From:	Shawn Hargreaves <Shawn AT talula DOT demon DOT co DOT uk>
Newsgroups:	comp.os.msdos.djgpp
Subject:	Re: (Allegro) Datafiles within Datafiles
Date:	Mon, 1 Jun 1998 21:20:06 +0100
Organization:	None
Message-ID:	<x9zblIA2zwc1Ewo7@talula.demon.co.uk>
References:	<6kssb7$itn AT nnrp4 DOT farm DOT idt DOT net>
NNTP-Posting-Host:	talula.demon.co.uk
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To:	djgpp AT delorie DOT com
DJ-Gateway:	from newsgroup comp.os.msdos.djgpp

Chia writes:
>I saw in the grabber that you can have a datafile object within an
>datafile.
>
>    How would I get data out of the second datafile?

From the Allegro grabber.txt file:

If a datafile contains nested child datafiles, the header will prefix
the names of objects in the sub-files with the name of their parent
datafile. It will also define a count of the number of objects in the
child file, which may be useful if for example the child datafile
contains several bitmaps which form a 'run' animation, and you want your
code to automatically adjust to the number of frames in the datafile.

For example, the datafile:

   "FILE" - NESTED_FILE
            |- "BMP" - A_BITMAP
            |- "FONT" - A_FONT
   "DATA" - SOME_DATA
   "DATA" - SOME_MORE_DATA

produces the header:

   #define NESTED_FILE                      0        /* FILE */

   #define NESTED_FILE_A_BITMAP             0        /* BMP  */
   #define NESTED_FILE_A_FONT               1        /* FONT */
   #define NESTED_FILE_COUNT                2

   #define SOME_DATA                        1        /* DATA */
   #define SOME_MORE_DATA                   2        /* DATA */

The main datafile contains three objects (NESTED_FILE, SOME_DATA, and
SOME_MORE_DATA) with consecutive indexes, while the child datafile
contains the two objects A_BITMAP and A_FONT. To access these objects
you need to reference both the parent and child datafiles, eg:

   DATAFILE *dat = load_datafile("whatever.dat");
   DATAFILE *nested = (DATAFILE *)dat[NESTED_FILE].dat;
   FONT *thefont = (FONT *)nested[NESTED_FILE_A_FONT].dat;


--
Shawn Hargreaves - shawn AT talula DOT demon DOT co DOT uk - http://www.talula.demon.co.uk/
"Miracles are nothing if you've got the wrong intentions" - Mike Keneally

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