gcc/fortran/doc/gfortran/intrinsic-procedures/systemclock.rst

   1 ..
   2   Copyright 1988-2022 Free Software Foundation, Inc.
   3   This is part of the GCC manual.
   4   For copying conditions, see the copyright.rst file.
   5
   6 .. index:: SYSTEM_CLOCK, time, clock ticks, clock ticks
   7
   8 .. _system_clock:
   9
  10 SYSTEM_CLOCK --- Time function
  11 ******************************
  12
  13 .. function:: SYSTEM_CLOCK(COUNT, COUNT_RATE, COUNT_MAX)
  14
  15   Determines the :samp:`{COUNT}` of a processor clock since an unspecified
  16   time in the past modulo :samp:`{COUNT_MAX}`, :samp:`{COUNT_RATE}` determines
  17   the number of clock ticks per second.  If the platform supports a
  18   monotonic clock, that clock is used and can, depending on the platform
  19   clock implementation, provide up to nanosecond resolution.  If a
  20   monotonic clock is not available, the implementation falls back to a
  21   realtime clock.
  22
  23   :param COUNT:
  24     (Optional) shall be a scalar of type
  25     ``INTEGER`` with ``INTENT(OUT)``.
  26
  27   :param COUNT_RATE:
  28     (Optional) shall be a scalar of type
  29     ``INTEGER`` or ``REAL``, with ``INTENT(OUT)``.
  30
  31   :param COUNT_MAX:
  32     (Optional) shall be a scalar of type
  33     ``INTEGER`` with ``INTENT(OUT)``.
  34
  35   Standard:
  36     Fortran 90 and later
  37
  38   Class:
  39     Subroutine
  40
  41   Syntax:
  42     .. code-block:: fortran
  43
  44       CALL SYSTEM_CLOCK([COUNT, COUNT_RATE, COUNT_MAX])
  45
  46   Example:
  47     .. code-block:: fortran
  48
  49       PROGRAM test_system_clock
  50         INTEGER :: count, count_rate, count_max
  51         CALL SYSTEM_CLOCK(count, count_rate, count_max)
  52         WRITE(*,*) count, count_rate, count_max
  53       END PROGRAM
  54
  55   See also:
  56     :ref:`DATE_AND_TIME`,
  57     :ref:`CPU_TIME`