clocks(2)                                                         clocks(2)




 NAME    [Toc]    [Back]
      clock_settime(), clock_gettime(), clock_getres() - clock operations

 SYNOPSIS    [Toc]    [Back]
      #include <time.h>

      int clock_settime(
           clockid_t clock_id,
           const struct timespec *tp
      );

      int clock_gettime(
           clockid_t clock_id,
           struct timespec *tp
      );

      int clock_getres(
           clockid_t clock_id,
           struct timespec *res
      );

 DESCRIPTION    [Toc]    [Back]
    clock_settime()
      The clock_settime() function sets the specified clock, clock_id, to
      the value specified by tp.  Time values that are between two
      consecutive non-negative integer multiples of the resolution of the
      specified clock are truncated down to the smaller multiple of the
      resolution.

    clock_gettime()
      The clock_gettime() function returns the current value tp for the
      specified clock, clock_id.

    clock_getres()
      The resolution of any clock can be obtained by calling clock_getres().
      Clock resolutions are implementation defined and are not settable by a
      process.  If the argument res is not NULL, the resolution of the
      specified clock is stored into the location pointed to by res.  If res
      is NULL, the clock resolution is not returned.

      A clock may be system wide, that is, visible to all processes; or
      per-process, measuring time that is meaningful only within a process.

      The following clocks are supported:

           CLOCK_REALTIME    [Toc]    [Back]
                       This clock represents the realtime clock for the
                       system.  For this clock, the values returned by
                       clock_gettime() and specified by clock_settime()
                       represent the amount of time (in seconds and
                       nanoseconds) since the Epoch.  It is a system wide



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 clocks(2)                                                         clocks(2)




                       clock.  Appropriate privileges are required to set
                       this clock.

           CLOCK_VIRTUAL    [Toc]    [Back]
                       This clock represents the amount of time (in seconds
                       and nanoseconds) that the calling process has spent
                       executing code in the user's context.  It is a perprocess
 clock.  It cannot be set by the user.

           CLOCK_PROFILE    [Toc]    [Back]
                       This clock represents the amount of time (in seconds
                       and nanoseconds) that the calling process has spent
                       executing code in both the user's context and in the
                       operating system on behalf of the calling process.
                       It is a per-process clock.  It cannot be set by the
                       user.

           RTTIMER0 RTTIMER1    [Toc]    [Back]
                       These clocks are high resolution hardware clocks
                       present on HP-RT realtime systems.  It is included
                       here so that applications accessing this hardware can
                       be compiled on HP-UX systems and then ported to an
                       HP-RT target.  HP-UX does not support RTTIMER0 or
                       RTTIMER1.

 RETURN VALUE    [Toc]    [Back]
      A return of zero indicates that the call succeeded.  A return value of
      -1 indicates that an error occurred, and errno is set to indicate the
      error.

 ERRORS    [Toc]    [Back]
      If any of the following conditions occur, the clock_settime(),
      clock_gettime(), and clock_getres() functions return -1 and set errno
      (see errno(2)) to the corresponding value:

           [ENOSYS]    The functions clock_settime(), clock_gettime(), and
                       clock_getres() are not supported by this
                       implementation.

           [EINVAL]    The clock_id argument does not specify a known clock.

           [EINVAL]    The tp argument to clock_settime() is outside the
                       range for the given clock_id.

           [EINVAL]    The tp argument specified a nanosecond value less
                       than zero or greater than or equal to 1000 million.

           [EPERM]     The requesting process does not have the necessary
                       privileges to set the specified clock.





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 clocks(2)                                                         clocks(2)




           [EFAULT]    The tp or res argument points to an invalid address.

 EXAMPLES    [Toc]    [Back]
      Advance the system wide realtime clock approximately one hour:

           #include <time.h>
           #include <errno.h>

           struct timespec cur_time, new_time;

           if (clock_gettime(CLOCK_REALTIME, &cur_time)) {
                perror("clock_gettime(CLOCK_REALTIME) failed");
                exit(1);
           }
           new_time.tv_sec = cur_time.tv_sec + 3600;
           new_time.tv_nsec = cur_time.tv_nsec;
           if (clock_settime(CLOCK_REALTIME, &new_time)) {
                perror("clock_settime(CLOCK_REALTIME) failed");
                exit(2);
           }

      Get the resolution of the user profiling clock:

           #include <time.h>
           #include <errno.h>

           struct timespec resolution;

           if (clock_getres(CLOCK_PROFILE, &resolution)) {
                perror("clock_getres(CLOCK_PROFILE) failed");
                exit(1);
           }
           (void)printf("Resolution of user profiling clock is:\n");
           (void)printf("%d seconds and %d nanoseconds.\n",
                     resolution.tv_sec, resolution.tv_nsec);

 AUTHOR    [Toc]    [Back]
      clock_settime(), clock_gettime(), and clock_getres() were derived from
      the proposed IEEE POSIX P1003.4 Standard, Draft 14.

 SEE ALSO    [Toc]    [Back]
      timers(2).

 STANDARDS CONFORMANCE    [Toc]    [Back]
      clock_getres(): POSIX.4

      clock_gettime(): POSIX.4

      clock_settime(): POSIX.4





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 clocks(2)                                                         clocks(2)


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