RE: Based variables

[Joel Fritz <JFritz@xxxxxxxxxxxxxxxx>]

A singly linked list, where you can only traverse it in one direction, isn't
real complicated.  I don't think it would perform as well as data stored in
some way that guarantees at least the appearance of contiguity, i.e. allows
access by indexing or pointer arithmetic.  It would be interesting to test
it.  If you have to sort the data after loading it, or insert at a specific
point, the linked list gets more complicated.  
 

I've never used one in RPG, except once to prove to myself I still
remembered how to build one.  

> -----Original Message-----
> From: M. Lazarus [mailto:mlazarus@ttec.com]
> Sent: Friday, December 08, 2000 11:01 AM
> To: RPG400-L@midrange.com
> Subject: RE: Based variables
> 
> 
> At 12/8/00 11:33 AM -0600, you wrote:
> >The way you do this is to NOT use a field, ONLY use a 
> pointer that is first
> >Allocated to 1 record, and then Reallocated for an 
> additional record each
> >time you read another record in.  This creates a completely 
> dynamic and
> >contiguous memory block that holds the records for the file. 
>  The externally
> >described Data Structure to the file is Based on a Pointer, and you
> >re-calculate this pointer to the correct position in the 
> dynamic memory
> >block.
> 
>   Let me get this straight.  If the DS is based, the pointer 
> is set for the 
> first record read.  I increment the pointer to point to the 
> byte right 
> after the DS.  How do I know I'm not stepping on some valid data in 
> memory?  Do I use ALLOC / REALLOC to reserve it?  If yes, 
> then that should 
> work well.
> 
>   Does it make sense (performance wise) to only add one record to the 
> memory allocation?  Or should I just add, say, 500 records worth.
> 
> 
> >Another technique in the RPG Programmer's guide is to create 
> a Linked List.
> >The problem with this is that it requires at least 2 
> pointers per record,
> >and possibly 3, and creates a lot of pointer management 
> issues.  The above
> >technique requires only 1 pointer for the data, and an 
> additional pointer
> >for the Based Data Structure.
> 
>   I agree that a linked list is too complicated for this application.
> 
>   -mark
> 
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