question on timing results

Matthew Saltzman mjs at ces.clemson.edu
Thu Jun 9 13:57:34 UTC 2005


On Thu, 9 Jun 2005, Globe Trotter wrote:

>
>>> clock() returns an approximation of the CPU time used by the actual
>> process,
>>> so while load from other programs is a factor (particularly since it'll
>> make
>>> your program wait for IO, etc.) it should do basically what you want.
>>
>> Also check out the times(2) facility.  It's not ISO C, but it is POSIX and
>> it has some advantages over clock(3).
>>
>> --
>>
>
> Thanks, what exactly are the advantages? These are sometimes long 
> calculations so the processor will be running for long. Also, is there

clock() will wrap after about 75 CPU minutes.  I believe times() will not.

Also times() tracks user and system time separately, and it tracks parent 
and child process times separately.

> an example on using times(2) somewhere? A Google search on times(2) 
> example C did not reveal much, but the choice of keywords may not have 
> been apt. (One problem with the name of the language called C is that is 
> just a letter, as opposed to fortran/C++/pascal et al, which is more 
> distinctive.

Don't know of a handy URL, sorry.  The man page ("man 2 times") and a 
little experimentation should be enough.

>
> Sorry and thanks for all the help!
>
> Best wishes!
>
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-- 
 		Matthew Saltzman

Clemson University Math Sciences
mjs AT clemson DOT edu
http://www.math.clemson.edu/~mjs




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