229 lines
18 KiB
HTML
229 lines
18 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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<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
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<title>asctime, asctime_r, asctime_s</title>
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<link rel="stylesheet" href="ext.css" />
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<link rel="stylesheet" href="site_modules.css" />
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</head>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-c_chrono_asctime 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">asctime, asctime_r, asctime_s</h1>
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<div id="bodyContent">
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<div id="contentSub"><span class="subpages">< <a href="c.html">c</a>‎ | <a href="c-chrono.html">chrono</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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<tr class="t-dsc-header">
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<td>
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<div>定义于头文件 <code><time.h></code></div>
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</td>
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<td></td>
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<td></td>
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</tr>
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<tr class="t-dcl">
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<td>
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<div><span class="mw-geshi c source-c"><span class="kw4">char</span><span class="sy2">*</span> asctime <span class="br0">(</span> <span class="kw4">const</span> <span class="kw1">struct</span> <a href="c-chrono-tm.html"><span class="kw522">tm</span></a><span class="sy2">*</span> time_ptr <span class="br0">)</span><span class="sy4">;</span></span></div>
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</td>
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<td>(1)</td>
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<td class="t-dcl-nopad"></td>
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</tr>
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<tr class="t-dcl t-since-c23">
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<td>
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<div><span class="mw-geshi c source-c"><span class="kw4">char</span><span class="sy2">*</span> asctime_r<span class="br0">(</span> <span class="kw4">const</span> <span class="kw1">struct</span> <a href="c-chrono-tm.html"><span class="kw522">tm</span></a><span class="sy2">*</span> time_ptr, <span class="kw4">char</span><span class="sy2">*</span> buf <span class="br0">)</span><span class="sy4">;</span></span></div>
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</td>
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<td>(2)</td>
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<td><span class="t-mark-rev t-since-c23">(C23 起)</span></td>
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</tr>
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<tr class="t-dcl t-since-c11">
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<td>
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<div><span class="mw-geshi c source-c">errno_t asctime_s<span class="br0">(</span> <span class="kw4">char</span><span class="sy2">*</span> buf, rsize_t bufsz, <span class="kw4">const</span> <span class="kw1">struct</span> <a href="c-chrono-tm.html"><span class="kw522">tm</span></a><span class="sy2">*</span> time_ptr <span class="br0">)</span><span class="sy4">;</span></span></div>
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</td>
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<td>(3)</td>
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<td><span class="t-mark-rev t-since-c11">(C11 起)</span></td>
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</tr>
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<tr class="t-dcl-sep">
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<td></td>
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<td></td>
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<td></td>
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</tr>
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</tbody>
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</table>
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<div class="t-li1"><span class="t-li">1)</span> 转换日历时间 <span class="t-lc"><a href="c-chrono-tm.html">tm</a></span> 为以下固定的 25 字符表示形式： <span class="t-c"><span class="mw-geshi c source-c">Www Mmm dd hh<span class="sy4">:</span>mm<span class="sy4">:</span>ss yyyy\n</span></span>
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<ul>
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<li><code>Www</code> ——来自 <span class="t-c"><span class="mw-geshi c source-c">time_ptr<span class="sy2">-</span><span class="sy1">></span>tm_wday</span></span> 的星期之日的三字母英文缩写， <code>Mon</code> 、 <code>Tue</code> 、 <code>Wed</code> 、 <code>Thu</code> 、 <code>Fri</code> 、 <code>Sat</code> 、 <code>Sun</code> 之一。</li>
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<li><code>Mmm</code> ——来自 <span class="t-c"><span class="mw-geshi c source-c">time_ptr<span class="sy2">-</span><span class="sy1">></span>tm_mon</span></span> 的月名的三字母英文缩写， <code>Jan</code> 、 <code>Feb</code> 、 <code>Mar</code> 、 <code>Apr</code> 、 <code>May</code> 、 <code>Jun</code> 、 <code>Jul</code> 、 <code>Aug</code> 、 <code>Sep</code> 、 <code>Oct</code> 、 <code>Nov</code> 、 <code>Dec</code> 之一。</li>
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<li><code>dd</code> ——来自 <span class="t-c"><span class="mw-geshi c source-c">timeptr<span class="sy2">-</span><span class="sy1">></span>tm_mday</span></span> 的 2 位月之日，如同由 <span class="t-lc"><a href="c-io-fprintf.html">sprintf</a></span> 以 <span class="t-c"><span class="mw-geshi c source-c"><span class="sy2">%</span>2d</span></span> 打印</li>
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<li><code>hh</code> ——来自 <span class="t-c"><span class="mw-geshi c source-c">timeptr<span class="sy2">-</span><span class="sy1">></span>tm_hour</span></span> 的 2 位时，如同由 <span class="t-lc"><a href="c-io-fprintf.html">sprintf</a></span> 以 <span class="t-c"><span class="mw-geshi c source-c"><span class="sy2">%</span>.2d</span></span> 打印</li>
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<li><code>mm</code> ——来自 <span class="t-c"><span class="mw-geshi c source-c">timeptr<span class="sy2">-</span><span class="sy1">></span>tm_min</span></span> 的 2 位分，如同由 <span class="t-lc"><a href="c-io-fprintf.html">sprintf</a></span> 以 <span class="t-c"><span class="mw-geshi c source-c"><span class="sy2">%</span>.2d</span></span> 打印</li>
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<li><code>ss</code> ——来自 <span class="t-c"><span class="mw-geshi c source-c">timeptr<span class="sy2">-</span><span class="sy1">></span>tm_sec</span></span> 的 2 位秒，如同由 <span class="t-lc"><a href="c-io-fprintf.html">sprintf</a></span> 以 <span class="t-c"><span class="mw-geshi c source-c"><span class="sy2">%</span>.2d</span></span> 打印</li>
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<li><code>yyyy</code> ——来自 <span class="t-c"><span class="mw-geshi c source-c">timeptr<span class="sy2">-</span><span class="sy1">></span>tm_year <span class="sy2">+</span> <span class="nu0">1900</span></span></span> 的 4 位年，如同由 <span class="t-lc"><a href="c-io-fprintf.html">sprintf</a></span> 以 <span class="t-c"><span class="mw-geshi c source-c"><span class="sy2">%</span>4d</span></span> 打印</li>
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</ul>
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</div>
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<div class="t-li1"><span class="t-li"></span> 若 <span class="t-c"><span class="mw-geshi c source-c"><span class="sy2">*</span>time_ptr</span></span> 的任何成员在其正常范围外则行为未定义</div>
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<div class="t-li1"><span class="t-li"></span> 若 <span class="t-c"><span class="mw-geshi c source-c">time_ptr<span class="sy2">-</span><span class="sy1">></span>tm_year</span></span> 所指示的历年拥有多于 4 位数或小于 1000 年则行为未定义。</div>
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<div class="t-li1"><span class="t-li"></span> 函数不支持本地化，且不能移除换行符。</div>
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<div class="t-li1"><span class="t-li"></span> 函数修改静态存储且非线程安全。</div>
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<div class="t-li1"><span class="t-li">2)</span> 同 <span class="t-v">(1)</span> ，除了写入消息到用户提供的存储 <code>buf</code> 中，保证它是空终止的。</div>
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<div class="t-li1"><span class="t-li"></span> 若存储始于 <code>buf</code> 的可用大小小于 26 字节则行为未定义。</div>
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<div class="t-li1"><span class="t-li">3)</span> 同 <span class="t-v">(1)</span> ，除了写入消息到用户提供的存储 <code>buf</code> 中，保证它是空终止的。且在运行是检测下列错误并调用当前安装的<a href="c-error-set_constraint_handler_s.html">制约处理</a>函数：
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<dl>
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<dd>
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<ul>
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<li><code>buf</code> 或 <code>time_ptr</code> 为空指针</li>
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<li><code>bufsz</code> 小于 26 或大于 <span class="t-lc">RSIZE_MAX</span></li>
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<li>不是所有 <span class="t-c"><span class="mw-geshi c source-c"><span class="sy2">*</span>time_ptr</span></span> 的成员都在其正常范围内</li>
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<li><span class="t-c"><span class="mw-geshi c source-c">time_ptr<span class="sy2">-</span><span class="sy1">></span>tm_year</span></span> 所指示的年小于 0 或大于 9999</li>
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</ul>
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</dd>
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<dd>同所有边界检查函数， <code>asctime_s</code> 仅若实现定义 <span class="t-c"><span class="mw-geshi c source-c">__STDC_LIB_EXT1__</span></span> 且用户在包含 <code>time.h</code> 前定义 <span class="t-c"><span class="mw-geshi c source-c">__STDC_WANT_LIB_EXT1__</span></span> 为整数常量 1 才保证可用。</dd>
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</dl>
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</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>time_ptr</td>
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<td>-</td>
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<td>指向指定待打印时间的 <span class="t-lc"><a href="c-chrono-tm.html">tm</a></span> 对象的指针</td>
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</tr>
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<tr class="t-par">
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<td>buf</td>
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<td>-</td>
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<td>指向用户提供的至少有 26 字节的缓冲区的指针</td>
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</tr>
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<tr class="t-par">
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<td>bufsz</td>
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<td>-</td>
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<td>用户提供的缓冲区大小</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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<div class="t-li1"><span class="t-li">1)</span> 指向保有如上描述的日期与时间的静态空终止字符串指针。该字符串可能在 <code>asctime</code> 与 <span class="t-lc"><a href="c-chrono-ctime.html">ctime</a></span> 间共享，且可能在每次调用这些函数时被重写。</div>
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<div class="t-li1"><span class="t-li">2)</span> <code>buf</code> ，在返回后指向保有如上描述的日期与时间的静态空终止字符串。</div>
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<div class="t-li1"><span class="t-li">3)</span> 成功时为零，失败时为非零，并设置 <span class="t-c"><span class="mw-geshi c source-c">buf<span class="br0">[</span><span class="nu0">0</span><span class="br0">]</span></span></span> 为零（除非 <code>buf</code> 为空指针或 <code>bufsz</code> 为零或大于 <span class="t-lc">RSIZE_MAX</span> ）。</div>
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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><code>asctime</code> 返回指向静态数据的指针从而不是线程安全的。 POSIX 标记此函数为过时并推荐用 <span class="t-lc"><a href="c-chrono-strftime.html">strftime</a></span> 代替。 C 标准亦推荐用 <span class="t-lc"><a href="c-chrono-strftime.html">strftime</a></span> 代替 <code>asctime</code> 、 <code>asctime_r</code> 及 <code>asctime_s</code> 因为 <code>strftime</code> 更灵活且为本地环境相关。</p>
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<p>POSIX 限制未定义行为仅为当输出字符串将会长于 25 个字符、当 <code>timeptr->tm_wday</code> 或 <code>timeptr->tm_mon</code> 不在期待范围内，或当 <code>timeptr->tm_year</code> 超出 <span class="t-c"><span class="mw-geshi c source-c">INT_MAX<span class="sy2">-</span><span class="nu0">1990</span></span></span> 。</p>
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<p>一些实现处置 <span class="t-c"><span class="mw-geshi c source-c">timeptr<span class="sy2">-</span><span class="sy1">></span>tm_mday<span class="sy1">==</span><span class="nu0">0</span></span></span> 为表示前一月的最后一日。</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="c source-c">
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<pre class="de1"><span class="co2">#define __STDC_WANT_LIB_EXT1__ 1</span>
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<span class="co2">#include <time.h></span>
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<span class="co2">#include <stdio.h></span>
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<span class="kw4">int</span> main<span class="br0">(</span><span class="kw4">void</span><span class="br0">)</span>
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<span class="br0">{</span>
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<span class="kw1">struct</span> <a href="c-chrono-tm.html"><span class="kw522">tm</span></a> <a href="c-chrono-tm.html"><span class="kw522">tm</span></a> <span class="sy1">=</span> <span class="sy2">*</span><a href="c-chrono-localtime.html"><span class="kw519">localtime</span></a><span class="br0">(</span><span class="sy3">&</span><span class="br0">(</span><a href="c-chrono-time_t.html"><span class="kw523">time_t</span></a><span class="br0">)</span><span class="br0">{</span><a href="c-chrono-time.html"><span class="kw513">time</span></a><span class="br0">(</span><a href="c-types-NULL.html"><span class="kw103">NULL</span></a><span class="br0">)</span><span class="br0">}</span><span class="br0">)</span><span class="sy4">;</span>
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<a href="c-io-fprintf.html"><span class="kw850">printf</span></a><span class="br0">(</span><span class="st0">"%s"</span>, asctime<span class="br0">(</span><span class="sy3">&</span><a href="c-chrono-tm.html"><span class="kw522">tm</span></a><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="co2">#ifdef __STDC_LIB_EXT1__</span>
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<span class="kw4">char</span> str<span class="br0">[</span><span class="nu0">26</span><span class="br0">]</span><span class="sy4">;</span>
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asctime_s<span class="br0">(</span>str, <span class="kw4">sizeof</span> str, <span class="sy3">&</span><a href="c-chrono-tm.html"><span class="kw522">tm</span></a><span class="br0">)</span><span class="sy4">;</span>
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<a href="c-io-fprintf.html"><span class="kw850">printf</span></a><span class="br0">(</span><span class="st0">"%s"</span>, str<span class="br0">)</span><span class="sy4">;</span>
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<span class="co2">#endif</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">Tue May 26 21:51:50 2015
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Tue May 26 21:51:50 2015</pre></div>
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</div>
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</div>
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<h3><span class="mw-headline" id=".E5.BC.95.E7.94.A8">引用</span></h3>
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<div class="t-ref-std-17">
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<ul>
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<li>C17 标准（ISO/IEC 9899:2018）：</li>
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</ul>
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<dl>
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<dd>
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<ul>
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<li>7.27.2.1 The asctime function (p: 287)</li>
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</ul>
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</dd>
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</dl>
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<dl>
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<dd>
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<ul>
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<li>K.3.8.2.1 The asctime_s function (p: 453-454)</li>
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</ul>
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</dd>
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</dl>
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</div>
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<div class="t-ref-std-11">
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<ul>
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<li>C11 标准（ISO/IEC 9899:2011）：</li>
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</ul>
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<dl>
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<dd>
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<ul>
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<li>7.27.2.1 The asctime function (p: 392-393)</li>
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</ul>
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</dd>
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</dl>
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<dl>
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<dd>
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<ul>
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<li>K.3.8.2.1 The asctime_s function (p: 624-625)</li>
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</ul>
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</dd>
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</dl>
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</div>
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<div class="t-ref-std-c99">
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<ul>
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<li>C99 标准（ISO/IEC 9899:1999）：</li>
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</ul>
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<dl>
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<dd>
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<ul>
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<li>7.23.3.1 The asctime function (p: 341-342)</li>
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</ul>
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</dd>
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</dl>
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</div>
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<div class="t-ref-std-c89">
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<ul>
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<li>C89/C90 标准（ISO/IEC 9899:1990）：</li>
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</ul>
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<dl>
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<dd>
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<ul>
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<li>4.12.3.1 The asctime function</li>
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</ul>
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</dd>
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</dl>
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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="c-chrono-ctime.html"><span class="t-lines"><span>ctime</span><span>ctime_r</span><span>ctime_s</span></span></a></div>
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<div><span class="t-lines"><span></span><span><span class="t-mark-rev t-since-c23">(C23)</span></span><span><span class="t-mark-rev t-since-c11">(C11)</span></span></span></div>
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</div>
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</td>
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<td>将 <code>struct time_t</code> 对象转换成文本表示<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="c-chrono-strftime.html"><span class="t-lines"><span>strftime</span></span></a></div>
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</div>
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</td>
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<td>将 <code>struct tm</code> 对象转换成自定义文本表示<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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</div>
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</div>
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</body>
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</html>
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