Re: Getting into pointers

[Scott Klement <rpg400-l@xxxxxxxxxxxxxxxx>]

Hello David,

I have a question regarding the following code:

D MyDS            DS                  LIKEDS ( gMyOtherDS ) DIM ( 100 )
D                                     BASED ( MyPtr )
D MyPtr           S               *

My question: Why did you use the BASED keyword?  Why bother using BASED 
and then %ALLOC?  Why not just do this?

D MyDS            DS                  LIKEDS ( gMyOtherDS ) DIM ( 100 )
D MyPtr           S               *

   MyPtr = %addr(MyDS);
   PGM2(MyPtr);

Why tell the OS to let you handle the allocation if you're just going to 
allocate the exact size of the structure?



David FOXWELL wrote:
> Hi,
>
> I just wrote my first program ever that passed a pointer from one program to another. I used it to access a data structure in the calling program that was alimented by the program being called. I won't explain why I did not just pass the data structure as a parameter. Anyway, it seems to work. I was a little surprised and found it good fun. However, having rather stumbled upon the solution when it didn't work, I ask the experts out there for confirmation :
>
>
>
> Code simplified.
> D PGM2            PR                  EXTPGM ( 'PGM2' )
> D OutParm                         *
>
>
> D MyDS            DS                  LIKEDS ( gMyOtherDS ) DIM ( 100 )
> D                                     BASED ( MyPtr )
> D MyPtr           S               *
>
>  /free
>
>   PGM2 ( MyPtr );
>
> /end-free
>
>
>
> This crashed because I understand I need to allocate storage for MyPtr before the call.
>
> So I inserted this and it worked :
>  wLen  = %LEN ( wMrsAdh ( 1 ));
>  MyPtr = %ALLOC ( wLen * 100 );
>
> Is this the right way to initialize the pointer?
>
> Thanks.