Re: Variable length MODS

[James David Rich <james@xxxxxxxxxxx>]

On Tue, 17 Apr 2001, Jim Langston wrote:

> Does it really matter how many elements are in an array that is being
> used as a pointer anyway?

If a DIM is given it should be honored (i.e. that amount of space should
be allocated) but an ALLOC should be able to increase the size, allowing
the program to reference occurences beyond those given in the DIM.

I believe that the structure definition given below is illegal in other
languages, i.e. you can't have:

char array[];

so a DIM with no size is probably bad.

> This is pseudo code
>
> D SomeStructure  DS             DIM() BASED(SomePointer)
> D SomeString         10A
> D SomeInt            10U
> D SomeZoned           9S 0
> D SomePointer     S    *
>
> D SomeCounter         9P 0
> D SomeMax             9P 0
>
> C            Eval    SomePointer = SomeAddressToSomeArray
> C            Eval    SomeMax = MaxRangeOfTheArrayPointingTo

[snip]

> The whole point being, RPG or the AS/400 shouldn't care what the upper
> limit is.  It does not have to allocate any memory, since we are using a
> pointer anyway, and just looking at memory that's already there.  The
> program math is fairly simple behind the covers, the array element X
> starts at SizeOfStructure * (X - 1) + 1

It should care if the struct is being accessed "the old way", i.e. not
pointer based.  If the definition is not "BASED" then the current way is
fine.  If the struct is pointer based then all bets are off and accesses
outside of allocated memory should result in a segmentation fault (or
whatever).

James Rich
james@eaerich.com

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