Re: RPGIV MoveA issue.

[bmorris@xxxxxxxxxx]

>Date: Mon, 22 Jan 2001 13:25:45 -0800
>From: JohnJ@pacinfosys.com
>
>0103.00 C     *ENTRY        PLIST
>0103.01 C                   PARM                    PA              128
>0103.02 C                   PARM                    PRM1            256
>0103.03 C                   PARM                    PRM2            256
>
>0326.00 C                   CALL      CALD
>0326.01 C                   PARM                    PA
>0326.02 C                   PARM                    PRM1
>0326.03 C                   PARM                    PRM2

John, what's critical here, and for every parameter passing issue,
is the _lengths_ of the parameters as they are defined in calling
program.  If any of those parameters are shorter than the definitions
in the *ENTRY PLIST of the called program, you can get strange storage
corruption problems like you're seeing.  In general, you should always
pass parameters that are at least as long as the called program
expects.

The reason is that the parameters are passed by reference; that is, a
pointer to the parameter is passed to the called program.

Here's a simpler example:

--------- PGM1 ---------
D ds         DS
D   sub1              5a
D   sub2              5a

C          CALL 'PGM2'
C          PARM            sub1
C          PARM            sub2

--------- PGM2 ---------

C  *ENTRY  PLIST
C          PARM            p1         10
C          PARM            p2          5

Entry parm p1 refers to subfield sub1.

Any change to p1 will immediately update subfield sub1.
But p1 is defined longer than sub1, so if p1 is changed
to say 'abcdefghij', then not only sub1 will get changed,
but also the 5 bytes following sub1, which is sub2.

Since entry parm p2 refers to subfield sub2, changing p1
to 'abcdefghij' will change sub2 and p2 to be 'fghij'.

Barbara Morris


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