clock(3)

1CLOCK(3)                   Linux Programmer's Manual                  CLOCK(3)
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NAME

6       clock - Determine processor time
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SYNOPSIS

9       #include <time.h>
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11       clock_t clock(void);
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DESCRIPTION

14       The clock() function returns an approximation of processor time used by
15       the program.
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RETURN VALUE

18       The value returned is the CPU time used so far as a clock_t; to get the
19       number  of  seconds  used,  divide by CLOCKS_PER_SEC.  If the processor
20       time used is not available or its  value  cannot  be  represented,  the
21       function returns the value (clock_t) -1.
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CONFORMING TO

24       C89,  C99,  POSIX.1-2001.   POSIX  requires  that CLOCKS_PER_SEC equals
25       1000000 independent of the actual resolution.
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NOTES

28       The C standard allows for arbitrary values at the start of the program;
29       subtract  the value returned from a call to clock() at the start of the
30       program to get maximum portability.
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32       Note that  the  time  can  wrap  around.   On  a  32-bit  system  where
33       CLOCKS_PER_SEC  equals 1000000 this function will return the same value
34       approximately every 72 minutes.
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36       On several other implementations, the value returned  by  clock()  also
37       includes  the times of any children whose status has been collected via
38       wait(2) (or another wait-type call).  Linux does not include the  times
39       of  waited-for children in the value returned by clock().  The times(2)
40       function, which explicitly returns  (separate)  information  about  the
41       caller and its children, may be preferable.
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COLOPHON

47       This  page  is  part of release 3.22 of the Linux man-pages project.  A
48       description of the project, and information about reporting  bugs,  can
49       be found at http://www.kernel.org/doc/man-pages/.
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53GNU                               2008-08-28                          CLOCK(3)