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std::chrono::time_point_cast

template <class ToDuration, class Clock, class Duration>
time_point<Clock, ToDuration> time_point_cast(
                                 const time_point<Clock, Duration> &t);

(since C++11)
(until C++14)

template <class ToDuration, class Clock, class Duration>
constexpr time_point<Clock, ToDuration> time_point_cast(
                                 const time_point<Clock, Duration> &t);

(since C++14)

Converts a std::chrono::time_point from one duration to another.

Parameters

t - time_point to convert from

Return value

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

Notes

time_point_cast will only participate in overload resolution if ToDuration is an instantiation of duration.

Example

#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));
 
    // implicit cast, no precision loss
    TimePoint<Ms> time_point_ms(time_point_sec);
    print_ms(time_point_ms); // 4000 ms
 
    time_point_ms = TimePoint<Ms>(Ms(5756));
 
    // explicit cast, need when precision loss may happens
    // 5756 truncated to 5000
    time_point_sec = std::chrono::time_point_cast<Sec>(time_point_ms);
    print_ms(time_point_sec); // 5000 ms
}

Output:

4000 ms
5000 ms

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