Date: Thu, 29 Aug 1996 17:47:05 +0200 (MET DST)
From: Mark Habersack <grendel AT ananke DOT amu DOT edu DOT pl>
Reply-To: grendel AT ananke DOT amu DOT edu DOT pl
To: Alex Demko <ademko AT mbnet DOT mb DOT ca>
cc: djgpp AT delorie DOT com
Subject: Re: djgpp/allegro - help! - quick question
In-Reply-To: <3223B9FC.5C79@mbnet.mb.ca>
Message-ID: <Pine.NEB.3.95.960829174019.15952A-100000@ananke.amu.edu.pl>
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On Tue, 27 Aug 1996, Alex Demko wrote:

>=A6PALETTE *new_truepal()                     =20
>=A6{                                                   =20
>=A6  PALETTE *pal =3D (PALETTE *)malloc(sizeof(PALETTE));         =20
>=A6  unsigned char r,g,b,i=3D0;                                 =20
>=A6  for (r=3D0; r<6; r++)                                    =20
>=A6   for (g=3D0; g<6; g++)                                    =20
>=A6    for (b=3D0; b<6; b++)                                    =20
>=A6     {                                                    =20
>=A6     pal[i]->r=3Dr*12;//causes GPF here                   =20
>=A6     pal[i]->g=3Dg*12;                              =20
>=A6     pal[i]->b=3Db*12;                                =20
>=A6     pal[i]->filler=3D0;                            =20
>=A6     i++;                                               =20
>=A6     }                                                =20
>=A6  return pal;                                           =20
>=A6}                                                  =20
>
>After I use the above routine in my code, I get a GPF in the marked
>area. It won't GPF the first time it hits the marked code area, but
>it will interate the inner loop about 40 (actual number depends on
>phase of the moons) times, then GPFs. Am I dereferencing the
>array/struct wrong? Please help, this thing is killing me :)
The problem here is that you misunderstood what the PALETTE type is. It
defines just ONE entry in the palette table, not the ENTIRE array. So calli=
ng
malloc as you did above allocates an array with ONE entry (or just one obje=
ct
of the PALETTE type, if you will). Then, when trying to access the next mem=
ory
location at which you think the next palette entry is, you hit an
undefined/uncommited region which lies in the middle of nowhere and causes
your program to GP-fault.
The solution is simple:
 =20
PALETTE* pal =3D (PALETTE*)malloc(sizeof(PALETTE) * palette_entries_count);

Where palette_entries_count is variable/literal/constant/etc which specifie=
s
how many palette entries you want allocated.
=20
>
>The code compiled error free.
There was no error in your code ;-)))))

>Thanks
Anytime

Mark

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