20 General utilities library [utilities]

20.11 Time utilities [time]

20.11.5 Class template duration [time.duration]

20.11.5.7 duration_cast [time.duration.cast]

template <class ToDuration, class Rep, class Period> constexpr ToDuration duration_cast(const duration<Rep, Period>& d);

1

Remarks: This function shall not participate in overload resolution unless ToDuration is an instantiation of duration.

2

Returns: Let CF be ratio_divide<Period, typename ToDuration::period>, and CR be common_type< typename ToDuration::rep, Rep, intmax_t>::type.

  • (2.1)

    If CF::num == 1 and CF::den == 1, returns 

    ToDuration(static_cast<typename ToDuration::rep>(d.count()))
  • (2.2)

    otherwise, if CF::num != 1 and CF::den == 1, returns 

    ToDuration(static_cast<typename ToDuration::rep>(
  static_cast<CR>(d.count()) * static_cast<CR>(CF::num)))
  • (2.3)

    otherwise, if CF::num == 1 and CF::den != 1, returns 

    ToDuration(static_cast<typename ToDuration::rep>(
  static_cast<CR>(d.count()) / static_cast<CR>(CF::den)))
  • (2.4)

    otherwise, returns 

    ToDuration(static_cast<typename ToDuration::rep>(
  static_cast<CR>(d.count()) * static_cast<CR>(CF::num) / static_cast<CR>(CF::den)))

Notes: This function does not use any implicit conversions; all conversions are done with static_cast. It avoids multiplications and divisions when it is known at compile time that one or more arguments is 1. Intermediate computations are carried out in the widest representation and only converted to the destination representation at the final step.