Sun Studio 12: Fortran Programming Guide

7.7 Time and Date Functions

Library functions that return the time of day or elapsed CPU time vary from system to system.

The time functions supported in the Fortran library are listed in the following table:

Table 7–3 Fortran Time Functions


Name	Function	Man Page
`time`	Returns the number of seconds elapsed since January, 1, 1970	`time`(3F)
`date`	Returns date as a character string	`date`(3F)
`fdate`	Returns the current time and date as a character string	`fdate`(3F)
`idate`	Returns the current month, day, and year in an integer array	`idate`(3F)
`itime`	Returns the current hour, minute, and second in an integer array	`itime`(3F)
`ctime`	Converts the time returned by the `time` function to a character string	`ctime`(3F)
`ltime`	Converts the time returned by the `time` function to the local time	`ltime`(3F)
`gmtime`	Converts the time returned by the `time` function to Greenwich time	`gmtime`(3F)
`etime`	Single processor: Returns elapsed user and system time for program execution Multiple processors: Returns the wall clock time	`etime`(3F)
`dtime`	Returns the elapsed user and system time since last call to `dtime`	`dtime`(3F)
`date_and_time`	Returns date and time in character and numeric form	`date_and_time`(3F)

For details, see Fortran Library Reference Manual or the individual man pages for these functions. Here is a simple example of the use of these time functions (TestTim.f):

      subroutine startclock
      common / myclock / mytime
      integer mytime, time
      mytime = time()
      return
      end
      function wallclock()
      integer wallclock
      common / myclock / mytime
      integer mytime, time, newtime
      newtime = time()
      wallclock = newtime - mytime
      mytime = newtime
      return
      end
      integer wallclock, elapsed
      character*24 greeting
      real dtime, timediff, timearray(2)
c      print a heading
      call fdate( greeting )
      print*,  "      Hello, Time Now Is: ",  greeting
      print*,      "See how long ’sleep 4’ takes, in seconds"
      call startclock
      call system( ’sleep 4’ )
      elapsed = wallclock()
      print*, "Elapsed time for sleep 4 was: ", elapsed," seconds"
c      now test the cpu time for some trivial computing
      timediff = dtime( timearray )
      q = 0.01
      do 30 i = 1, 100000
            q = atan( q )
30      continue
      timediff = dtime( timearray )
      print*, "atan(q) 100000 times took: ", timediff ," seconds"
      end

Running this program produces the following results:

demo% TimeTest
       Hello, Time Now Is: Thu Feb  8 15:33:36 2001
 See how long ’sleep 4’ takes, in seconds
 Elapsed time for sleep 4 was:  4  seconds
 atan(q) 100000 times took:  0.01  seconds
demo%

The routines listed in the following table provide compatibility with VMS Fortran system routines idate and time. To use these routines, you must include the -lV77 option on the f95 command line, in which case you also get these VMS versions instead of the standard f95 versions.

Table 7–4 Summary: Nonstandard VMS Fortran System Routines


Name	Definition	Calling Sequence	Argument Type
`idate`	Date as day, month, year	`call idate( d, m, y )`	`integer`
`time`	Current time as `hhmmss`	`call time( t )`	*`character8`**

Note –

The date(3F) routine and the VMS version of idate(3F) cannot be Year 2000 safe because they return 2-digit values for the year. Programs that compute time duration by subtracting dates returned by these routines will compute erroneous results after December 31, 1999. The Fortran 95 routine date_and_time(3F) should be used instead. See the Fortran Library Reference Manual for details.