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Q32164: BASIC Example of CALL SetUEvent, ON UEVENT GOSUB Trapping

Article: Q32164
Product(s): See article
Version(s): 4.00b 4.50
Operating System(s): MS-DOS
Keyword(s): ENDUSER | B_BasicCom | mspl13_basic
Last Modified: 21-DEC-1989

The following products support user-defined event trapping with the
statements ON UEVENT GOSUB, UEVENT ON, and SetUEvent:

1. QuickBASIC Compiler Versions 4.00b and 4.50

2. Microsoft BASIC Compiler Versions 6.00 and 6.00b for MS-DOS and MS
   OS/2

3. Microsoft BASIC PDS Version 7.00 for MS-DOS and MS OS/2

Microsoft QuickBASIC Versions 4.00 and earlier do not support
user-defined events.

Below is a short example of how to trap a user-defined event.

You can cause a user-defined event in a program by executing the CALL
SetUEvent statement whenever a desired condition occurs. To CALL the
SetUEvent routine in the QuickBASIC environment, you must invoke
QB.EXE with the /L switch to load QB.QLB. For BASIC PDS 7.00 you must
start QBX with /L to load QBX.QLB. An .EXE program that CALLs
SetUEvent must be linked to QB.LIB because the SetUEvent routine is
located in the QB.LIB library provided on the product disk. For BASIC
PDS 7.00 you must link with QBX.LIB.

The UEVENT ON statement turns on trapping of user-defined events. The
< ON UEVENT GOSUB label > statement instructs a program where to go
when a user-defined event occurs.

The following example invokes the event handler if the value 5 is
accepted from the keyboard:

ON UEVENT GOSUB event1
UEVENT ON
INPUT "enter a number"; a
IF a = 5 THEN CALL setuevent
END
event1:
   PRINT "invoked event handler with value"; a
   RETURN

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