gettimeofday, settimeofday - get / set time
#include <sys/time.h>
int gettimeofday(struct timeval *restrict tv,
struct timezone *_Nullable restrict tz);
int settimeofday(const struct timeval *tv,
const struct timezone *_Nullable tz);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
The functions gettimeofday() and settimeofday() can get and set the time as well as a timezone.
The tv
argument is a struct timeval
(as specified
in <sys/time.h>
):
struct timeval {
time_t tv_sec; /* seconds */
suseconds_t tv_usec; /* microseconds */
};
and gives the number of seconds and microseconds since the Epoch (see time(2)).
The tz
argument is a struct timezone
:
struct timezone {
int tz_minuteswest; /* minutes west of Greenwich */
int tz_dsttime; /* type of DST correction */
};
If either tv
or tz
is NULL, the corresponding
structure is not set or returned. (However, compilation warnings will
result if tv
is NULL.)
The use of the timezone
structure is obsolete; the
tz
argument should normally be specified as NULL. (See NOTES
below.)
Under Linux, there are some peculiar "warp clock" semantics
associated with the settimeofday() system call if on
the very first call (after booting) that has a non-NULL tz
argument, the tv
argument is NULL and the
tz_minuteswest
field is nonzero. (The tz_dsttime
field
should be zero for this case.) In such a case it is assumed that the
CMOS clock is on local time, and that it has to be incremented by this
amount to get UTC system time. No doubt it is a bad idea to use this
feature.
gettimeofday() and settimeofday()
return 0 for success. On error, -1 is returned and errno
is set
to indicate the error.