clock() returning negative value

[BrunoBruck]

Hi, i have a program that runs for severel hours and i'm using the clock function to extract some time data. But I recently notice some weird values and through debugging I found out that sometimes the clock funtion is returning a negative value that is messing my calculations. Does anyone know how can I fix this issue?

PS: I'm using codeblocks running on ubuntu 11.01

Thanks in advance.
Bruno.

[hamsterman]

In http://cplusplus.com/reference/clibrary/ctime/clock/ it is written that clock may return -1. Also, if you're storing your time in a type smaller than clock_t this could happen. Other than that, I have no ideas.

[BrunoBruck]

In my case I'm sure it's not returning -1 and I don't know if it's a matter of variable type either, cause I'm storing in a float variable that I think it's big enought for the return of clock function. Besides i also have put the return of clock() in a debug watch and I still get a negative number.

But thanks.

[Peter87]

If the program runs long enough the type will no longer be able to represent the number correctly so maybe the time wraps around and becomes negative.

[BrunoBruck]

So I'll try with the clock_t as hamsterman said and I'll report back to you...

Thanks.

[hamsterman]

Do you only get this when the program runs for a long time? You could cout the time every once in a while to see how it changes.

[BrunoBruck]

I was able to fix the problem using clock_t...

My code is like this now, for those with similar problem:

clock_t beginTime = clock();

//Do something here

double totalTime = (double)(clock()-beginTime)/CLOCKS_PER_SECOND;

The only way I could make this work was by casting the calc (clock()-beginTtime) to double, otherwise it doesn't work. I guess without the cast it tries to make all the calculations converting the values to int.

Thank you guys for the quickly help!
Bruno.