This document is a Mac OS X manual page. Manual pages are a command-line technology for providing documentation. You can view these manual pages locally using the man(1) command. These manual pages come from many different sources, and thus, have a variety of writing styles.

This manual page is associated with the Mac OS X developer tools. The software or headers described may not be present on your Mac OS X installation until you install the developer tools package. This package is available on your Mac OS X installation DVD, and the latest versions can be downloaded from developer.apple.com.

For more information about the manual page format, see the manual page for manpages(5).

GETTIMEOFDAY(2)             BSD System Calls Manual            GETTIMEOFDAY(2)

NAME
     gettimeofday, settimeofday -- get/set date and time

SYNOPSIS
     #include <sys/time.h>

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

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

DESCRIPTION
     Note: timezone is no longer used; this information is kept outside the kernel.

     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 or tzp is NULL, the associ-ated associated
     ated time information will not be returned or set.

     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 Green-wich), Greenwich),
     wich), 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 init(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 back-wards backwards
     wards using the adjtime(2) system call even when the system is secure.

RETURN
     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.

ERRORS
     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.

LEGACY SYNOPSIS
     #include <sys/time.h>

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

     The type of tzp has changed.

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

HISTORY
     The gettimeofday() function call appeared in 4.2BSD.

4th Berkeley Distribution        May 26, 1995        4th Berkeley Distribution