RE: Procedure changing not passed values

[Joel Fritz <JFritz@xxxxxxxxxxxxxxxx>]

Hmm...

Could you expand a little on "messing up the operating system, requiring a
reinstall."  It sounds like overwriting command.com in memory on the pc back
in the good old days of totally unprotected memory locations, only lots
worse.

-----Original Message-----
From: bmorris@ca.ibm.com [mailto:bmorris@ca.ibm.com]
Sent: Tuesday, July 10, 2001 1:56 PM
To: RPG400-L@midrange.com
Subject: Re: Procedure changing not passed values



>Date: Tue, 10 Jul 2001 12:00:31 +0200
>From: "Marcin Sagan" <marcin_sagan@wp.pl>
>
>why when I call ProcA (code below) without parameters it gives me
>"MCH3601-Pointer not set for location referenced." (what I am expected)
but
>when first call is with parms and second without  ProcA change values of
>this (not passed!) parameters anyway?
> ...
>p ProcA           b
>d ProcA           pi
>d  Par1                          2a   Options( *NoPass : *Omit )
>d  Par2                          2a   Options( *NoPass : *Omit )
>d  Par2                          2a   Options( *NoPass : *Omit )
>d  Par3                          2a   Options( *NoPass : *Omit )
>
>  ... snip correct parameter-checking code
>
>  * What if we try to reach parms without checking?
>c                   Eval      Par1 = 'AA'

Marcin, when you make your first call, the parameters (pointers)
get put on the "parameter stack".  The stack is not cleared when the
call returns, so those pointers are still there for the second call.

In your case, the values that got changed were "your" variables; in
other cases of changing unpassed parameters, they could be anything.

You shouldn't experiment with such illegal things.  You can't
guess what is on the parameter stack even in a simple case like
yours.  You could cause many bad things to happen:
  - corrupting the data in your database
  - crashing your program
  - messing up the operating system, requiring a reinstall

Barbara Morris

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