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Path: utzoo!linus!philabs!seismo!ut-sally!cyb-eng!shell!starr
From: starr@shell.UUCP (Bob Starr)
Newsgroups: net.micro.pc
Subject: Question about DOS int 21
Message-ID: <154@shell.UUCP>
Date: Tue, 20-Dec-83 01:32:32 EST
Article-I.D.: shell.154
Posted: Tue Dec 20 01:32:32 1983
Date-Received: Fri, 23-Dec-83 00:53:32 EST
Organization: Shell Development CS Group, Houston, Texas
Lines: 28

Is  there  something  which  prevents  DOS function 21 from being
called recursively?

For example, let's say function 21 calls function  A.  I  replace
function  A with my own routine. Within function A, I need to use
a facility in function 21, so I invoke it via  an  interrupt  21.
After  invoking function 21 from within function A, I am returned
to function A (as I should be). Function A cannot seem to perform
a proper return  back  to  function  21,  though  (where  it  was
originally called from).

Perhaps  I  am	doing  something  wrong,  as this problem is more
complicated than presented above (i.e. when interrupt 21  invokes
(my)  function A, and function A invokes int 21, int 21 reinvokes
function A... but I think I am protected against internal  (func-
tion A, specifically) recursion problems).

Can  anyone  help?  I  have been struggling with this for several
days. My routine A works peachy until I invoke int 21.


P.S.	  I am using DOS 2.0, but want this to work  under  lower
	  versions too. Please respond via mail.



Thanks,
RF Starr