Re: EXTFILE/EXTDESC: what problem does it solve

[Michael Schutte <mschutte369@xxxxxxxxx>]

The EXTFILE eliminates the need to do a RUN-TIME OVRDBF.  EXTDESC
eliminates the need of a COMPILE-TIME OVRDBF.

For example, lets say you wanted to bring the same file in twice within the
same program.  Obviously, you can't put FILEA in the FSPEC twice.  It will
not compile.  So you would normally put a bogus file name in the FSPEC i.e.
FILEA@.

Before EXTFILE, you would have to OVRDBF FILE(FILEA@) TOFILE(FILEA) in a CL
prior to calling the program, and you also had to do it to prior to
compling the program.

With EXTFILE, you no longer needed the OVRDBF in a CL prior to calling the
program, however, you did in order to compile.

Now with EXTDESC, you no longer need to do OVRDBF when compiling now too.
 EXTDESC will look at the value within it and pull in those fields to
compile with.

Typically you will see    EXTDESC(*EXTFILE) EXTFILE('LIB2/FILEA')   in the
keywords


On Tue, Mar 20, 2012 at 11:25 PM, John Yeung <gallium.arsenide@xxxxxxxxx>wrote:

> Any time you can use a variable instead of a hard-coded value, that's
> a significant gain in flexibility.  One simple convenience the EXTFILE
> keyword provides is the ability to do what amounts to OVRDBF, but
> without a separate CLP.
>
> In principle, you can actually do much more powerful things, like get
> user input within your RPG program, and have that very same program
> choose different files to open (so long as their record formats are
> compatible) based on that user input.  I don't know if there was a way
> to choose a file at run-time before the EXTFILE keyword (V5R1), but
> even if there was, it was surely much more difficult and convoluted.
>
> EXTDESC is even newer, and is comparatively less powerful.  It's a
> convenience, saving you from having to have the compile-time file with
> the proper name in the proper place in the library list.  For example,
> suppose you have four existing files:  LIB1/FILEA, LIB1/FILEB,
> LIB2/FILEA, and LIB2/FILEB.  LIB1/FILEA is not compatible with
> LIB2/FILEA and LIB1/FILEB is not compatible with LIB2/FILEB.  If your
> program needs to be compiled with LIB1/FILEA and LIB2/FILEB, it is
> much trickier (or at least much more annoying) to accomplish without
> the EXTDESC keyword.
>
> John
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