int
gettimeofday(
struct timeval * restrict tp
, void * restrict tzp
)
int
settimeofday(
const struct timeval * restrict tp
, const void * restrict tzp
)
The system's notion of the current UTC time 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, the time will not be returned or set.
Despite being declared
void
*
,
the objects pointed to by
tzp
shall be of type
struct
timezone
.
The structures pointed to by
tp
and
tzp
are defined in
sys/time.h<.blm Pp
>
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 is provided only for source compatibility.
It is ignored by
settimeofday(),
and
gettimeofday(
)
will always return zeroes.
If the calling user is not the super-user, then the
settimeofday()
function in the standard C library will try to use the
clockctl(4)
device if present, thus making possible for non privileged users to
set the system time.
If
clockctl(4)
is not present or not accessible, then
settimeofday(
)
reverts to the
settimeofday(
)
system call, which is restricted to the super user.
EFAULT
]
EPERM
]
)
function call appeared in
4.2BSD.
The
tzp
argument was deprecated in
4.4BSD
(and many other systems).