From:	silkwodj AT my-dejanews DOT com
Newsgroups:	comp.os.msdos.djgpp
Subject:	Re: Question from a beginner
Date:	Tue, 22 Dec 1998 14:14:33 GMT
Organization:	Deja News - The Leader in Internet Discussion
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References:	<75licm$pm9$1 AT toto DOT tig DOT com DOT au>
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In article <75licm$pm9$1 AT toto DOT tig DOT com DOT au>,
  "Tim Czvetics" <grunter AT tig DOT com DOT au> wrote:
> I am writing some code in which I use a pointer to an unsigned char, and I
> need to find the segment and offset of that pointer. How do I go about doing
> it?
>
> Thanks.
>

Welcome to 32-bit protected mode.  You probably only need the offset.  We
have selectors, not segments.  Of course you can get an offset by
dereferencing the pointer int offset = &ptr.  If you really want to know what
selector the OS has given your (flat model) code, the following is copied
from the libc help file:

_my_ds

Syntax
#include <sys/segments.h>
unsigned short _my_ds();
Description
Returns the current `DS'.  This is useful for setting up interrupt vectors and
such.
Return Value
`DS'

You obviously wish to port some example code from 16-bit real mode.  DGJPP is
a bit more advanced in that it is a 32-bit protected mode compiler only. 
Don't lose heart, it's not that difficult and I have found the challenge very
interesting.

There is an introduction in the FAQ, but it's not that comprehendable to a
beginner.  Matt Mastracci wrote a tutorial that turned the light on for me.

http://www.acs.ucalgary.ca/~mmastrac/files/djgppasm.html

After a while you will put your nose in the DPMI specification, then you know
you've gone over the edge.


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