RE: CL pgm and pointer variables

[rob@xxxxxxxxx]

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The User space API's are an excellent reason for pointers.  The code is
actually MORE maintainable with pointers than with the repetitious calls
to QUSRTVUS.

Rob Berendt
--
"They that can give up essential liberty to obtain a little temporary
safety deserve neither liberty nor safety."
Benjamin Franklin




Joel Fritz <JFritz@sharperimage.com>
Sent by: rpg400-l-admin@midrange.com
11/21/2002 12:12 PM
Please respond to rpg400-l

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        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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