From:	Erik Max Francis <max AT alcyone DOT com>
Newsgroups:	comp.os.msdos.djgpp
Subject:	Re: HELP! Unidentifiable bug in code
Date:	Sun, 27 Jul 1997 10:54:41 -0700
Organization:	Alcyone Systems
Lines:	39
Message-ID:	<33DB8B61.701B64E6@alcyone.com>
References:	<5r5p46$bj0$1 AT excalibur DOT flash DOT net>
NNTP-Posting-Host:	newton.alcyone.com
Mime-Version:	1.0
To:	djgpp AT delorie DOT com
DJ-Gateway:	from newsgroup comp.os.msdos.djgpp

Joshua Eckstein wrote:

> I have written a small program, below, that I'm trying to have fade in
> and
> out several PCX images. It seems to do fine with only one, but two it
> just
> can't handle! What is wrong?

It in fact seems to be (though there may be other problems too) a simple
uninitialized pointer.  My suggestion is you get a good book on ANSI C
programming and study the sections on pointers, arrays, and strings.

>    COLOR *Pal1, *Pal2;//, *Pal3;
>    PCXheader head1, head2;//, head3;
>
>    LoadPCXinfo(file1, &head1, Pal1);

Pal1 and Pal2 are uninitialized pointers before they're being passed to
the LoadPCXInfo function, which attempts to fill out the color tables --
this will cause a crash.

What you need instead is

    COLOR *pal1;
    // ...
    LoadPCXInfo(file1, &head1, &pal1);

LoadPCXInfo takes a COLOR *, which means that it needs a COLOR to actually
point to.

Using a source-level debugger would have easily revealed this problem.

-- 
       Erik Max Francis, &tSftDotIotE / email / max AT alcyone DOT com
                     Alcyone Systems /   web / http://www.alcyone.com/max/
San Jose, California, United States /  icbm / 37 20 07 N  121 53 38 W
                                   \
   "Love is not love which alters / when it alternation finds."
                                 / William Shakespeare, _Sonnets_, 116

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