CLOCK(3) manual page
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clock - determine processor time
#include <time.h>
clock_t clock(void);
The clock() function returns an approximation
of processor time used by the program.
The value returned is
the CPU time used so far as a clock_t; to get the number of seconds used,
divide by CLOCKS_PER_SEC. If the processor time used is not available or
its value cannot be represented, the function returns the value (clock_t) -1.
C89, C99, POSIX.1-2001. POSIX requires that CLOCKS_PER_SEC 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 clock() at the start of the program to get maximum portability.
Note that the time can wrap around. On a 32-bit system where CLOCKS_PER_SEC
equals 1000000 this function will return the same value approximately every
72 minutes.
On several other implementations, the value returned by clock()
also includes the times of any children whose status has been collected
via wait(2)
(or another wait-type call). Linux does not include the times
of waited-for children in the value returned by clock(). The times(2)
function, which explicitly returns (separate) information about the caller
and its children, may be preferable.
In glibc 2.17 and earlier, clock()
was implemented on top of times(2)
. For improved accuracy, since glibc 2.18,
it is implemented on top of clock_gettime(2)
(using the CLOCK_PROCESS_CPUTIME_ID
clock).
clock_gettime(2)
, getrusage(2)
, times(2)
This page
is part of release 3.78 of the Linux man-pages project. A description of the
project, information about reporting bugs, and the latest version of this
page, can be found at http://www.kernel.org/doc/man-pages/.
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