125 lines
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125 lines
12 KiB
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<title>std::asctime</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_chrono_c_asctime 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::</span>asctime</h1>
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<div id="contentSub"><span class="subpages">< <a href="cpp.html">cpp</a>‎ | <a href="cpp-chrono.html">chrono</a>‎ | <a href="cpp-chrono-c.html">c</a></span></div>
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<div>定义于头文件 <code><a href="cpp-header-ctime.html"><ctime></a></code></div>
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<td></td>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw4">char</span><span class="sy2">*</span> asctime<span class="br0">(</span> <span class="kw4">const</span> <a href="cpp-chrono-c-tm.html"><span class="kw1022">std::<span class="me2">tm</span></span></a><span class="sy2">*</span> time_ptr <span class="br0">)</span><span class="sy4">;</span></span></div>
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<p>转换给定日历时间 <span class="t-lc"><a href="cpp-chrono-c-tm.html">std::tm</a></span> 为拥有下列固定 25 字符形式的文本表示： <span class="t-c"><span class="mw-geshi cpp source-cpp">Www Mmm dd hh<span class="sy4">:</span>mm<span class="sy4">:</span>ss yyyy\n</span></span></p>
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<ul>
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<li><code>Www</code> ——星期之日的三字母英文缩写，来自 <span class="t-c"><span class="mw-geshi cpp source-cpp">time_ptr<span class="sy2">-</span><span class="sy1">></span>tm_wday</span></span> ，为 <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> ——月名的三字母英文缩写，来自 <span class="t-c"><span class="mw-geshi cpp source-cpp">time_ptr<span class="sy2">-</span><span class="sy1">></span>tm_mon</span></span> ，为 <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> —— 2 位数月之日 ，来自 <span class="t-c"><span class="mw-geshi cpp source-cpp">timeptr<span class="sy2">-</span><span class="sy1">></span>tm_mday</span></span> ，如同 <span class="t-lc">sprintf</span> 用 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">%</span>2d</span></span> 打印</li>
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<li><code>hh</code> —— 2 位小时，来自 <span class="t-c"><span class="mw-geshi cpp source-cpp">timeptr<span class="sy2">-</span><span class="sy1">></span>tm_hour</span></span> ，如同 <span class="t-lc">sprintf</span> 用 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">%</span>.2d</span></span> 打印</li>
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<li><code>mm</code> —— 2 位分，来自 <span class="t-c"><span class="mw-geshi cpp source-cpp">timeptr<span class="sy2">-</span><span class="sy1">></span>tm_min</span></span> ，如同 <span class="t-lc">sprintf</span> 用 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">%</span>.2d</span></span> 打印</li>
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<li><code>ss</code> —— 2 位秒，来自 <span class="t-c"><span class="mw-geshi cpp source-cpp">timeptr<span class="sy2">-</span><span class="sy1">></span>tm_sec</span></span> ，如同 <span class="t-lc">sprintf</span> 用 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">%</span>.2d</span></span> 打印</li>
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<li><code>yyyy</code> —— 4 位年，来自 <span class="t-c"><span class="mw-geshi cpp source-cpp">timeptr<span class="sy2">-</span><span class="sy1">></span>tm_year <span class="sy2">+</span> <span class="nu0">1900</span></span></span> ，如同 <span class="t-lc">sprintf</span> 用 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">%</span>4d</span></span> 打印</li>
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</ul>
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<p>若 <span class="t-c"><span class="mw-geshi cpp source-cpp"><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。</p>
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<p>若 <span class="t-c"><span class="mw-geshi cpp source-cpp">time_ptr<span class="sy2">-</span><span class="sy1">></span>tm_year</span></span> 所指示的日历年份多于 4 位数字或小于 1000 年，则行为未定义。</p>
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<p>函数不支持本地化，而写不能移除换行符。</p>
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<p>函数修改静态存储，而且不是线程安全的。</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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<table class="t-par-begin">
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<td>time_ptr</td>
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<td>-</td>
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<td>指向指定要打印时间的 <span class="t-lc"><a href="cpp-chrono-c-tm.html">std::tm</a></span> 对象的指针</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>指向空终止字符串的指针，字符串保有日期和时间的文本表示。字符串可能在 <code>std::asctime</code> 与 <span class="t-lc"><a href="cpp-chrono-c-ctime.html">std::ctime</a></span> 之间共享，而且可能在每次调用任何这些函数时被重写。</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>此函数返回指向静态数据的指针，且非线程安全。 POSIX 标记此函数为过时，并推荐使用 <span class="t-lc"><a href="cpp-chrono-c-strftime.html">std::strftime</a></span> 替代。</p>
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<p>POSIX 限制了仅当输出字符串将长于 25 字符时、 <code>timeptr->tm_wday</code> 或 <code>timeptr->tm_mon</code> 不在预期范围时，或 <code>timeptr->tm_year</code> 超过 <span class="t-c"><span class="mw-geshi cpp source-cpp">INT_MAX<span class="sy2">-</span><span class="nu0">1990</span></span></span> 时是未定义行为。</p>
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<p>一些实现把 <span class="t-c"><span class="mw-geshi cpp source-cpp">timeptr<span class="sy2">-</span><span class="sy1">></span>tm_mday<span class="sy1">==</span><span class="nu0">0</span></span></span> 处理成上个月最后一天的含义。</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 <ctime></span>
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<span class="co2">#include <iostream></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-chrono-c-time_t.html"><span class="kw1023">std::<span class="me2">time_t</span></span></a> result <span class="sy1">=</span> <a href="cpp-chrono-c-time.html"><span class="kw1011">std::<span class="me2">time</span></span></a><span class="br0">(</span><a href="cpp-types-NULL.html"><span class="kw103">NULL</span></a><span class="br0">)</span><span class="sy4">;</span>
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<a href="cpp-io-cout.html"><span class="kw1757">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> std<span class="sy4">::</span><span class="me2">asctime</span><span class="br0">(</span><a href="cpp-chrono-c-localtime.html"><span class="kw1019">std::<span class="me2">localtime</span></span></a><span class="br0">(</span><span class="sy3">&</span>result<span class="br0">)</span><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>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">Mon Apr 3 20:26:26 2017</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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<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-chrono-c-ctime.html"><span class="t-lines"><span>ctime</span></span></a></div>
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</div>
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</td>
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<td>转换 <code>time_t</code> 对象为文本表示<br />
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<span class="t-mark">(函数)</span></td>
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<tr class="t-dsc">
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<div class="t-dsc-member-div">
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<div><a href="cpp-chrono-c-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>转换 <code>tm</code> 对象到自定义的文本表示<br />
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<span class="t-mark">(函数)</span></td>
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<tr class="t-dsc">
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<div class="t-dsc-member-div">
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<div><a href="cpp-io-manip-put_time.html"><span class="t-lines"><span>put_time</span></span></a></div>
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<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div>
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</div>
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</td>
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<td>按照指定格式格式化并输出日期/时间值<br />
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<span class="t-mark">(函数模板)</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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