30 Time library [time]

30.6 Class template time_point [time.point]

30.6.8 Conversions [time.point.cast]

template<class ToDuration, class Clock, class Duration> constexpr time_point<Clock, ToDuration> time_point_cast(const time_point<Clock, Duration>& t);
Constraints: ToDuration is a specialization of duration.
Returns: time_point<Clock, ToDuration>(duration_cast<ToDuration>(t.time_since_epoch()))
template<class ToDuration, class Clock, class Duration> constexpr time_point<Clock, ToDuration> floor(const time_point<Clock, Duration>& tp);
Constraints: ToDuration is a specialization of duration.
Returns: time_point<Clock, ToDuration>(floor<ToDuration>(tp.time_since_epoch())).
template<class ToDuration, class Clock, class Duration> constexpr time_point<Clock, ToDuration> ceil(const time_point<Clock, Duration>& tp);
Constraints: ToDuration is a specialization of duration.
Returns: time_point<Clock, ToDuration>(ceil<ToDuration>(tp.time_since_epoch())).
template<class ToDuration, class Clock, class Duration> constexpr time_point<Clock, ToDuration> round(const time_point<Clock, Duration>& tp);
Constraints: ToDuration is a specialization of duration, and treat_as_floating_point_v<typename ToDuration​::​rep> is false.
Returns: time_point<Clock, ToDuration>(round<ToDuration>(tp.time_since_epoch())).