In message <87372ECCA42DD3118E3200508B2E1146C576DA@GGEXSF>, Tracy Pierce
<[log in to unmask]> writes

>[Roy B, please keep your tongue in your cheek ;-), I know there's a better
>way: steer completely clear of btrees!  But they're a feature, so I'm trying
>to use that (since it's already in use and sometimes works nicely.]

Heavy snips on problem descriptions:

>QUESTION 1: can anybody explain the seemingly anomalous next=0 at the DBGET
>breakpoints?  this occurs whether or not I go after the appropriate header
>record or not, and coincides with switches to the next real entry in the
>master set aka 'chink in the chain'.  And yes, the program works, so far.

>QUESTION 2: I'm trying to enhance the program by adding a subpgm call at
>"*2".  That subpgm will do some goofing around in the same detail set, so
>I've carefully added 'typical' save-my-place code:  After each

(Looks for and finds):

>MOVE 4 TO IMAGE-MODE

>PERFORM DBGET (which really does get back the previous record, and
>which would ordinarily (ie no btrees) re-establish my exact position on the
>chain.  But the subsequent DBGET mode 5 returns record 19, not record 48;
>that produces a loop.

B-trees are good! I've used then quite a bit.....

I'll start with Qu2, the easy one :-)

If you look in the Image manual, you will be told that doing DBGET Mode
4s is known to disrupt the Superchain.

As you have found.... :-(

However, despite this being documented, HP still regarded it as a bug,
and the latest versions of TurboImage (C.07.27 onwards) have it fixed,
I'm told..

Qu 1 is harder :-)

I *think* that the Next=0s that you are seeing may also be a
manifestation of the bug. But if you ignore them and just keep reading,
then as you have found, it all works.

OTOH, maybe even the fixed versions of TurboImage will do this, and you
will still see the end of each 'real' chain with Next, although the code
will now correctly traverse the superchain.


Fix Summary: get TurboImage C.07.27 or later. Install it. Retry the
above.


BTW, there's still one outstanding Btree issue to do with handling
Detail datasets while traversing the superchain (in case you were
thinking of doing that); it's in the HP3000-L archives at

116654 02/05/24 11:08 61  Re: FW: Image: btree & dbfind

No fix, but an entirely usable workaround.
Worth a read lest you fall foul of the issue.....

--
Roy Brown
Kelmscott Ltd

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