Re: Pointer usage danger?

["M. Lazarus" <mlazarus@xxxxxxxx>]

Vern,

 Warnings noted.  Just confirming if sliding the window around in 
itself will overlay the memory past Array1.  Obviously, writing past 
the "real" end of the array is a no-no and reading past would produce 
unknown results.  Thanks.

 -mark


At 3/8/2011 01:11 PM, you wrote:
> Hi Mark
>
> I'll take a run at this - Array2 is based on that pointer, Array1Ptr -
> that is, the data structure as a whole is based on the pointer. This is
> what you described.
>
> I think this is safe enough. Array2 could be described as a window over
> memory - its holes are the elements in that array or DS - nothing is
> changed by setting the basing pointer, so far as I know. You are merely
> sliding the window over a new part of memory.
>
> You could even try to access element 2 of Array2 for reading - don't
> write to it!! Or put another way, don't throw a hammer at window number 2!
>
> That does constitute a risk, though, so it would require much care if
> you are modifying anything.
>
> Vern
>
> On 3/8/2011 11:13 AM, M. Lazarus wrote:
> >    Given this code:
> >
> > D Array1       DS              Dim( 10 )
> > D  Field1                2a
> > D  Field2               75a
> >
> > D Array2       DS              Dim( %Elem( Array1 ))
> > D                              Based( Array1Ptr ) Inz( %Addr( Array1 ))
> > D  Field1a                     Like( Field1 )
> > D  Field2a                     Like( Field2 )
> >
> > D Array1Ptr    s          *
> >
> >    /Free
> >        Array1Ptr = %Addr( Array1( 10 )) ;
> >    ...
> >
> >    At this point, the first element of Array2 should be positioned
> > over the last element (#10) of Array1.  Assuming I don't attempt to
> > access element 2 in Array2, is this safe to do or will the shift of
> > Array2, elements 2-10, overlay memory it shouldn't?
> >
> >    -mark
> >
> --
> This is the RPG programming on the IBM i / System i (RPG400-L) mailing list
> To post a message email: RPG400-L@xxxxxxxxxxxx
> To subscribe, unsubscribe, or change list options,
> visit: http://lists.midrange.com/mailman/listinfo/rpg400-l
> or email: RPG400-L-request@xxxxxxxxxxxx
> Before posting, please take a moment to review the archives
> at http://archive.midrange.com/rpg400-l.