Remapping Externally Described Fields to Arrays

http://systeminetwork.com/node/60402

The following RPG IV example illustrates the technique.
The code is missing from the iSeries Network website so I
am including it here.

General ledger master file GlMst includes fields GlBal01 to GlBal12 to 
store the balances for each month of the year, shown below:
 *-----------------------------------------------------------
 * GlMst      - General Ledger Master
 *-----------------------------------------------------------
A                                      UNIQUE
A          R GLMSTR                    TEXT( 'GL Master' )
A            GLACT          7P 0       TEXT( 'Account' )
A            GLBAL01        9P 2       TEXT( 'Balance  1' )
A            GLBAL02        9P 2       TEXT( 'Balance  2' )
.
.
.
A            GLBAL11        9P 2       TEXT( 'Balance 11' )
A            GLBAL12        9P 2       TEXT( 'Balance 12' )
A          K GLACT 

The snippet of code below remaps the GlBal fields as the elements of 
array GlBalAry:
FGlMst     IP   E             Disk
D GlBalDs         Ds
D  GlBal01
D  GlBal02
.
.
.
D  GlBal11
D  GlBal12
D GlBalAry        S                   Like( GlBal01 )  Dim( 12 )
D                                     Based( GlBalPtr )
D GlBalPtr        S               *   Inz( %Addr( GlBalDs ) )

The GlBal fields are redefined as subfields in the data structure 
GlBalDs, and array GlBalAry is defined with 12 elements like GlBal01. 
The array is based on the pointer GlBalPtr, which the code initializes 
to the address of data structure GlBalDs. As a result, the array 
overlays the memory address of the data structure: GlBalAry(1) 
overlays GlBal01, GlBalAry(2) overlays GlBal02, and so on. In your 
program's C-specs, you can reference the GlBal fields using the 
subfields in data structure GlBalDs or the elements in array GlBalAry.

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