RE: Help a pointer Newbie out...

["Bob Cozzi \(RPGIV\)" <cozzi@xxxxxxxxx>]

Adding to what Joep said...
You might consider a multiple occurrence data structure. But I would
suggest that if you don't know how many elements you need at runtime and
that number may be large you might consider using a based keyword with
ALLOC and DeAlloc.
If it is small, just add the OCCURS() keyword to the data structure and
get all the storage you need without dealing with the pointer crap.
If you need up to 50 occurrences, then you would code something like
this:

> D LDADS           DS           OCCURS(50)
> D  CusKeyErr        14     28
> D  RefErr           29     38
> D  MsgCode          39     45
> D  ErrElmAry        46     93
> D  ErrMsgAry        94    261

If you really want to use dynamic occurrences, use a point variable as
follows:

     D pData           S               *
     D LDADS           DS                  Occurs(32766) Based(pData)
     D  CusKeyErr             14     28
     D  RefErr                29     38
     D  MsgCode               39     45
     D  ErrElmAry             46     93
     D  ErrMsgAry             94    261

     D nByteCount      S             10I 0
     D nNumNeeded      S             10I 0

     C                   Eval      nNumNeeded = 200
     C                   Eval      nByteCount = %Size(LDADS) *
nNumNeeded
     C                   Alloc     nByteCount    pData
     C** I now have 200 occurrences of LDADS available

     C                   Eval      nNumNeeded = 750
     C                   Eval      nByteCount = %Size(LDADS) *
nNumNeeded
     C                   ReAlloc   nByteCount    pData
     C** I now have 750 occurrences of LDADS available


Just remember, storage returned by ALLOC and REALLOC is not initialized,
while it is usually blank, it is not guaranteed to be blank.

Bob Cozzi
cozzi@rpgiv.com
Visit the on-line  Midrange  Developer  forum at: http://www.rpgiv.com


> -----Original Message-----
> From: rpg400-l-admin@midrange.com [mailto:rpg400-l-admin@midrange.com]
On
> Behalf Of Joep Beckeringh
> Sent: Tuesday, January 08, 2002 2:29 PM
> To: rpg400-l@midrange.com
> Subject: Re: Help a pointer Newbie out...
>
> I think you will have to supply some information:
>
> - What are you trying to achieve?
> - Why do you think you need a linked list?
> - Why do you think you need pointers to process this list?
> (And while you're at it: What is wrong with using a file in QTEMP?)
>
> There are several ways to handle lists of information in RPG (arrays,
> multiple occurrence data structures and, yes, files).  Arrays and MODS
> usually have a predefined size limit.  When you don't want to define
the
> size at compile time, you will have to do your own memory
housekeeping; in
> that case you will have to deal with pointers.
>
> A list is a linked list when elements contain one or more links to
other
> elements.  These links don't have to be pointers (in the technical
sense);
> in an array they could be indexes to other elements; in a MODS they
could be
> indexes to other occurrences; in a file they could be keys to other
records.
>
> Joep Beckeringh
>
>
> ----- Original Message -----
> From: <SCarter@rsrcorp.com>
> To: <rpg400-l@midrange.com>
> Sent: Tuesday, January 08, 2002 9:03 PM
> Subject: Help a pointer Newbie out...
>
>
> > I searched the archives and the FAQ for information on using
pointers to
> > linked lists
> > and I did not find anything useful to ME...
> > that having been said can some one give me an example of using
pointers
> for
> > linked lists
> > I have the classic list problem I know what type of data I need but
i
> don't
> > know how much.
> > I could write the data out to a file in QTEMP and just process the
file
> but
> > I did not want to do
> > that unless I can't wrap my brain around this pointer thing in a
> reasonable
> > amount of time.
> >
> > I want to be able to store this information in a list and then
reprocess
> > the list how would I
> > do this with pointers...
> > D LDADS           DS
> > D  CusKeyErr        14     28
> > D  RefErr           29     38
> > D  MsgCode          39     45
> > D  ErrElmAry        46     93
> > D  ErrMsgAry        94    261
>
>
>
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