y</span></span> 并推导参数和返回类型的函数对象<br />
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<span class="t-mark">(类模板特化)</span></td>
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<h3><span class="mw-headline" id=".E6.88.90.E5.91.98.E7.B1.BB.E5.9E.8B">成员类型</span></h3>
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<table class="t-dsc-begin">
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<td>类型</td>
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<td>定义</td>
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<td><code>result_type</code> <span class="t-mark-rev t-deprecated-cxx17">(C++17 中弃用)</span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></td>
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<td><span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">bool</span></span></span></td>
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<td><code>first_argument_type</code> <span class="t-mark-rev t-deprecated-cxx17">(C++17 中弃用)</span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></td>
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<td><code>T</code></td>
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<td><code>second_argument_type</code> <span class="t-mark-rev t-deprecated-cxx17">(C++17 中弃用)</span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></td>
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<td><code>T</code></td>
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<p>这些成员类型由公开继承 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-utility-functional-binary_function.html"><span class="kw1125">std::<span class="me2">binary_function</span></span></a><span class="sy1"><</span>T, T, <span class="kw4">bool</span><span class="sy1">></span></span></span> 获得。</p>
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<td><span class="t-mark-rev t-until-cxx11">(C++11 前)</span></td>
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<h3><span class="mw-headline" id=".E6.88.90.E5.91.98.E5.87.BD.E6.95.B0">成员函数</span></h3>
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<div class="t-dsc-member-div">
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<div><span class="t-lines"><span>operator()</span></span></div>
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<td>检查第一参数是否<i>小于</i>或<i>等于</i>第二个<br />
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<span class="t-mark">(公开成员函数)</span></td>
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<div class="t-member">
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<h2><span class="mw-headline" id="std::less_equal::operator.28.29"><span style="font-size:0.7em; line-height:130%">std::less_equal::</span>operator()</span></h2>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw4">bool</span> operator<span class="br0">(</span><span class="br0">)</span><span class="br0">(</span> <span class="kw4">const</span> T<span class="sy3">&</span> lhs, <span class="kw4">const</span> T<span class="sy3">&</span> rhs <span class="br0">)</span> <span class="kw4">const</span><span class="sy4">;</span></span></div>
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</td>
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<td class="t-dcl-nopad"></td>
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<td><span class="t-mark-rev t-until-cxx14">(C++14 前)</span></td>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw4">constexpr</span> <span class="kw4">bool</span> operator<span class="br0">(</span><span class="br0">)</span><span class="br0">(</span> <span class="kw4">const</span> T<span class="sy3">&</span> lhs, <span class="kw4">const</span> T<span class="sy3">&</span> rhs <span class="br0">)</span> <span class="kw4">const</span><span class="sy4">;</span></span></div>
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</td>
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<td class="t-dcl-nopad"></td>
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<td><span class="t-mark-rev t-since-cxx14">(C++14 起)</span></td>
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<p>检查 <code>lhs</code> 是否<i>小于</i>或<i>等于</i> <code>rhs</code> 。</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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<td>lhs, rhs</td>
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<td>-</td>
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<td>要比较的值</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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<p>对于不是指针类型的 <code>T</code> ，若 <span class="t-c"><span class="mw-geshi cpp source-cpp">lhs <span class="sy1"><=</span> rhs</span></span> 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> 。</p>
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<p>对于是指针类型的 <code>T</code> ，若 <code>lhs</code> 在实现定义的严格全序中不后继 <code>rhs</code> 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> 。</p>
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<h3><span class="mw-headline" id=".E5.BC.82.E5.B8.B8">异常</span></h3>
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<p>可能抛出实现定义的异常。</p>
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<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>
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<table class="eq-fun-cpp-table">
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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="kw4">constexpr</span> <span class="kw4">bool</span> operator<span class="br0">(</span><span class="br0">)</span><span class="br0">(</span><span class="kw4">const</span> T <span class="sy3">&</span>lhs, <span class="kw4">const</span> T <span class="sy3">&</span>rhs<span class="br0">)</span> <span class="kw4">const</span>
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<span class="br0">{</span>
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<span class="kw1">return</span> lhs <span class="sy1"><=</span> rhs<span class="sy4">;</span> <span class="co1">// 假定实现使用平坦地址空间</span>
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<span class="br0">}</span></pre></div>
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<div class="visualClear"></div>
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