Introduction
Hello everyone. This little code snippet shows you how to read in scan codes from the keyboard. It is slightly different than reading in a regular character. When you use the getch() function, it is normally returning an ASCII value. Some keyboards have extra keys though. These include the F1 - F12 function keys and the directional arrows to start. These keys do not have an ASCII code. A char data type is a one byte item. When you press a key that doesn't have an ASCII code, it returns two bytes. If the first byte is 0, then the next byte contains the scan code. In the following code, I include the scan code for many typical keys and how to read them.
Notes:
- Even though there are two calls to
getch(), it does not require two keystrokes. - Not all of these scan codes may be 100% accurate for all computers. It may, of course, need some modifications.
/* This program shows how to pick up the scan codes from a keyboard */
/* These define the scan codes(IBM) for the keys. All numbers are in decimal.*/
#define PAGE_UP 73
#define HOME 71
#define END 79
#define PAGE_DOWN 81
#define UP_ARROW 72
#define LEFT_ARROW 75
#define DOWN_ARROW 80
#define RIGHT_ARROW 77
#define F1 59
#define F2 60
#define F3 61
#define F4 62
#define F5 63
#define F6 64
#define F7 65
#define F8 66
#define F9 67
#define F10 68
#include <iostream>
#include <conio.h>
using namespace std;
void main()
{
char KeyStroke;
cout << "Press Escape to quit." << endl;
do
{
KeyStroke = getch();
if (KeyStroke == 0)
{
KeyStroke = getch(); // Even though there are 2 getch() it reads one keystroke
switch (KeyStroke)
{
case PAGE_UP:
cout << "PAGE UP" << endl;
break;
case PAGE_DOWN:
cout << "PAGE DOWN" << endl;
break;
case HOME:
cout << "HOME" << endl;
break;
case END:
cout << "END" << endl;
break;
case UP_ARROW:
cout << "UP ARROW" << endl;
break;
case DOWN_ARROW:
cout << "DOWN ARROW" << endl;
break;
case LEFT_ARROW:
cout << "LEFT_ARROW" << endl;
break;
case RIGHT_ARROW:
cout << "RIGHT_ARROW" << endl;
break;
case F1:
cout << "F1" << endl;
break;
case F2:
cout << "F2" << endl;
break;
case F3:
cout << "F3" << endl;
break;
case F4:
cout << "F4" << endl;
break;
case F5:
cout << "F5" << endl;
break;
case F6:
cout << "F6" << endl;
break;
case F7:
cout << "F7" << endl;
break;
case F8:
cout << "F8" << endl;
break;
case F9:
cout << "F9" << endl;
break;
case F10:
cout << "F10" << endl;
break;
default:
cout << "Some other key." << endl;
}
}
else
cout << KeyStroke << endl;
}
while (KeyStroke != 27); // 27 = Escape key
}
