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
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 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 backwards using the adjtime(2) system call even when the sys-
tem 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 August 5, 2008 4th Berkeley Distribution
Mac OS X 10.9.1 - Generated Mon Jan 6 07:33:56 CST 2014