Re: [Swarm-Support] Discrete2d peculiar behavior

[Paul Johnson]

Remember this is C.  If you access an array at -1 or N, you get whatever 
crap happens to be sitting in memory there.  So sometimes you get a 
non-nil piece of nonsense.  I've done it and it is really hard to bug shoot.

And, when  you are doing the "look one on the left and one on the right" 
kind of thing, you always have to make sur eyou are inside the 
boundaries, 0 and N-1 are the edges, and you can get gibberish if you go 
outside.

pj


Alex Olivas wrote:
> I found the problem so my last post can be neglected.
> It turns out the problem was getting objects near the boundaries
> (i.e. negative values for x and/or y).  My code lookes like...
>
>
>  int deltaX,deltaY;
>  for(deltaX=-1;deltaX<=1;deltaX++)
>    for(deltaY=-1;deltaY<=1;deltaY++)
>      if((deltaX!=0)||(deltaY!=0))
>    if([world getObjectAtX: xPos+deltaX Y: yPos+deltaY]!= nil){
>      printf("x: %d y: %d\n",xPos+deltaX,yPos+deltaY);
>      xprint([world getObjectAtX: xPos+deltaX Y: yPos+deltaY]);
>
> My code would crash at the last line above (the xprint statement).
> I was wondering if x=-1 (for example) why does [world getObjectAtX: 
> xPos+deltaX Y: yPos+deltaY]
> return a non-nil value?
>
> This is a hack of heatbugs, so world is a Grid2d object and the space 
> contains modified heatbugs.
> Thanks,
> Alex.
> _______________________________________________
> Support mailing list
> address@hidden
> http://www.swarm.org/mailman/listinfo/support


--
Paul E. Johnson                       email: address@hidden
Dept. of Political Science            http://lark.cc.ku.edu/~pauljohn
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