92 lines
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92 lines
8.0 KiB
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<title>std::chrono::year_month_day::year_month_day</title>
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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::chrono::year_month_day::</span>year_month_day</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-year_month_day.html">year month day</a></span></div>
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<div><span class="mw-geshi cpp source-cpp">year_month_day<span class="br0">(</span><span class="br0">)</span> <span class="sy1">=</span> <span class="kw1">default</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> year_month_day<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">year</span><span class="sy3">&</span> y,<br /></span>
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<p> <span class="kw4">const</span> std<span class="sy4">::</span><span class="me2">chrono</span><span class="sy4">::</span><span class="me2">month</span><span class="sy3">&</span> m,<br /></p>
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<span class="kw4">const</span> std<span class="sy4">::</span><span class="me2">chrono</span><span class="sy4">::</span><span class="me2">day</span><span class="sy3">&</span> d<span class="br0">)</span> <span class="kw1">noexcept</span><span class="sy4">;</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> year_month_day<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">year_month_day_last</span><span class="sy3">&</span> ymdl<span class="br0">)</span> <span class="kw1">noexcept</span><span class="sy4">;</span></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="kw4">constexpr</span> year_month_day<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">sys_days</span><span class="sy3">&</span> dp<span class="br0">)</span> <span class="kw1">noexcept</span><span class="sy4">;</span></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">explicit</span> <span class="kw4">constexpr</span> year_month_day<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_days</span><span class="sy3">&</span> dp<span class="br0">)</span> <span class="kw1">noexcept</span><span class="sy4">;</span></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>构造 <code>year_month_day</code> 对象。</p>
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<div class="t-li1"><span class="t-li">1)</span> 默认构造函数保留日期未初始化。</div>
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<div class="t-li1"><span class="t-li">2)</span> 构造存储年 <code>y</code> 、月 <code>m</code> 和日 <code>d</code> 的 <code>year_month_day</code> 对象。</div>
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<div class="t-li1"><span class="t-li">3)</span> 构造存储年 <span class="t-c"><span class="mw-geshi cpp source-cpp">ymdl.<span class="me1">year</span><span class="br0">(</span><span class="br0">)</span></span></span> 、月 <span class="t-c"><span class="mw-geshi cpp source-cpp">ymdl.<span class="me1">month</span><span class="br0">(</span><span class="br0">)</span></span></span> 和日 <span class="t-c"><span class="mw-geshi cpp source-cpp">ymdl.<span class="me1">day</span><span class="br0">(</span><span class="br0">)</span></span></span> 的 <code>year_month_day</code> 对象。</div>
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<div class="t-li1"><span class="t-li">4)</span> 构造与 <code>dp</code> 表示相同日期的 <code>year_month_day</code> 对象。</div>
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<div class="t-li1"><span class="t-li">5)</span> 如同用 <span class="t-c"><span class="mw-geshi cpp source-cpp">year_month_day<span class="br0">(</span>sys_days<span class="br0">(</span>dp.<span class="me1">time_since_epoch</span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span><span class="br0">)</span></span></span> 构造与 <code>dp</code> 表示相同日期的 <code>year_month_day</code> 对象。</div>
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<p>构造函数 <span class="t-v">(3-4)</span> 分别定义来自 <span class="t-lc">std::chrono::year_month_day_last</span> 和 <span class="t-lc">std::chrono::sys_days</span> 的隐式转换。</p>
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<p>对于任何表示合法日期的 <code>year_month_day</code> 对象 <code>ymd</code> （ <span class="t-c"><span class="mw-geshi cpp source-cpp">ymd.<span class="me1">ok</span><span class="br0">(</span><span class="br0">)</span> <span class="sy1">==</span> <span class="kw2">true</span></span></span> ），转换 <code>ymd</code> 为 <code>sys_days</code> 再转换回来生成相同值。</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>亦能由将部分日期类型 <span class="t-lc">std::chrono::year_month</span> 及 <span class="t-lc">std::chrono::month_day</span> 与缺失组分（分别为 <code>day</code> 和 <code>year</code> ）结合，用 <code>operator/</code> 创建 <code>year_month_day</code> 。</p>
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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-operator_slash.html"><span class="t-lines"><span>operator/</span></span></a></div>
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<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx20">(C++20)</span></span></span></div>
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</div>
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</td>
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<td>创建格里高利历日期的约定语法<br />
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<span class="t-mark">(函数)</span></td>
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