NAME

     timeval, timespec — time structures

LIBRARY

     library “libbsd”

SYNOPSIS

     #include <sys/time.h>
     (See libbsd(7) for include usage.)

     void
     TIMEVAL_TO_TIMESPEC(struct timeval *tv, struct timespec *ts);

     void
     TIMESPEC_TO_TIMEVAL(struct timeval *tv, struct timespec *ts);

DESCRIPTION

     The <sys/time.h> header, included by <time.h>, defines various structures related to time
     and timers.

      1.   The following structure is used by gettimeofday(2), among others:

                 struct timeval {
                         time_t          tv_sec;
                         suseconds_t     tv_usec;
                 };

           The tv_sec member represents the elapsed time, in whole seconds.  The tv_usec member
           captures rest of the elapsed time, represented as the number of microseconds.

      2.   The following structure is used by nanosleep(2), among others:

                 struct timespec {
                         time_t          tv_sec;
                         long            tv_nsec;
                 };

           The tv_sec member is again the elapsed time in whole seconds.  The tv_nsec member
           represents the rest of the elapsed time in nanoseconds.

           A microsecond is equal to one millionth of a second, 1000 nanoseconds, or 1/1000
           milliseconds.  To ease the conversions, the macros TIMEVAL_TO_TIMESPEC() and
           TIMESPEC_TO_TIMEVAL() can be used to convert between struct timeval and struct
           timespec.

EXAMPLES

     It can be stressed that the traditional UNIX timeval and timespec structures represent
     elapsed time, measured by the system clock.  The following sketch implements a function
     suitable for use in a context where the timespec structure is required for a conditional
     timeout:

           static void
           example(struct timespec *spec, time_t minutes)
           {
                   struct timeval elapsed;

                   (void)gettimeofday(&elapsed, NULL);

                   _DIAGASSERT(spec != NULL);
                   TIMEVAL_TO_TIMESPEC(&elapsed, spec);

                   /* Add the offset for timeout in minutes. */
                   spec->tv_sec = spec->tv_sec + minutes * 60;
           }

     A better alternative would use the more precise clock_gettime(2).

SEE ALSO

     timeradd(3bsd)