Re: Externally-Described Field used as array name.

>From: "Peter Dow" <pcdow@yahoo.com>
>Date: Thu, 23 Aug 2001 15:30:17 -0700
>
>The compiler sees PDLB02 in the data structure first, and allocates memory
>for it there.
>
>Then it sees PDLB02 in the input specs and wants to allocate memory for it
>within the input buffer, but it can't have a unique field name pointing to
>two different memory locations.

Peter, the compiler doesn't allocate memory for input fields in the
input buffer.  The input specs actually describe "move" operations
from the input buffer to program fields.  The compiler uses the
input spec information to generate definitions for you, if you don't
already have explicit definitions.  (The memory for the input buffer
is already allocated by database.)

So it's perfectly normal and reasonable to have a D-spec definition
for a field that appears in an input spec.  Just like it's normal and
reasonable to have the same field in two different input specs, for
two different files.

Example:

D FLD1        S        5P 0
I              S   11   15 0  FLD1

FLD1 is zoned(5,0) in the input spec.
FLD1 is packed(5,0) on the D spec.
The input spec says "move the zoned field in positions
11-15 of the input buffer to FLD1, whereever FLD1 happens
to be".  This is one of the central features of RPG that
makes it different from other languages.

(You're not alone in thinking that I-specs are definitions.  It's
one of the most common misconceptions about RPG.  The more common
symptom of this misconception is thinking that if a field is zoned
in the database, it must also be zoned in RPG.)

Barbara Morris