Q46182: ON TIMER Can Wrongly Trigger CALL SETUEVENT, ON UEVENT Trap

Article: Q46182
Product(s): See article
Version(s): 4.00b 4.50
Operating System(s): MS-DOS
Keyword(s): ENDUSER | buglist4.00b buglist4.50 SR# S890614-84 B_BasicCom | mspl13_basic
Last Modified: 26-FEB-1990

You cannot use the UEVENT and TIMER event trapping simultaneously.
After CALL SETUEVENT is invoked just once, each subsequent timer event
from the ON TIMER statement improperly activates the user-defined
event (UEVENT) trap.

Microsoft has confirmed this to be a problem in Microsoft QuickBASIC
Versions 4.00b and 4.50, and in Microsoft BASIC Compiler Versions 6.00
and 6.00b (buglist6.00, buglist6.00b). This problem was corrected in
Microsoft BASIC Professional Development System (PDS) Version 7.00 for
MS-DOS and MS OS/2 (fixlist7.00).

SETUEVENT improperly activates at the same frequency as the ON TIMER
event. This behavior continues to occur until the TIMER OFF statement
is used. The problem occurs both in a compiled .EXE program and in the
QB.EXE environment. SETUEVENT can be called from another language or
from the BASIC program itself to reproduce the problem.

The problem does not apply to QuickBASIC Version 4.00 and earlier
versions because they don't support user-defined event trapping (ON
UEVENT GOSUB and CALL SETUEVENT).

The following sample code demonstrates the problem in a compiled .EXE
program or in the QB.EXE environment:

' Turn the timer and uevent on:
TIMER ON
UEVENT ON

' Set up the handler routines for events:
ON UEVENT GOSUB ueventhandler
ON TIMER(1) GOSUB timerhandler   ' Timer event occurs every 1 second.

'Invoke a user-defined event just once:
CALL setuevent
PRINT "Press any key to end."
WHILE INKEY$ = ""
WEND
END

ueventhandler:
  PRINT "This uevent should only occur once."
  RETURN

timerhandler:
  PRINT "A timer event occurred."
  ' TIMER OFF   'Add this line to work around the problem.
  RETURN

Related Problem
---------------

In the QB.EXE environment, simply stopping the execution of the
program and commenting out the ON TIMER statement fails to stop the
activation of the SETUEVENT event during subsequent program runs. For
more information on this separate QB.EXE environment problem, query on
the following words:

   SETUEVENT and buglist4.50

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