Question about function "settimeofday"

[Martin.Dong]

Hi,

Which standard does the function "settimeofd ay" belong to, ISO C or
POSIX, or .... ??

I have checked that the header <sys/time.hneeds to be included to
use above function, and this header is not part of ISO C, but the XSI
extension part of POSIX.

But in GNU C library, it really declares above function, and what's
more strange, the implementation of this function looks like this:

--------------------------------------------------------------------------------------------------
/* Set the current time of day and timezone information.
This call is restricted to the super-user. */
int
__settimeofday (tv, tz)
const struct timeval *tv;
const struct timezone *tz;
{
__set_errno (ENOSYS);
return -1;
}
-----------------------------------------------------------------------------------------------------

Obviously, this function can't be used by normal user, but what if I'm
root? If a root user writes some code of calling this function, what
will happen? Which function will be exactly invoked, above one, or
other inside OS?

Appreciate your help!

- Martin