271 lines
23 KiB
HTML
271 lines
23 KiB
HTML
<!DOCTYPE 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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<head><meta http-equiv="x-ua-compatible" content="ie=edge">
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<title>std::filesystem::is_fifo</title>
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<link rel="stylesheet" href="site_modules.css" />
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_filesystem_is_fifo skin-cppreference2 action-view cpp-navbar">
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<div id="cpp-content-base">
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<div id="content"><a id="top"></a>
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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::filesystem::</span>is_fifo</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></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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<td>
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<div>定义于头文件 <code><a href="cpp-header-filesystem.html"><filesystem></a></code></div>
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</td>
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<td></td>
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<td></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">bool</span> is_fifo<span class="br0">(</span> <a href="cpp-filesystem-file_status.html"><span class="kw2206">std::<span class="me2">filesystem</span><span class="sy4">::</span><span class="me2">file_status</span></span></a> s <span class="br0">)</span> <span class="kw1">noexcept</span><span class="sy4">;</span></span></div>
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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">bool</span> is_fifo<span class="br0">(</span> <span class="kw4">const</span> <a href="cpp-filesystem-path.html"><span class="kw2199">std::<span class="me2">filesystem</span><span class="sy4">::</span><span class="me2">path</span></span></a><span class="sy3">&</span> p <span class="br0">)</span><span class="sy4">;</span><br />
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<span class="kw4">bool</span> is_fifo<span class="br0">(</span> <span class="kw4">const</span> <a href="cpp-filesystem-path.html"><span class="kw2199">std::<span class="me2">filesystem</span><span class="sy4">::</span><span class="me2">path</span></span></a><span class="sy3">&</span> p, <a href="cpp-error-error_code.html"><span class="kw877">std::<span class="me2">error_code</span></span></a><span class="sy3">&</span> ec <span class="br0">)</span> <span class="kw1">noexcept</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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<td></td>
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<p>检查给定文件状态或路径是否对应一个 FIFO 或管道文件，以 POSIX <a rel="nofollow" class="external text" href="http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/sys_stat.h.html">S_ISFIFO</a> 确定。</p>
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<div class="t-li1"><span class="t-li">1)</span> 等价于 <span class="t-c"><span class="mw-geshi cpp source-cpp">s.<span class="me1">type</span><span class="br0">(</span><span class="br0">)</span> <span class="sy1">==</span> file_type<span class="sy4">::</span><span class="me2">fifo</span></span></span> 。</div>
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<div class="t-li1"><span class="t-li">2)</span> 分别等价于 <span class="t-c"><span class="mw-geshi cpp source-cpp">is_fifo<span class="br0">(</span>status<span class="br0">(</span>p<span class="br0">)</span><span class="br0">)</span></span></span> 或 <span class="t-c"><span class="mw-geshi cpp source-cpp">is_fifo<span class="br0">(</span>status<span class="br0">(</span>p, ec<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>s</td>
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<td>-</td>
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<td>要检查的文件状态</td>
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</tr>
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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>要查询的状态</td>
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</tr>
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<tr class="t-par">
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<td>ec</td>
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<td>-</td>
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<td>错误情况下修改的错误码</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>p</code> 所指示的文件或 <code>s</code> 所指示的类型指代 FIFO 管道则为 <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> 。不抛出重载在错误发生时返回 <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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<div class="t-li1"><span class="t-li">2)</span> 不接受 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-error-error_code.html"><span class="kw877">std::<span class="me2">error_code</span></span></a><span class="sy3">&</span></span></span> 参数的重载在底层 OS API 错误时抛出 <a href="cpp-filesystem-filesystem_error.html"><tt>filesystem_error</tt></a> ，以第一 path 参数 <code>p</code> 和作为错误码参数的 OS 错误码构造。若 OS API 调用失败，则接受 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-error-error_code.html"><span class="kw877">std::<span class="me2">error_code</span></span></a><span class="sy3">&</span></span></span> 参数的重载设置该参数为 OS API 错误码，而若不出现错误则执行 <span class="t-c"><span class="mw-geshi cpp source-cpp">ec.<span class="me1">clear</span><span class="br0">(</span><span class="br0">)</span></span></span> 。若内存分配失败，则任何不标记为 <code>noexcept</code> 的重载可能抛出 <span class="t-lc"><a href="cpp-memory-new-bad_alloc.html">std::bad_alloc</a></span> 。</div>
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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 <fstream></span>
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<span class="co2">#include <cstdio></span>
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<span class="co2">#include <cstring></span>
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<span class="co2">#include <filesystem></span>
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<span class="co2">#include <unistd.h></span>
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<span class="co2">#include <sys/socket.h></span>
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<span class="co2">#include <sys/un.h></span>
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<span class="co2">#include <sys/stat.h></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_status<span class="br0">(</span><span class="kw4">const</span> fs<span class="sy4">::</span><span class="me2">path</span><span class="sy3">&</span> p, fs<span class="sy4">::</span><span class="me2">file_status</span> s<span class="br0">)</span>
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<span class="br0">{</span>
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<a href="cpp-io-cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> p<span class="sy4">;</span>
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<span class="co1">// 变体： switch(s.type()) { case fs::file_type::regular: ...}</span>
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<span class="kw1">if</span><span class="br0">(</span>fs<span class="sy4">::</span><span class="me2">is_regular_file</span><span class="br0">(</span>s<span class="br0">)</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> <span class="st0">" is a regular file<span class="es1">\n</span>"</span><span class="sy4">;</span>
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<span class="kw1">if</span><span class="br0">(</span>fs<span class="sy4">::</span><span class="me2">is_directory</span><span class="br0">(</span>s<span class="br0">)</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> <span class="st0">" is a directory<span class="es1">\n</span>"</span><span class="sy4">;</span>
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<span class="kw1">if</span><span class="br0">(</span>fs<span class="sy4">::</span><span class="me2">is_block_file</span><span class="br0">(</span>s<span class="br0">)</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> <span class="st0">" is a block device<span class="es1">\n</span>"</span><span class="sy4">;</span>
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<span class="kw1">if</span><span class="br0">(</span>fs<span class="sy4">::</span><span class="me2">is_character_file</span><span class="br0">(</span>s<span class="br0">)</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> <span class="st0">" is a character device<span class="es1">\n</span>"</span><span class="sy4">;</span>
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<span class="kw1">if</span><span class="br0">(</span>fs<span class="sy4">::</span><span class="me2">is_fifo</span><span class="br0">(</span>s<span class="br0">)</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> <span class="st0">" is a named IPC pipe<span class="es1">\n</span>"</span><span class="sy4">;</span>
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<span class="kw1">if</span><span class="br0">(</span>fs<span class="sy4">::</span><span class="me2">is_socket</span><span class="br0">(</span>s<span class="br0">)</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> <span class="st0">" is a named IPC socket<span class="es1">\n</span>"</span><span class="sy4">;</span>
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<span class="kw1">if</span><span class="br0">(</span>fs<span class="sy4">::</span><span class="me2">is_symlink</span><span class="br0">(</span>s<span class="br0">)</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> <span class="st0">" is a symlink<span class="es1">\n</span>"</span><span class="sy4">;</span>
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<span class="kw1">if</span><span class="br0">(</span><span class="sy3">!</span>fs<span class="sy4">::</span><span class="me2">exists</span><span class="br0">(</span>s<span class="br0">)</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> <span class="st0">" does not exist<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>
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<span class="br0">{</span>
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<span class="co1">// 创建不同种类的文件</span>
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fs<span class="sy4">::</span><span class="me2">create_directory</span><span class="br0">(</span><span class="st0">"sandbox"</span><span class="br0">)</span><span class="sy4">;</span>
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<a href="cpp-io-basic_ofstream.html"><span class="kw1733">std::<span class="me2">ofstream</span></span></a><span class="br0">(</span><span class="st0">"sandbox/file"</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 创建常规文件</span>
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fs<span class="sy4">::</span><span class="me2">create_directory</span><span class="br0">(</span><span class="st0">"sandbox/dir"</span><span class="br0">)</span><span class="sy4">;</span>
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mkfifo<span class="br0">(</span><span class="st0">"sandbox/pipe"</span>, <span class="nu8">0644</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="kw1">struct</span> sockaddr_un addr<span class="sy4">;</span>
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addr.<span class="me1">sun_family</span> <span class="sy1">=</span> AF_UNIX<span class="sy4">;</span>
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<a href="cpp-string-byte-strcpy.html"><span class="kw1140">std::<span class="me2">strcpy</span></span></a><span class="br0">(</span>addr.<span class="me1">sun_path</span>, <span class="st0">"sandbox/sock"</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="kw4">int</span> fd <span class="sy1">=</span> socket<span class="br0">(</span>PF_UNIX, SOCK_STREAM, <span class="nu0">0</span><span class="br0">)</span><span class="sy4">;</span>
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bind<span class="br0">(</span>fd, <span class="br0">(</span><span class="kw1">struct</span> sockaddr<span class="sy2">*</span><span class="br0">)</span><span class="sy3">&</span>addr, sizeof addr<span class="br0">)</span><span class="sy4">;</span>
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fs<span class="sy4">::</span><span class="me2">create_symlink</span><span class="br0">(</span><span class="st0">"file"</span>, <span class="st0">"sandbox/symlink"</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="co1">// 演示不同的状态访问器</span>
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<span class="kw1">for</span><span class="br0">(</span><span class="kw4">auto</span> it <span class="sy1">=</span> fs<span class="sy4">::</span><span class="me2">directory_iterator</span><span class="br0">(</span><span class="st0">"sandbox"</span><span class="br0">)</span><span class="sy4">;</span> it <span class="sy3">!</span><span class="sy1">=</span> fs<span class="sy4">::</span><span class="me2">directory_iterator</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span> <span class="sy2">++</span>it<span class="br0">)</span>
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demo_status<span class="br0">(</span><span class="sy2">*</span>it, it<span class="sy2">-</span><span class="sy1">></span>symlink_status<span class="br0">(</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 从 directory_entry 使用缓冲的状态</span>
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demo_status<span class="br0">(</span><span class="st0">"dev/null"</span>, fs<span class="sy4">::</span><span class="me2">status</span><span class="br0">(</span><span class="st0">"/dev/null"</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 直接调用 status</span>
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demo_status<span class="br0">(</span><span class="st0">"dev/sda"</span>, fs<span class="sy4">::</span><span class="me2">status</span><span class="br0">(</span><span class="st0">"/dev/sda"</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
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demo_status<span class="br0">(</span><span class="st0">"sandbox/no"</span>, fs<span class="sy4">::</span><span class="me2">status</span><span class="br0">(</span><span class="st0">"/sandbox/no"</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="co1">// 清理</span>
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close<span class="br0">(</span>fd<span class="br0">)</span><span class="sy4">;</span>
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fs<span class="sy4">::</span><span class="me2">remove_all</span><span class="br0">(</span><span class="st0">"sandbox"</span><span class="br0">)</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>可能的输出：</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">"sandbox/file" is a regular file
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"sandbox/dir" is a directory
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"sandbox/pipe" is a named IPC pipe
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"sandbox/sock" is a named IPC socket
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"sandbox/symlink" is a symlink
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"dev/null" is a character device
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"dev/sda" is a block device
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"sandbox/no" does not exist</pre></div>
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</div>
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</div>
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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-status.html"><span class="t-lines"><span>status</span><span>symlink_status</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><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>确定文件属性<br />
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确定文件属性，检查符号链接目标<br />
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<span class="t-mark">(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-file_status.html"><span class="t-lines"><span>file_status</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>表示文件类型及权限<br />
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<span class="t-mark">(类)</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-status_known.html"><span class="t-lines"><span>status_known</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>检查文件状态是否已知<br />
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<span class="t-mark">(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-is_block_file.html"><span class="t-lines"><span>is_block_file</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>检查给定的路径是否表示块设备<br />
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<span class="t-mark">(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-is_character_file.html"><span class="t-lines"><span>is_character_file</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>检查给定的路径是否表示字符设备<br />
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<span class="t-mark">(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-is_directory.html"><span class="t-lines"><span>is_directory</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>检查给定的路径是否表示一个目录<br />
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<span class="t-mark">(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-is_other.html"><span class="t-lines"><span>is_other</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>检查参数是否表示一个<i>其他</i>文件<br />
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<span class="t-mark">(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-is_regular_file.html"><span class="t-lines"><span>is_regular_file</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>检查参数是否表示一个常规文件<br />
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<span class="t-mark">(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-is_socket.html"><span class="t-lines"><span>is_socket</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>检查参数是否表示一个具名 IPC 套接字<br />
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<span class="t-mark">(函数)</span></td>
|
|
</tr>
|
|
<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-is_symlink.html"><span class="t-lines"><span>is_symlink</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>检查参数是否表示一个符号链接<br />
|
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<span class="t-mark">(函数)</span></td>
|
|
</tr>
|
|
<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-exists.html"><span class="t-lines"><span>exists</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>检查路径是否指代既存的文件系统对象<br />
|
|
<span class="t-mark">(函数)</span></td>
|
|
</tr>
|
|
<tr class="t-dsc">
|
|
<td>
|
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<div class="t-dsc-member-div">
|
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<div><a href="cpp-filesystem-directory_entry-is_fifo.html"><span class="t-lines"><span>is_fifo</span></span></a></div>
|
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</div>
|
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</td>
|
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<td>检查 directory_entry 是否代表具名管道<br />
|
|
<span class="t-mark">(<code>std::filesystem::directory_entry</code> 的公开成员函数)</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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</div>
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</div>
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</body>
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</html>
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