142 lines
13 KiB
HTML
142 lines
13 KiB
HTML
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<title>std::filesystem::path::compare</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_filesystem_path_compare 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::filesystem::path::</span>compare</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-filesystem.html">filesystem</a>‎ | <a href="cpp-filesystem-path.html">path</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><span class="mw-geshi cpp source-cpp"><span class="kw4">int</span> compare<span class="br0">(</span> <span class="kw4">const</span> path<span class="sy3">&</span> p <span class="br0">)</span> <span class="kw4">const</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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<div><span class="mw-geshi cpp source-cpp"><span class="kw4">int</span> compare<span class="br0">(</span> <span class="kw4">const</span> string_type<span class="sy3">&</span> str <span class="br0">)</span> <span class="kw4">const</span><span class="sy4">;</span><br />
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<span class="kw4">int</span> compare<span class="br0">(</span> <a href="cpp-string-basic_string_view.html"><span class="kw1246">std::<span class="me2">basic_string_view</span></span></a><span class="sy1"><</span>value_type<span class="sy1">></span> str <span class="br0">)</span> <span class="kw4">const</span><span class="sy4">;</span></span></div>
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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 class="t-dcl t-since-cxx17">
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<div><span class="mw-geshi cpp source-cpp"><span class="kw4">int</span> compare<span class="br0">(</span> <span class="kw4">const</span> value_type<span class="sy2">*</span> s <span class="br0">)</span> <span class="kw4">const</span><span class="sy4">;</span></span></div>
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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 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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</tbody>
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</table>
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<p>比较 <code>path</code> 与另一 <code>path</code> 的字典表示。</p>
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<div class="t-li1"><span class="t-li">1)</span> 若 <span class="t-c"><span class="mw-geshi cpp source-cpp">root_name<span class="br0">(</span><span class="br0">)</span>.<span class="me1">native</span><span class="br0">(</span><span class="br0">)</span>.<span class="me1">compare</span><span class="br0">(</span>p.<span class="me1">root_name</span><span class="br0">(</span><span class="br0">)</span>.<span class="me1">native</span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span></span></span> 非零，则返回该值。</div>
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<div class="t-li1"><span class="t-li"></span> 否则若 <span class="t-c"><span class="mw-geshi cpp source-cpp">has_root_directory<span class="br0">(</span><span class="br0">)</span> <span class="sy3">!</span><span class="sy1">=</span> p.<span class="me1">has_root_directory</span><span class="br0">(</span><span class="br0">)</span></span></span> ，则若 <a href="cpp-filesystem-path-has_path.html"><code>has_root_directory()</code></a> 为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">false</span></span></span> 则返回小于零的值，否则返回大于零的值。</div>
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<div class="t-li1"><span class="t-li"></span> 否则返回比较小于、等于或大于 <span class="texhtml" style="white-space: nowrap;">0</span> 的值，若 <code>path</code> 的相对部分 (<a href="cpp-filesystem-path-relative_path.html"><code>relative_path()</code></a>) 分别按字典序小于、等于或大于 <code>p</code> 的相对部分 (<span class="t-c"><span class="mw-geshi cpp source-cpp">p.<span class="me1">relative_path</span><span class="br0">(</span><span class="br0">)</span></span></span>) 。逐元素进行比较，如同从<a href="cpp-filesystem-path-begin.html"><code>begin()</code></a> 到 <a href="cpp-filesystem-path-begin.html"><code>end()</code></a> 迭代 <code>path</code> 。</div>
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<div class="t-li1"><span class="t-li">2)</span> 等价于 <span class="t-c"><span class="mw-geshi cpp source-cpp">compare<span class="br0">(</span>path<span class="br0">(</span>str<span class="br0">)</span><span class="br0">)</span></span></span> 。</div>
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<div class="t-li1"><span class="t-li">3)</span> 等价于 <span class="t-c"><span class="mw-geshi cpp source-cpp">compare<span class="br0">(</span>path<span class="br0">(</span>s<span class="br0">)</span><span class="br0">)</span></span></span> 。</div>
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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>p</td>
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<td>-</td>
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<td>要比较的 <code>path</code></td>
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</tr>
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<tr class="t-par">
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<td>str</td>
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<td>-</td>
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<td>表示要比较的表示路径的字符串或字符串视图</td>
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</tr>
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<tr class="t-par">
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<td>s</td>
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<td>-</td>
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<td>表示要比较的路径的空终止字符串</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>若 <code>path</code> 按字典序小于给定 <code>path</code> 则为小于 <span class="texhtml" style="white-space: nowrap;">0</span> 的值。</p>
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<p>若 <code>path</code> 按字典序等于给定 <code>path</code> 则为等于 <span class="texhtml" style="white-space: nowrap;">0</span> 的值。</p>
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<p>若 <code>path</code> 按字典序大于给定 <code>path</code> 则为大于 <span class="texhtml" style="white-space: nowrap;">0</span> 的值。</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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<div class="t-li1"><span class="t-li">2-3)</span> 可能抛出实现定义的异常。</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>对于双路比较，<a href="cpp-filesystem-path-operator_cmp.html">二元运算符</a>可能更适合。</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 <filesystem></span>
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<span class="kw1">namespace</span> fs <span class="sy1">=</span> std<span class="sy4">::</span><span class="me2">filesystem</span><span class="sy4">;</span>
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<span class="kw4">void</span> demo<span class="br0">(</span><span class="kw4">int</span> rc, fs<span class="sy4">::</span><span class="me2">path</span> p1, fs<span class="sy4">::</span><span class="me2">path</span> p2<span class="br0">)</span> <span class="br0">{</span>
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<span class="kw1">if</span><span class="br0">(</span>rc <span class="sy1"><</span> <span class="nu0">0</span><span class="br0">)</span> <a href="cpp-io-cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> p1 <span class="sy1"><<</span> <span class="st0">" < "</span> <span class="sy1"><<</span> p2 <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
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<span class="kw1">else</span> <span class="kw1">if</span><span class="br0">(</span>rc <span class="sy1">></span> <span class="nu0">0</span><span class="br0">)</span> <a href="cpp-io-cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> p1 <span class="sy1"><<</span> <span class="st0">" > "</span> <span class="sy1"><<</span> p2 <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
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<span class="kw1">else</span> <span class="kw1">if</span><span class="br0">(</span>rc <span class="sy1">==</span> <span class="nu0">0</span><span class="br0">)</span> <a href="cpp-io-cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> p1 <span class="sy1"><<</span> <span class="st0">" == "</span> <span class="sy1"><<</span> p2 <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>
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<span class="kw4">int</span> main<span class="br0">(</span><span class="br0">)</span> <span class="br0">{</span>
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fs<span class="sy4">::</span><span class="me2">path</span> p1 <span class="sy1">=</span> <span class="st0">"/a/b/"</span><span class="sy4">;</span> <span class="co1">// 对于字典序迭代如同 "/a/b"</span>
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fs<span class="sy4">::</span><span class="me2">path</span> p2 <span class="sy1">=</span> <span class="st0">"/a/b/c"</span><span class="sy4">;</span>
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demo<span class="br0">(</span>p1.<span class="me1">compare</span><span class="br0">(</span>p2<span class="br0">)</span>, p1, p2<span class="br0">)</span><span class="sy4">;</span>
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demo<span class="br0">(</span>p1.<span class="me1">compare</span><span class="br0">(</span><span class="st0">"a/c"</span><span class="br0">)</span>, p1, <span class="st0">"a/c"</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 绝对路径先序于相对路径</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">"/a/b/" < "/a/b/c"
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"/a/b/" > "a/c"</pre></div>
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</div>
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</div>
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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/issue2936">LWG 2936</a></td>
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<td>C++17</td>
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<td>直接比较所有路径元素</td>
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<td>分开处理根名与根目录</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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<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-path-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>
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<div><span class="t-lines"><span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 前)</span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 前)</span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 前)</span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 前)</span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 前)</span></span><span><span class="t-mark-rev t-since-cxx20">(C++20)</span></span></span></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<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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