You can read ROM bios data address :

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

#define KEY_ADDRESS 0x417 /* ROM BIOS data address */
#define KEY_RSHIFT   0x01
#define KEY_LSHIFT   0x02
#define KEY_CTRL     0x04
#define KEY_ALT      0x08
#define KEY_SCROLL   0x10
#define KEY_NUMLOCK  0x20
#define KEY_CAPSLOCK 0x40
#define KEY_INS      0x80


int main( void )
{
  getch();

  if( *((char*)KEY_ADDRESS) & KEY_ALT ) {
    puts( "Alt key was pressed" );
  }
  return 0;
}

Compile and execute this program. And then it waits
a key input and you can press alt key at that time.
Hold the alt key and now press any key ( if you
use a dos console on Windows, esc, enter, space, ...
keys can give the special meaning to Windows so use
an alphabet or a digit key for this case. )
to return the 'getch' function. If this program
works fine for you, you can see the message
"Alt key was pressed".

Hee S. Chung
heesc@netian.com
http://www.netian.com/~heesc

thanks anyway but that's no good, i want to capture the ALT without having to press another key.. eg: press ALT and a pop-up menu opens

You can detect whether ALT key is pressed or not
by using my source code. Surely you can capture
ALT without having to press another key. The
reason why I commented to use some other keys
is that, you need to confirm my source can
detect that ALT key is pressed.

As I mentioned it is very simple and fast
to detect ALT key is pressed.

if( *((char*)KEY_ADDRESS) & KEY_ALT ) {
  /* alt key is pressed now */
}

KET_ADDRESS and KEY_ALT are defined in the
source which I previously supplied.

Above code is not related to other keys -
it just detect ALT key status.

Thanks.

Hee S. Chung
heesc@netian.com
http://www.netian.com/~heesc

dammit, you're right.. i just didn't try to implememt it it any other way

by doing:

while(1) {
   sleep(1);
   if( *((char*)KEY_ADDRESS) & KEY_ALT ) {
      //bla
   }
}

it clearly does work, thanks alot ;-)

Is it really helpful? Can you give me a vote ?

Thank you! Enjoy your programming!

Hee S. Chung
heesc@netian.com
http://www.netian.com/~heesc