Re: Pointer usage danger?

[Scott Klement <rpg400-l@xxxxxxxxxxxxxxxx>]

Hi Mark,


On 3/8/2011 11:13 AM, M. Lazarus wrote:
> D Array2       DS              Dim( %Elem( Array1 ))
> D                              Based( Array1Ptr ) Inz( %Addr( Array1 ))
> D  Field1a                     Like( Field1 )
> D  Field2a                     Like( Field2 )
>
> D Array1Ptr    s          *

The preceding code won't compile. You can't use INZ and BASED on the 
same variable.

However, assuming I understand the intent of your code, you could do it 
this way:

 D Array2       DS              Dim( %Elem( Array1 ))
 D                              Based( Array1Ptr )
 D  Field1a                     Like( Field1 )
 D  Field2a                     Like( Field2 )

 D Array1Ptr    s          *    Inz(%Addr(Array1))


>    /Free
>        Array1Ptr = %Addr( Array1( 10 )) ;

>    At this point, the first element of Array2 should be positioned
> over the last element (#10) of Array1.

Correct.


> 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?

This is safe to do, provided that you don't attempt access elements 
2-10.  Elements 2-10 do overlay memory that they shouldn't -- but if you 
don't access them your program will work as expected.

However, I don't understand /why/ you'd do that. It seems silly when you 
can already access the same data as Array1(10).