Re: Getting into pointers

[Stuart Rowe <rowestu@xxxxxxxxx>]

Sure, that's as good a way as any (not knowing what wMrsAdh is).  All you
need is enough space to hold the entirety of MyDS which could also be
represented as:

    myPtr = %alloc( %size( myDS ) * 100 );

You could also have not based the DS on the pointer, but rather set the
pointer to the address of the DS.  This way you can use your DS without
allocating memory for it, and just tell the called routine "where" the DS is
in your program.

    myPtr = %addr( myDS );

Pointers are handy.  Play with them.  They only occasionally bite.

Stu



On Wed, Aug 12, 2009 at 07:41, David FOXWELL <David.FOXWELL@xxxxxxxxx>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.
> --
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