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std::chrono::system_clock(3)   C++ Standard Libary  std::chrono::system_clock(3)

NAME
     std::chrono::system_clock - std::chrono::system_clock

Synopsis
	Defined in header <chrono>
	class system_clock;	    (since C++11)

	Class  std::chrono::system_clock  represents  the  system-wide real time
     wall clock.

	It may not be monotonic: on most systems, the system  time  can  be  ad-
     justed at any
	moment.  It  is  the only C++ clock that has the ability to map its time
     points to
	C-style time.

	std::chrono::system_clock meets the requirements of TrivialClock.

	The epoch of system_clock is unspecified, but most implementations use
	Unix Time (i.e., time since 00:00:00 Coordinated Universal  Time  (UTC),
     (until C++20)
	Thursday, 1 January 1970, not counting leap seconds).
	system_clock measures Unix Time (i.e., time since 00:00:00 Coordinated
	Universal  Time  (UTC),  Thursday,  1  January	1970,  not counting leap
     (since C++20)
	seconds).

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::system_clock>

Member constants
				 true if the time between ticks is  always  con-
     stant, i.e.
	constexpr  bool is_steady calls to now() return values that increase mo-
     notonically
	[static]		 even in case of some external clock adjustment,
     otherwise
				 false
				 (public static member constant)

Member functions
	now	    returns a std::chrono::time_point representing  the  current
     point in time
	[static]    (public static member function)
	to_time_t   converts a system clock time point to std::time_t
	[static]    (public static member function)
	from_time_t converts std::time_t to a system clock time point
	[static]    (public static member function)

Notes
	The  system_clock's time value can be internally adjusted at any time by
     the
	operating system, for example due to NTP  synchronization  or  the  user
     changing the
	system's  clock. Daylight Saving Time and time zone changes, however, do
     not affect
	it since it is based on the UTC time-zone.

See also
	steady_clock	      monotonic clock that will never be adjusted
	(C++11) 	      (class)
	high_resolution_clock the clock with the shortest tick period available
	(C++11) 	      (class)

http://cppreference.com 	   2024.06.10	    std::chrono::system_clock(3)
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