Ext-desc I/O using data structures (was:Field record relatio

Hi David!  Yes, you're right.  DS I/O is not allowed for ext-desc files in
RPG.

Would you (or any other RPG programmer watching) like that limitation
removed in a future release?  IMHO, ext-desc data structures are very
useful and we should do more to support them.

Hans Boldt, ILE RPG Development, IBM Toronto Lab, boldt@ca.ibm.com




owner-midrange-l@midrange.com on 98-04-01 19:04:15
Please respond to MIDRANGE-L@midrange.com
To: MIDRANGE-L@midrange.com
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Subject: Re: Field record relation indicators


Hans,

I don't think you can read to a data structure with an external file.  Has that
changed?  Anyway I was under the impression (have no interest in finding out)
that the look ahead still works for program described files.  So I think you
might want to swap the data using an intermediate variable.  Or you could swap
pointers.  Create two based externally described files, in one prefix the
names.  After a record is read swap the basing pointers using an intermediate
pointer.

d Rcd     E DS  extname(file) inz based(pRcd)
d Nxt      E DS  extname(file) inz prefix(Nxt) based(pNxt)

If I didn't need to compare the two record images I would just use a MODS and
use occur 1 for current record and occur 2 for look ahead data.  I agree this
should be very low on the priority list.  Back there with auto report and
increasing the number of level indicators.

David Morris


>>> Hans Boldt <boldt@ca.ibm.com> 04/01 8:31 AM >>>
Mark wrote:
>>If you need some sort of lookahead on sequential reads to an externally
>>described file, you could probably manage nicely using externally
>>described data structures and READ into DS.
>
> Wouldn't you still have to define the from and to positions in the
>look-ahead area?

No.  The technique I described works like this:  You define 2 externally
described data structures
(called, say, CURREC and LOOKREC) from the file you want to read from, using
PREFIX to rename
all the fields in one of them.  Keep the current record in CURREC and the
lookahead record in
LOOKREC.   To start reading, do:

       C                          READ        FILE              CURREC
       C                          READ        FILE              LOOKREC

To read the next record, do:

       C                          EVAL        CURREC = LOOKREC
       C                          READ        FILE              LOOKREC





!
!





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