RE: RPG400-L Digest V2 #306

["Sims, Ken" <KSIMS@xxxxxxxxxxxxxxxx>]

Hi Jon and Lorne -

>I also pointers (and sometimes dynamic memory) with Multiple Occurrence
>Data Structures because it gives me the ability to directly
>compare/calculate/etc. between two or more occurrences.
>
>I also use pointers a lot when interacting with C functions (no choice but
>to use them) but haven't found a use for linked lists lately.

I haven't yet used dynamic memory allocation, but I recently wrote a program
where I ended up using a doubly-link list in a MODS.  I linked by the
occurrence number, not using pointers.

But I did end up using pointers to be able access multiple occurrences
simultaneously, particularly since I needed to be able to update the data,
so just making a copy wouldn't do.

For Lorne, here are some code snippets.

Here is the MODS.  It is just a regular MODS, no pointers or dynamic memory
allocation.
It actually has a lot more fields than this.  The contents is immaterial.

     d @detail         ds            96    occurs(2000)
     d   @areof                        n               
     d   @aivno#                      7p 0             
     d   @aivdt                       7p 0             
     d   @aoi@                        3p 0             
     d   @aramt$                      9p 2             
     d   @arpay$                      9p 2             
     d   @ardiv#                      1p 0             
     d   @ariref                      7p 0             

Here is the data structure (not a MODS) that I want to be able to use as a
particular occurrence of the MODS.  It has the same definition but with
different names, and is based on a pointer.  The pointer definition follows
the data structure definition.

     d @crddet         ds            96    based(@crddet@)
     d   @crd_areof                    n                  
     d   @crd_aivno#                  7p 0                
     d   @crd_aivdt                   7p 0                
     d   @crd_aoi@                    3p 0                
     d   @crd_aramt$                  9p 2                
     d   @crd_arpay$                  9p 2                
     d   @crd_ardiv#                  1p 0                
     d   @crd_ariref                  7p 0                
     d @crddet@        s               *                   

I set the occurrence of @detail to the occurrence that I want to reference
through @crddet.  I then execute this code:

     c*                                                     
     c*  Point the @crddet data structure to this occurrence
     c*                                                     
     c                   eval      @crddet@ = %addr(@detail)

I set the pointer to the address of the particular occurrence.  Since the
@crddet data structure is based on this pointer, it will continue to
reference this occurrence of @detail, even after I set the occurrence of
@detail to something else.  This allows me to reference two occurrences of
the data structure simultaneously.  In this particular program I also had a
@invdet data structure that I used the same way, so I was accessing three
occurrences of the MODS simultaneously; one directly, using the current
occurrence of @detail, and two indirectly using data structures based on
pointers pointing to specific occurrences.

Some of the fields in the MODS that I didn't copy into this message are the
linked list fields,  pointers to the next and previous elements in the list.
Pointers in the generic sense; they are numeric fields containing the
occurrence numbers of the next and previous occurrences.  It could be done
with actual pointer fields as well, but there was no reason to.

Ken
Southern Wine and Spirits of Nevada, Inc.
Opinions expressed are my own and do not necessarily represent the views of
my employer or anyone in their right mind.


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