Knowledge Base

PRB: INKEY() May Return Same ASCII Values for Different Keys

Article ID: 138558

Article Last Modified on 2/11/2000

APPLIES TO

Microsoft Visual FoxPro 3.0 Standard Edition

This article was previously published under Q138558

SYMPTOMS

Using INKEY() to trap for a keystroke can sometimes lead to unexpected results. For example, INKEY() will return the same value, 19, for the LEFT ARROW key and ALT+R. This effect may be altered by using the following command before using the INKEY():

   SET COMPATIBLE DB4

RESOLUTION

Use the SET COMPATIBLE DB4 command immediately before you use the INKEY() function. Then use the SET COMPATIBLE OFF command after using INKEY(). This may have side effects. Please see SET COMPATIBLE DB4 in the Help file.

STATUS

This behavior is by design.

MORE INFORMATION

Certain commands and functions in FoxPro, including INKEY(), behave differently depending on the SET COMPATIBLE setting. For more information, please see the following article in the Microsoft Knowledge Base:

114752 Commands and Functions Affected by SET COMPATIBLE

Step-by-Step Resolution

Using INKEY(0,'M') to trap for a key or mouse click, you can distinguish which key was pressed by using the following loop example.

Place the following code into a program (.prg) file, and then run it.

   i=1
   tmpcompt=SET('COMPATIBLE')
   SET COMPATIBLE OFF
   FOR i= 1 TO 2                         && Sets up 2 passes in loop
      DEFINE WINDOW keypress FROM 4,4 TO 20,75 DOUBLE TITLE "This is with ;
          Set Compatible "+ IIF(SET('COMPATIBLE') ='ON','DB4','OFF')
      ACTIVATE WINDOW keypress
      @ 6,16 SAY 'Press a key to start or press the Esc key to quit'
      @ 8,16 SAY ':'
      keyvar = 0             && Initialize inkey system memory variable


      *** Main program loop ***
      DO WHILE .T.
         keyvar = INKEY(0,'M')    && Get INKEY() value
         IF keyvar = 0            && No key press or mouse click
             LOOP                 && Creates Wait State
         ENDIF
         IF keyvar = 27           && ESC key pressed, exit main loop
             EXIT
         ENDIF
         IF keyvar # 151          && Not a mouse click
             CLEAR
             @ 10,16 SAY 'The ASCII code for the key you hit is ' + ;
                 ALLTRIM(STR(keyvar))
         ENDIF
      ENDDO                       && End of Main loop
      RELEASE WINDOW keypress
      SET COMPATIBLE DB4
   ENDFOR
   SET COMPATIBLE &tmpcompt

Try pressing ALT+R and the LEFT ARROW key. Each will return an ASCII equivalent of 19 because the first time through, COMPATIBLE is set OFF.
Press the ESC key. The window will come back up with SET COMPATIBLE DB4.
Try pressing ALT+R, and the LEFT ARROW key again. ALT+R returns -418 and LEFT ARROW still returns 19.

You can use this technique to maintain a distinction between hot keys and other keystrokes.

Additional query words: VFoxWin

Keywords: KB138558

Microsoft KB Archive/138558

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