148 lines
14 KiB
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148 lines
14 KiB
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<title>std::chrono::is_am, std::chrono::is_pm, std::chrono::make12, std::chrono::make24</title>
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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::chrono::</span>is_am, <span style="font-size:0.7em; line-height:130%">std::chrono::</span>is_pm, <span style="font-size:0.7em; line-height:130%">std::chrono::</span>make12, <span style="font-size:0.7em; line-height:130%">std::chrono::</span>make24</h1>
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<div id="contentSub"><span class="subpages">< <a href="cpp.html">cpp</a>‎ | <a href="cpp-chrono.html">chrono</a></span></div>
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<div>定义于头文件 <code><a href="cpp-header-chrono.html"><chrono></a></code></div>
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<td></td>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw4">constexpr</span> <span class="kw4">bool</span> is_am<span class="br0">(</span> <span class="kw4">const</span> <a href="cpp-chrono-duration.html"><span class="kw999">std::<span class="me2">chrono</span><span class="sy4">::</span><span class="me2">hours</span></span></a><span class="sy3">&</span> h <span class="br0">)</span> <span class="kw1">noexcept</span><span class="sy4">;</span></span></div>
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<td>(1)</td>
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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="kw4">constexpr</span> <span class="kw4">bool</span> is_pm<span class="br0">(</span> <span class="kw4">const</span> <a href="cpp-chrono-duration.html"><span class="kw999">std::<span class="me2">chrono</span><span class="sy4">::</span><span class="me2">hours</span></span></a><span class="sy3">&</span> h <span class="br0">)</span> <span class="kw1">noexcept</span><span class="sy4">;</span></span></div>
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<td>(2)</td>
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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="kw4">constexpr</span> <a href="cpp-chrono-duration.html"><span class="kw999">std::<span class="me2">chrono</span><span class="sy4">::</span><span class="me2">hours</span></span></a> make12<span class="br0">(</span> <span class="kw4">const</span> <a href="cpp-chrono-duration.html"><span class="kw999">std::<span class="me2">chrono</span><span class="sy4">::</span><span class="me2">hours</span></span></a><span class="sy3">&</span> h <span class="br0">)</span> <span class="kw1">noexcept</span><span class="sy4">;</span></span></div>
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<td>(3)</td>
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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="kw4">constexpr</span> <a href="cpp-chrono-duration.html"><span class="kw999">std::<span class="me2">chrono</span><span class="sy4">::</span><span class="me2">hours</span></span></a> make24<span class="br0">(</span> <span class="kw4">const</span> <a href="cpp-chrono-duration.html"><span class="kw999">std::<span class="me2">chrono</span><span class="sy4">::</span><span class="me2">hours</span></span></a><span class="sy3">&</span> h,<br />
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<span class="kw4">bool</span> is_pm <span class="br0">)</span> <span class="kw1">noexcept</span><span class="sy4">;</span></span></div>
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<td>(4)</td>
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<td><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></td>
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<p>这些函数辅助在 12 时格式与 24 时格式的日之时间之间翻译。</p>
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<div class="t-li1"><span class="t-li">1)</span> 检测 24 时格式时间是否为 a.m. （ <i>ante meridiem</i> ，午前）。</div>
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<div class="t-li1"><span class="t-li">2)</span> 检测 24 时格式时间是否为 p.m. （ <i>post meridiem</i> ，午后）。</div>
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<div class="t-li1"><span class="t-li">3)</span> 返回 24 时格式时间的 12 时等价版本。</div>
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<div class="t-li1"><span class="t-li">4)</span> 返回 12 时格式时间 <code>h</code> 的 24 时等价版本，其中 <code>is_pm</code> 确定时间是否为 p.m. 。</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>h</td>
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<td>-</td>
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<td>要检测的 12 时或 24 时格式时间</td>
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</tr>
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<tr class="t-par">
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<td>is_pm</td>
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<td>-</td>
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<td>确定 12 时格式时间是否为 p.m.</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> <span class="t-c"><span class="mw-geshi cpp source-cpp">0h <span class="sy1"><=</span> h <span class="sy3">&&</span> h <span class="sy1"><=</span> 11h</span></span>。</div>
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<div class="t-li1"><span class="t-li">2)</span> <span class="t-c"><span class="mw-geshi cpp source-cpp">12h <span class="sy1"><=</span> h <span class="sy3">&&</span> h <span class="sy1"><=</span> 23h</span></span>。</div>
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<div class="t-li1"><span class="t-li">3)</span> 若 <code>h</code> 在范围 <code>[0h, 23h]</code> 内，则返回范围 <code>[1h, 12h]</code> 内的 12 时等价版本。否则返回值未指定。</div>
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<div class="t-li1"><span class="t-li">4)</span> 若 <code>h</code> 在范围 <code>[1h, 12h]</code> 内，则返回范围 <code>[0h, 11h]</code> 内的 24 时等价版本，若 <code>is_pm</code> 为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">false</span></span></span> ，否则结果在范围 <code>[12h, 23h]</code> 内。否则返回值未指定。</div>
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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 <iostream></span>
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<span class="co2">#include <iomanip></span>
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<span class="co2">#include <utility></span>
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<span class="co2">#include <chrono></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="kw1">using</span> <span class="kw1">namespace</span> std<span class="sy4">::</span><span class="me2">chrono</span><span class="sy4">;</span>
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static_assert<span class="br0">(</span>
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is_am<span class="br0">(</span>10h<span class="br0">)</span> <span class="sy3">&&</span> is_am<span class="br0">(</span>11h<span class="br0">)</span> <span class="sy3">&&</span> <span class="sy3">!</span>is_am<span class="br0">(</span>12h<span class="br0">)</span> <span class="sy3">&&</span> <span class="sy3">!</span>is_am<span class="br0">(</span>23h<span class="br0">)</span> <span class="sy3">&&</span>
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<span class="sy3">!</span>is_pm<span class="br0">(</span>10h<span class="br0">)</span> <span class="sy3">&&</span> <span class="sy3">!</span>is_pm<span class="br0">(</span>11h<span class="br0">)</span> <span class="sy3">&&</span> is_pm<span class="br0">(</span>12h<span class="br0">)</span> <span class="sy3">&&</span> is_pm<span class="br0">(</span>23h<span class="br0">)</span>
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<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">"make12():<span class="es1">\n</span>"</span><span class="sy4">;</span>
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<span class="kw1">for</span> <span class="br0">(</span><span class="kw4">const</span> hours hh <span class="sy4">:</span> <span class="br0">{</span> 0h, 1h, 11h, 12h, 13h, 23h <span class="br0">}</span><span class="br0">)</span> <span class="br0">{</span>
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<span class="kw4">const</span> hours am<span class="br0">{</span>make12<span class="br0">(</span>hh<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> <a href="cpp-io-manip-setw.html"><span class="kw1797">std::<span class="me2">setw</span></span></a><span class="br0">(</span><span class="nu0">2</span><span class="br0">)</span> <span class="sy1"><<</span> hh.<span class="me1">count</span><span class="br0">(</span><span class="br0">)</span> <span class="sy1"><<</span> <span class="st0">"h == "</span>
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<span class="sy1"><<</span> <a href="cpp-io-manip-setw.html"><span class="kw1797">std::<span class="me2">setw</span></span></a><span class="br0">(</span><span class="nu0">2</span><span class="br0">)</span> <span class="sy1"><<</span> am.<span class="me1">count</span><span class="br0">(</span><span class="br0">)</span> <span class="sy1"><<</span> <span class="br0">(</span>is_am<span class="br0">(</span>hh<span class="br0">)</span> <span class="sy4">?</span> <span class="st0">"h a.m.<span class="es1">\n</span>"</span> <span class="sy4">:</span> <span class="st0">"h p.m.<span class="es1">\n</span>"</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="br0">}</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">"<span class="es1">\n</span>make24():<span class="es1">\n</span>"</span><span class="sy4">;</span>
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<span class="kw1">using</span> p <span class="sy1">=</span> <a href="cpp-utility-pair.html"><span class="kw1096">std::<span class="me2">pair</span></span></a><span class="sy1"><</span>hours, <span class="kw4">bool</span><span class="sy1">></span><span class="sy4">;</span>
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<span class="kw1">for</span> <span class="br0">(</span><span class="kw4">const</span> <span class="kw4">auto</span><span class="sy3">&</span> <span class="br0">[</span>hh, pm<span class="br0">]</span> <span class="sy4">:</span> <span class="br0">{</span> p<span class="br0">{</span>1h, <span class="nu0">0</span><span class="br0">}</span>, p<span class="br0">{</span>12h, <span class="nu0">0</span><span class="br0">}</span>, p<span class="br0">{</span>1h, <span class="nu0">1</span><span class="br0">}</span>, p<span class="br0">{</span>12h, <span class="nu0">1</span><span class="br0">}</span> <span class="br0">}</span><span class="br0">)</span> <span class="br0">{</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> <a href="cpp-io-manip-setw.html"><span class="kw1797">std::<span class="me2">setw</span></span></a><span class="br0">(</span><span class="nu0">2</span><span class="br0">)</span> <span class="sy1"><<</span> hh.<span class="me1">count</span><span class="br0">(</span><span class="br0">)</span>
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<span class="sy1"><<</span> <span class="br0">(</span>pm <span class="sy4">?</span> <span class="st0">"h p.m."</span> <span class="sy4">:</span> <span class="st0">"h a.m."</span><span class="br0">)</span>
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<span class="sy1"><<</span> <span class="st0">" == "</span> <span class="sy1"><<</span> <a href="cpp-io-manip-setw.html"><span class="kw1797">std::<span class="me2">setw</span></span></a><span class="br0">(</span><span class="nu0">2</span><span class="br0">)</span>
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<span class="sy1"><<</span> make24<span class="br0">(</span>hh, pm<span class="br0">)</span>.<span class="me1">count</span><span class="br0">(</span><span class="br0">)</span> <span class="sy1"><<</span> <span class="st0">"h<span class="es1">\n</span>"</span><span class="sy4">;</span>
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<span class="br0">}</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">make12():
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0h == 12h a.m.
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1h == 1h a.m.
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11h == 11h a.m.
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12h == 12h p.m.
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13h == 1h p.m.
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23h == 11h p.m.
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make24():
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1h a.m. == 1h
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12h a.m. == 0h
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1h p.m. == 13h
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12h p.m. == 12h</pre></div>
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