The <chrono> header provides classes for representing points in time
and durations, and clock classes which act as a source of time_points. Each clock has an
is_steady static data member
which indicates whether or not it is a steady clock
that advances at a uniform rate (and cannot be adjusted). The std::chrono::steady_clock
class and std::chrono::monotonic_clock
class are the only clocks guaranteed to be steady.
namespace std { namespace chrono { template< typename Rep,typename Period = ratio<1>> class duration; template< typename Clock, typename Duration = typename Clock::duration> class time_point; class system_clock; class steady_clock; typedef unspecified-clock-type high_resolution_clock; // for backwards compatibility only class monotonic_clock; } }