165 lines
15 KiB
HTML
165 lines
15 KiB
HTML
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<title>operator==,!=,<,<=,>,>=,<=>(std::filesystem::path)</title>
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<h1 id="firstHeading" class="firstHeading">operator==,!=,<,<=,>,>=,<=><span style="font-size:0.7em; line-height:130%">(std::filesystem::path)</span></h1>
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<div id="contentSub"><span class="subpages">< <a href="cpp.html">cpp</a>‎ | <a href="cpp-filesystem.html">filesystem</a>‎ | <a href="cpp-filesystem-path.html">path</a></span></div>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">friend</span> <span class="kw4">bool</span> operator<span class="sy1">==</span><span class="br0">(</span> <span class="kw4">const</span> path<span class="sy3">&</span> lhs, <span class="kw4">const</span> path<span class="sy3">&</span> rhs <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><span class="t-mark-rev t-since-cxx17">(C++17 起)</span></td>
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<tr class="t-dcl t-since-cxx17 t-until-cxx20">
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">friend</span> <span class="kw4">bool</span> operator<span class="sy3">!</span><span class="sy1">=</span><span class="br0">(</span> <span class="kw4">const</span> path<span class="sy3">&</span> lhs, <span class="kw4">const</span> path<span class="sy3">&</span> rhs <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><span class="t-mark-rev t-since-cxx17">(C++17 起)</span><br />
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<span class="t-mark-rev t-until-cxx20">(C++20 前)</span></td>
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</tr>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">friend</span> <span class="kw4">bool</span> operator<span class="sy1"><</span><span class="br0">(</span> <span class="kw4">const</span> path<span class="sy3">&</span> lhs, <span class="kw4">const</span> path<span class="sy3">&</span> rhs <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>(3)</td>
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<td><span class="t-mark-rev t-since-cxx17">(C++17 起)</span><br />
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<span class="t-mark-rev t-until-cxx20">(C++20 前)</span></td>
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</tr>
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<tr class="t-dcl t-since-cxx17 t-until-cxx20">
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">friend</span> <span class="kw4">bool</span> operator<span class="sy1"><=</span><span class="br0">(</span> <span class="kw4">const</span> path<span class="sy3">&</span> lhs, <span class="kw4">const</span> path<span class="sy3">&</span> rhs <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>(4)</td>
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<td><span class="t-mark-rev t-since-cxx17">(C++17 起)</span><br />
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<span class="t-mark-rev t-until-cxx20">(C++20 前)</span></td>
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</tr>
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<tr class="t-dcl t-since-cxx17 t-until-cxx20">
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">friend</span> <span class="kw4">bool</span> operator<span class="sy1">></span><span class="br0">(</span> <span class="kw4">const</span> path<span class="sy3">&</span> lhs, <span class="kw4">const</span> path<span class="sy3">&</span> rhs <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>(5)</td>
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<td><span class="t-mark-rev t-since-cxx17">(C++17 起)</span><br />
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<span class="t-mark-rev t-until-cxx20">(C++20 前)</span></td>
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</tr>
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<tr class="t-dcl t-since-cxx17 t-until-cxx20">
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">friend</span> <span class="kw4">bool</span> operator<span class="sy1">>=</span><span class="br0">(</span> <span class="kw4">const</span> path<span class="sy3">&</span> lhs, <span class="kw4">const</span> path<span class="sy3">&</span> rhs <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>(6)</td>
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<td><span class="t-mark-rev t-since-cxx17">(C++17 起)</span><br />
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<span class="t-mark-rev t-until-cxx20">(C++20 前)</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">friend</span> std<span class="sy4">::</span><span class="me2">strong_ordering</span><br />
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operator<span class="sy1"><=></span><span class="br0">(</span> <span class="kw4">const</span> path<span class="sy3">&</span> lhs, <span class="kw4">const</span> path<span class="sy3">&</span> rhs <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>(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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<p>以字典序比较二个<code>path</code> 。</p>
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<div class="t-li1"><span class="t-li">1)</span> 检查 <code>lhs</code> 与 <code>rhs</code> 是否相等。等价于 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy3">!</span><span class="br0">(</span>lhs <span class="sy1"><</span> rhs<span class="br0">)</span> <span class="sy3">&&</span> <span class="sy3">!</span><span class="br0">(</span>rhs <span class="sy1"><</span> lhs<span class="br0">)</span></span></span> 。</div>
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<div class="t-li1"><span class="t-li">2)</span> 检查 <code>lhs</code> 与 <code>rhs</code> 是否不相等，等价于 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy3">!</span><span class="br0">(</span>lhs <span class="sy1">==</span> rhs<span class="br0">)</span></span></span> 。</div>
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<div class="t-li1"><span class="t-li">3)</span> 检查 <code>lhs</code> 是否小于 <code>rhs</code> 。等价于 <span class="t-c"><span class="mw-geshi cpp source-cpp">lhs.<span class="me1">compare</span><span class="br0">(</span>rhs<span class="br0">)</span> <span class="sy1"><</span> <span class="nu0">0</span></span></span> 。</div>
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<div class="t-li1"><span class="t-li">4)</span> 检查 <code>lhs</code> 是否小于或等于 <code>rhs</code> 。等价于 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy3">!</span><span class="br0">(</span>rhs <span class="sy1"><</span> lhs<span class="br0">)</span></span></span> 。</div>
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<div class="t-li1"><span class="t-li">5)</span> 检查 <code>lhs</code> 是否大于 <code>rhs</code> 。等价于 <span class="t-c"><span class="mw-geshi cpp source-cpp">rhs <span class="sy1"><</span> lhs</span></span> 。</div>
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<div class="t-li1"><span class="t-li">6)</span> 检查 <code>lhs</code> 是否大于或等于 <code>rhs</code> 。等价于 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy3">!</span><span class="br0">(</span>lhs <span class="sy1"><</span> rhs<span class="br0">)</span></span></span> 。</div>
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<div class="t-li1"><span class="t-li">7)</span> 获得 <code>lhs</code> 与 <code>rhs</code> 的三路比较结果。等价于 <span class="t-c"><span class="mw-geshi cpp source-cpp">lhs.<span class="me1">compare</span><span class="br0">(</span>rhs<span class="br0">)</span> <span class="sy1"><=></span> <span class="nu0">0</span></span></span> 。</div>
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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::filesystem::path</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。这阻止 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw1">using</span> <span class="kw1">namespace</span> std<span class="sy4">::</span><span class="me2">filesystem</span><span class="sy4">;</span></span></span> <i>using 指令</i>存在的情况下的不想要的转换。</p>
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<table class="t-rev-begin">
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<tr class="t-rev t-since-cxx20">
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<td>
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<p><code><</code>、 <code><=</code>、 <code>></code>、 <code>>=</code> 及 <code>!=</code> 运算符分别从 <code>operator<=></code> 与 <code>operator==</code> <a href="cpp-language-operators.html#.E5.85.B3.E7.B3.BB.E8.BF.90.E7.AE.97.E7.AC.A6">合成</a>。</p>
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</td>
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<td><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></td>
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</tr>
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</table>
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<h3><span class="mw-headline" id=".E5.8F.82.E6.95.B0">参数</span></h3>
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<table class="t-par-begin">
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<tr class="t-par">
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<td>lhs, rhs</td>
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<td>-</td>
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<td>要比较的路径</td>
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</tr>
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</table>
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<h3><span class="mw-headline" id=".E8.BF.94.E5.9B.9E.E5.80.BC">返回值</span></h3>
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<div class="t-li1"><span class="t-li">1-6)</span> 若对应比较关系成立则返回 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">true</span></span></span> ，否则返回 <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">7)</span> 若 <code>lhs</code> 小于 <code>rhs</code> 则为 <span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">strong_ordering</span><span class="sy4">::</span><span class="me2">less</span></span></span> ，否则若 <code>rhs</code> 小于 <code>lhs</code> 则为 <span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">strong_ordering</span><span class="sy4">::</span><span class="me2">greater</span></span></span> ，否则为 <span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">string_ordering</span><span class="sy4">::</span><span class="me2">equal</span></span></span> 。</div>
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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>路径相等与等价有不同语义。</p>
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<p>相等情况下，以 <code>operator==</code> 确定，只比较字典表示。从而 <span class="t-c"><span class="mw-geshi cpp source-cpp">path<span class="br0">(</span><span class="st0">"a"</span><span class="br0">)</span> <span class="sy1">==</span> path<span class="br0">(</span><span class="st0">"b"</span><span class="br0">)</span></span></span> 决不可能为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">true</span></span></span> 。</p>
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<p>等价情况下，以 <span class="t-lc"><a href="cpp-filesystem-equivalent.html">std::filesystem::equivalent()</a></span> 确定，检查二个路径是否<i>解析</i>到同一文件系统对象。从而若路径解析到同一文件，则 <span class="t-c"><span class="mw-geshi cpp source-cpp">equivalent<span class="br0">(</span><span class="st0">"a"</span>, <span class="st0">"b"</span><span class="br0">)</span></span></span> 将返回 <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=".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=".E7.BC.BA.E9.99.B7.E6.8A.A5.E5.91.8A">缺陷报告</span></h3>
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<p>下列更改行为的缺陷报告追溯地应用于以前出版的 C++ 标准。</p>
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<table class="dsctable" style="font-size:0.8em">
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<tr>
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<th>DR</th>
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<th>应用于</th>
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<th>出版时的行为</th>
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<th>正确行为</th>
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</tr>
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<tr>
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<td><a rel="nofollow" class="external text" href="https://cplusplus.github.io/LWG/issue3065">LWG 3065</a></td>
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<td>C++17</td>
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<td>允许 <i>using 指令</i>存在的情况下比较任何能转换成 <code>path</code> 的类型</td>
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<td>使之为隐藏的友元</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>
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<table class="t-dsc-begin">
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<td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-filesystem-path-compare.html"><span class="t-lines"><span>compare</span></span></a></div>
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</div>
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</td>
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<td>以字典序比较二个路径的字典表示<br />
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<span class="t-mark">(公开成员函数)</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><a href="cpp-filesystem-equivalent.html"><span class="t-lines"><span>equivalent</span></span></a></div>
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<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx17">(C++17)</span></span></span></div>
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</div>
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</td>
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<td>检查两个路径是否指代同一文件系统对象<br />
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<span class="t-mark">(函数)</span></td>
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</tr>
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</table>
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</div>
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<div class="visualClear"></div>
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</div>
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</body>
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