std::chrono::duration_cast

Converts a std::chrono::duration to a duration of different type ToDuration.

The function only participate in overload resolution if ToDuration is a specialization of std::chrono::duration.

Let

• ToRep be typename ToDuration::rep,
• ToPeriod be typename ToDuration::period,
• CF be std::ratio_divide<Period, ToPeriod>
• CR be std::common_type <Rep, ToRep, std::intmax_t > :: type
• cr_count be static_cast <CR> (d.count ( ) )
• cr_num be static_cast <CR> (CF:: num )
• cr_den be static_cast <CR> (CF:: den )

the result is:

Parameters

Return value

d converted to a duration of type ToDuration.

Notes

No implicit conversions are used. Multiplications and divisions are avoided where possible, if it is known at compile time that one or more parameters are 1. Computations are done in the widest type available and converted, as if by static_cast

Casting between integer durations where the source period is exactly divisible by the target period (e.g. hours to minutes) or between floating-point durations can be performed with ordinary casts or implicitly via std::chrono::duration constructors, no duration_cast

Casting from a floating-point duration to an integer duration is subject to undefined behavior static_cast

Example

#include <chrono>
#include <iostream>
#include <ratio>
#include <thread>
 
void f()
{
    std::this_thread::sleep_for(std::chrono::seconds(1));
}
 
int main()
{
    const auto t1 = std::chrono::high_resolution_clock::now();
    f();
    const auto t2 = std::chrono::high_resolution_clock::now();
 
    // floating-point duration: no duration_cast needed
    const std::chrono::duration<double, std::milli> fp_ms = t2 - t1;
 
    // integral duration: requires duration_cast
    const auto int_ms = std::chrono::duration_cast<std::chrono::milliseconds>(t2 - t1);
 
    // converting integral duration to integral duration of
    // shorter divisible time unit: no duration_cast needed
    const std::chrono::duration<long, std::micro> int_usec = int_ms;
 
    std::cout << "f() took " << fp_ms << ", or "
              << int_ms << " (whole milliseconds), or "
              << int_usec << " (whole microseconds)\n";
}

f() took 1000.14ms, or 1000ms (whole milliseconds), or 1000000us (whole microseconds)

See also