105 lines
9.7 KiB
HTML
105 lines
9.7 KiB
HTML
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<title>std::mktime</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_chrono_c_mktime 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>mktime</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"><a href="cpp-chrono-c-time_t.html"><span class="kw1023">std::<span class="me2">time_t</span></span></a> mktime<span class="br0">(</span> <a href="cpp-chrono-c-tm.html"><span class="kw1022">std::<span class="me2">tm</span></span></a><span class="sy2">*</span> time <span class="br0">)</span><span class="sy4">;</span></span></div>
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<p>转换本地日历时间为从纪元起的时间，作为 <span class="t-c"><span class="mw-geshi cpp source-cpp">time_t</span></span> 对象。忽略 <code>time->tm_wday</code> 与 <code>time->tm_yday</code> 。容许 <code>time</code> 中的值在其正常范围外。</p>
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<p><code>time->tm_isdst</code> 的负值会导致 <code>mktime</code> 尝试确定在指定时间夏时令是否有效。</p>
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<p>若转换到 <code>time_t</code> 成功，则修改 <code>time</code> 会被修改。更新 <code>time</code> 的所有域为符合其正确范围的值。用可用于其他域的信息重新计算 <code>time->tm_wday</code> 与 <code>time->tm_yday</code> 。</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</td>
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<td>-</td>
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<td>指向 <span class="t-lc"><a href="cpp-chrono-c-tm.html">std::tm</a></span> 对象的指针，它指定要转换的本地日历时间</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>成功时为表示从纪元开始时间的 <span class="t-lc"><a href="cpp-chrono-c-time_t.html">std::time_t</a></span> 对象，若 <code>time</code> 不能表示成 <span class="t-lc"><a href="cpp-chrono-c-time_t.html">std::time_t</a></span> 对象则返回 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">-</span><span class="nu0">1</span></span></span> （ POSIX 亦要求此情况下存储 <code>EOVERFLOW</code> 于 <span class="t-lc"><a href="cpp-error-errno.html">errno</a></span> 中）。</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>若 <span class="t-lc"><a href="cpp-chrono-c-tm.html">std::tm</a></span> 对象从 <span class="t-lc"><a href="cpp-io-manip-get_time.html">std::get_time</a></span> 或 POSIX <a rel="nofollow" class="external text" href="http://pubs.opengroup.org/onlinepubs/009695399/functions/strptime.html">strptime</a> 获得，则 <code>tm_isdst</code> 的值不确定，而且需要在调用 <code>mktime</code> 前显式设置。</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>显示 100 个月前的时间。</p>
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<div class="t-example-live-link"></div>
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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 <ctime></span>
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<span class="co2">#include <stdlib.h></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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setenv<span class="br0">(</span><span class="st0">"TZ"</span>, <span class="st0">"/usr/share/zoneinfo/America/New_York"</span>, <span class="nu0">1</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// POSIX 限定</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> t <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>nullptr<span class="br0">)</span><span class="sy4">;</span>
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<a href="cpp-chrono-c-tm.html"><span class="kw1022">std::<span class="me2">tm</span></span></a> tm <span class="sy1">=</span> <span class="sy2">*</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>t<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> <span class="st0">"Today is "</span> <span class="sy1"><<</span> <a href="cpp-io-manip-put_time.html"><span class="kw1800">std::<span class="me2">put_time</span></span></a><span class="br0">(</span><span class="sy3">&</span>tm, <span class="st0">"%c %Z"</span><span class="br0">)</span>
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<span class="sy1"><<</span> <span class="st0">" and DST is "</span> <span class="sy1"><<</span> <span class="br0">(</span>tm.<span class="me1">tm_isdst</span> <span class="sy4">?</span> <span class="st0">"in effect"</span> <span class="sy4">:</span> <span class="st0">"not in effect"</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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tm.<span class="me1">tm_mon</span> <span class="sy2">-</span><span class="sy1">=</span> <span class="nu0">100</span><span class="sy4">;</span> <span class="co1">// tm_mon 现在在正常范围外</span>
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std<span class="sy4">::</span><span class="me2">mktime</span><span class="br0">(</span><span class="sy3">&</span>tm<span class="br0">)</span><span class="sy4">;</span> <span class="co1">// tm_dst 不被设为 -1 ；使用今日的 DST 状态</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> <span class="st0">"100 months ago was "</span> <span class="sy1"><<</span> <a href="cpp-io-manip-put_time.html"><span class="kw1800">std::<span class="me2">put_time</span></span></a><span class="br0">(</span><span class="sy3">&</span>tm, <span class="st0">"%c %Z"</span><span class="br0">)</span>
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<span class="sy1"><<</span> <span class="st0">" and DST was "</span> <span class="sy1"><<</span> <span class="br0">(</span>tm.<span class="me1">tm_isdst</span> <span class="sy4">?</span> <span class="st0">"in effect"</span> <span class="sy4">:</span> <span class="st0">"not in effect"</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></pre></div>
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<p>输出：</p>
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<div class="text source-text">
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<pre class="de1">Today is Fri Apr 22 11:40:36 2016 EDT and DST is in effect
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100 months ago was Sat Dec 22 10:40:36 2007 EST and DST was not in effect</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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<div><a href="cpp-chrono-c-localtime.html"><span class="t-lines"><span>localtime</span></span></a></div>
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</td>
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<td>转换纪元起时间为以本地时间表示的日历时间<br />
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<span class="t-mark">(函数)</span></td>
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<div class="visualClear"></div>
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