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clock — determine processor time
#include <time.h>
clock_t
clock( |
void); |
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
precision, since glibc 2.18, it is implemented on top of
clock_gettime(2) (using the
CLOCK_PROCESS_CPUTIME_ID
clock).
This page is part of release 3.54 of the Linux man-pages project. A
description of the project, and information about reporting
bugs, can be found at
http://www.kernel.org/doc/man−pages/.
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Copyright (c) 1993 by Thomas Koenig (ig25rz.uni-karlsruhe.de) %%%LICENSE_START(VERBATIM) Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Since the Linux kernel and libraries are constantly changing, this manual page may be incorrect or out-of-date. The author(s) assume no responsibility for errors or omissions, or for damages resulting from the use of the information contained herein. The author(s) may not have taken the same level of care in the production of this manual, which is licensed free of charge, as they might when working professionally. Formatted or processed versions of this manual, if unaccompanied by the source, must acknowledge the copyright and authors of this work. %%%LICENSE_END 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 waited-for children. |