NAME¶

std::common_type(std::chrono::duration) - std::common_type(std::chrono::duration)

Synopsis¶

Defined in header <chrono>
template <class Rep1, class Period1, class Rep2, class Period2>

struct common_type<std::chrono::duration<Rep1, Period1>,
std::chrono::duration<Rep2, Period2>> { (since C++11)
typedef std::chrono::duration<
typename std::common_type<Rep1, Rep2>::type, /*see note*/> type;

};

Exposes the type named type, which is the common type of two std::chrono::durations,
whose period is the greatest common divisor of Period1 and Period2.

Note¶

The period of the resulting duration can be computed by forming a ratio of the
greatest common divisor of Period1::num and Period2::num and the least common
multiple of Period1::den and Period2::den.

Example¶

// Run this code

#include <type_traits>
#include <iostream>
#include <chrono>

// std::chrono already finds the greatest common divisor,
// likely using std::common_type<>. We make the type
// deduction externally.

template <typename T,typename S>
constexpr auto durationDiff(const T& t, const S& s)
-> typename std::common_type<T,S>::type
{
typedef typename std::common_type<T,S>::type Common;
return Common(t) - Common(s);
}

int main()
{
using namespace std::literals;

constexpr auto ms = 30ms;
constexpr auto us = 1100us;
constexpr auto diff = durationDiff(ms, us);

std::cout << ms.count() << "ms - " << us.count() << "μs = " << diff.count()
<< (std::is_same<decltype(diff), decltype(ms)>() ? "ms" : "μs")
<< '\n';
}

Output:¶

30ms - 1100μs = 28900μs

See also¶

std::common_type<std::chrono::time_point> specializes the std::common_type trait
(C++11) (class template specialization)
common_type determines the common type of a group of
(C++11) types
(class template)