RE: bsearch on partial array elements -- RPG400-L

RPG supports pointer arithmetic although not as neatly as C since pointers
in RPG aren't pointers to a specific data type.  You have to write a little
code to translate the difference between the beginning of the array and the
offset returned into an index number.  Write a procedure once--use it
forever.

Here's some examples from TFM that should help:

The following shows how you can add and subtract offsets from pointers and
also determine the difference in offsets between two pointers.
 
+---------------------------------------------------------------------------
-----------------------+
�
�
�
�
�   *.. 1 ...+... 2 ...+... 3 ...+... 4 ...+... 5 ...+... 6 ...+... 7
...+...8                     �
�
DName+++++++++++ETDsFrom+++To/L+++IDc.Keywords+++++++++++++++++++++++++++++
�
�
D.....................................Keywords+++++++++++++++++++++++++++++
�
�    *
�
�   D P1              s               *
�
�   D P2              s               *
�
�
�
�
CL0N01Factor1+++++++Opcode(E)+Factor2+++++++Result++++++++Len++D+HiLoEq....
�
�   CL0N01++++++++++++++Opcode(E)+Extended Factor
2++++++++++++++++++++++++++++                    �
�    *
�
�    * Allocate 20 bytes of storage for pointer P1.
�
�   C                   ALLOC     20            P1
�
�
�
�    * Initialize the storage to 'abcdefghij'
�
�   C                   EVAL      %STR(P1:20) = 'abcdefghij'
�
�
�
�    * Set P2 to point to the 9th byte of this storage.
�
�   C                   EVAL      P2 = P1 + 8
�
�
�
�    * Show that P2 is pointing at 'i'.  %STR returns the data that
�
�    * the pointer is pointing to up to but not incuding the first
�
�    * null-terminator x'00' that it finds, but it only searches for
�
�    * the given length, which is 1 in this case.
�
�   C                   EVAL      Result = %STR(P2:1)
�
�   C                   DSPLY                   Result            1
�
�
�
�    * Set P2 to point to the previous byte
�
�   C                   EVAL      P2 = P2 - 1
�
�
�
�    * Show that P2 is pointing at 'h'
�
�   C                   EVAL      Result = %STR(P2:1)
�
�   C                   DSPLY                   Result
�
�
�
�    * Find out how far P1 and P2 are apart.  (7 bytes)
�
�   C                   EVAL      Diff = P2 - P1
�
�   C                   DSPLY                   Diff              5 0
�
�
�
�    * Free P1's storage
�
�   C                   DEALLOC                 P1
�
�   C                   RETURN
�
�
�
�
�
+---------------------------------------------------------------------------
-----------------------+
Figure 88. Pointer Arithmetic

> -----Original Message-----
> From: David.Biggs@bernardmatthews.com
> [mailto:David.Biggs@bernardmatthews.com]
> Sent: Friday, January 14, 2000 5:55 AM
> To: RPG400-L@midrange.com
> Subject: Re: bsearch on partial array elements
> 
> 
> 
> 
> Thanks Jon and others.
>  I knew about the basing pointers but wasn't sure what the C 
> routine would do
> when comparing (in my case) a 30 byte key with a 37 byte 
> element. I've tried it
> for myself and it works just fine.
> 
> I have another question though: in RPG LOKUP (or LOOKUP), you 
> can specify a
> field that is set to the element number of the search 
> argument if the search is
> successful. The C 'bsearch' returns a pointer to the key 
> value being sought, not
> its ordinal position in the array. This seems a bit stupid as 
> I already know
> what I'm looking for, what I want is whereabouts it is. Any 
> way I can get this
> directly ?
> 
> Regards,
> Dave
> 
> 
> 
> 
> 
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