get time of day
function returns the number of seconds elapsed since Jan 1 1970 00:00:00
UTC. This value is also written to now unless
time() function is always successful,
and no return value is reserved to indicate an error.
clock_gettime(2), gettimeofday(2), ctime(3)
time() function conforms to
IEEE Std 1003.1-2008 (“POSIX.1”).
time() system call first appeared in
Version 1 AT&T UNIX. That version counted
time in sixtieths of a second with a 32-bit return value, ensuring an
integer overflow crisis every 2.26 years. In
Version 6 AT&T UNIX the granularity of
the return value was reduced to whole seconds, delaying the aforementioned
crisis until 2038. In 4.1cBSD the function was moved
out of the kernel into the C standard library and reimplemented with