Re: Mathlib functions always returning 0

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#199

From: Logan Shaw
Date: Tue, 21 Oct 2003 03:19

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Luc M. wrote:

> I get '0' from a mathlib functions when I try to pass a parameter.
> The functions return the proper value if the parameter is checked before
> calling the function.
> 
> Assuming 'index' is equal to 2, why does the function 'sqrt(index)' return 0
> in the following code:
> 
>    Int32 index;
>    double c;
> 
>    index = StrAToI(FldGetTextPtr(fldInput));     /* field set so that index
> is 2 */
>    c = sqrt(index);                                              /* Returns
> 0 ? */
> 
> 
> But it returns the proper value in the following code:
> 
>     index = StrAToI(FldGetTextPtr(fldInput));   /* field set so that index
> is 2 */
>     if(index == 2)
>     {
>       c = sqrt(index);                                          /* Returns
> proper value !!! */
>     }

I don't know why, but my advice is to disassemble the compiler's
output.  Something funny is going on.  Maybe one piece of code
ends up with index as a register variable and the other doesn't
or something along those lines.

Obviously, you also want to be sure that you have included some
.h file with a prototype for sqrt(), because if you haven't, it
will be passing in values as if they're ints, in which case I think
the behavior is undefined.

Also, it might help to go through your code with a debugger and be
sure that the value of index really is 2 just before the call to
sqrt(), because maybe something unexpected is happening before then.

   - Logan

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