Re: Pointer usage danger?

[Vern Hamberg <vhamberg@xxxxxxxxxxx>]

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