gettimeofday (2)

NAME

       gettimeofday, settimeofday - get / set time

SYNOPSIS

       #include <sys/time.h>

       int gettimeofday(struct timeval *tv, struct timezone *tz);
       int settimeofday(const struct timeval *tv , const struct timezone *tz);

DESCRIPTION

       The functions gettimeofday and settimeofday can get and set the time as
       well  as a timezone.  The tv argument is a timeval struct, as specified
       in /usr/include/sys/time.h:

       struct timeval {
               long tv_sec;        /* seconds */
               long tv_usec;  /* microseconds */
       };

       and gives the number of seconds and microseconds since the  Epoch  (see
       time(2)).  The tz argument is a timezone :

       struct timezone {
               int  tz_minuteswest; /* minutes W of Greenwich */
               int  tz_dsttime;     /* type of dst correction */
       };

       The  use  of  the timezone struct is obsolete; the tz_dsttime field has
       never been used under Linux - it has not been and will not be supported
       by  libc or glibc.  Each and every occurrence of this field in the ker-
       nel source (other than the declaration) is a bug. Thus,  the  following
       is purely of historic interest.

       The  field  tz_dsttime  contains  a symbolic constant (values are given
       below) that indicates in which part of the year Daylight Saving Time is
       in  force.  (Note:  its value is constant throughout the year - it does
       not indicate that DST is in force, it just selects an algorithm.)   The
       daylight saving time algorithms defined are as follows :

        DST_NONE     /* not on dst */
        DST_USA      /* USA style dst */
        DST_AUST     /* Australian style dst */
        DST_WET      /* Western European dst */
        DST_MET      /* Middle European dst */
        DST_EET      /* Eastern European dst */
        DST_CAN      /* Canada */
        DST_GB       /* Great Britain and Eire */
        DST_RUM      /* Rumania */
        DST_TUR      /* Turkey */
        DST_AUSTALT  /* Australian style with shift in 1986 */

       Of  course  it turned out that the period in which Daylight Saving Time
       is in force cannot be given by a simple  algorithm,  one  per  country;
       indeed, this period is determined by unpredictable political decisions.
       So this method of representing time zones  has  been  abandoned.  Under

       The following macros are defined to operate on a struct timeval :
       #define       timerisset(tvp)\
               ((tvp)->tv_sec || (tvp)->tv_usec)
       #define       timercmp(tvp, uvp, cmp)\
               ((tvp)->tv_sec cmp (uvp)->tv_sec ||\
               (tvp)->tv_sec == (uvp)->tv_sec &&\
               (tvp)->tv_usec cmp (uvp)->tv_usec)
       #define       timerclear(tvp)\
               ((tvp)->tv_sec = (tvp)->tv_usec = 0)

       If  either  tv or tz is null, the corresponding structure is not set or
       returned.

       Only the super user may use settimeofday.

RETURN VALUE

       gettimeofday and settimeofday return 0 for success, or -1  for  failure
       (in which case errno is set appropriately).

ERRORS

       EPERM  settimeofday is called by someone other than the superuser.

       EINVAL Timezone (or something else) is invalid.

       EFAULT One of tv or tz pointed outside your accessible address space.

NOTE

       The  prototype  for settimeofday and the defines for timercmp, timeris-
       set, timerclear, timeradd, timersub are (since glibc2.2.2) only  avail-
       able  if  _BSD_SOURCE  is defined (either explicitly, or implicitly, by
       not defining _POSIX_SOURCE or compiling with the -ansi flag).

CONFORMING TO

       SVr4, BSD 4.3

SEE ALSO

       date(1), adjtimex(2), time(2), ctime(3), ftime(3)

Linux 2.0.32                      1997-12-10                   gettimeofday(2)