Important Notice

The pages on this site contain documentation for very old MS-DOS software, purely for historical purposes. If you're looking for up-to-date documentation, particularly for programming, you should not rely on the information found here, as it will be woefully out of date.

  ◄Syntax►  ◄Details►  ◄Example►                 ◄Contents►  ◄Index►  ◄Back►
──────────────────────────────────────────────────────────────────────────────
The KEY (event trapping) statements enable, disable, or suspend trapping
of specified keys.
 
KEY(n%) ON
KEY(n%) OFF
KEY(n%) STOP
 
    ■ The values of n% are shown below:
 
        n%       Key
        ═════    ═════════════════════════════
        0        All keys listed in this table
        1-10     F1-F10
        11       Up Arrow key
        12       Left Arrow key
        13       Right Arrow key
        14       Down Arrow key
        15-25    User-defined keys
        30-31    F11-F12 on 101-key keyboards
 
Usage Notes
    ■ KEY(n%) ON enables trapping of function keys, direction keys, and
      user-defined keys. If key n% is pressed after a KEY(n%) ON statement,
      the routine specified in the ON KEY statement is executed.
    ■ KEY(n%) OFF disables trapping of key n%. No trapping takes place
      until another KEY(n%) ON statement is executed. Events occurring while
      trapping is off are ignored.
    ■ KEY(n%) STOP suspends trapping of key n%. No trapping takes place
      until a KEY(n%) ON statement is executed. Events occurring while
      trapping is suspended are remembered and processed when the next
      KEY(n%) ON statement is executed. However, remembered events are lost
      if KEY(n%) OFF is executed.
    ■ When a key event trap occurs (that is, the GOSUB is performed), an
      automatic KEY STOP is executed so that recursive traps cannot take
      place. The RETURN from the trapping routine automatically executes a
      KEY ON statement unless an explicit KEY OFF was performed inside the
      routine.
    ■ If your program contains event-handling statements and you are
      compiling from the BC command line, use the BC /W or /V option.
      (The /W option checks for events at every label or line number; the
      /V option checks at every statement.) If you do not use these
      options and your program contains event traps, BASIC generates the
      error message, "ON event without /V or /W on command line."
    ■ For more information, see Chapter 9, "Event Handling" in the
      Programmer's Guide.
 
User-Defined Keys
    ■ In addition to providing the preassigned key numbers 1-14 (plus 30
      and 31 with the 101-key keyboard), BASIC enables you to create user-
      defined keys. You do this by assigning the numbers 15-25 to any of
      the remaining keys on the keyboard. Use ◄KEY (Assignment)►
      to create user-defined keys.
    ■ You can also set a trap for "shifted" keys. A key is shifted when
      you press it simultaneously with one or more of the special keys
      Shift, Ctrl, or Alt, or if you press it after pressing NumLock or
      Caps Lock. Use the KEY statements (assignment) to define shifted keys
      before you can trap them. The syntax for KEY (Assignment) is shown
      below:
 
        KEY n%, CHR$(keyboardflag) + CHR$(scancode)
 
          n%              Is between 15 and 25 and indicates a user-defined
                          key.
 
          keyboardflag    Can be any combination of the values in the
                          ◄Keyboard Flag Table►
 
          scancode        A number that identifyies one of 83 keys to trap.
                          See the ◄Scan Code Table►
 
    ■ You can add the values in the Keyboard Flag Table together to test
      for multiple shift states. A keyboardflag value of 12 would test
      for both Ctrl and Alt being pressed, for example.
    ■ To define Shift, Ctrl, Alt, NumLock, or Caps Lock as a user-defined
      key (by itself, not in combination with another key), use a keyboard
      flag of 0. For example, to define Alt as a user-defined key:
 
        KEY CHR$(0) + CHR$(56)
 
      To define Alt + Alt as a user-defined key (the second Alt will be
      trapped as it is being pressed only if the first Alt key is
      already pressed):
 
        KEY CHR$(8) + CHR$(56)
 
    ■ Because key trapping assumes the left and right Shift keys are the
      same, you can use either 1, 2, or 3 to indicate a Shift key. The
      scancode argument is a number identifying one of the 83 keys to trap,
      as shown in the ◄Scan Code Table►.
 
    ■ The scan codes in the Scan Code Table are equivalent to the first
      column of the scan code table in Appendix A, "Keyboard Codes and
      ASCII Character Codes" in the BASIC Language Reference. The codes in
      the other columns of the table in the appendix should not be used for
      key trapping.