How to modify Keyboard interrupt (under Windows XP) from a C++ Program ?

Question

Hi everyone !

• We have been given a little project (As part of my OS course) to make a Windows program that modifies keyboard input, so that it transforms any lowercase character entered into an uppercase one (without using caps-lock) ! so when you type on the keyboard you'll see what you're typing transformed into uppercase !

• I have done this quite easily using Turbo C by calling geninterrupt() and using variables _AH, _AL, i had to read a character using:

  _AH = 0x07;          // Reading a character without echo
  geninterrupt(0x21);  // Dos interrupt 
  

• Then to transform it into an Upercase letter i have to mask the 5th bit by using:

  _AL = _AL & 0xDF;    // Masking the entered character with 11011111
  

• and then i will display the character using any output routine.

Now, this solution will only work under old C DOS compilers. But what we intend to do is to make a close or similar solution to this by using any modern C/C++ compiler under Windows XP ! What i have first thought of is modifying the Keyboard ISR so that it masks the fifth bit of any entered character to turn it uppercase ! But i do not know how exactly to do this. Second, I wanted to create a Win32 console program to either do the same solution (but to no avail) or make a windows-compatible solution, still i do not know which functions to use ! Third I thought to make a windows program that modifies the ISR directly to suit my needs ! and i'm still looking for how to do this !

So please, If you could help me out on this, I would greatly appreciate it !

Thank you in advance !

(I'm using Windows XP on intel X86 with mingw-GCC compiler.)

Answer 1

You can't get access to the Keyboard ISR unless you write a Ring 0 device driver. You are better off investigating the Windows Hook APIs. These accomplish the same thing.

Start here: http://msdn.microsoft.com/en-us/library/ms644990%28v=VS.85%29.aspx

Answer 2

How soon do you plan to graduate? Hopefully you'll have time, Windows doesn't work this way anymore. You'll need to write a keyboard filter driver using the WDK. It comes with a sample implementation in the src\input\kbfiltr directory. You can't use the tools you're familiar with, the WDK includes a compiler and a kernel debugger. Available at no cost, go here to get started.