| Defined in header <chrono> | ||
|---|---|---|
template <class ToDuration, class Rep, class Period> constexpr ToDuration round(const 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 an instance of std::chrono::duration and std::chrono::treat_as_floating_point<typename ToDuration::rep>::value is false.
Parameters
| d | - | duration to convert |
Return value
d rounded to the nearest duration of type ToDuration, rounding to even in halfway cases.
Possible implementation
template <class T> struct is_duration : std::false_type {};
template <class Rep, class Period> struct is_duration<
std::chrono::duration<Rep, Period>> : std::true_type {};
template <class To, class Rep, class Period,
class = std::enable_if_t<is_duration<To>{} &&
!std::chrono::treat_as_floating_point<typename To::rep>{}>>
constexpr To round(const std::chrono::duration<Rep, Period>& d)
{
To t0 = std::chrono::duration::floor<To>(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;
} |
Example
See also
| converts a duration to another, with a different tick interval (function template) | |
| (C++17) | converts a duration to another, rounding down (function template) |
| (C++17) | converts a duration to another, rounding up (function template) |
| (C++17) | converts a time_point to another, rounding to nearest, ties to even (function template) |
| (C++11)(C++11)(C++11) | nearest integer, rounding away from zero in halfway cases (function) |
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