128 lines
11 KiB
HTML
128 lines
11 KiB
HTML
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<title>std::filesystem::resize_file</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_filesystem_resize_file 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::</span>resize_file</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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<table class="t-dcl-begin">
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<tbody>
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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></td>
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<td></td>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw4">void</span> resize_file<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,<br /></span>
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<p> <a href="cpp-types-integer.html"><span class="kw132">std::<span class="me2">uintmax_t</span></span></a> new_size<span class="br0">)</span><span class="sy4">;</span><br />
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<span class="kw4">void</span> resize_file<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,<br />
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<a href="cpp-types-integer.html"><span class="kw132">std::<span class="me2">uintmax_t</span></span></a> new_size,<br /></p>
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<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></div>
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<td class="t-dcl-nopad"></td>
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<td><span class="t-mark-rev t-since-cxx17">(C++17 起)</span></td>
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<p>更改 <code>p</code> 所指名的的常规文件大小，如同用 POSIX <a rel="nofollow" class="external text" href="http://pubs.opengroup.org/onlinepubs/9699919799/functions/truncate.html">truncate</a> ：若先前的文件大小大于 <code>new_size</code> ，则文件的剩余部分被舍弃。若先前的文件大小小于 <code>new_size</code> ，则增加文件大小，而且新区域如同以零填充。</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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<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>要重设大小的路径</td>
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</tr>
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<tr class="t-par">
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<td>new_size</td>
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<td>-</td>
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<td>文件将会拥有的大小</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>不抛出重载中报告错误的输出参数</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>（无）</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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<p>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> 。</p>
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<h3><span class="mw-headline" id=".E6.B3.A8.E6.84.8F">注意</span></h3>
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<p>在支持稀疏文件的系统上，增加文件大小并不会增加其在文件系统上占用的空间：空间分配仅当非零字节写入文件时发生。</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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<p>演示在空闲空间创建稀疏文件的效果</p>
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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 <iomanip></span>
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<span class="co2">#include <fstream></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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fs<span class="sy4">::</span><span class="me2">path</span> p <span class="sy1">=</span> fs<span class="sy4">::</span><span class="me2">current_path</span><span class="br0">(</span><span class="br0">)</span> <span class="sy2">/</span> <span class="st0">"example.bin"</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>p<span class="br0">)</span>.<span class="me1">put</span><span class="br0">(</span><span class="st0">'a'</span><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> <span class="st0">"File size: "</span> <span class="sy1"><<</span> <a href="cpp-io-manip-setw.html"><span class="kw1797">std::<span class="me2">setw</span></span></a><span class="br0">(</span><span class="nu0">10</span><span class="br0">)</span> <span class="sy1"><<</span> fs<span class="sy4">::</span><span class="me2">file_size</span><span class="br0">(</span>p<span class="br0">)</span>
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<span class="sy1"><<</span> <span class="st0">" Free space: "</span> <span class="sy1"><<</span> fs<span class="sy4">::</span><span class="me2">space</span><span class="br0">(</span>p<span class="br0">)</span>.<span class="me1">free</span> <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
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fs<span class="sy4">::</span><span class="me2">resize_file</span><span class="br0">(</span>p, <span class="nu0">1024</span><span class="sy2">*</span><span class="nu0">1024</span><span class="sy2">*</span><span class="nu0">1024</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 重设大小为 1 G</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> <span class="st0">"File size: "</span> <span class="sy1"><<</span> fs<span class="sy4">::</span><span class="me2">file_size</span><span class="br0">(</span>p<span class="br0">)</span>
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<span class="sy1"><<</span> <span class="st0">" Free space: "</span> <span class="sy1"><<</span> fs<span class="sy4">::</span><span class="me2">space</span><span class="br0">(</span>p<span class="br0">)</span>.<span class="me1">free</span> <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
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fs<span class="sy4">::</span><span class="me2">remove</span><span class="br0">(</span>p<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">File size: 1 Free space: 3724541952
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File size: 1073741824 Free space: 3724476416</pre></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-file_size.html"><span class="t-lines"><span>file_size</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>返回文件的大小<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-space.html"><span class="t-lines"><span>space</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>确定文件系统上的可用空闲空间<br />
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<span class="t-mark">(函数)</span></td>
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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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