manpagez: man(ual) pages & more
man settimeofday(2)
Home | html | info | man

gettimeofday(2)             BSD System Calls Manual            gettimeofday(2)


     gettimeofday, settimeofday -- get/set date and time


     #include <sys/time.h>

     gettimeofday(struct timeval *restrict tp, void *restrict tzp);

     settimeofday(const struct timeval *tp, const struct timezone *tzp);


     The system's notion of the current Greenwich time and the current time
     zone is obtained with the gettimeofday() call, and set with the
     settimeofday() call.  The time is expressed in seconds and microseconds
     since midnight (0 hour), January 1, 1970.  The resolution of the system
     clock is hardware dependent, and the time may be updated continuously or
     in ``ticks.''  If tp is NULL and tzp is non-NULL, gettimeofday() will
     populate the timezone struct in tzp.  If tp is non-NULL and tzp is NULL,
     then only the timeval struct in tp is populated. If both tp and tzp are
     NULL, nothing is returned.

     The structures pointed to by tp and tzp are defined in <sys/time.h> as:

     struct timeval {
             time_t       tv_sec;   /* seconds since Jan. 1, 1970 */
             suseconds_t  tv_usec;  /* and microseconds */

     struct timezone {
             int     tz_minuteswest; /* of Greenwich */
             int     tz_dsttime;     /* type of dst correction to apply */

     The timeval structure specifies a time value in seconds and microseconds.
     The values in timeval are opaque types whose length may vary on different
     machines; depending on them to have any given length may lead to errors.

     The timezone structure indicates the local time zone (measured in minutes
     of time westward from Greenwich), and a flag that, if nonzero, indicates
     that Daylight Saving time applies locally during the appropriate part of
     the year.

     Only the super-user may set the time of day or time zone.  If the system
     securelevel is greater than 1 (see launchd(8) ), the time may only be
     advanced.  This limitation is imposed to prevent a malicious super-user
     from setting arbitrary time stamps on files.  The system time can still
     be adjusted backwards using the adjtime(2) system call even when the sys-
     tem is secure.


     A 0 return value indicates that the call succeeded.  A -1 return value
     indicates an error occurred, and in this case an error code is stored
     into the global variable errno.


     The following error codes may be set in errno:

     [EFAULT]  An argument address referenced invalid memory.

     [EPERM]   A user other than the super-user attempted to set the time.


     #include <sys/time.h>

     gettimeofday(struct timeval *tp, struct timezone *tzp);

     The type of tzp has changed.


     date(1), adjtime(2), ctime(3), compat(5), timed(8)


     The gettimeofday() function call appeared in 4.2BSD.

4th Berkeley Distribution       August 5, 2008       4th Berkeley Distribution

Mac OS X 10.11.6 - Generated Fri Feb 3 06:48:47 CST 2017
© 2000-2017
Individual documents may contain additional copyright information.