RE: CL pgm and pointer variables

Apparently our e-mail system had a problem with a clogged queue.  Part of
the fallout was duplicate messages.  They tell me it's fixed now.

Sorry.

> -----Original Message-----
> From: Joel Fritz
> Sent: Thursday, November 21, 2002 9:13 AM
> To: 'rpg400-l@midrange.com'
> Subject: RE: CL pgm and pointer variables
>
>
> I was trained as a C programmer, although I haven't used it
> in almost ten
> years.  Pointers are necessary in C because there's no
> passing by reference,
> for support of dynamic memory allocation, and the way that arrays are
> defined.  There's a lot of cool things you can do with
> pointers like direct
> access to hardware if the OS permits it.  By allocating memory to a
> void--typeless--pointer and then type casting it, you can do
> darned near
> anything, just like an RPG pointer.   It's interesting that one of the
> features of C++ is reference variables.
>
> IMHO, there is very little need for pointers in business application
> programming in RPG.  There are some situations where dynamic memory
> allocation makes sense, and you may need them for some API
> calls.  Mind you,
> I'm willing to sacrifice some performance for
> maintainability.  I think
> they're nice to have, but should be used when they're the
> only reasonable
> option for solving a problem.
>
>
> > -----Original Message-----
> > From: Hans Boldt [mailto:boldt@ca.ibm.com]
> > Sent: Thursday, November 21, 2002 7:26 AM
> > To: rpg400-l@midrange.com
> > Subject: Re: CL pgm and pointer variables
> >
> >
> > Booth wrote:
> >  > Wouldn't an even easier solution to these inherent
> >  > problems with pointers be to just not use pointers?
> >
> > To which Rob answered:
> > > Wouldn't an easy solution to divide-by-zero errors
> >  > be to just not use division?
> >
> > Yes, that would in fact be acceptable. As those who've used division
> > in RPG expressions have learned (sometimes the hard way), it is
> > sometimes best to avoid division in expressions if at all possible.
> >
> > ;-)
> >
> > I do see your point, though. Why avoid something just because it is
> > potentially troublesome? The difference here is that when you have a
> > problem with division, you can normally easily locate the bug to the
> > appropriate expression.
> >
> > On the other hand, pointer bugs can often be very difficult to trace
> > down. For example, let's say you DEALLOC some piece of storage, but
> > somewhere else you still have a pointer pointing at that piece of
> > storage. Since that storage may then be returned on subsequent
> > %ALLOC operations, unpredictable results can happen when accessing
> > data through the original pointer, or worse, when the storage is
> > changed using the original pointer. Even worse, the problems can
> > often *seem* to disappear just by changing one seemingly unrelated
> > thing.
> >
> > I can attest to the problems you can have with pointers from my own
> > experience with the ILE RPG compiler, and that's using a language
> > with strong type checking of pointers! With untyped pointers (as in
> > RPG), the potential problems are much worse. At first glance,
> > debugging pointer problems can seem unsurmountable. Even at second
> > or third glance!
> >
> > Cheers!  Hans
> >
> >
> >
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