std::common_type<std::chrono::duration>

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Helper classes
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)

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

Member types

Member type Definition
type std::chrono::duration < typename std::common_type <Rep1, Rep2> :: type, /* see note */ >

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 <chrono>
#include <iostream>
#include <type_traits>
 
// 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 << " - " << us << " = " << diff << '\n';
}

Output: 

30ms - 1100us = 28900us

See also

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