Defined in header <chrono> | ||
|---|---|---|
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.
| d | - | duration to convert |
d rounded to the nearest duration of type ToDuration, rounding to even in halfway cases.
namespace detail {
template<class> 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<To> &&
!std::chrono::treat_as_floating_point_v<typename To::rep>>>
constexpr To round(const std::chrono::duration<Rep, Period>& d)
{
To t0 = std::chrono::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;
} |
#include <iostream>
#include <iomanip>
#include <chrono>
int main()
{
using namespace std::chrono_literals;
using Sec = std::chrono::seconds;
for (std::cout << "Duration\tFloor\tRound\tCeil\n"
"(ms)\t\t(sec)\t(sec)\t(sec)\n";
auto const d: {
+4999ms, +5000ms, +5001ms, +5499ms, +5500ms, +5999ms,
-4999ms, -5000ms, -5001ms, -5499ms, -5500ms, -5999ms, }) {
std::cout << std::showpos << d.count() << "\t\t"
<< std::chrono::floor<Sec>(d).count() << '\t'
<< std::chrono::round<Sec>(d).count() << '\t'
<< std::chrono::ceil <Sec>(d).count() << '\n';
}
}Output:
Duration Floor Round Ceil (ms) (sec) (sec) (sec) +4999 +4 +5 +5 +5000 +5 +5 +5 +5001 +5 +5 +6 +5499 +5 +5 +6 +5500 +5 +6 +6 +5999 +5 +6 +6 -4999 -5 -5 -4 -5000 -5 -5 -5 -5001 -6 -5 -5 -5499 -6 -5 -5 -5500 -6 -6 -5 -5999 -6 -6 -5
|
(C++11) | 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)(C++11)(C++11)(C++11)(C++11)(C++11)(C++11) | nearest integer, rounding away from zero in halfway cases (function) |
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