std::chrono::round(std::chrono::duration) - cppreference.com (original) (raw)
| | | | | ------------------------------------------------------------------------------------------------------------------------------------------------------ | | ------------- | | template< class ToDuration, class Rep, class Period > constexpr ToDuration round( const std::chrono::duration<Rep, Period>& d ); | | (since C++17) |
Returns the value t representable in ToDuration that is the closest to d. If there are two such values, returns the even value (that is, the value t such that t % 2 == 0).
The function does not participate in the overload resolution unless ToDuration is a specialization of std::chrono::duration and std::chrono::treat_as_floating_point_v<typename ToDuration::rep> is false.
[edit] Parameters
[edit] Return value
d rounded to the nearest duration of type ToDuration, rounding to even in halfway cases.
[edit] Possible implementation
namespace detail
{
template inline constexpr bool is_duration_v = false;
template<class Rep, class Period> inline constexpr bool is_duration_v<
std::chrono::duration<Rep, Period>> = true;
}
template<class To, class Rep, class Period,
class = std::enable_if_t<detail::is_duration_v &&
>>
constexpr To round(const std::chrono::duration<Rep, Period>& d)
{
To t0 = std::chrono::floor(d);
To t1 = t0 + To{1};
auto diff0 = d - t0;
auto diff1 = t1 - d;
if (diff0 == diff1)
{
if (t0.count() & 1)
return t1;
return t0;
}
else if (diff0 < diff1)
return t0;
return t1;
}
[edit] Example
#include #include #include int main() { using namespace std::chrono_literals; std::cout << "Duration\tFloor\tRound\tCeil\n"; for (using Sec = std::chrono::seconds; auto const d : {+4999ms, +5000ms, +5001ms, +5499ms, +5500ms, +5999ms, -4999ms, -5000ms, -5001ms, -5499ms, -5500ms, -5999ms}) std::cout << std::showpos << d << "\t\t" << std::chrono::floor(d) << '\t' << std::chrono::round(d) << '\t' << std::chrono::ceil (d) << '\n'; }
Output:
Duration Floor Round Ceil +4999ms +4s +5s +5s +5000ms +5s +5s +5s +5001ms +5s +5s +6s +5499ms +5s +5s +6s +5500ms +5s +6s +6s +5999ms +5s +6s +6s -4999ms -5s -5s -4s -5000ms -5s -5s -5s -5001ms -6s -5s -5s -5499ms -6s -5s -5s -5500ms -6s -6s -5s -5999ms -6s -6s -5s