clock — determine processor time
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.
For an explanation of the terms used in this section, see attributes(7).
POSIX.1-2001, POSIX.1-2008, C89, C99. XSI 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
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
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Copyright (c) 1993 by Thomas Koenig (ig25rz.uni-karlsruhe.de)
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Modified Sat Jul 24 21:27:01 1993 by Rik Faith (faithcs.unc.edu)
Modified 14 Jun 2002, Michael Kerrisk <mtk.manpagesgmail.com>
Added notes on differences from other UNIX systems with respect to