class
<chrono>

std::chrono::system_clock

class system_clock;
System clock
Clock classes provide access to the current time_point.

Specifically, system_clock is a system-wide realtime clock.

Clock properties

realtime
It is intended to represent the real time, and thus it can be translated in some way to and from calendar representations (see to_time_t and from_time_t member functions).
signed count
Its time_point values can refer to times before the epoch (with negative values).
system-wide
All processes running on the system shall retrieve the same time_point values by using this clock.

Member types

The following aliases are member types of system_clock:

member typedefinitionnotes
repA signed arithmetic type (or a class that emulates it)Used to store a count of periods.
periodA ratio typeRepresents the length of a period in seconds.
durationduration<rep,period>The clock's duration type.
time_pointtime_point<system_clock>The clock's time_point type.

Member constants

member constantdefinition
is_steadya bool value specifying whether the clock always advances, and whether it does at a steady state relative to physical time. If true, this implies that the system clock may not be adjusted.

Static member functions

now
Get current time (public static member function )
to_time_t
Convert to time_t ( public static member function )
from_time_t
Convert from time_t ( public static member function )

Example

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// system_clock example
#include <iostream>
#include <ctime>
#include <ratio>
#include <chrono>

int main ()
{
  using std::chrono::system_clock;

  std::chrono::duration<int,std::ratio<60*60*24> > one_day (1);

  system_clock::time_point today = system_clock::now();
  system_clock::time_point tomorrow = today + one_day;

  std::time_t tt;

  tt = system_clock::to_time_t ( today );
  std::cout << "today is: " << ctime(&tt);

  tt = system_clock::to_time_t ( tomorrow );
  std::cout << "tomorrow will be: " << ctime(&tt);

  return 0;
}


Possible output:
today is: Wed May 30 12:25:03 2012
tomorrow will be: Thu May 31 12:25:03 2012

See also

steady_clock
Steady clock (class )
high_resolution_clock
High resolution clock (class )

C++