From: "Glynne Casteel" <glynnec AT ix DOT netcom DOT com>
Newsgroups: comp.os.msdos.djgpp
Subject: Re: PROBLEM WITH ARRAY IN STRUCT
Date: Sat, 28 Mar 1998 22:50:44 -0700
Organization: Netcom
Lines: 76
Message-ID: <6fknpm$dmr@dfw-ixnews11.ix.netcom.com>
References: <351D93C1 DOT 60A91521 AT mail DOT ucsm DOT edu DOT pe>
NNTP-Posting-Host: den-co11-19.ix.netcom.com
To: djgpp AT delorie DOT com
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rpinnell AT characato DOT ucsm DOT edu DOT pe wrote in message
<351D93C1 DOT 60A91521 AT mail DOT ucsm DOT edu DOT pe>...
>Hi I am trying to write a program using DJGPP and the Allegro graphics
>library.  I am having a problem with an array inside a struct.  Here is
>example of the type of thing I am doing.
>
>#include <stdio.h>
>#include <stdlib.h>
>#include <allegro.h>
>#include <string.h>
>#include "my.h"
>
>struct my
>{
>char block[336];
>}*pt;
>
>/* START OF MAIN */
>int main()
>{
>int i=0;
>DATAFILE *df;
>char *buf;
>
>   /* INITIALISE ALLEGRO */
>   allegro_init();
>   install_keyboard();
>
>    /* LOAD DATAFILE */
>   strcpy(get_filename(buf), "my.dat");
>   df = load_datafile(buf);
>
>   /* SET GRAFICS MODE */
>   set_gfx_mode(GFX_AUTODETECT, 320, 200, 0, 0);
>   set_palette(df[mypal].dat);
>
>   /*   FILL  BLOCK WITH ZEROS  */
>   while(i<336)                  /* THIS SEEMS TO CAUSE LOTS OF PROBS */
>
>      pt->block[i++]=0;         /* WHY? WHY? WHY?                    */
>
>readkey();
>return 0;
>}
>
>The above code does nothing of course it is just to demonstrate, it
>compiles ok.  The program I am writting is much more complex and
>contains multiple files.  The problem is the line which writes data to
>the array in the struct my..  In my program I am passing a  pointer to
>this struct to various functions and manipulating the data within the
>array. However whenever I try and initialise the array in the struct
>with 0īs, as in the above examples I get all sorts of problems. The
>problems donīt seem to be consistent, sometimes it works ok when I
>compile other times it compiles ok but I get exiting due to signal
>SIGSERV.  I tried running the program through the  rhide debugger and
>again the errores seem to be inconsistent, somtimes the error is when
>the program  loads in the allegro datafile sometimes elsewhere.  There
>is no problem before I add the loop to initialise the array in the
>struct however.  Iīm sure I am doing something very very silly here can
>someone please tell me what it is.
>Richard Pinnell
>Arequipa Peru
>
>
>
You forgot to allocate your struct pointer, e.g.
pt= malloc( sizeof(pt[0]) );

You can either do this, or simply declare pt as a struct instead of a
pointer-to-struct.
Then use the struct member operator (.) instead of the struct pointer
operator (->)