int
clock_settime(
clockid_t clock_id
, const struct timespec *tp
)
int
clock_gettime(
clockid_t clock_id
, struct timespec *tp
)
int
clock_getres(
clockid_t clock_id
, struct timespec *res
)
)
function sets the clock identified by
clock_id
to the absolute time specified by
tp
.
If the time specified by
tp
is not a multiple of the resolution of the clock,
tp
is truncated to a multiple of the resolution.
clock_gettime()
function stores the time of the clock identified by
clock_id
into the location specified by
tp
.
The
clock_getres()
function stores the resolution of the clock identified by
clock_id
into the location specified by
res
,
unless
res
is
NULL
.
A
clock_id
of
CLOCK_REALTIME
identifies the realtime clock for the system.
For this clock, the values specified by
clock_settime()
and obtained by
clock_gettime(
)
represent the amount of time (in seconds and nanoseconds)
since 00:00 Universal Coordinated Time, January 1, 1970.
A
clock_id
of
CLOCK_MONOTONIC
identifies a clock that increases at a steady rate (monotonically).
This clock
is not affected by calls to
adjtime(2)
and
settimeofday(2)
and will
fail with an
EINVAL
error if it's the clock specified in a call to
clock_settime().
The origin of the clock is unspecified.
If the calling user is not the super-user, then the
clock_settime()
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
clock_settime(
)
reverts to the
clock_settime(
)
system call, which is restricted to the super user.
),
clock_gettime(
)
and
clock_getres(
)
functions will fail if:
EINVAL
]
clock_id
argument does not specify a known clock.
ENOSYS
]
The
clock_settime()
function will fail if:
EINVAL
]
tp
argument is outside the range for the specified clock,
clock_id
.
EINVAL
]
tp
argument specified a nanosecond value less than zero of greater than or equal
1000 million.
EINVAL
]
clock_id
argument is a clock that can not be adjusted.
EPERM
]
clock_id
.
The
clock_gettime()
function will fail if:
EFAULT
]
tp
argument specifies an address that is not a valid part of the process address
space.
),
clock_gettime(
)
and
clock_getres(
)
functions conform to
IEEE Std 1003.1b-1993 (``POSIX.1'') .