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@(#)gettimeofday.2 6.9 (Berkeley) 05/18/89

C 4 gettimeofday, settimeofday - get/set date and time

#include <sys/time.h>

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

settimeofday(tp, tzp)
struct timeval *tp;
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 or tzp is NULL, the associated 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 {
 long tv_sec; /* seconds since Jan. 1, 1970 */
 long tv_usec; /* and microseconds */
};
struct timezone {
 int tz_minuteswest; /* of Greenwich */
 int tz_dsttime; /* type of dst correction to apply */
};

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.

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:

15 [EFAULT] An argument address referenced invalid memory.

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

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