Q33034: How to Trap CTRL+BREAK, CTRL+C on Standard & Enhanced Keyboard

Article: Q33034
Product(s): See article
Version(s): 2.00 2.10 3.00 4.00 4.00b 4.50
Operating System(s): MS-DOS
Keyword(s): ENDUSER | B_BasicCom | mspl13_basic
Last Modified: 21-DEC-1989

The scan code for the BREAK key is &H46 (listed as SCROLL LOCK on Page
237 of the "Microsoft QuickBASIC 4.0: BASIC Language Reference" manual
for Versions 4.00 and 4.00b). The CTRL+BREAK key combination is
trapped differently, depending on whether or not the program is run on
a standard or enhanced keyboard.

This information also applies to Microsoft QuickBASIC 4.50, Microsoft
BASIC Compiler Versions 6.00 and 6.00b for MS-DOS and MS OS/2, and to
Microsoft BASIC PDS Version 7.00 for MS-DOS and MS OS/2.

For a standard keyboard, CTRL+BREAK is defined as follows

   KEY n, CHR$(&H04) + CHR$(&H46)

where n is in the range 15 through 25 in QuickBASIC Version 4.00, and
in 15 through 20 in QuickBASIC Versions 2.00, 2.01, and 3.00.

On an enhanced keyboard, CTRL+BREAK is defined as follows:

   KEY n, CHR$(&H84) + CHR$(&H46)

Please note that you must make separate user-defined KEY statements
for trapping CTRL+BREAK in combination with the SHIFT, ALT, NUM LOCK,
and CAPS LOCK keys. The keyboard flags for these other key
combinations must be added together to define a given key sequence.

Examples of trapping CTRL+BREAK and CTRL+C (when the SHIFT, ALT, NUM
LOCK, or CAPS LOCK keys are NOT active) are shown below.

Code Example 1
--------------

KEY 15, CHR$(&H84) + CHR$(&H46)  'Traps CTRL+BREAK on enhanced keyboard.
KEY 16, CHR$(&H4) + CHR$(&H46)   'Traps CTRL+BREAK on standard keyboard.
KEY(15) ON
KEY(16) ON
ON KEY(16) GOSUB trap
ON KEY(15) GOSUB trap
FOR i = 1 TO 500
   PRINT i
NEXT
END
trap:
   PRINT "trapped"
   RETURN

Code Example 2
--------------

Use the following code to trap a CTRL+C on either keyboard (standard
or extended):

KEY 18, CHR$(&H4)+CHR$(&H2E)    ' The &H4 is the CTRL Key
KEY (18) ON            ' The &H2E is the C key
ON KEY(18) GOSUB ctrlctrap
10 : GOTO 10
END
ctrlctrap:
    PRINT "CONTROL+C Trapped"
    RETURN

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