Re: Procedure changing not passed values

["Marcin Sagan" <marcin_sagan@xxxxx>]

Barbara
This example was for testing purpose only and not intended to use in
porductoin or wherever of course :) Just to see what happen when parameters
are passed in diferent ways to procedure. But If I Understood You correctly
I can corrupt databases only by runing this small "illegal" program? Even
when I do not use/open any files in it?


Regards
Marcin

----- Original Message -----
From: <bmorris@ca.ibm.com>
To: <RPG400-L@midrange.com>
Sent: Tuesday, July 10, 2001 10:56 PM
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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