72 lines
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72 lines
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<title>std::chrono::get_tzdb_list, std::chrono::get_tzdb, std::chrono::remote_version, std::chrono::reload_tzdb</title>
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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::chrono::</span>get_tzdb_list, <span style="font-size:0.7em; line-height:130%">std::chrono::</span>get_tzdb, <span style="font-size:0.7em; line-height:130%">std::chrono::</span>remote_version, <span style="font-size:0.7em; line-height:130%">std::chrono::</span>reload_tzdb</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><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">chrono</span><span class="sy4">::</span><span class="me2">tzdb_list</span><span class="sy3">&</span> get_tzdb_list<span class="br0">(</span><span class="br0">)</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">const</span> std<span class="sy4">::</span><span class="me2">chrono</span><span class="sy4">::</span><span class="me2">tzdb</span><span class="sy3">&</span> get_tzdb<span class="br0">(</span><span class="br0">)</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"><a href="cpp-string-basic_string.html"><span class="kw1230">std::<span class="me2">string</span></span></a> remote_version<span class="br0">(</span><span class="br0">)</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">const</span> std<span class="sy4">::</span><span class="me2">chrono</span><span class="sy4">::</span><span class="me2">tzdb</span><span class="sy3">&</span> reload_tzdb<span class="br0">(</span><span class="br0">)</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>这些函数提供到程序范围的时区数据库访问。</p>
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<div class="t-li1"><span class="t-li">1)</span> 返回到全局 <span class="t-lc">std::chrono::tzdb_list</span> 单例的引用。若这是到数据库的首次访问,则初始化数据库。初始化后,数据库将保有单个初始化的 <span class="t-lc">std::chrono::tzdb</span> 对象 。此函数是线程安全的:同时调用此函数不引入数据竞争。</div>
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<div class="t-li1"><span class="t-li">2)</span> 返回到 <code>tzdb_list</code> 单例所保有的首个 <span class="t-lc">std::chrono::tzdb</span> 对象的引用。等价于 <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">get_tzdb_list</span><span class="br0">(</span><span class="br0">)</span>.<span class="me1">front</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> 返回含有最新远程数据库版本的 string 。</div>
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<div class="t-li1"><span class="t-li">4)</span> 若 <span class="t-c"><span class="mw-geshi cpp source-cpp">remote_version<span class="br0">(</span><span class="br0">)</span> <span class="sy3">!</span><span class="sy1">=</span> get_tzdb<span class="br0">(</span><span class="br0">)</span>.<span class="me1">version</span></span></span> ,则推入表示远程数据库的新 <code>tzdb</code> 对象到 <code>get_tzdb_list()</code> 所引用的 <code>tzdb_list</code> 单例的前部。否则无效果。不非法化任何引用、指针或迭代器。同时与 <span class="t-c"><span class="mw-geshi cpp source-cpp">get_tzdb_list<span class="br0">(</span><span class="br0">)</span>.<span class="me1">front</span><span class="br0">(</span><span class="br0">)</span></span></span> 或 <span class="t-c"><span class="mw-geshi cpp source-cpp">get_tzdb_list<span class="br0">(</span><span class="br0">)</span>.<span class="me1">erase_after</span><span class="br0">(</span><span class="br0">)</span></span></span> 调用此函数不引入数据竞争。</div>
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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> 若因任何原因,到 <code>tzdb_list</code> 的引用含有一或多个不能返回的 <code>tzdb</code> 则为 <span class="t-lc"><a href="cpp-error-runtime_error.html">std::runtime_error</a></span> 。</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)</span> 到全局 <span class="t-lc">std::chrono::tzdb_list</span> 单例的引用。</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">std<span class="sy4">::</span><span class="me2">chrono</span><span class="sy4">::</span><span class="me2">get_tzdb_list</span><span class="br0">(</span><span class="br0">)</span>.<span class="me1">front</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> 含有最新远程数据库版本的 string 。</div>
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<div class="t-li1"><span class="t-li">4)</span> (此函数所作的任何更新后的) <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">get_tzdb_list</span><span class="br0">(</span><span class="br0">)</span>.<span class="me1">front</span><span class="br0">(</span><span class="br0">)</span></span></span> 。</div>
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