Q31885: ON <Event> GOSUB Suspended Until INPUT or INPUT$ Is Satisfied

Article: Q31885
Product(s): See article
Version(s): 1.00 1.01 1.02 2.00 2.01 3.00 4.00 4.00b 4.50
Operating System(s): MS-DOS
Keyword(s): ENDUSER | B_BasicCom B_GWBasicI B_GWBasicC B_MQuickB B_BasicInt | mspl13_basic
Last Modified: 8-NOV-1990

Execution of event trapping GOSUB routines is suspended in BASIC until
an INPUT or LINE INPUT statement or INPUT$ function is satisfied.
Events suspended during INPUT, INPUT$, or LINE INPUT include the
following:

1. ON TIMER(n) GOSUB
   (found in many Microsoft BASICs, including GW-BASIC, QuickBASIC
   for MS-DOS, and QuickBASIC for Macintosh)

2. ON KEY(n) GOSUB
   (found in QuickBASIC and GW-BASIC for MS-DOS, but not in QuickBASIC
   for Macintosh)

3. ON DIALOG GOSUB, ON MENU GOSUB, and ON MOUSE GOSUB
   (found in QuickBASIC for the Apple Macintosh, but not in QuickBASIC
   for MS-DOS)

The suspending of event GOSUBs during INPUT, INPUT$, or LINE INPUT is
an intentional design requirement and occurs in all Microsoft BASIC
products that support event trapping, including the following
products:

1. Microsoft QuickBASIC versions 1.00, 1.01, 1.02, 2.00, 2.01, 3.00,
   4.00, 4.00b, and 4.50 for MS-DOS

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

3. Microsoft BASIC Professional Development System (PDS) versions 7.00
   and 7.10 for MS-DOS and MS OS/2

4. Microsoft GW-BASIC Interpreter versions 3.20, 3.22, and 3.23 for
   MS-DOS

5. Microsoft QuickBASIC version 1.00 for the Apple Macintosh

6. Microsoft BASIC Compiler version 1.00 for the Apple Macintosh

7. Microsoft BASIC Interpreter versions 2.00, 2.10, and 3.00 for
   the Apple Macintosh (Event trapping is not supported in Microsoft
   BASIC Interpreter versions 1.00 and 1.01 for the Apple Macintosh.)

Suppose you write a program with ON TIMER(5) GOSUB so that every five
seconds a message is displayed on the screen. If an INPUT$ function or
INPUT or LINE INPUT statement is executed that expects a value from
the keyboard, the ON TIMER(5) GOSUB will not execute until the ENTER
key is pressed to terminate the input. Only one TIMER event is
remembered on the stack, no matter how much time passed during the
INPUT$, INPUT, or LINE INPUT. An example of this event suspension is
demonstrated in Program 1 below.

If you want to trap events and also input from the keyboard, you can
poll the INKEY$ function as shown in program 2 below instead of using
INPUT$, INPUT, or LINE INPUT. The INKEY$ function returns one key
press at a time, and allows event GOSUB traps to occur between
invocations.

BASIC checks between statements to see if an event has occurred. When
the INPUT$, INPUT, or LINE INPUT executes, execution of the ON event
GOSUB statement is suspended until the INPUT$, INPUT, or LINE INPUT is
satisfied. This behavior is intentional and occurs in all Microsoft
BASIC products that support event trapping.

If you are using ON KEY(n) GOSUB to trap keys (in GW-BASIC or
QuickBASIC for MS-DOS), only one key press during INPUT$, INPUT, or
LINE INPUT will be remembered on the stack for a given defined KEY, no
matter how many times that key is pressed. This behavior is by design
(to prevent stack overflow).

The following are code examples:

Program 1
---------

The following program shows that ON TIMER(n) GOSUB waits while the
INPUT statement is pending:

   REM  Program 1, using the INPUT statement.
   ON TIMER(5) GOSUB MESSAGE     ' TRAP EVERY 5 SECONDS
   TIMER ON
   INPUT X$   ' NO GOSUB IS DONE UNTIL THIS INPUT IS SATISFIED.
   FOR I=1 TO 2000
    PRINT X$
   NEXT
   END
   MESSAGE:
       PRINT " FIVE SECONDS "
       RETURN

Program 2
---------

The following program polls the INKEY$ function for INPUT and lets the
ON TIMER(5) GOSUB statement successfully perform the TIMER event trap
every five seconds:

   REM  ********   Program 2, using the INKEY$ function.
   ON TIMER(5) GOSUB MESSAGE          ' TRAP EVERY 5 SECONDS
   TIMER ON
   CLS
   MOREIN:
      A$ = INKEY$
      IF A$ = "" GOTO MOREIN
      IF A$ = CHR$(13) GOTO DONE   'Input until ENTER key is pressed.
      X$ = X$ + A$: J = J + 1
      PRINT A$;
      IF J > 79 THEN PRINT "Exceeded 79 characters.": GOTO DONE
   GOTO MOREIN
   DONE:
       PRINT
       FOR I = 1 TO 2000
         PRINT X$
       NEXT
       END
   MESSAGE:
       PRINT " FIVE SECONDS "    ' DISPLAY MESSAGE AFTER 5 SECONDS.
       RETURN

Note: The following Microsoft BASIC products do NOT support event
trapping features, such as ON TIMER(n) GOSUB or ON KEY(n) GOSUB:

1. Microsoft Business BASIC Compiler versions 1.00 and 1.10 for
   MS-DOS

2. Microsoft BASIC Compiler versions 5.35 and 5.36 for MS-DOS

THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL, CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES SO THE FOREGOING LIMITATION MAY NOT APPLY.

Copyright Microsoft Corporation 1986-2002.