Path: utzoo!attcan!uunet!mcsun!unido!rwthinf!cip-s01!pmk
From: pmk@cip-s01.informatik.rwth-aachen.de (Michael Keukert)
Newsgroups: comp.lang.pascal
Subject: Re: Help with stack overflow
Keywords: turbo  error trapping  help   stack
Message-ID: <2577@rwthinf.UUCP>
Date: 12 Apr 90 11:09:43 GMT
References: <22863@uflorida.cis.ufl.EDU>
Sender: news@rwthinf.UUCP
Reply-To: pmk@cip-s01.UUCP (Michael Keukert)
Distribution: comp
Organization: Informatik RWTH Aachen
Lines: 87

In article <22863@uflorida.cis.ufl.EDU> dor@beach.cis.ufl.edu (Douglas R. Oosting) writes:
>I have a fairly large communications program in Turbo 5.0 which just 
>(apparently) dumped with a stack overflow.  Ouch.  How can I trap something
>like this?  I have the ExitPtr pointer set to a FAR routine {$F+} that
>has no local variables (everything called in it is global to that unit)
>

Hi,

There are three variables, which are useful to you.

ExitProc has to be set on the (far-compiled) error handling routine,
like you already did it. For the others:
  ExitProc := @own_exit_proc_name;

ExitCode get`s a number between 0 and 255 which will indicate, what
  error occured.

ErrorAddr is a pointer variable, which includes the segment and offset
  of the address where the error occured.

You now have to declare your own, error handling procedure, which has to 
be far-compiled and whic mustn`t use external parameters. Within the
procedure, you can reference other procedure or use as much variables
you like.

DANGER!!!!

The normal TPascal exit-procedure HAS TO BE executed also, because it
closes the files, reconstructs the interrupt vectors etc. So you have
to save the original pointer first:

 SaveExitProc := ExitProc;

Within your own procedure, you can set ErrorAddr to NIL. Doing this will
cause no other errors. This means, your own procedure isn`t itself 
interrupted by a runtime error.
Don`t forget to reload the exitproc BEFORE exiting your own procedure:
 ExitProc := SaveExitProc;

Now a tiny example:

{$f+}
PROCEDURE myexit;
VAR i:INETEGER;
BEGIN
 WRITELN(`Error Number : `,ExitCode);
 ErrorAddr := NIL;
 ExitProc := SaveExitProc;
END;

{$F-}


BEGIN {main}
 SaveExitProc := ExitProc;
 ExitProc := @myexit;
 [...]
END.

If you want to get the address of ErrorAddr, use this:

TYPE errorptr =
	 segment:word;
	 offset:word;
        end;

WRITELN (`Error at : `,errorptr(erroraddr).segment,`:`,errorptr(erroraddr).offset;

This is known as TYPECASTING and allows you, to enable the compiler-range
check. For example:

VAR a:BYTE;
    b:STRING;

a:=12;
b:=STRING(a);

For the results of typecasting, the programmer has to take care. No
garantees are given ;-)

OK, hope I helped you....

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