RE: Classic traps EXTFILE and EXTMBR

This is also a trap for OVRDBF, but we noticed it here by using EXTFILE
and EXTMBR in RPG.

We rely on *LIBL for our library names to allow the library lists to
control the actual file locations.

If you ask for member 'Y' in file 'X'...
The system will look through the library list.
If it finds file X but doesn't find member Y, it will keep looking until
it finds a match - or exhausts the library list.

This means that if you have the file in more than one place in the
library list, you may not be in the library you expect after the file is
open.

Without members this isn't much of an issue because files will have a
member *FIRST that should always be there - so it will resolve *LIBL to
the FIRST library it finds the file in.
But when you specify a member, it won't stop at the first file like I
indicated - it will try it's best to find your member for you.

Should files ever be in more than one library? I don't want to go into
THAT discussion here. That's not the point. In some cases in our shop
they do - so I have to consider and handle that since I can't change the
facts.

The best work-around I found is to:
1) Specify the member *FIRST and open the file.
2) Use the INFDS to get and store the actual library used.
3) Close the file, and open it again specifying the exact member name
you want
4) Compare the library in the 2nd open. If it is not the same as the
first one you have 'jumped' libraries between the *FIRST member and the
member you wanted. This might not be an error depending on the structure
of your shop, but in our case it would be (the error being that the
member does not exist)

Yes - file opens are expensive. But I need to make sure that I have
found the member and file in the right library.

Oh - please, don't make this a 'should you use members?' discussion. I
can't control what we have. I just try to manage it :-)

James P. Wiant
Testing Coordinator
Foodstuffs, Auckland, Ltd.
60 Roma Road
Auckland, New Zealand
09-621-0774
jim.wiant@xxxxxxxxxxxxxxxx




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