Re: EXC_BAD_ACCESS error

On Oct 11, 2010, at 3:49 PM, McLaughlin, Michael P. wrote:

> Using Xcode 3.2.4 under Mac OS 10.6.4 on a 64-bit Mac Pro, I am getting a
> runtime error of
> 
> EXC_BAD_ACCESS
> 
> The project is a C++/CoreServices tool.  The error seems to arise because
> some legacy (Mersenne Twister) code is trying to dereference a pointer with
> a negative index.
> 
> for (j = M;--j;p++)
>   *p = p[M-N] ^ TWIST(p[0], p[1]);     // M = 397, N = 624
> 
> However, the underlying algorithm is really OK and, in fact, I do *not* get
> this error with exactly the same code when it is part of another
> Cocoa/Objective-C++ project.

Maybe this is unlikely, but did you check this:
Before you enter this for loop (there are two in the state generator function), 
you need to initialize the pointer p properly. According the Mersenne Twister 
algorithm, this should be:

p = &state[N - M];

where state is the state array, which you have defined and which has N elements.

And M and N shall be signed int constants.


best

> 
> Can anyone shed any light on this?  I have used this code for a long time
> and have never gotten this error before.
> 
> I tried to look at the Build Results but that window says only "Build
> Succeeded" and there seems to be no icon (that I could find) that will bring
> up the gcc build command unless there is some warning or compile error.
> 
> Thanks for any tips.
> 
> -- 
> Mike McLaughlin
> 
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