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

• Microsoft Visual FoxPro for Windows, version 3.0

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:

   ARTICLE-ID: Q114752
   TITLE     : 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.

1. 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
   
   

2. 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.

3. Press the ESC key. The window will come back up with SET COMPATIBLE DB4.

4. Try pressing ALT+R, and the LEFT ARROW key again. ALT+R returns -418 and LEFT ARROW still returns 19.