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Q32788: Example of Trapping CTRL+ALT+DEL Keys in QuickBASIC

Article: Q32788
Product(s): See article
Version(s): 4.00 4.00b 4.50
Operating System(s): MS-DOS
Keyword(s): ENDUSER | docerr B_BasicCom | mspl13_basic
Last Modified: 22-DEC-1989

The correction below applies to the KEY statement on Page 236 of the
following manuals:

1. Page 236 of "Microsoft QuickBASIC 4.0: BASIC Language Reference"
   for Versions 4.00 and 4.00b

2. Page 236 of "Microsoft BASIC Compiler 6.0: BASIC Language
   Reference" for Versions 6.00 and 6.00b for MS-DOS and MS OS/2

3. Page 180 of the "Microsoft BASIC 7.0: Language Reference" manual
   for Microsoft BASIC PDS Version 7.00

4. Page 198 of the "Microsoft QuickBASIC: BASIC Language Reference" manual
   for QuickBASIC Version 4.50

The following phrase for the KEY(n) statement is incorrect:

   ...a keyboardflag value of &H12 would test for both CTRL and ALT
   being pressed.

The keyboardflag value should be &H0C on a non-extended keyboard, not
&H12, to test for both CTRL and ALT being pressed. The keyboardflag
value should be &H8C on an extended keyboard. This example incorrectly
uses decimal addition on hexadecimal numbers.

The following BASIC program gives an example of trapping the
CTRL+ALT+DEL key sequence for both extended and non-extended
keyboards:

  ' This example works in QuickBASIC Versions 4.00 and later.
  ' &H80 = keyboard flag value to add for extended keyboard keys
  ' &H0C = keyboard flag for CTRL (&H04) plus ALT (&H08), pressed
  '        together.
  ' &H53 = scan code for DELETE (or DEL) key
  CLS
  KEY 15, CHR$(&HC) + CHR$(&H53)    '   Trap CTRL+ALT+DEL for
  ON KEY(15) GOSUB ctrlaltdelwhite  '   white DEL key
  KEY(15) ON
  KEY 16, CHR$(&H8C) + CHR$(&H53)   '   Trap CTRL+ALT+DELETE for
  ON KEY(16) GOSUB ctrlaltdelgrey   '   grey (extended) DELETE key
  KEY(16) ON
  DO
  LOOP UNTIL INKEY$ = "q"         '  Idle loop
  END
ctrlaltdelgrey:
  PRINT "pressed CTRL+ALT+DELETE (grey DELETE key) on extended keyboard"
  RETURN
ctrlaltdelwhite:
  PRINT "Pressed CTRL+ALT+DEL (white DEL key) on either keyboard"
  RETURN

Please note that when you run this program, pressing CTRL+ALT+DEL will
reboot the computer if any of the following key states are also
active:

   SHIFT, NUM LOCK, or CAPS LOCK

You must define separate ON KEY(n) statements for trapping
CTRL+ALT+DEL in combination with the different states of the SHIFT,
NUM LOCK, or CAPS LOCK keys. In the ON KEY(n) statement, n can be 15
through 25; this limits you to 11 user-defined keys.

The keyboardflag value &H0C in the KEY statement is obtained by adding
together the keyboardflag values from Page 236 for the CTRL and ALT
keys, as in the following example:

      &H04   +  &H08   =>  &H0C
      (CTRL)    (ALT)      (keyboardflag for KEY statement)

When adding together keyboardflag values to trap different
combinations of SHIFT, CTRL, ALT, NUM LOCK, CAPS LOCK, or
Advanced-101-keyboard extended keys, it is important to remember that
the values on Page 236 are in hexadecimal (base 16) notation, where
numbers are preceded with &H. If you wish, you can convert the number
to decimal notation (base 10) and use that value. Be sure not to use
&H in front of the value in BASIC if the value is in decimal notation.

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