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Full Discussion: problem with clock()
Top Forums Programming problem with clock() Post 302440494 by Corona688 on Tuesday 27th of July 2010 10:47:38 AM
Old 07-27-2010
From the manpage:
Code:
       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.

...so you may be corrupting your clock() call by running commands in system(), though it's still odd that it'd mung it that far. Try removing the system() calls and just printing the clock() values, running the program with 'time ./program' to see how your values compare to the ones time sees.
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CLOCK(3)						     Linux Programmer's Manual							  CLOCK(3)

NAME
clock - Determine processor time SYNOPSIS
#include <time.h> clock_t clock(void); DESCRIPTION
The clock() function returns an approximation of processor time used by the program. RETURN VALUE
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. CONFORMING TO
C89, C99, POSIX.1-2001. POSIX requires that CLOCKS_PER_SEC equals 1000000 independent of the actual resolution. NOTES
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. SEE ALSO
clock_gettime(2), getrusage(2), times(2) COLOPHON
This page is part of release 3.25 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/. GNU
2008-08-28 CLOCK(3)
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