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Top Forums Programming find CPU Time for a function (subsecond precision) Post 63127 by zynnel on Tuesday 22nd of February 2005 09:41:51 PM
Old 02-22-2005
find CPU Time for a function (subsecond precision)

Hi,

I need to time a certain function in my C/C++ code and I am experiencing some difficulties. I timed it using wallclock time so I know that it takes approximately 500-600 microseconds with

gettimeofday(&start, NULL);
// my function call
gettimeofday(&end, NULL);
answer = (end.tv_sec - start.tv_sec)*1000000 + (end.tv_usec - start.tv_usec);

What I actually need is to get the CPU time used for this function. Unfortunately, the widely used clock() function does not give me a good precision because well... clock_t/CLOCKS_PER_SEC is in seconds.

Anyone had a similar problem? Thank you in advance.

Note: I couldn't find anything relevant on the Unix man pages or anywhere on this forum but it's always possible that I have overlooked...
 

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clock(3C)						   Standard C Library Functions 						 clock(3C)

NAME
clock - report CPU time used SYNOPSIS
#include <time.h> clock_t clock(void); DESCRIPTION
The clock() function returns the amount of CPU time (in microseconds) used since the first call to clock() in the calling process. The time reported is the sum of the user and system times of the calling process and its terminated child processes for which it has executed the wait(3C) function, the pclose(3C) function, or the system(3C) function. RETURN VALUES
Dividing the value returned by clock() by the constant CLOCKS_PER_SEC, defined in the <time.h> header, will give the time in seconds. If the process time used is not available or cannot be represented, clock returns the value (clock_t) -1. USAGE
The value returned by clock() is defined in microseconds for compatibility with systems that have CPU clocks with much higher resolution. Because of this, the value returned will wrap around after accumulating only 2147 seconds of CPU time (about 36 minutes). ATTRIBUTES
See attributes(5) for descriptions of the following attributes: +-----------------------------+-----------------------------+ | ATTRIBUTE TYPE | ATTRIBUTE VALUE | +-----------------------------+-----------------------------+ |Interface Stability |Standard | +-----------------------------+-----------------------------+ |MT-Level |MT-Safe | +-----------------------------+-----------------------------+ SEE ALSO
times(2), popen(3C), system(3C), wait(3C), attributes(5), standards(5) SunOS 5.11 24 Jul 2002 clock(3C)
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