194 lines
31 KiB
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194 lines
31 KiB
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<title>operator==, !=, <, <=, >, >=, <=>(std::variant)</title>
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<h1 id="firstHeading" class="firstHeading">operator==, !=, <, <=, >, >=, <=><small>(std::variant)</small></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-variant.html">variant</a></span></div>
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<div>定义于头文件 <code><a href="cpp-header-variant.html"><variant></a></code></div>
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<tr class="t-dcl t-since-cxx17">
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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>... <span class="me1">Types</span> <span class="sy1">></span><br /></span>
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<p><span class="kw4">constexpr</span> <span class="kw4">bool</span> operator<span class="sy1">==</span><span class="br0">(</span> <span class="kw4">const</span> <a href="cpp-utility-variant.html"><span class="kw1085">std::<span class="me2">variant</span></span></a><span class="sy1"><</span>Types...<span class="sy1">></span><span class="sy3">&</span> v,<br /></p>
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<span class="kw4">const</span> <a href="cpp-utility-variant.html"><span class="kw1085">std::<span class="me2">variant</span></span></a><span class="sy1"><</span>Types...<span class="sy1">></span><span class="sy3">&</span> w <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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<td><span class="t-mark-rev t-since-cxx17">(C++17 起)</span></td>
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</tr>
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<tr class="t-dcl t-since-cxx17">
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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>... <span class="me1">Types</span> <span class="sy1">></span><br /></span>
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<p><span class="kw4">constexpr</span> <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-utility-variant.html"><span class="kw1085">std::<span class="me2">variant</span></span></a><span class="sy1"><</span>Types...<span class="sy1">></span><span class="sy3">&</span> v,<br /></p>
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<span class="kw4">const</span> <a href="cpp-utility-variant.html"><span class="kw1085">std::<span class="me2">variant</span></span></a><span class="sy1"><</span>Types...<span class="sy1">></span><span class="sy3">&</span> w <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-since-cxx17">(C++17 起)</span></td>
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</tr>
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<tr class="t-dcl t-since-cxx17">
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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>... <span class="me1">Types</span> <span class="sy1">></span><br /></span>
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<p><span class="kw4">constexpr</span> <span class="kw4">bool</span> operator<span class="sy1"><</span><span class="br0">(</span> <span class="kw4">const</span> <a href="cpp-utility-variant.html"><span class="kw1085">std::<span class="me2">variant</span></span></a><span class="sy1"><</span>Types...<span class="sy1">></span><span class="sy3">&</span> v,<br /></p>
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<span class="kw4">const</span> <a href="cpp-utility-variant.html"><span class="kw1085">std::<span class="me2">variant</span></span></a><span class="sy1"><</span>Types...<span class="sy1">></span><span class="sy3">&</span> w <span class="br0">)</span><span class="sy4">;</span></div>
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</td>
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<td>(3)</td>
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<td><span class="t-mark-rev t-since-cxx17">(C++17 起)</span></td>
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</tr>
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<tr class="t-dcl t-since-cxx17">
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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>... <span class="me1">Types</span> <span class="sy1">></span><br /></span>
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<p><span class="kw4">constexpr</span> <span class="kw4">bool</span> operator<span class="sy1">></span><span class="br0">(</span> <span class="kw4">const</span> <a href="cpp-utility-variant.html"><span class="kw1085">std::<span class="me2">variant</span></span></a><span class="sy1"><</span>Types...<span class="sy1">></span><span class="sy3">&</span> v,<br /></p>
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<span class="kw4">const</span> <a href="cpp-utility-variant.html"><span class="kw1085">std::<span class="me2">variant</span></span></a><span class="sy1"><</span>Types...<span class="sy1">></span><span class="sy3">&</span> w <span class="br0">)</span><span class="sy4">;</span></div>
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</td>
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<td>(4)</td>
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<td><span class="t-mark-rev t-since-cxx17">(C++17 起)</span></td>
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</tr>
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<tr class="t-dcl t-since-cxx17">
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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>... <span class="me1">Types</span> <span class="sy1">></span><br /></span>
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<p><span class="kw4">constexpr</span> <span class="kw4">bool</span> operator<span class="sy1"><=</span><span class="br0">(</span> <span class="kw4">const</span> <a href="cpp-utility-variant.html"><span class="kw1085">std::<span class="me2">variant</span></span></a><span class="sy1"><</span>Types...<span class="sy1">></span><span class="sy3">&</span> v,<br /></p>
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<span class="kw4">const</span> <a href="cpp-utility-variant.html"><span class="kw1085">std::<span class="me2">variant</span></span></a><span class="sy1"><</span>Types...<span class="sy1">></span><span class="sy3">&</span> w <span class="br0">)</span><span class="sy4">;</span></div>
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</td>
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<td>(5)</td>
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<td><span class="t-mark-rev t-since-cxx17">(C++17 起)</span></td>
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</tr>
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<tr class="t-dcl t-since-cxx17">
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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>... <span class="me1">Types</span> <span class="sy1">></span><br /></span>
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<p><span class="kw4">constexpr</span> <span class="kw4">bool</span> operator<span class="sy1">>=</span><span class="br0">(</span> <span class="kw4">const</span> <a href="cpp-utility-variant.html"><span class="kw1085">std::<span class="me2">variant</span></span></a><span class="sy1"><</span>Types...<span class="sy1">></span><span class="sy3">&</span> v,<br /></p>
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<span class="kw4">const</span> <a href="cpp-utility-variant.html"><span class="kw1085">std::<span class="me2">variant</span></span></a><span class="sy1"><</span>Types...<span class="sy1">></span><span class="sy3">&</span> w <span class="br0">)</span><span class="sy4">;</span></div>
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</td>
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<td>(6)</td>
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<td><span class="t-mark-rev t-since-cxx17">(C++17 起)</span></td>
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</tr>
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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>... <span class="me1">Types</span> <span class="sy1">></span><br /></span>
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<p><span class="kw4">constexpr</span> std<span class="sy4">::</span><span class="me2">common_comparison_category_t</span><span class="sy1"><</span><br />
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std<span class="sy4">::</span><span class="me2">compare_three_way_result_t</span><span class="sy1"><</span>Types<span class="sy1">></span>...<span class="sy1">></span><br />
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operator<span class="sy1"><=></span><span class="br0">(</span> <span class="kw4">const</span> <a href="cpp-utility-variant.html"><span class="kw1085">std::<span class="me2">variant</span></span></a><span class="sy1"><</span>Types...<span class="sy1">></span><span class="sy3">&</span> v,<br /></p>
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<span class="kw4">const</span> <a href="cpp-utility-variant.html"><span class="kw1085">std::<span class="me2">variant</span></span></a><span class="sy1"><</span>Types...<span class="sy1">></span><span class="sy3">&</span> w <span class="br0">)</span><span class="sy4">;</span></div>
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</td>
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<td>(7)</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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<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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<div class="t-li1"><span class="t-li">1)</span> <code>variant</code> 的相等运算符：
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<ul>
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<li>若 <span class="t-c"><span class="mw-geshi cpp source-cpp">v.<span class="me1">index</span><span class="br0">(</span><span class="br0">)</span> <span class="sy3">!</span><span class="sy1">=</span> w.<span class="me1">index</span><span class="br0">(</span><span class="br0">)</span></span></span> ，则返回 <code>false</code> ；</li>
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<li>否则，若 <span class="t-c"><span class="mw-geshi cpp source-cpp">v.<span class="me1">valueless_by_exception</span><span class="br0">(</span><span class="br0">)</span></span></span> ，则返回 <code>true</code> ；</li>
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<li>否则返回 <span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">get</span><span class="sy1"><</span>v.<span class="me1">index</span><span class="br0">(</span><span class="br0">)</span><span class="sy1">></span><span class="br0">(</span>v<span class="br0">)</span> <span class="sy1">==</span> std<span class="sy4">::</span><span class="me2">get</span><span class="sy1"><</span>v.<span class="me1">index</span><span class="br0">(</span><span class="br0">)</span><span class="sy1">></span><span class="br0">(</span>w<span class="br0">)</span></span></span> 。若对于任何一个 <code>i</code> ， <span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">get</span><span class="sy1"><</span>i<span class="sy1">></span><span class="br0">(</span>v<span class="br0">)</span> <span class="sy1">==</span> std<span class="sy4">::</span><span class="me2">get</span><span class="sy1"><</span>i<span class="sy1">></span><span class="br0">(</span>w<span class="br0">)</span></span></span> 不是返回值能转换为 <code>bool</code> 的合法表达式，则<span class="t-rev-inl t-until-cxx20"><span>行为未定义</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>程序为谬构</span> <span><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></span></span>。</li>
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</ul>
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</div>
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<div class="t-li1"><span class="t-li">2)</span> <code>variant</code> 的不相等运算符：
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<ul>
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<li>若 <span class="t-c"><span class="mw-geshi cpp source-cpp">v.<span class="me1">index</span><span class="br0">(</span><span class="br0">)</span> <span class="sy3">!</span><span class="sy1">=</span> w.<span class="me1">index</span><span class="br0">(</span><span class="br0">)</span></span></span> ，则返回 <code>true</code> ；</li>
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<li>否则，若 <span class="t-c"><span class="mw-geshi cpp source-cpp">v.<span class="me1">valueless_by_exception</span><span class="br0">(</span><span class="br0">)</span></span></span> ，则返回 <code>false</code> ；</li>
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<li>否则返回 <span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">get</span><span class="sy1"><</span>v.<span class="me1">index</span><span class="br0">(</span><span class="br0">)</span><span class="sy1">></span><span class="br0">(</span>v<span class="br0">)</span> <span class="sy3">!</span><span class="sy1">=</span> std<span class="sy4">::</span><span class="me2">get</span><span class="sy1"><</span>v.<span class="me1">index</span><span class="br0">(</span><span class="br0">)</span><span class="sy1">></span><span class="br0">(</span>w<span class="br0">)</span></span></span> 。若对于任何一个 <code>i</code> ， <span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">get</span><span class="sy1"><</span>i<span class="sy1">></span><span class="br0">(</span>v<span class="br0">)</span> <span class="sy3">!</span><span class="sy1">=</span> std<span class="sy4">::</span><span class="me2">get</span><span class="sy1"><</span>i<span class="sy1">></span><span class="br0">(</span>w<span class="br0">)</span></span></span> 不是返回值能转换为 <code>bool</code> 的合法表达式，则<span class="t-rev-inl t-until-cxx20"><span>行为未定义</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>程序为谬构</span> <span><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></span></span>。</li>
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</ul>
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</div>
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<div class="t-li1"><span class="t-li">3)</span> <code>variant</code> 的小于运算符：
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<ul>
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<li>若 <span class="t-c"><span class="mw-geshi cpp source-cpp">w.<span class="me1">valueless_by_exception</span><span class="br0">(</span><span class="br0">)</span></span></span> ，则返回 <code>false</code> ；</li>
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<li>否则，若 <span class="t-c"><span class="mw-geshi cpp source-cpp">v.<span class="me1">valueless_by_exception</span><span class="br0">(</span><span class="br0">)</span></span></span> ，则返回 <code>true</code> ；</li>
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<li>否则，若 <span class="t-c"><span class="mw-geshi cpp source-cpp">v.<span class="me1">index</span><span class="br0">(</span><span class="br0">)</span> <span class="sy1"><</span> w.<span class="me1">index</span><span class="br0">(</span><span class="br0">)</span></span></span> ，则返回<code>true</code> ；</li>
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<li>否则，若 <span class="t-c"><span class="mw-geshi cpp source-cpp">v.<span class="me1">index</span><span class="br0">(</span><span class="br0">)</span> <span class="sy1">></span> w.<span class="me1">index</span><span class="br0">(</span><span class="br0">)</span></span></span> ，则返回<code>false</code> ；</li>
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<li>否则返回 <span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">get</span><span class="sy1"><</span>v.<span class="me1">index</span><span class="br0">(</span><span class="br0">)</span><span class="sy1">></span><span class="br0">(</span>v<span class="br0">)</span> <span class="sy1"><</span> std<span class="sy4">::</span><span class="me2">get</span><span class="sy1"><</span>v.<span class="me1">index</span><span class="br0">(</span><span class="br0">)</span><span class="sy1">></span><span class="br0">(</span>w<span class="br0">)</span></span></span> 。若对于任何一个 <code>i</code> ， <span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">get</span><span class="sy1"><</span>i<span class="sy1">></span><span class="br0">(</span>v<span class="br0">)</span> <span class="sy1"><</span> std<span class="sy4">::</span><span class="me2">get</span><span class="sy1"><</span>i<span class="sy1">></span><span class="br0">(</span>w<span class="br0">)</span></span></span> 不是返回值能转换为 <code>bool</code> 的合法表达式，则<span class="t-rev-inl t-until-cxx20"><span>行为未定义</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>程序为谬构</span> <span><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></span></span>。</li>
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</ul>
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</div>
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<div class="t-li1"><span class="t-li">4)</span> <code>variant</code> 的大于运算符：
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<ul>
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<li>若 <span class="t-c"><span class="mw-geshi cpp source-cpp">v.<span class="me1">valueless_by_exception</span><span class="br0">(</span><span class="br0">)</span></span></span> ，则返回 <code>false</code> ；</li>
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<li>否则，若 <span class="t-c"><span class="mw-geshi cpp source-cpp">w.<span class="me1">valueless_by_exception</span><span class="br0">(</span><span class="br0">)</span></span></span> ，则返回 <code>true</code> ；</li>
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<li>否则，若 <span class="t-c"><span class="mw-geshi cpp source-cpp">v.<span class="me1">index</span><span class="br0">(</span><span class="br0">)</span> <span class="sy1">></span> w.<span class="me1">index</span><span class="br0">(</span><span class="br0">)</span></span></span> ，则返回 <code>true</code> ；</li>
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<li>否则，若 <span class="t-c"><span class="mw-geshi cpp source-cpp">v.<span class="me1">index</span><span class="br0">(</span><span class="br0">)</span> <span class="sy1"><</span> w.<span class="me1">index</span><span class="br0">(</span><span class="br0">)</span></span></span> ，则返回 <code>false</code> ；</li>
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<li>否则返回 <span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">get</span><span class="sy1"><</span>v.<span class="me1">index</span><span class="br0">(</span><span class="br0">)</span><span class="sy1">></span><span class="br0">(</span>v<span class="br0">)</span> <span class="sy1">></span> std<span class="sy4">::</span><span class="me2">get</span><span class="sy1"><</span>v.<span class="me1">index</span><span class="br0">(</span><span class="br0">)</span><span class="sy1">></span><span class="br0">(</span>w<span class="br0">)</span></span></span> 。若对于任何一个 <code>i</code> ， <span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">get</span><span class="sy1"><</span>i<span class="sy1">></span><span class="br0">(</span>v<span class="br0">)</span> <span class="sy1">></span> std<span class="sy4">::</span><span class="me2">get</span><span class="sy1"><</span>i<span class="sy1">></span><span class="br0">(</span>w<span class="br0">)</span></span></span> 不是返回值能转换为 <code>bool</code> 的合法表达式，则<span class="t-rev-inl t-until-cxx20"><span>行为未定义</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>程序为谬构</span> <span><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></span></span>。</li>
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</ul>
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</div>
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<div class="t-li1"><span class="t-li">5)</span> <code>variant</code> 的小于或等于运算符：
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<ul>
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<li>若 <span class="t-c"><span class="mw-geshi cpp source-cpp">v.<span class="me1">valueless_by_exception</span><span class="br0">(</span><span class="br0">)</span></span></span> ，则返回 <code>true</code> ；</li>
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<li>否则，若 <span class="t-c"><span class="mw-geshi cpp source-cpp">w.<span class="me1">valueless_by_exception</span><span class="br0">(</span><span class="br0">)</span></span></span> ，则返回 <code>false</code> ；</li>
|
|
<li>否则，若 <span class="t-c"><span class="mw-geshi cpp source-cpp">v.<span class="me1">index</span><span class="br0">(</span><span class="br0">)</span> <span class="sy1"><</span> w.<span class="me1">index</span><span class="br0">(</span><span class="br0">)</span></span></span> ，则返回<code>true</code>；</li>
|
|
<li>否则，若 <span class="t-c"><span class="mw-geshi cpp source-cpp">v.<span class="me1">index</span><span class="br0">(</span><span class="br0">)</span> <span class="sy1">></span> w.<span class="me1">index</span><span class="br0">(</span><span class="br0">)</span></span></span> ，则返回<code>false</code>；</li>
|
|
<li>否则返回 <span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">get</span><span class="sy1"><</span>v.<span class="me1">index</span><span class="br0">(</span><span class="br0">)</span><span class="sy1">></span><span class="br0">(</span>v<span class="br0">)</span> <span class="sy1"><=</span> std<span class="sy4">::</span><span class="me2">get</span><span class="sy1"><</span>v.<span class="me1">index</span><span class="br0">(</span><span class="br0">)</span><span class="sy1">></span><span class="br0">(</span>w<span class="br0">)</span></span></span> 。若对于任何一个 <code>i</code> ， <span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">get</span><span class="sy1"><</span>i<span class="sy1">></span><span class="br0">(</span>v<span class="br0">)</span> <span class="sy1"><=</span> std<span class="sy4">::</span><span class="me2">get</span><span class="sy1"><</span>i<span class="sy1">></span><span class="br0">(</span>w<span class="br0">)</span></span></span> 不是返回值能转换为 <code>bool</code> 的合法表达式，则<span class="t-rev-inl t-until-cxx20"><span>行为未定义</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>程序为谬构</span> <span><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></span></span>。</li>
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|
</ul>
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</div>
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<div class="t-li1"><span class="t-li">6)</span> <code>variant</code> 的大于或等于运算符：
|
|
<ul>
|
|
<li>若 <span class="t-c"><span class="mw-geshi cpp source-cpp">w.<span class="me1">valueless_by_exception</span><span class="br0">(</span><span class="br0">)</span></span></span> ，则返回 <code>true</code> ；</li>
|
|
<li>否则，若 <span class="t-c"><span class="mw-geshi cpp source-cpp">v.<span class="me1">valueless_by_exception</span><span class="br0">(</span><span class="br0">)</span></span></span> ，则返回 <code>false</code> ；</li>
|
|
<li>否则，若 <span class="t-c"><span class="mw-geshi cpp source-cpp">v.<span class="me1">index</span><span class="br0">(</span><span class="br0">)</span> <span class="sy1">></span> w.<span class="me1">index</span><span class="br0">(</span><span class="br0">)</span></span></span> ，则返回 <code>true</code> ；</li>
|
|
<li>否则，若 <span class="t-c"><span class="mw-geshi cpp source-cpp">v.<span class="me1">index</span><span class="br0">(</span><span class="br0">)</span> <span class="sy1"><</span> w.<span class="me1">index</span><span class="br0">(</span><span class="br0">)</span></span></span> ，则返回 <code>false</code> ；</li>
|
|
<li>否则返回 <span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">get</span><span class="sy1"><</span>v.<span class="me1">index</span><span class="br0">(</span><span class="br0">)</span><span class="sy1">></span><span class="br0">(</span>v<span class="br0">)</span> <span class="sy1">>=</span> std<span class="sy4">::</span><span class="me2">get</span><span class="sy1"><</span>v.<span class="me1">index</span><span class="br0">(</span><span class="br0">)</span><span class="sy1">></span><span class="br0">(</span>w<span class="br0">)</span></span></span> 。若对于任何一个 <code>i</code> ， <span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">get</span><span class="sy1"><</span>i<span class="sy1">></span><span class="br0">(</span>v<span class="br0">)</span> <span class="sy1">>=</span> std<span class="sy4">::</span><span class="me2">get</span><span class="sy1"><</span>i<span class="sy1">></span><span class="br0">(</span>w<span class="br0">)</span></span></span> 不是返回值能转换为 <code>bool</code> 的合法表达式，则<span class="t-rev-inl t-until-cxx20"><span>行为未定义</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>程序为谬构</span> <span><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></span></span>。</li>
|
|
</ul>
|
|
</div>
|
|
<div class="t-li1"><span class="t-li">7)</span> <code>variant</code> 的三路比较运算符：
|
|
<ul>
|
|
<li>若 <span class="t-c"><span class="mw-geshi cpp source-cpp">v.<span class="me1">valueless_by_exception</span><span class="br0">(</span><span class="br0">)</span></span></span> 与 <span class="t-c"><span class="mw-geshi cpp source-cpp">w.<span class="me1">valueless_by_exception</span><span class="br0">(</span><span class="br0">)</span></span></span> 均为 <code>true</code> ，则返回 <code>std::strong_ordering::equal</code> ；</li>
|
|
<li>否则，若 <span class="t-c"><span class="mw-geshi cpp source-cpp">v.<span class="me1">valueless_by_exception</span><span class="br0">(</span><span class="br0">)</span></span></span> 为 <code>true</code> ，则返回 <code>std::strong_ordering::less</code> ；</li>
|
|
<li>否则，若 <span class="t-c"><span class="mw-geshi cpp source-cpp">w.<span class="me1">valueless_by_exception</span><span class="br0">(</span><span class="br0">)</span></span></span> 为 <code>true</code> ，则返回 <code>std::strong_ordering::greater</code> ；</li>
|
|
<li>否则，若 <span class="t-c"><span class="mw-geshi cpp source-cpp">v.<span class="me1">index</span><span class="br0">(</span><span class="br0">)</span> <span class="sy3">!</span><span class="sy1">=</span> w.<span class="me1">index</span><span class="br0">(</span><span class="br0">)</span></span></span> ，则返回 <span class="t-c"><span class="mw-geshi cpp source-cpp">v.<span class="me1">index</span><span class="br0">(</span><span class="br0">)</span> <span class="sy1"><=></span> w.<span class="me1">index</span><span class="br0">(</span><span class="br0">)</span></span></span> ；</li>
|
|
<li>否则等价于 <span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">get</span><span class="sy1"><</span>v.<span class="me1">index</span><span class="br0">(</span><span class="br0">)</span><span class="sy1">></span><span class="br0">(</span>v<span class="br0">)</span> <span class="sy1"><=></span> std<span class="sy4">::</span><span class="me2">get</span><span class="sy1"><</span>v.<span class="me1">index</span><span class="br0">(</span><span class="br0">)</span><span class="sy1">></span><span class="br0">(</span>w<span class="br0">)</span></span></span> 。</li>
|
|
</ul>
|
|
</div>
|
|
<h3><span class="mw-headline" id=".E5.8F.82.E6.95.B0">参数</span></h3>
|
|
<table class="t-par-begin">
|
|
<tr class="t-par">
|
|
<td>v,w</td>
|
|
<td>-</td>
|
|
<td>要比较的 <code>variant</code></td>
|
|
</tr>
|
|
</table>
|
|
<h3><span class="mw-headline" id=".E8.BF.94.E5.9B.9E.E5.80.BC">返回值</span></h3>
|
|
<p>描述于上的比较结果。</p>
|
|
<h3><span class="mw-headline" id=".E7.A4.BA.E4.BE.8B">示例</span></h3>
|
|
<table class="metadata plainlinks ambox mbox-small-left ambox-notice" style="">
|
|
<tr>
|
|
<td class="mbox-empty-cell"></td>
|
|
<td class="mbox-text" style="">本节未完成<br />
|
|
原因：暂无示例</td>
|
|
</tr>
|
|
</table>
|
|
<h3><span class="mw-headline" id=".E5.8F.82.E9.98.85">参阅</span></h3>
|
|
<table class="t-dsc-begin">
|
|
<tr class="t-dsc">
|
|
<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="cpp-utility-optional-operator_cmp.html"><span class="t-lines"><span>operator==</span><span>operator!=</span><span>operator<</span><span>operator<=</span><span>operator></span><span>operator>=</span><span>operator<=></span></span></a></div>
|
|
<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx17">(C++17)</span></span><span><span class="t-mark-rev t-since-cxx17">(C++17)</span></span><span><span class="t-mark-rev t-since-cxx17">(C++17)</span></span><span><span class="t-mark-rev t-since-cxx17">(C++17)</span></span><span><span class="t-mark-rev t-since-cxx17">(C++17)</span></span><span><span class="t-mark-rev t-since-cxx17">(C++17)</span></span><span><span class="t-mark-rev t-since-cxx20">(C++20)</span></span></span></div>
|
|
</div>
|
|
</td>
|
|
<td>比较 <code>optional</code> 对象<br />
|
|
<span class="t-mark">(函数模板)</span></td>
|
|
</tr>
|
|
</table>
|
|
</div>
|
|
<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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