66 lines
7.3 KiB
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66 lines
7.3 KiB
HTML
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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::chrono::time_zone::</span>to_sys</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-time_zone.html">time zone</a></span></div>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span><span class="sy1"><</span> <span class="kw1">class</span> Duration <span class="sy1">></span><br /></span>
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<p><span class="kw4">auto</span> to_sys<span class="br0">(</span><span class="kw4">const</span> std<span class="sy4">::</span><span class="me2">chrono</span><span class="sy4">::</span><span class="me2">local_time</span><span class="sy1"><</span>Duration<span class="sy1">></span><span class="sy3">&</span> tp<span class="br0">)</span> <span class="kw4">const</span><br /></p>
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<span class="sy2">-</span><span class="sy1">></span> std<span class="sy4">::</span><span class="me2">chrono</span><span class="sy4">::</span><span class="me2">sys_time</span><span class="sy1"><</span><a href="cpp-types-common_type.html"><span class="kw636">std::<span class="me2">common_type_t</span></span></a><span class="sy1"><</span>Duration, <a href="cpp-chrono-duration.html"><span class="kw997">std::<span class="me2">chrono</span><span class="sy4">::</span><span class="me2">seconds</span></span></a><span class="sy1">>></span><span class="sy4">;</span></div>
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<td><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></td>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span><span class="sy1"><</span> <span class="kw1">class</span> Duration <span class="sy1">></span><br /></span>
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<p><span class="kw4">auto</span> to_sys<span class="br0">(</span><span class="kw4">const</span> std<span class="sy4">::</span><span class="me2">chrono</span><span class="sy4">::</span><span class="me2">local_time</span><span class="sy1"><</span>Duration<span class="sy1">></span><span class="sy3">&</span> tp, std<span class="sy4">::</span><span class="me2">chrono</span><span class="sy4">::</span><span class="me2">choose</span> z<span class="br0">)</span> <span class="kw4">const</span><br /></p>
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<span class="sy2">-</span><span class="sy1">></span> std<span class="sy4">::</span><span class="me2">chrono</span><span class="sy4">::</span><span class="me2">sys_time</span><span class="sy1"><</span><a href="cpp-types-common_type.html"><span class="kw636">std::<span class="me2">common_type_t</span></span></a><span class="sy1"><</span>Duration, <a href="cpp-chrono-duration.html"><span class="kw997">std::<span class="me2">chrono</span><span class="sy4">::</span><span class="me2">seconds</span></span></a><span class="sy1">>></span><span class="sy4">;</span></div>
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<td><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></td>
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<p>转换此时区中的 <code>local_time</code> <code>tp</code> 为对应的 <code>sys_time</code> 。</p>
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<div class="t-li1"><span class="t-li">1)</span> 若转换有歧义或 <code>tp</code> 表示不存在的时间则抛出异常。</div>
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<div class="t-li1"><span class="t-li">2)</span> 按照 <code>z</code> 的值解决歧义：
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<li>若 <span class="t-c"><span class="mw-geshi cpp source-cpp">z <span class="sy1">==</span> std<span class="sy4">::</span><span class="me2">chrono</span><span class="sy4">::</span><span class="me2">choose</span><span class="sy4">::</span><span class="me2">earliest</span></span></span> ，则返回较早的 <code>sys_time</code> 。</li>
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<li>若 <span class="t-c"><span class="mw-geshi cpp source-cpp">z <span class="sy1">==</span> std<span class="sy4">::</span><span class="me2">chrono</span><span class="sy4">::</span><span class="me2">choose</span><span class="sy4">::</span><span class="me2">latest</span></span></span> ，则返回较晚的 <code>sys_time</code> 。</li>
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<div class="t-li1"><span class="t-li"></span> 若 <code>tp</code> 表示二个 UTC <code>time_point</code> 间不存在的时间，则二个 <code>time_point</code> 将相同，并将返回该 <code>time_point</code> 。</div>
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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>按照此时区规则的 <code>tp</code> 的 UTC 等价版本。</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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<div class="t-li1"><span class="t-li">1)</span> 若转换有歧义则抛出 <span class="t-lc">std::chrono::ambiguous_local_time</span> 。若 <code>tp</code> 表示不存在的时间则抛出 <span class="t-lc">std::chrono::nonexistent_local_time</span> 。</div>
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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>结果的精度至少为 <code>std::chrono::seconds</code> ，而且若参数有更精细的精度则将更精细。</p>
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<p>歧义和不存在的本地时间能作为时区转变（例如夏时令）的结果出现。例如， "2016-03-13 02:30:00" 不存在于 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="st0">"America/New_York"</span></span></span> 时区，而该时区中的 "2016-11-06 01:30:00" 能对应二个 UTC 时间点： 2016-11-06 05:30:00 UTC 和 2016-11-06 06:30:00 UTC 。</p>
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