 | |
Avoiding interference with active list
comp.databases.pick comp.databases.pick
 |
| | Thread Tools | Display Modes |
#11
 
| |||
| |||
|
Re: Avoiding interference with active list -
09-12-2005
, 12:48 PM
|
Yes, you're right, I was thinking in terms of *always* using RTNLIST which would solve the problem, but of course require you to check *all* calling programs. I never leave the RTNLIST out, so select list0 is never active. Scott's solution is probably the only one, it could be simplified as you don't have to write and read the list to a file: restore.list = 0 svlist = "" if system(11) then loop readnext id else exit svlist<-1> = id repeat restore.list=1 end ... whatever ... if svlist # '' then select svlist You also want to avoid using select list0 in [whatever], or make sure you exhaust it, or the select svlist will not work. Chandru Murthi michael (AT) preece (DOT) net> wrote in message news:1126490893.791888.134950 (AT) g49g2000cwa (DOT) googlegroups.com... murthi wrote: Do you mean you want to EXECUTE "S{S}ELECT ...." ? Yes. If so, don't see the problem, since you can return the list to any variable via "RTNLIST var" and that will not interfere, by definition, with any other extant lists. If there was a select-list active then wouldn't the S{S}ELECT I execute attempt to return a subset of the active list? If the calling program/subroutine had just executed a SELECT (without specifying a list number or variable) so that list0 is currently active, and my subroutine then executes another select on a totally different file/directory, then wouldn't the latest select use the already active list? Like: . . . EXECUTE "SELECT FILE1" CALL MYSUB . . . SUBROUTINE MYSUB . . . EXECUTE "SELECT DIR1 ":SELECTCRITERIA:" ":SORTORDER:" TO ":LISTNO * or ...RTNLIST LISTNO LOOP READNEXT KEY FROM LISTNO ELSE EXIT . . . REPEAT . . . RETURN Wouldn't LISTNO always be a subset of the keys from FILE1? The thing to bear in mind here is that I don't want to change any of the existing program code - other than to plug in a call to my subroutine as and when needed. I think Unidata probably has the SELECT file_variable TO variable syntax, which then is the same solution as for the external list. I'm working on UniData which differs from D3 in that it caters for active list numbers 0-9. What that seems to mean is that, outside of UniBasic, you can have up to 10 lists "active" at a time. That's a little misleading though, because only select-list 0 is *really* active as far as the system monitor is concerned. You can "SELECT..TO 1". It will say "x records selected to list 1", but there will be no active list as far as the system monitor is concerned. If you now "LIST filename" it will not use the x records in list 1 - it will use whatever was active as list 0 or, if list 0 wasn't active, list the whole file. You can "SAVE.LIST listname FROM 1" though, which will use the x records in list 1. It seems that the only other way, apart from SAVE.LIST, to use lists 1-9 is in UniBasic READNEXT statements. In UniBasic you can go ahead and "LOOP...READNEXT KEY FROM n". There is also the ability, in UniBasic, to use list variables - as you suggest - so you can READNEXT FROM a list number or a list variable. The thing is though that that (the ability to specify a list variable as opposed to a number) only seems to apply to UniBasic (internal) SELECTs - and not EXECUTEd selects. With EXECUTEd selects you can have ...TO {listno} as part of the EXECUTEd SELECT statement and then READNEXT FROM {listno}, or you can have ...RTNLIST {listno} as part of the UniBasic EXECUTE statement. In both cases you have to specify a numeric list number in the range 0-9. I therefore need to know if any or all of them are already "active". Is the issue more complicated? Why do you need to know what lists are active, or suspend them? Fwiw - what I'm trying to do is develop a generic OS file handling subroutine; something similar to one I wrote when on a contract a few years back (back then I just had to call a pre-existing subroutine (or function) to get a free list number). Two of its capabilities will be to open the next new OS file in a directory (given some rules on how the file name is to be constructed) and/or to open the next existing OS file in a directory. The OS files in a directory are equivalent to UniData records in a file. I can therefore SSELECT them WITH PREFIX LIKE whatever WITH DATE LIKE whatever BY SEQNO to get a select-list, and then use the resulting list to find out which filename to OPENSEQ/OSOPEN. Mike. Chandru Murthi michael (AT) preece (DOT) net> wrote in message news:1126229351.493276.290860 (AT) z14g2000cwz (DOT) googlegroups.com... Hi I would like, in a low level subroutine, to EXECUTE a SELECT statement without interfering in any way with any select lists that might be active belonging to a higher level calling program. How do I find out whether there is a select list currently active? How do I find out which list number it is? How can I temporarily suspend the active list? I am thinking along the lines of saving the list, doing what I have to do and getting the saved list back again afterwards - but in order to do that I have to have answers to the preceding questions so that I can reactivate the right list number. I'm working with UniData. TIA, Mike. |
|
« Previous Thread
|
Next Thread »
| Thread Tools | |
| Display Modes | |
Linear Mode
| |
Powered by vBulletin Version 3.5.3
Copyright ©2000 - 2012, Jelsoft Enterprises Ltd.
Copyright ©2000 - 2012, Jelsoft Enterprises Ltd.