Section: Linux Programmer's Manual (3)
Return to Main Contents
clock - determine processor time
function returns an approximation of processor time used by the program.
The value returned is the CPU time used so far as a
to get the number of seconds used, divide by
If the processor time used is not available or its value cannot
be represented, the function returns the value
C89, C99, POSIX.1-2001.
POSIX requires that
equals 1000000 independent
of the actual resolution.
The C standard allows for arbitrary values at the start of the program;
subtract the value returned from a call to
at the start of the program to get maximum portability.
Note that the time can wrap around.
On a 32-bit system where
equals 1000000 this function will return the same
value approximately every 72 minutes.
On several other implementations,
the value returned by
also includes the times of any children whose status has been
(or another wait-type call).
Linux does not include the times of waited-for children in the
value returned by
function, which explicitly returns (separate) information about the
caller and its children, may be preferable.
In glibc 2.17 and earlier,
was implemented on top of
For improved accuracy,
since glibc 2.18, it is implemented on top of
This page is part of release 3.74 of the Linux
A description of the project,
information about reporting bugs,
and the latest version of this page,
can be found at
- RETURN VALUE
- CONFORMING TO
- SEE ALSO