212 lines
15 KiB
HTML
212 lines
15 KiB
HTML
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<title>std::rel_ops::operator!=,>,<=,>=</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_utility_rel_ops_operator_cmp 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::rel_ops::</span>operator!=,>,<=,>=</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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<table class="t-dcl-begin">
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<div>定义于头文件 <code><a href="cpp-header-utility.html"><utility></a></code></div>
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</td>
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<td></td>
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<td></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><br />
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<span class="kw4">bool</span> operator<span class="sy3">!</span><span class="sy1">=</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="sy4">;</span></span></div>
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<td>(1)</td>
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<td><span class="t-mark">(C++20 中弃用)</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><br />
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<span class="kw4">bool</span> operator<span class="sy1">></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="sy4">;</span></span></div>
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<td>(2)</td>
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<td><span class="t-mark">(C++20 中弃用)</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><br />
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<span class="kw4">bool</span> operator<span class="sy1"><=</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="sy4">;</span></span></div>
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<td>(3)</td>
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<td><span class="t-mark">(C++20 中弃用)</span></td>
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</tr>
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<tr class="t-dcl">
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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="kw4">bool</span> operator<span class="sy1">>=</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="sy4">;</span></span></div>
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<td>(4)</td>
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<td><span class="t-mark">(C++20 中弃用)</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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<p>给定用户为类型 <code>T</code> 对象提供的 <span class="t-c"><span class="mw-geshi cpp source-cpp">operator<span class="sy1">==</span></span></span> 和 <span class="t-c"><span class="mw-geshi cpp source-cpp">operator<span class="sy1"><</span></span></span> ，实现其他比较运算符的通常语义。</p>
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<p>1) 用 <span class="t-c"><span class="mw-geshi cpp source-cpp">operator<span class="sy1">==</span></span></span> 实现 <span class="t-c"><span class="mw-geshi cpp source-cpp">operator<span class="sy3">!</span><span class="sy1">=</span></span></span> 。</p>
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<p>2) 用 <span class="t-c"><span class="mw-geshi cpp source-cpp">operator<span class="sy1"><</span></span></span> 实现 <span class="t-c"><span class="mw-geshi cpp source-cpp">operator<span class="sy1">></span></span></span> 。</p>
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<p>3) 用 <span class="t-c"><span class="mw-geshi cpp source-cpp">operator<span class="sy1"><</span></span></span> 实现 <span class="t-c"><span class="mw-geshi cpp source-cpp">operator<span class="sy1"><=</span></span></span> 。</p>
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<p>4) 用 <span class="t-c"><span class="mw-geshi cpp source-cpp">operator<span class="sy1"><</span></span></span> 实现 <span class="t-c"><span class="mw-geshi cpp source-cpp">operator<span class="sy1">>=</span></span></span> 。</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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<tr class="t-par">
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<td>lhs</td>
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<td>-</td>
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<td>左侧参数</td>
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</tr>
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<tr class="t-par">
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<td>rhs</td>
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<td>-</td>
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<td>右侧参数</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>1) 若 <code>lhs</code> <i>不等于</i> <code>rhs</code> 则返回 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">true</span></span></span> 。</p>
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<p>2) 若 <code>lhs</code> <i>大于</i> <code>rhs</code> 则返回 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">true</span></span></span> 。</p>
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<p>3) 若 <code>lhs</code> <i>小于或等于</i> <code>rhs</code> 则返回 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">true</span></span></span> 。</p>
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<p>4) 若 <code>lhs</code> <i>大于或等于</i> <code>rhs</code> 则返回 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">true</span></span></span> 。</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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<th>版本一</th>
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<td>
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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="kw1">namespace</span> rel_ops <span class="br0">{</span>
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<span class="kw1">template</span><span class="sy1"><</span> <span class="kw1">class</span> T <span class="sy1">></span>
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<span class="kw4">bool</span> operator<span class="sy3">!</span><span class="sy1">=</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>
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<span class="br0">{</span>
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<span class="kw1">return</span> <span class="sy3">!</span><span class="br0">(</span>lhs <span class="sy1">==</span> rhs<span class="br0">)</span><span class="sy4">;</span>
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<span class="br0">}</span>
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<span class="br0">}</span></pre></div>
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</div>
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<tr>
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<th>版本二</th>
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</tr>
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<td>
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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="kw1">namespace</span> rel_ops <span class="br0">{</span>
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<span class="kw1">template</span><span class="sy1"><</span> <span class="kw1">class</span> T <span class="sy1">></span>
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<span class="kw4">bool</span> operator<span class="sy1">></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>
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<span class="br0">{</span>
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<span class="kw1">return</span> rhs <span class="sy1"><</span> lhs<span class="sy4">;</span>
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<span class="br0">}</span>
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<span class="br0">}</span></pre></div>
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</div>
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<tr>
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<th>版本三</th>
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</tr>
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<tr>
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<td>
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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="kw1">namespace</span> rel_ops <span class="br0">{</span>
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<span class="kw1">template</span><span class="sy1"><</span> <span class="kw1">class</span> T <span class="sy1">></span>
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<span class="kw4">bool</span> operator<span class="sy1"><=</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>
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<span class="br0">{</span>
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<span class="kw1">return</span> <span class="sy3">!</span><span class="br0">(</span>rhs <span class="sy1"><</span> lhs<span class="br0">)</span><span class="sy4">;</span>
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<span class="br0">}</span>
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<span class="br0">}</span></pre></div>
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</div>
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</td>
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</tr>
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<tr>
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<th>版本四</th>
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</tr>
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<tr>
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<td>
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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="kw1">namespace</span> rel_ops <span class="br0">{</span>
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<span class="kw1">template</span><span class="sy1"><</span> <span class="kw1">class</span> T <span class="sy1">></span>
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<span class="kw4">bool</span> operator<span class="sy1">>=</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>
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<span class="br0">{</span>
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<span class="kw1">return</span> <span class="sy3">!</span><span class="br0">(</span>lhs <span class="sy1"><</span> rhs<span class="br0">)</span><span class="sy4">;</span>
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<span class="br0">}</span>
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<span class="br0">}</span></pre></div>
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</div>
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</td>
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<h3><span class="mw-headline" id=".E6.B3.A8.E8.A7.A3">注解</span></h3>
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<p><a rel="nofollow" class="external text" href="http://www.boost.org/doc/libs/release/libs/utility/operators.htm">Boost.operators</a> 提供更为通用的 <code>std::rel_ops</code> 替代品。</p>
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<p>C++20 起， <code>std::rel_ops</code> 由于让位给 <a href="cpp-language-default_comparisons.html"><tt>operator<=></tt></a> 而被弃用。</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 <utility></span>
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<span class="kw1">struct</span> Foo <span class="br0">{</span>
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<span class="kw4">int</span> n<span class="sy4">;</span>
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<span class="br0">}</span><span class="sy4">;</span>
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<span class="kw4">bool</span> operator<span class="sy1">==</span><span class="br0">(</span><span class="kw4">const</span> Foo<span class="sy3">&</span> lhs, <span class="kw4">const</span> Foo<span class="sy3">&</span> rhs<span class="br0">)</span>
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<span class="br0">{</span>
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<span class="kw1">return</span> lhs.<span class="me1">n</span> <span class="sy1">==</span> rhs.<span class="me1">n</span><span class="sy4">;</span>
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<span class="br0">}</span>
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<span class="kw4">bool</span> operator<span class="sy1"><</span><span class="br0">(</span><span class="kw4">const</span> Foo<span class="sy3">&</span> lhs, <span class="kw4">const</span> Foo<span class="sy3">&</span> rhs<span class="br0">)</span>
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<span class="br0">{</span>
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<span class="kw1">return</span> lhs.<span class="me1">n</span> <span class="sy1"><</span> rhs.<span class="me1">n</span><span class="sy4">;</span>
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<span class="br0">}</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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Foo f1 <span class="sy1">=</span> <span class="br0">{</span><span class="nu0">1</span><span class="br0">}</span><span class="sy4">;</span>
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Foo f2 <span class="sy1">=</span> <span class="br0">{</span><span class="nu0">2</span><span class="br0">}</span><span class="sy4">;</span>
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<span class="kw1">using</span> <span class="kw1">namespace</span> std<span class="sy4">::</span><span class="me2">rel_ops</span><span class="sy4">;</span>
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<a href="cpp-io-cout.html"><span class="kw1757">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <a href="cpp-io-manip-boolalpha.html"><span class="kw1763">std::<span class="me2">boolalpha</span></span></a><span class="sy4">;</span>
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<a href="cpp-io-cout.html"><span class="kw1757">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"not equal? : "</span> <span class="sy1"><<</span> <span class="br0">(</span>f1 <span class="sy3">!</span><span class="sy1">=</span> f2<span class="br0">)</span> <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
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<a href="cpp-io-cout.html"><span class="kw1757">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"greater? : "</span> <span class="sy1"><<</span> <span class="br0">(</span>f1 <span class="sy1">></span> f2<span class="br0">)</span> <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
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<a href="cpp-io-cout.html"><span class="kw1757">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"less equal? : "</span> <span class="sy1"><<</span> <span class="br0">(</span>f1 <span class="sy1"><=</span> f2<span class="br0">)</span> <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
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<a href="cpp-io-cout.html"><span class="kw1757">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"greater equal? : "</span> <span class="sy1"><<</span> <span class="br0">(</span>f1 <span class="sy1">>=</span> f2<span class="br0">)</span> <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></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">not equal? : true
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greater? : false
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less equal? : true
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greater equal? : false</pre></div>
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