BUG: getch() Returns Incorrect Extended Key Codes

• The C Run-Time (CRT), used with:
  • Microsoft Visual C++, 32-bit Editions, versions 1.0, 2.0, 2.1, 4.0, 4.1, 4.2, 5.0, 6.0

SYMPTOMS

The getch() run-time library function fails to return the correct extended character code for certain key sequences. There are two known situations in which incorrect codes are generated:

• The ALT key is combined with the ASCII characters A - Z.


-or-


• The RIGHT CTRL key is combined with any of the function or editing keys.

STATUS

Microsoft has confirmed this to be a bug in the Microsoft products listed at the beginning of this article.

MORE INFORMATION

In the sample code below, the ALT key combined with any ASCII character returns the ASCII character code instead of the extended character code. The RIGHT CTRL key combined with any of the function or editing keys also fails with Visual C++ 1.0, returning the code for the function or editing key alone. The LEFT CTRL key combined with a function key or editing key returns the correct code. The set of affected editing keys are: END, PAGE UP, PAGE DOWN, HOME, RIGHT ARROW, and LEFT ARROW.

The table below demonstrates some of the actual versus expected values that result when the sample below is run with the input shown:

Input            Expected          Actual                VC 6.0

ALT+C            0 - 2eH           63H    (C)             63H
RT CTRL+F4       0 - 61H         0 - 3eH  (F4)           0 - 61H
RT CTRL+PAGE UP  0 - 84H         0 - 49H  (PAGEUP)      e0 - 86H
RT CTRL+END      0 - 75H         0 - 4fH  (END)          0 - 75H 

Sample Code

   /* Compile options needed: none
   */ 

   void main(void)
   {
      int testChar;

      do {
            testChar = getch();
            printf("%x - ", testChar);
            testChar = getch();
            printf("%x \n", testChar);
      } while (testChar != 0x001B);  /* Repeat until ESC key*/ 
   } 

Additional query words: kbVC400bug

Keywords : kbCRT kbVC kbVC100bug kbVC200bug kbVC210bug kbVC400bug kbVC410bug kbVC420bug kbVC500bug kbVC600bug
Version : winnt:1.0,2.0,2.1,4.0,4.1,4.2,5.0,6.0
Platform : winnt
Issue type : kbbug