Q41469: QuickC 2.00 Does Not Debug KBHIT() Correctly

Article: Q41469
Product(s): See article
Version(s): 2.00
Operating System(s): MS-DOS
Keyword(s): ENDUSER | buglist2.00 | mspl13_c
Last Modified: 31-OCT-1989

The following code shows an error in the Microsoft QuickC Version
2.00's Run-Time function KBHIT(). The problem is that this function
effectively ignores some keystrokes, yet these bypassed keystrokes are
placed in your source file (if you are in the QC environment) or on
the DOS command line (if you run the code from DOS).

Microsoft has confirmed this to be a problem in Version 2.00. We are
researching this problem and will post new information as it becomes
available.

The workaround is to define your own KBHIT() function and link it
in as an .obj file.  This will override the KBHIT() routine in
the library.  An example of this user define kbhit() routine
follows the code example below which demonstrates the problem.

MoreInfo:

The following source code illustrates the problem:

To duplicate the error in the QC environment, do the following:

1. Turn debugging on.

2. Compile and link the program.

3. Set a breakpoint on the second printf statement and start the
   program.

4. When you press a key you will notice that it take a few keystrokes
   before any action is taken by the program.

When you return to the QC environment, the keystrokes that were not
noticed by KBHIT() are now in your source file.

The following is the sample program:

#include <conio.h>
#include <stdio.h>

main()
{
  printf("waiting\n");
  while ( !kbhit() );
  printf(" key struck was '%c'\n",getch() );
}

A workaround to this problem is to link in a KBHIT() routine
as an .obj file.  The following is an example of such
a routine:

int kbhit(void) ;    /* prototype */

int kbhit ()
{
  int key ;

  _asm
   {
           mov  ah, 0Bh        ;setup for function 0Bh
           int  21h        ;call DOS interrupt
           and  ax, 0001h    ;Determine if Key was hit
           mov  key, ax        ;Initialize Key
                ;0 = no key   1 = a key was hit
   }
  return (key) ;
}

You can either place this routine in one of your existing
source modules, or in a separate module.

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