148 lines
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148 lines
15 KiB
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<title>std::filesystem::last_write_time</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_filesystem_last_write_time 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>last_write_time</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>定义于头文件 <code><a href="cpp-header-filesystem.html"><filesystem></a></code></div>
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<div><span class="mw-geshi cpp source-cpp"><a href="cpp-filesystem-file_time_type.html"><span class="kw2258">std::<span class="me2">filesystem</span><span class="sy4">::</span><span class="me2">file_time_type</span></span></a> last_write_time<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 /></span>
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<p><a href="cpp-filesystem-file_time_type.html"><span class="kw2258">std::<span class="me2">filesystem</span><span class="sy4">::</span><span class="me2">file_time_type</span></span></a> last_write_time<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 /></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></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">void</span> last_write_time<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-filesystem-file_time_type.html"><span class="kw2258">std::<span class="me2">filesystem</span><span class="sy4">::</span><span class="me2">file_time_type</span></span></a> new_time<span class="br0">)</span><span class="sy4">;</span><br />
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<span class="kw4">void</span> last_write_time<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-filesystem-file_time_type.html"><span class="kw2258">std::<span class="me2">filesystem</span><span class="sy4">::</span><span class="me2">file_time_type</span></span></a> new_time,<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="sy4">;</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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<div class="t-li1"><span class="t-li">1)</span> 返回 <code>p</code> 的最后修改时间，如同通过访问 POSIX <a rel="nofollow" class="external text" href="http://pubs.opengroup.org/onlinepubs/9699919799/functions/stat.html">stat</a> 的 <code>st_mtime</code> 确定（跟随符号链接） 不抛出重载在错误时返回 <span class="t-c"><span class="mw-geshi cpp source-cpp">file_time_type<span class="sy4">::</span><span class="me2">min</span><span class="br0">(</span><span class="br0">)</span></span></span> 。</div>
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<div class="t-li1"><span class="t-li">2)</span> 更改 <code>p</code> 的最后修改时间，如同用 POSIX <a rel="nofollow" class="external text" href="http://pubs.opengroup.org/onlinepubs/9699919799/functions/futimens.html">futimens</a> （跟随符号链接）</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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<td>p</td>
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<td>-</td>
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<td>要检验或修改的路径</td>
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<td>new_time</td>
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<td>-</td>
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<td>新的修改时间</td>
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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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<div class="t-li1"><span class="t-li">1)</span> <code>p</code> 的最后修改时间</div>
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<div class="t-li1"><span class="t-li">2)</span> （无）</div>
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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>不保证在设置写入时间后， <span class="t-v">(1)</span> 的返回值立即等于传递给 <span class="t-v">(2)</span> 的参数，因为文件系统时间可能比 <code>file_time_type</code> 更为颗粒化。</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 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 <chrono></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">using</span> <span class="kw1">namespace</span> std<span class="sy4">::</span><span class="me2">chrono_literals</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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<span class="kw4">auto</span> p <span class="sy1">=</span> <a href="cpp-filesystem-temp_directory_path.html"><span class="kw2287">std::<span class="me2">filesystem</span><span class="sy4">::</span><span class="me2">temp_directory_path</span></span></a><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="me1">c_str</span><span class="br0">(</span><span class="br0">)</span><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> <span class="co1">// 创建文件</span>
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<span class="kw4">auto</span> print_last_write_time <span class="sy1">=</span> <span class="br0">[</span><span class="br0">]</span><span class="br0">(</span><a href="cpp-filesystem-file_time_type.html"><span class="kw2258">std::<span class="me2">filesystem</span><span class="sy4">::</span><span class="me2">file_time_type</span></span></a> <span class="kw4">const</span><span class="sy3">&</span> ftime<span class="br0">)</span> <span class="br0">{</span>
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<a href="cpp-chrono-c-time_t.html"><span class="kw1024">std::<span class="me2">time_t</span></span></a> cftime <span class="sy1">=</span> std<span class="sy4">::</span><span class="me2">chrono</span><span class="sy4">::</span><span class="me2">system_clock</span><span class="sy4">::</span><span class="me2">to_time_t</span><span class="br0">(</span>
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std<span class="sy4">::</span><span class="me2">chrono</span><span class="sy4">::</span><span class="me2">file_clock</span><span class="sy4">::</span><span class="me2">to_sys</span><span class="br0">(</span>ftime<span class="br0">)</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 write time is "</span> <span class="sy1"><<</span> <a href="cpp-chrono-c-asctime.html"><span class="kw1015">std::<span class="me2">asctime</span></span></a><span class="br0">(</span><a href="cpp-chrono-c-localtime.html"><span class="kw1020">std::<span class="me2">localtime</span></span></a><span class="br0">(</span><span class="sy3">&</span>cftime<span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="br0">}</span><span class="sy4">;</span>
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<span class="kw4">auto</span> ftime <span class="sy1">=</span> std<span class="sy4">::</span><span class="me2">filesystem</span><span class="sy4">::</span><span class="me2">last_write_time</span><span class="br0">(</span>p<span class="br0">)</span><span class="sy4">;</span>
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print_last_write_time<span class="br0">(</span>ftime<span class="br0">)</span><span class="sy4">;</span>
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std<span class="sy4">::</span><span class="me2">filesystem</span><span class="sy4">::</span><span class="me2">last_write_time</span><span class="br0">(</span>p, ftime <span class="sy2">+</span> 1h<span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 向未来移动文件时间 1 小时</span>
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ftime <span class="sy1">=</span> std<span class="sy4">::</span><span class="me2">filesystem</span><span class="sy4">::</span><span class="me2">last_write_time</span><span class="br0">(</span>p<span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 从文件系统回读</span>
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print_last_write_time<span class="br0">(</span>ftime<span class="br0">)</span><span class="sy4">;</span>
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<a href="cpp-filesystem-remove.html"><span class="kw2280">std::<span class="me2">filesystem</span><span class="sy4">::</span><span class="me2">remove</span></span></a><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 write time is Sun May 9 23:29:58 2021
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File write time is Mon May 10 00:29:58 2021</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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<td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-filesystem-file_time_type.html"><span class="t-lines"><span>file_time_type</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>表示文件时间值<br />
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<span class="t-mark">(typedef)</span></td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-filesystem-directory_entry-last_write_time.html"><span class="t-lines"><span>last_write_time</span></span></a></div>
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</div>
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</td>
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<td>获取或设置 directory_entry 所代表的文件的最后数据修改时间<br />
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<span class="t-mark">(<code>std::filesystem::directory_entry</code> 的公开成员函数)</span></td>
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