116 lines
11 KiB
HTML
116 lines
11 KiB
HTML
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<title>std::filesystem::directory_entry::file_size</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_filesystem_directory_entry_file_size 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::directory_entry::</span>file_size</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-directory_entry.html">directory entry</a></span></div>
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<div><span class="mw-geshi cpp source-cpp"><a href="cpp-types-integer.html"><span class="kw132">std::<span class="me2">uintmax_t</span></span></a> file_size<span class="br0">(</span><span class="br0">)</span> <span class="kw4">const</span><span class="sy4">;</span><br />
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<a href="cpp-types-integer.html"><span class="kw132">std::<span class="me2">uintmax_t</span></span></a> file_size<span class="br0">(</span> <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="kw4">const</span> <span class="kw1">noexcept</span><span class="sy4">;</span></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>若文件大小缓存于此 <code>directory_entry</code> ，则返回缓存值。否则各返回 <span class="t-lc">std::filesystem::file_size(path())</span> 或 <span class="t-lc">std::filesystem::file_size(path(), ec)</span></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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<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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<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>所指代文件系统对象的大小</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=".E7.A4.BA.E4.BE.8B">示例</span></h3>
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<div class="t-example">
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<p>以下程序以人类可读的形式打印出给定目录中的文件以及其大小。</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 <filesystem></span>
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<span class="co2">#include <iostream></span>
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<span class="co2">#include <cstdint></span>
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<span class="co2">#include <cmath></span>
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<span class="kw1">struct</span> HumanReadable <span class="br0">{</span>
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uintmax_t size <span class="br0">{</span><span class="br0">}</span><span class="sy4">;</span>
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<span class="kw1">template</span> <span class="sy1"><</span><span class="kw1">typename</span> Os<span class="sy1">></span> <span class="kw1">friend</span> Os<span class="sy3">&</span> operator<span class="sy1"><<</span> <span class="br0">(</span>Os<span class="sy3">&</span> os, HumanReadable hr<span class="br0">)</span>
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<span class="br0">{</span>
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<span class="kw4">int</span> i<span class="br0">{</span><span class="br0">}</span><span class="sy4">;</span>
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<span class="kw4">double</span> mantissa <span class="sy1">=</span> hr.<span class="me1">size</span><span class="sy4">;</span>
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<span class="kw1">for</span> <span class="br0">(</span><span class="sy4">;</span> mantissa <span class="sy1">>=</span> <span class="nu0">1024</span>.<span class="sy4">;</span> <span class="sy2">++</span>i<span class="br0">)</span> <span class="br0">{</span>
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mantissa <span class="sy2">/</span><span class="sy1">=</span> <span class="nu0">1024</span>.<span class="sy4">;</span>
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<span class="br0">}</span>
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mantissa <span class="sy1">=</span> <a href="cpp-numeric-math-ceil.html"><span class="kw1350">std::<span class="me2">ceil</span></span></a><span class="br0">(</span>mantissa <span class="sy2">*</span> <span class="nu0">10</span>.<span class="br0">)</span> <span class="sy2">/</span> <span class="nu0">10</span>.<span class="sy4">;</span>
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os <span class="sy1"><<</span> mantissa <span class="sy1"><<</span> <span class="st0">"BKMGTPE"</span><span class="br0">[</span>i<span class="br0">]</span><span class="sy4">;</span>
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<span class="kw1">return</span> i <span class="sy1">==</span> <span class="nu0">0</span> <span class="sy4">?</span> os <span class="sy4">:</span> os <span class="sy1"><<</span> <span class="st0">"B ("</span> <span class="sy1"><<</span> hr.<span class="me1">size</span> <span class="sy1"><<</span> <span class="st0">')'</span><span class="sy4">;</span>
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<span class="br0">}</span>
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<span class="br0">}</span><span class="sy4">;</span>
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<span class="kw4">int</span> main<span class="br0">(</span><span class="kw4">int</span> argc, <span class="kw4">const</span> <span class="kw4">char</span><span class="sy2">*</span> argv<span class="br0">[</span><span class="br0">]</span><span class="br0">)</span>
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<span class="br0">{</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">const</span> <span class="kw4">auto</span> dir <span class="sy1">=</span> argc <span class="sy1">==</span> <span class="nu0">2</span> <span class="sy4">?</span> fs<span class="sy4">::</span><span class="me2">path</span> <span class="br0">{</span> argv<span class="br0">[</span><span class="nu0">1</span><span class="br0">]</span> <span class="br0">}</span> <span class="sy4">:</span> fs<span class="sy4">::</span><span class="me2">current_path</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="kw1">for</span> <span class="br0">(</span>fs<span class="sy4">::</span><span class="me2">directory_entry</span> <span class="kw4">const</span><span class="sy3">&</span> entry <span class="sy4">:</span> fs<span class="sy4">::</span><span class="me2">directory_iterator</span><span class="br0">(</span>dir<span class="br0">)</span><span class="br0">)</span> <span class="br0">{</span>
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<span class="kw1">if</span> <span class="br0">(</span>entry.<span class="me1">is_regular_file</span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span> <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> entry.<span class="me1">path</span><span class="br0">(</span><span class="br0">)</span>.<span class="me1">filename</span><span class="br0">(</span><span class="br0">)</span>
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<span class="sy1"><<</span> <span class="st0">" size: "</span> <span class="sy1"><<</span> HumanReadable<span class="br0">{</span>entry.<span class="me1">file_size</span><span class="br0">(</span><span class="br0">)</span><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>
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<span class="br0">}</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">"boost_1_73_0.tar.bz2" size: 104.2MB (109247910)
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"CppCon 2018 - Jon Kalb “Copy Elision”.mp4" size: 15.7MB (16411990)
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"cppreference-doc-20190607.tar.xz" size: 6.3MB (6531336)
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"hana.hpp" size: 6.7KB (6807)</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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<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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