std::chrono:: tai_clock

Defined in header <chrono>
class tai_clock ;		(since C++20)

The clock std::chrono::tai_clock is a Clock that represents International Atomic Time (TAI). It measures time since 00:00:00, 1 January 1958, and is offset 10 seconds ahead of UTC at that date (i.e., its epoch, 1958-01-01 00:00:00 TAI, is 1957-12-31 23:59:50 UTC).

Leap seconds are not inserted into TAI. Thus, every time a leap second is inserted into UTC, UTC falls another second behind TAI. As of December 2017, UTC is 37 seconds behind TAI, reflecting the 10-second initial offset and the 27 leap seconds inserted between 1958 and 2017. Thus, 2018-01-01 00:00:00 UTC is equivalent to 2018-01-01 00:00:37 TAI.

tai_clock meets the Clock requirements. It does not meet the TrivialClock requirements unless the implementation can guarantee that now() does not throw an exception.

Time point family

Defined in namespace std::chrono
template < class Duration > using tai_time = std:: chrono :: time_point < std :: chrono :: tai_clock , Duration > ;		(since C++20)
using tai_seconds = tai_time < std:: chrono :: seconds > ;		(since C++20)

operator<< (std::chrono::tai_time) (C++20)	performs stream output on a tai_time (function template)
from_stream (std::chrono::tai_time) (C++20)	parses a tai_time from a stream according to the provided format (function template)
std::formatter <std::chrono::tai_time> (C++20)	formatting support for tai_time (class template specialization)

Member types

Member type	Definition
rep	signed arithmetic type representing the number of ticks in the clock's duration
period	a std::ratio type representing the tick period of the clock, in seconds
duration	std:: chrono :: duration < rep, period > , capable of representing negative durations
time_point	std:: chrono :: time_point < std :: chrono :: tai_clock >

Member constants

constexpr bool is_steady [static]

true if the time between ticks is always constant, i.e. calls to now() return values that increase monotonically even in case of some external clock adjustment, otherwise false (public static member constant)

Member functions

now [static]	returns a std::chrono::time_point representing the current point in time (public static member function)
to_utc [static]	converts tai_time to utc_time (public static member function)
from_utc [static]	converts utc_time to tai_time (public static member function)