I've got an externally described file, from DDS roughly like (not all
fields shown):
A R WTEX01R
*
A CDATE 8S 0 TEXT('Created Date')
A CTIME 6S 0 TEXT('Created Time')
A CUSER 10A TEXT('Created By User')
. . .
A U01052 012A COLHDG('E-Unit#')
A U01053 008S00 COLHDG('E-Item#')
. . .
A U01265 010A COLHDG('Model Code')
A U01266 003A COLHDG('Major Equip. Class')
with a result something like:
Field T Len From To
CDATE S 8 1 8
CTIME S 6 9 14
CUSER A 10 15 24
. . .
U01052 A 12 87 98
U01053 S 8 99 106
. . .
U01265 A 10 502 511
U01266 A 3 512 514
And I have an RPG program that already opens the file as externally
described. Now, for a new function in the program, I would like to be
able to read a record from the file in such a way that everything from
byte 87 through byte 514 of the record is contained in a single field
(for comparison with a byte stream that contains a record image).
Overlaying a single field containing the "bytes of interest" over the
byte stream is of course trivial.
I'm trying to set up an overlay on the record. Preferably without having
to put all the file's fields into a DS, because that would be one more
big thing to go wrong.
First, knowing that starting in V6, files opened as externally described
can be read into a data structure (as opposed to traditional RPG
scatter-gather I/O), I tried setting up a data structure, containing
only my "bytes of interest" overlay field.
> D TESTREC DS
> D BYTESOFINT 87 514
and then doing
> C MYKEY CHAIN MYFILE TESTREC
That was rejected with an RNF7595, "The result data structure does not
include a subfield in position 1 . . . ."; I added a subfield starting
in position 1.
> D TESTREC DS
> D IGNORE 1 87
> D BYTESOFINT 87 514
That didn't work, so I looked up the error message, and found that I had
to use a data structure derived from the file, so I tried:
> D TESTREC DS LIKEREC(REALREC)
> D BYTESOFINT 87 514
and it gave me TWO error messages (an RNF3703 and an RNF3602) on the
"BYTESOFINT" field.
At this point, noticing that at some point, I'd put in a couple of
I-specs on the file, to rename a single field, I tried giving up on the
above approach, and plugging my overlay field in as another I-spec, and
it only took one failed compilation before I realized that wasn't going
to work, because of the mechanics of scatter-gather.
So I'm back to the "TESTREC" approach, but I can't figure out what it wants.
--
JHHL
midrange.com
