GETTIMEOFDAY(2) COMMAND REFERENCE GETTIMEOFDAY(2) NAME gettimeofday, settimeofday - get/set date and time SYNOPSIS #include <sys/time.h> gettimeofday(tp, tzp) struct timeval *tp; struct timezone *tzp; settimeofday(tp, tzp) struct timeval *tp; struct timezone *tzp; DESCRIPTION gettimeofday returns the system's current Greenwich time and time zone in the structures pointed to by tp and tzp. settimeofday sets the time using the contents of the structures. Only the superuser can set the time. Refer to date(1) for more details. Time returned is expressed relative in seconds and microseconds since midnight January 1, 1970. 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. The flag tz_dsttime, if nonzero, indicates that Daylight Saving time applies locally during the appropriate part of the year. DIAGNOSTICS If gettimeofday and settimeofday fail, they can set the following error in errno: [EFAULT] An argument address references invalid memory. In addition, settimeofday can set the following error: Printed 4/6/89 1
GETTIMEOFDAY(2) COMMAND REFERENCE GETTIMEOFDAY(2) [EPERM] The caller is not the super-user. RETURN VALUE Upon successful completion, a value of 0 is returned. Otherwise, a value of -1 is returned and errno is set to indicate the error. CAVEATS Time is never correct enough to believe the microsecond values. There should be a mechanism by which, at least, local clusters of systems might synchronize their clocks to millisecond granularity. If tp is NULL, the time system time will not be returned or set. If tzp is NULL, the time zone information will not be returned or set. SEE ALSO date(1) and ctime(3c). Printed 4/6/89 2
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