285 lines
20 KiB
HTML
285 lines
20 KiB
HTML
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<title>std::chrono::time_point</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_chrono_time_point skin-cppreference2 action-view cpp-navbar">
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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::chrono::</span>time_point</h1>
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<div id="bodyContent">
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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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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span><span class="sy1"><</span><br /></span>
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<p> <span class="kw1">class</span> Clock,<br />
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<span class="kw1">class</span> Duration <span class="sy1">=</span> <span class="kw1">typename</span> Clock<span class="sy4">::</span><span class="me2">duration</span><br /></p>
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<span class="sy1">></span> <span class="kw1">class</span> time_point<span class="sy4">;</span></div>
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<td><span class="t-mark-rev t-since-cxx11">(C++11 起)</span></td>
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<p>类模板 <code>std::chrono::time_point</code> 表示时间中的一个点。它被实现成如同存储一个 <code>Duration</code> 类型的自 <code>Clock</code> 的纪元起始开始的时间间隔的值。</p>
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<p><code>Clock</code> 必须满足<a href="cpp-named_req-Clock.html"><span style="font-style:italic">时钟</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(Clock)</span></a> 的要求<span class="t-rev-inl t-since-cxx20"><span>或为 <span class="t-lc">std::chrono::local_t</span></span> <span><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></span></span>。</p>
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<td><span class="t-mark-rev t-until-cxx23">(C++23 前)</span></td>
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<h3><span class="mw-headline" id=".E6.88.90.E5.91.98.E7.B1.BB.E5.9E.8B">成员类型</span></h3>
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<td>成员类型</td>
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<td>定义</td>
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<td><code>clock</code></td>
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<td><code>Clock</code> ，此时间点在此时钟上计量</td>
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<tr class="t-dsc">
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<td><code>duration</code></td>
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<td><code>Duration</code> ，用于计量从纪元起时间的 <span class="t-lc"><a href="cpp-chrono-duration.html">std::chrono::duration</a></span> 类型</td>
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<tr class="t-dsc">
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<td><code>rep</code></td>
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<td><code>Rep</code> ，表示时期的计次数的算术类型</td>
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<td><code>period</code></td>
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<td><code>Period</code> ，表示时期周期的 <span class="t-lc"><a href="cpp-numeric-ratio-ratio.html">std::ratio</a></span> 类型</td>
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</table>
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<h3><span class="mw-headline" id=".E6.88.90.E5.91.98.E5.87.BD.E6.95.B0">成员函数</span></h3>
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<div class="t-dsc-member-div t-dsc-member-nobold-div">
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<div><a href="cpp-chrono-time_point-time_point.html"><span class="t-lines"><span>(构造函数)</span></span></a></div>
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</div>
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</td>
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<td>构造新的 time_point<br />
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<span class="t-mark">(公开成员函数)</span></td>
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<td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-chrono-time_point-time_since_epoch.html"><span class="t-lines"><span>time_since_epoch</span></span></a></div>
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</td>
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<td>返回表示为从其时钟起点开始的时间点<br />
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<span class="t-mark">(公开成员函数)</span></td>
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<tr class="t-dsc">
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<div class="t-dsc-member-div">
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<div><a href="cpp-chrono-time_point-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>以给定的 duration 修改 time_point<br />
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<span class="t-mark">(公开成员函数)</span></td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-chrono-time_point-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><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>自增或自减 duration<br />
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<span class="t-mark">(公开成员函数)</span></td>
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</tr>
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<tr class="t-dsc">
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<td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-chrono-time_point-min.html"><span class="t-lines"><span>min</span></span></a></div>
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<div><span class="t-lines"><span><span class="t-cmark">[静态]</span></span></span></div>
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</div>
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</td>
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<td>返回对应最小时长的时间点<br />
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<span class="t-mark">(公开静态成员函数)</span></td>
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</tr>
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<tr class="t-dsc">
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<td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-chrono-time_point-max.html"><span class="t-lines"><span>max</span></span></a></div>
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<div><span class="t-lines"><span><span class="t-cmark">[静态]</span></span></span></div>
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</div>
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</td>
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<td>返回对应最大时长的时间点<br />
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<span class="t-mark">(公开静态成员函数)</span></td>
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</tr>
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</table>
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<h3><span class="mw-headline" id=".E9.9D.9E.E6.88.90.E5.91.98.E5.87.BD.E6.95.B0">非成员函数</span></h3>
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<div class="t-dsc-member-div">
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<div><a href="cpp-chrono-time_point-operator_arith2.html"><span class="t-lines"><span>operator+</span><span>operator-</span></span></a></div>
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<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div>
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</div>
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</td>
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<td>实施涉及时间点的加法和减法运算<br />
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<span class="t-mark">(函数模板)</span></td>
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<tr class="t-dsc">
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<div class="t-dsc-member-div">
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<div><a href="cpp-chrono-time_point-operator_cmp.html"><span class="t-lines"><span>operator==</span><span>operator!=</span><span>operator<</span><span>operator<=</span><span>operator></span><span>operator>=</span><span>operator<=></span></span></a></div>
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<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span><span><span class="t-mark-rev t-since-cxx11">(C++11)</span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span><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>比较两个时间点<br />
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<span class="t-mark">(函数模板)</span></td>
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<tr class="t-dsc">
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<div class="t-dsc-member-div">
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<div><a href="cpp-chrono-time_point-time_point_cast.html"><span class="t-lines"><span>time_point_cast</span></span></a></div>
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<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div>
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</div>
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</td>
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<td>转换时间点为同一时钟上拥有不同时长的另一时间点<br />
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<span class="t-mark">(函数模板)</span></td>
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</tr>
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<tr class="t-dsc">
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<td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-chrono-time_point-floor.html"><span class="t-lines"><span>floor<span class="t-dsc-small">(std::chrono::time_point)</span></span></span></a></div>
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<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx17">(C++17)</span></span></span></div>
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</div>
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</td>
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<td>转换 time_point 到另一个，向下取整<br />
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<span class="t-mark">(函数模板)</span></td>
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</tr>
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<tr class="t-dsc">
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<div class="t-dsc-member-div">
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<div><a href="cpp-chrono-time_point-ceil.html"><span class="t-lines"><span>ceil<span class="t-dsc-small">(std::chrono::time_point)</span></span></span></a></div>
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<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx17">(C++17)</span></span></span></div>
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</div>
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</td>
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<td>转换 time_point 到另一个，向上取整<br />
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<span class="t-mark">(函数模板)</span></td>
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</tr>
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<tr class="t-dsc">
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<td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-chrono-time_point-round.html"><span class="t-lines"><span>round<span class="t-dsc-small">(std::chrono::time_point)</span></span></span></a></div>
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<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx17">(C++17)</span></span></span></div>
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</div>
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</td>
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<td>转换 time_point 到另一个，就近取整，偶数优先<br />
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<span class="t-mark">(函数模板)</span></td>
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<h3><span class="mw-headline" id=".E8.BE.85.E5.8A.A9.E7.B1.BB">辅助类</span></h3>
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<table class="t-dsc-begin">
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<div class="t-dsc-member-div">
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<div><a href="cpp-chrono-time_point-common_type.html"><span class="t-lines"><span>std::common_type<span class="t-dsc-small"><std::chrono::time_point></span></span></span></a></div>
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<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div>
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</div>
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</td>
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<td>特化 <span class="t-lc"><a href="cpp-types-common_type.html">std::common_type</a></span> 特征<br />
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<span class="t-mark">(类模板特化)</span></td>
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</table>
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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 <algorithm></span>
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<span class="co2">#include <iostream></span>
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<span class="co2">#include <iomanip></span>
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<span class="co2">#include <ctime></span>
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<span class="co2">#include <chrono></span>
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<span class="kw4">void</span> slow_motion<span class="br0">(</span><span class="br0">)</span>
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<span class="br0">{</span>
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<span class="kw4">static</span> <span class="kw4">int</span> a<span class="br0">[</span><span class="br0">]</span> <span class="br0">{</span><span class="nu0">1</span>,<span class="nu0">2</span>,<span class="nu0">3</span>,<span class="nu0">4</span>,<span class="nu0">5</span>,<span class="nu0">6</span>,<span class="nu0">7</span>,<span class="nu0">8</span>,<span class="nu0">9</span>,<span class="nu0">10</span>,<span class="nu0">11</span>,<span class="nu0">12</span><span class="br0">}</span><span class="sy4">;</span>
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<span class="kw1">while</span> <span class="br0">(</span>std<span class="sy4">::</span><span class="me2">ranges</span><span class="sy4">::</span><span class="me2">next_permutation</span><span class="br0">(</span>a<span class="br0">)</span>.<span class="me1">found</span><span class="br0">)</span>
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<span class="br0">{</span> <span class="br0">}</span> <span class="co1">// 生成 12! 个排列</span>
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<span class="br0">}</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">literals</span><span class="sy4">;</span> <span class="co1">// 允许用 24h 、 1ms 、 1s 代替对应的</span>
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<span class="co1">// std::chrono::hours(24) 等待</span>
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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">time_point</span><span class="sy1"><</span><a href="cpp-chrono-system_clock.html"><span class="kw1003">std::<span class="me2">chrono</span><span class="sy4">::</span><span class="me2">system_clock</span></span></a><span class="sy1">></span> now <span class="sy1">=</span>
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std<span class="sy4">::</span><span class="me2">chrono</span><span class="sy4">::</span><span class="me2">system_clock</span><span class="sy4">::</span><span class="me2">now</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="co1">// “生产代码”可以简化为：</span>
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<span class="co1">// const auto now = std::chrono::system_clock::now();</span>
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<span class="kw4">const</span> <a href="cpp-chrono-c-time_t.html"><span class="kw1023">std::<span class="me2">time_t</span></span></a> t_c <span class="sy1">=</span> std<span class="sy4">::</span><span class="me2">chrono</span><span class="sy4">::</span><span class="me2">system_clock</span><span class="sy4">::</span><span class="me2">to_time_t</span><span class="br0">(</span>now <span class="sy2">-</span> 24h<span class="br0">)</span><span class="sy4">;</span>
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<a href="cpp-io-cout.html"><span class="kw1757">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"24 hours ago, the time was "</span>
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<span class="sy1"><<</span> <a href="cpp-io-manip-put_time.html"><span class="kw1800">std::<span class="me2">put_time</span></span></a><span class="br0">(</span><a href="cpp-chrono-c-localtime.html"><span class="kw1019">std::<span class="me2">localtime</span></span></a><span class="br0">(</span><span class="sy3">&</span>t_c<span class="br0">)</span>, <span class="st0">"%F %T.<span class="es1">\n</span>"</span><span class="br0">)</span> <span class="sy1"><<</span> <a href="cpp-io-manip-flush.html"><span class="kw1789">std::<span class="me2">flush</span></span></a><span class="sy4">;</span>
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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">time_point</span><span class="sy1"><</span><a href="cpp-chrono-steady_clock.html"><span class="kw1005">std::<span class="me2">chrono</span><span class="sy4">::</span><span class="me2">steady_clock</span></span></a><span class="sy1">></span> start <span class="sy1">=</span>
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std<span class="sy4">::</span><span class="me2">chrono</span><span class="sy4">::</span><span class="me2">steady_clock</span><span class="sy4">::</span><span class="me2">now</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="co1">// “现实生活”的替用写法会是：</span>
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<span class="co1">// const auto start = std::chrono::steady_clock::now();</span>
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slow_motion<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="kw4">const</span> <span class="kw4">auto</span> end <span class="sy1">=</span> std<span class="sy4">::</span><span class="me2">chrono</span><span class="sy4">::</span><span class="me2">steady_clock</span><span class="sy4">::</span><span class="me2">now</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
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<a href="cpp-io-cout.html"><span class="kw1757">std::<span class="me2">cout</span></span></a>
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<span class="sy1"><<</span> <span class="st0">"Slow calculations took "</span>
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<span class="sy1"><<</span> <a href="cpp-chrono-duration-duration_cast.html"><span class="kw999">std::<span class="me2">chrono</span><span class="sy4">::</span><span class="me2">duration_cast</span></span></a><span class="sy1"><</span><a href="cpp-chrono-duration.html"><span class="kw994">std::<span class="me2">chrono</span><span class="sy4">::</span><span class="me2">microseconds</span></span></a><span class="sy1">></span><span class="br0">(</span>end <span class="sy2">-</span> start<span class="br0">)</span>.<span class="me1">count</span><span class="br0">(</span><span class="br0">)</span> <span class="sy1"><<</span> <span class="st0">"µs ≈ "</span>
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<span class="sy1"><<</span> <span class="br0">(</span>end <span class="sy2">-</span> start<span class="br0">)</span> <span class="sy2">/</span> 1ms <span class="sy1"><<</span> <span class="st0">"ms ≈ "</span> <span class="co1">// 几乎等价于以上形式，</span>
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<span class="sy1"><<</span> <span class="br0">(</span>end <span class="sy2">-</span> start<span class="br0">)</span> <span class="sy2">/</span> 1s <span class="sy1"><<</span> <span class="st0">"s.<span class="es1">\n</span>"</span><span class="sy4">;</span> <span class="co1">// 但分别使用毫秒和秒</span>
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<span class="br0">}</span></pre></div>
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</div>
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<p>可能的输出：</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">24 hours ago, the time was 2021-02-15 18:28:52.
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Slow calculations took 2090448µs ≈ 2090ms ≈ 2s.</pre></div>
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</div>
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</div>
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<h3><span class="mw-headline" id=".E5.8F.82.E9.98.85">参阅</span></h3>
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<table class="t-dsc-begin">
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<tr class="t-dsc">
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<td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-chrono-duration.html"><span class="t-lines"><span>duration</span></span></a></div>
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<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div>
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</div>
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</td>
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<td>时间区间<br />
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<span class="t-mark">(类模板)</span></td>
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</tr>
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</table>
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</div>
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<div class="visualClear"></div>
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</div>
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</div>
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</div>
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</body>
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</html>
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