146 lines
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146 lines
15 KiB
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<title>std::chrono::operator+, std::chrono::operator- (std::chrono::year)</title>
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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::chrono::</span>operator+, <span style="font-size:0.7em; line-height:130%">std::chrono::</span>operator- <span style="font-size:0.7em; line-height:130%">(std::chrono::year)</span></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.html">year</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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<div><span class="mw-geshi cpp source-cpp"><span class="kw4">constexpr</span> std<span class="sy4">::</span><span class="me2">chrono</span><span class="sy4">::</span><span class="me2">year</span> operator<span class="sy2">+</span><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 />
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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">years</span><span class="sy3">&</span> ys<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> std<span class="sy4">::</span><span class="me2">chrono</span><span class="sy4">::</span><span class="me2">year</span> operator<span class="sy2">+</span><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">years</span><span class="sy3">&</span> ys,<br />
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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">year</span><span class="sy3">&</span> y<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> std<span class="sy4">::</span><span class="me2">chrono</span><span class="sy4">::</span><span class="me2">year</span> operator<span class="sy2">-</span><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 />
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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">years</span><span class="sy3">&</span> ys<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> std<span class="sy4">::</span><span class="me2">chrono</span><span class="sy4">::</span><span class="me2">years</span> operator<span class="sy2">-</span><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> y1,<br />
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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">year</span><span class="sy3">&</span> y2<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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<div class="t-li1"><span class="t-li">1-2)</span> 对 <code>y</code> 加 <code>ys.count()</code> 年。</div>
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<div class="t-li1"><span class="t-li">3)</span> 从 <code>y</code> 减去 <code>ys.count()</code> 年。</div>
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<div class="t-li1"><span class="t-li">4)</span> 返回 <code>y1</code> 与 <code>y2</code> 间按年计算的差。</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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<div class="t-li1"><span class="t-li">1-2)</span> <span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">chrono</span><span class="sy4">::</span><span class="me2">year</span><span class="br0">(</span><span class="kw4">int</span><span class="br0">(</span>y<span class="br0">)</span> <span class="sy2">+</span> ys.<span class="me1">count</span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span></span></span></div>
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<div class="t-li1"><span class="t-li">3)</span> <span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">chrono</span><span class="sy4">::</span><span class="me2">year</span><span class="br0">(</span><span class="kw4">int</span><span class="br0">(</span>y<span class="br0">)</span> <span class="sy2">-</span> ys.<span class="me1">count</span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span></span></span></div>
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<div class="t-li1"><span class="t-li">4)</span> <span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">chrono</span><span class="sy4">::</span><span class="me2">years</span><span class="br0">(</span><span class="kw4">int</span><span class="br0">(</span>y1<span class="br0">)</span> <span class="sy2">-</span> <span class="kw4">int</span><span class="br0">(</span>y2<span class="br0">)</span><span class="br0">)</span></span></span></div>
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<h3><span class="mw-headline" id=".E6.B3.A8.E8.A7.A3">注解</span></h3>
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<p>若 <span class="t-v">(1-3)</span> 产生的年份值在范围 [-32767,32767] 外，则实际存储值未指定。</p>
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<p>二个 <code>year</code> 值相减的结果是 <span class="t-lc">std::chrono::years</span> 类型时长。此时长单位表示格里高利年的平均长度，而结果与运算数所表示的具体年中的日数无关。例如 <span class="t-c"><span class="mw-geshi cpp source-cpp">2018y <span class="sy2">-</span> 2017y</span></span> 的结果是 <span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">chrono</span><span class="sy4">::</span><span class="me2">years</span><span class="br0">(</span><span class="nu0">1</span><span class="br0">)</span></span></span> ，它表示 365.2425 日，而非 365 日。</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="cpp source-cpp">
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<pre class="de1"><span class="co2">#include <iostream></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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std<span class="sy4">::</span><span class="me2">chrono</span><span class="sy4">::</span><span class="me2">year</span> y <span class="br0">{</span><span class="nu0">2020</span><span class="br0">}</span><span class="sy4">;</span>
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y <span class="sy1">=</span> y <span class="sy2">+</span> std<span class="sy4">::</span><span class="me2">chrono</span><span class="sy4">::</span><span class="me2">years</span><span class="br0">(</span><span class="nu0">12</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="kw1">if</span> <span class="br0">(</span>y <span class="sy1">==</span> std<span class="sy4">::</span><span class="me2">chrono</span><span class="sy4">::</span><span class="me2">year</span><span class="br0">(</span><span class="nu0">2032</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> <span class="st0">"Years added correctly"</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> <span class="kw1">else</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> <span class="st0">"Years not added correctly"</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>
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y <span class="sy1">=</span> y <span class="sy2">-</span> std<span class="sy4">::</span><span class="me2">chrono</span><span class="sy4">::</span><span class="me2">years</span><span class="br0">(</span><span class="nu0">33</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="kw1">if</span> <span class="br0">(</span>y <span class="sy1">==</span> std<span class="sy4">::</span><span class="me2">chrono</span><span class="sy4">::</span><span class="me2">year</span><span class="br0">(</span><span class="nu0">1999</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> <span class="st0">"Years subtracted correctly"</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> <span class="kw1">else</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> <span class="st0">"Years not subtracted correctly"</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>
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std<span class="sy4">::</span><span class="me2">chrono</span><span class="sy4">::</span><span class="me2">years</span> ys <span class="sy1">=</span> std<span class="sy4">::</span><span class="me2">chrono</span><span class="sy4">::</span><span class="me2">year</span><span class="br0">(</span><span class="nu0">2025</span><span class="br0">)</span> <span class="sy2">-</span> std<span class="sy4">::</span><span class="me2">chrono</span><span class="sy4">::</span><span class="me2">year</span><span class="br0">(</span><span class="nu0">2020</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="kw1">if</span> <span class="br0">(</span>ys <span class="sy1">==</span> std<span class="sy4">::</span><span class="me2">chrono</span><span class="sy4">::</span><span class="me2">years</span><span class="br0">(</span><span class="nu0">5</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> <span class="st0">"Years subtracted correctly"</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> <span class="kw1">else</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> <span class="st0">"Years not subtracted correctly"</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>
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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">Years added correctly
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Years subtracted correctly
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Years subtracted correctly</pre></div>
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</div>
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</div>
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<h3><span class="mw-headline" id=".E8.BF.94.E5.9B.9E.E5.80.BC_2">返回值</span></h3>
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<div class="t-dsc-member-div">
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<div><a href="cpp-chrono-month-operator_inc_dec.html"><span class="t-lines"><span>operator++</span><span>operator++<span class="t-dsc-small">(int)</span></span><span>operator--</span><span>operator--<span class="t-dsc-small">(int)</span></span></span></a></div>
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</div>
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<td>自增或自减 month<br />
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<span class="t-mark">(<code>std::chrono::month</code> 的公开成员函数)</span></td>
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<div><a href="cpp-chrono-month-operator_arith.html"><span class="t-lines"><span>operator+=</span><span>operator-=</span></span></a></div>
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</div>
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</td>
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<td>加或减月数<br />
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<span class="t-mark">(<code>std::chrono::month</code> 的公开成员函数)</span></td>
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</table>
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</div>
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