113 lines
9.6 KiB
HTML
113 lines
9.6 KiB
HTML
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<title>std::tmpfile</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_io_c_tmpfile 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::</span>tmpfile</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-io.html">io</a>‎ | <a href="cpp-io-c.html">c</a></span></div>
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<div id="mw-content-text" lang="zh" dir="ltr" class="mw-content-ltr" xml:lang="zh">
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<table class="t-dcl-begin">
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<div>定义于头文件 <code><a href="cpp-header-cstdio.html"><cstdio></a></code></div>
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<td></td>
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<div><span class="mw-geshi cpp source-cpp"><a href="cpp-io-c.html"><span class="kw1876">std::<span class="me2">FILE</span></span></a><span class="sy2">*</span> tmpfile<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span></span></div>
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<p>创建并打开临时文件。</p>
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<p>该文件作为二进制文件、更新模式（如同为 <span class="t-lc"><a href="cpp-io-c-fopen.html">std::fopen</a></span> 以 <code>"wb+"</code> 模式）打开。该文件的文件名保证在文件系统中唯一。至少可以在程序的生存期内能打开 <span class="t-lc"><a href="cpp-io-c.html">TMP_MAX</a></span> 个文件（此极限可能与 <span class="t-lc">tmpnam</span> 共享，并可能为 <span class="t-lc"><a href="cpp-io-c.html">FOPEN_MAX</a></span> 进一步限制）。</p>
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<p>若程序关闭文件，例如通过执行 <span class="t-lc"><a href="cpp-io-c-fclose.html">std::fclose</a></span> ，则自动删除文件。</p>
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<p>若程序正常退出（通过调用 <span class="t-lc"><a href="cpp-utility-program-exit.html">std::exit</a></span> 、从 <span class="t-c"><span class="mw-geshi cpp source-cpp">main</span></span> 返回等，则亦自动删除所有通过调用 <code>std::tmpfile</code> 打开的文件。</p>
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<p>若程序非正常退出，则是否删除这些临时文件是实现定义的。</p>
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<h3><span class="mw-headline" id=".E5.8F.82.E6.95.B0">参数</span></h3>
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<p>（无）</p>
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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>关联的文件流，或若出现错误则为空指针。</p>
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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>一些实现（如 Linux ）上，此函数确实从文件系统上创建、打开并立即删除该文件：只要被删除文件的文件开启描述符为程序所管理，该文件就会存在，但只要它被删除，其名就不会出现于任何目录中，从而再无其他进程能打开它。一旦文件描述符被关闭，或一旦程序终止（正常或异常），该文件所占有的空间将被文件系统回收。</p>
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<p>一些实现（如 Windows ）上要求提升的权限，因为该函数可能在系统目录中创建临时文件。</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 <cstdio></span>
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<span class="co2">#include <cstdlib></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">int</span> main<span class="br0">(</span><span class="br0">)</span>
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<span class="br0">{</span>
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<a href="cpp-io-c.html"><span class="kw1876">std::<span class="me2">FILE</span></span></a><span class="sy2">*</span> tmpf <span class="sy1">=</span> std<span class="sy4">::</span><span class="me2">tmpfile</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
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<a href="cpp-io-c-fputs.html"><span class="kw1826">std::<span class="me2">fputs</span></span></a><span class="br0">(</span><span class="st0">"Hello, world"</span>, tmpf<span class="br0">)</span><span class="sy4">;</span>
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<a href="cpp-io-c-rewind.html"><span class="kw1869">std::<span class="me2">rewind</span></span></a><span class="br0">(</span>tmpf<span class="br0">)</span><span class="sy4">;</span>
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<span class="kw4">char</span> buf<span class="br0">[</span><span class="nu0">6</span><span class="br0">]</span><span class="sy4">;</span>
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<a href="cpp-io-c-fgets.html"><span class="kw1823">std::<span class="me2">fgets</span></span></a><span class="br0">(</span>buf, sizeof buf, tmpf<span class="br0">)</span><span class="sy4">;</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> buf <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
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<span class="co1">// 显示临时文件名的 Linux 特定方法</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> fs<span class="sy4">::</span><span class="me2">read_symlink</span><span class="br0">(</span>
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fs<span class="sy4">::</span><span class="me2">path</span><span class="br0">(</span><span class="st0">"/proc/self/fd"</span><span class="br0">)</span> <span class="sy2">/</span> <a href="cpp-string-basic_string-to_string.html"><span class="kw1265">std::<span class="me2">to_string</span></span></a><span class="br0">(</span>fileno<span class="br0">(</span>tmpf<span class="br0">)</span><span class="br0">)</span>
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<span class="br0">)</span> <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
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<span class="br0">}</span></pre></div>
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</div>
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<p>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">Hello
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"/tmp/tmpfBlY1lI (deleted)"</pre></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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<td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-io-c-tmpnam.html"><span class="t-lines"><span>tmpnam</span></span></a></div>
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</div>
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</td>
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<td>返回一个唯一独有的文件名<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-temp_directory_path.html"><span class="t-lines"><span>temp_directory_path</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>返回一个适用于临时文件的目录<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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