From:	"George Kinney" <goober AT mail DOT net>
Subject:	Re: General protection fault because of modulus?
Newsgroups:	comp.os.msdos.djgpp
References:	<01bc8c6e$c991d480$3564a8c0 AT Kelly DOT ns1 DOT uswest DOT net>
Organization:	The Unknown Programmers
Message-ID:	<01bc8e80$de0ec800$fa8033cf@pentium>
NNTP-Posting-Host:	207.51.128.250
Date:	12 Jul 97 04:53:51 GMT
Lines:	53
To:	djgpp AT delorie DOT com
DJ-Gateway:	from newsgroup comp.os.msdos.djgpp

levity AT minn DOT net wrote in article
<01bc8c6e$c991d480$3564a8c0 AT Kelly DOT ns1 DOT uswest DOT net>...
> I am writing a program for the purpous of learing how to read binary
files.
>  I am using the modulus fo counting coloms for the out put but every time
I
> add the code to do this the program runs and then ends with a general
> protection fault.  Any ideas why I am getting the general protection
fault?
> 	Also for future reference should I include my code in a different way
when
> posting these questions?
> 
> #include	<stdio.h>
> #include	<stdlib.h>
> #include	".\bmphead.h"
> 
> int main(int argc, char *argv[])
> {
> 
> 	long pal[3][256];
[SNIP]
> 			pal[3][i] = palette.Pad;

BOOM!

[SNIP]
> 			(void)printf("%ld,%ld,%ld,%ld |\n", pal[0][i], pal[1][i], pal[2][i],
> pal[3][i]);

BLAM!

[SNIP]
> 			(void)printf("%ld,%ld,%ld,%ld |", pal[0][i], pal[1][i], pal[2][i],
> pal[3][i]);	

KABLOOEY!!!!

This is the infamous off by one bug,  sorta.

the statement:
long pal[3][256];

creates an array that is 3 by 256,  this is ok.
However,  you're code is referring to a *4* by 256 array.
Why?  C arrays start at 0,  and for an array of size N,  the
last element is N-1,  not N.

So either change the pal array to [4][256] or get rid of 
the references to non-existant indexes.

Good luck.  

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