std::chrono::time_point_cast

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C 风格日期和时间
 
std::chrono::time_point
 
template <class ToDuration, class Clock, class Duration>

time_point<Clock, ToDuration> time_point_cast(

                                 const time_point<Clock, Duration> &t);
 (C++11 起)
(C++14 前)
template <class ToDuration, class Clock, class Duration>

constexpr time_point<Clock, ToDuration> time_point_cast(

                                 const time_point<Clock, Duration> &t);
 (C++14 起)

将 std::chrono::time_point 从一个 duration 到另一个。

示例

t - 转换来源的 time_point

返回值

std::chrono::time_point<Clock, ToDuration>(std::chrono::duration_cast<ToDuration>(t.time_since_epoch()))

注意

仅若 ToDuration 为 duration 的实例， time_point_cast 才会参与重载决议。

示例

运行此代码
#include <iostream>
#include <chrono>
 
using Clock = std::chrono::high_resolution_clock;
using Ms = std::chrono::milliseconds;
using Sec = std::chrono::seconds;
 
template<class Duration>
using TimePoint = std::chrono::time_point<Clock, Duration>;
 
inline void print_ms(const TimePoint<Ms>& time_point) 
{
    std::cout << time_point.time_since_epoch().count() << " ms\n";
}
 
int main() 
{
    TimePoint<Sec> time_point_sec(Sec(4));
 
    // 隐式转换，无精度损失
    TimePoint<Ms> time_point_ms(time_point_sec);
    print_ms(time_point_ms); // 4000 ms
 
    time_point_ms = TimePoint<Ms>(Ms(5756));
 
    // 显式转型，在精度损失可能发生时需要
    // 5756 truncated to 5000
    time_point_sec = std::chrono::time_point_cast<Sec>(time_point_ms);
    print_ms(time_point_sec); // 5000 ms
}

输出： 

4000 ms
5000 ms