Lahey/GNU Fortran

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8.238 SYSTEM_CLOCK — Time function

Description:
Determines the COUNT of a processor clock since an unspecified time in the past modulo COUNT_MAX, COUNT_RATE determines the number of clock ticks per second. If the platform supports a high resolution monotonic clock, that clock is used and can provide up to nanosecond resolution. If a high resolution monotonic clock is not available, the implementation falls back to a potentially lower resolution realtime clock.

COUNT_RATE and COUNT_MAX vary depending on the kind of the arguments. For kind=8 arguments, COUNT represents nanoseconds, and for kind=4 arguments, COUNT represents milliseconds. Other than the kind dependency, COUNT_RATE and COUNT_MAX are constant, however the particular values are specific to gfortran.

If there is no clock, COUNT is set to -HUGE(COUNT), and COUNT_RATE and COUNT_MAX are set to zero.

When running on a platform using the GNU C library (glibc), or a derivative thereof, the high resolution monotonic clock is available only when linking with the rt library. This can be done explicitly by adding the -lrt flag when linking the application, but is also done implicitly when using OpenMP.

Standard:
Fortran 95 and later
Class:
Subroutine
Syntax:
CALL SYSTEM_CLOCK([COUNT, COUNT_RATE, COUNT_MAX])
Arguments:

COUNT (Optional) shall be a scalar of type INTEGER with INTENT(OUT).
COUNT_RATE (Optional) shall be a scalar of type INTEGER with INTENT(OUT).
COUNT_MAX (Optional) shall be a scalar of type INTEGER with INTENT(OUT).

Example:
          PROGRAM test_system_clock
            INTEGER :: count, count_rate, count_max
            CALL SYSTEM_CLOCK(count, count_rate, count_max)
            WRITE(*,*) count, count_rate, count_max
          END PROGRAM
     

See also:
DATE_AND_TIME, CPU_TIME