std::chrono::time_point_cast

C++

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Technical Specifications

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C-style date and time

std::chrono::time_point

Member functions

time_point::time_point

time_point::time_since_epoch

time_point::operator+time_point::operator-

time_point::operator++time_point::operator-- (C++20)(C++20)

time_point::min

time_point::max

Non-member functions

common_type

operator+operator-

operator==operator!=operator<operator<=operator>operator>=

time_point_cast

floor (C++17)

ceil (C++17)

round (C++17)

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

Run this code

#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