72 lines
6.2 KiB
HTML
72 lines
6.2 KiB
HTML
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<title>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::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><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span> <span class="sy1"><</span><span class="kw1">class</span> CharT, <span class="kw1">class</span> Traits<span class="sy1">></span><br /></span>
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<p><a href="cpp-io-basic_ostream.html"><span class="kw1715">std::<span class="me2">basic_ostream</span></span></a><span class="sy1"><</span>CharT, Traits<span class="sy1">></span><span class="sy3">&</span><br /></p>
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operator<span class="sy1"><<</span><span class="br0">(</span><a href="cpp-io-basic_ostream.html"><span class="kw1715">std::<span class="me2">basic_ostream</span></span></a><span class="sy1"><</span>CharT, Traits<span class="sy1">></span><span class="sy3">&</span> os, <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="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>构成由格式化为十进制数的存储于 <code>y</code> 的年值，若结果会少于四位则左填充 <code>0</code> 到四位组成的 <code>std::basic_string<CharT></code> <code>s</code> 。然后若 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy3">!</span>y.<span class="me1">ok</span><span class="br0">(</span><span class="br0">)</span></span></span> 则后附 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="st0">" is not a valid year"</span></span></span> 到格式化的字符串。插入该字符串到 <code>os</code> 中。</p>
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<p>等价于</p>
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<p><span class="t-cc"><span class="mw-geshi cpp source-cpp"><span class="kw1">return</span> os <span class="sy1"><<</span> <span class="br0">(</span>y.<span class="me1">ok</span><span class="br0">(</span><span class="br0">)</span> <span class="sy4">?</span><br />
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std<span class="sy4">::</span><span class="me2">format</span><span class="br0">(</span>STATICALLY_WIDEN<span class="sy1"><</span>CharT<span class="sy1">></span><span class="br0">(</span><span class="st0">"{:%Y}"</span><span class="br0">)</span>, y<span class="br0">)</span> <span class="sy4">:</span><br />
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std<span class="sy4">::</span><span class="me2">format</span><span class="br0">(</span>STATICALLY_WIDEN<span class="sy1"><</span>CharT<span class="sy1">></span><span class="br0">(</span><span class="st0">"{:%Y} is not a valid year"</span><span class="br0">)</span>, y<span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span></span></span></p>
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<p>其中 <span class="t-c"><span class="mw-geshi cpp source-cpp">STATICALLY_WIDEN<span class="sy1"><</span>CharT<span class="sy1">></span><span class="br0">(</span><span class="st0">"..."</span><span class="br0">)</span></span></span> 若 <code>CharT</code> 为 <code>char</code> 则为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="st0">"..."</span></span></span> ，而若 <code>CharT</code> 为 <code>wchar_t</code> 则为 <span class="t-c"><span class="mw-geshi cpp source-cpp">L<span class="st0">"..."</span></span></span> 。</p>
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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><code>os</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-utility-format-format.html"><span class="t-lines"><span>format</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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<td>在新 string 中存储参数的格式化表示<br />
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<span class="t-mark">(函数模板)</span></td>
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<div><a href="cpp-chrono-year-formatter.html"><span class="t-lines"><span>std::formatter<span class="t-dsc-small"><std::chrono::year></span></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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<td><span class="t-lc">std::formatter</span> 的特化，按照提供的格式格式化 <code>year</code><br />
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<span class="t-mark">(类模板特化)</span></td>
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