From:	Eli Zaretskii <eliz AT is DOT elta DOT co DOT il>
Newsgroups:	comp.os.msdos.djgpp
Subject:	Re: Question
Date:	Wed, 6 Nov 1996 09:08:05 +0200
Organization:	NetVision LTD.
Lines:	27
Message-ID:	<Pine.SUN.3.91.961106085836.304M-100000@is>
References:	<327FF0BE DOT 27B8 AT fab DOT net>
NNTP-Posting-Host:	is.elta.co.il
Mime-Version:	1.0
In-Reply-To:	<327FF0BE.27B8@fab.net>
To:	djgpp AT delorie DOT com
DJ-Gateway:	from newsgroup comp.os.msdos.djgpp

On Tue, 5 Nov 1996, Eric Christopherson wrote:

> There is a program, called A.
> Program A has a variable V.
> Program A shells out and runs Program B, passing a pointer to V (in
> hex).
> Is it at all possible for B to read V (if A and B are compiled with
> DJGPP)?

DJGPP does this trick all the time to pass long command line to child 
DJGPP programs.

Here's the deal: allocate a buffer in low (below 1MByte mark) memory by
calling the `__dpmi_allocate_dos_memory' library function.  Move whatever
info you want the child program to access to that buffer (with `dosmemput'
or `movedata' functions).  Then pass the real-mode address (segment and
offset) of this buffer to the child on the command line that invokes the
child.  The child should use `dosmemget' or `movedata' to access that
buffer. 

If the buffer you want to pass is longer than 64KB, this is a bit more 
complicated, but still doable.

If you are sure you will always run under DPMI 0.9, you can do the same 
with protected-mode memory (where you don't have the 64KB limits), but I 
don't recommend it, since you will risk surprises with some DPMI hosts.

- Raw text -