#include <sys/time.h>
int gettimeofday(struct timeval *tp, void *tzp);
int settimeofday(struct timeval *tp, void *tzp);
The gettimeofday() function gets and the settimeofday() function sets the system's notion of the current time. The current time is expressed in elapsed seconds and microseconds since 00:00 Universal Coordinated Time, January 1, 1970. The resolution of the system clock is hardware dependent; the time may be updated continuously or in clock ticks.
The tp argument points to a timeval structure, which includes the following members:
long tv_sec; /* seconds since Jan. 1, 1970 */ long tv_usec; /* and microseconds */
If tp is a null pointer, the current time information is not returned or set.
The TZ environment variable holds time zone information. See TIMEZONE(4).
The tzp argument to gettimeofday() and settimeofday() is ignored.
Only privileged processes can set the time of day.
Upon successful completion, 0 is returned. Otherwise, -1 is returned and errno is set to indicate the error.
The settimeofday() function will fail if:
EINVAL The structure pointed to by tp specifies an invalid time.
EPERM The {PRIV_SYS_TIME} privilege was not asserted in the effective set of the calling process.
The gettimeofday() function will fail for 32-bit interfaces if:
EOVERFLOW The system time has progressed beyond 2038, thus the size of the tv_sec member of the timeval structure pointed to by tp is insufficient to hold the current time in seconds.
If the tv_usec member of tp is > 500000, settimeofday() rounds the seconds upward. If the time needs to be set with better than one second accuracy, call settimeofday() for the seconds and then adjtime(2) for finer accuracy.
See attributes(5) for descriptions of the following attributes:
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
| Interface Stability | gettimeofday() is Standard. |
| MT-Level | MT-Safe |
adjtime(2), ctime(3C), gethrtime(3C), TIMEZONE(4), attributes(5), privileges(5), standards(5)