getch and arrow codes

So, after alot of struggle, I miraculously solved this everannoying issue ! I was trying to mimic a linux terminal and got stuck at the part where it keeps a command history which can be accessed by pressing up or down arrow keys. I found ncurses lib to be painfuly hard to comprehend and slow to learn.

char ch = 0, k = 0;
while(1)
{
  ch = getch();
  if(ch == 27)                  // if ch is the escape sequence with num code 27, k turns 1 to signal the next
    k = 1;
  if(ch == 91 && k == 1)       // if the previous char was 27, and the current 91, k turns 2 for further use
    k = 2;
  if(ch == 65 && k == 2)       // finally, if the last char of the sequence matches, you've got a key !
    printf("You pressed the up arrow key !!\n");
  if(ch == 66 && k == 2)                             
    printf("You pressed the down arrow key !!\n");
  if(ch != 27 && ch != 91)      // if ch isn't either of the two, the key pressed isn't up/down so reset k
    k = 0;
  printf("%c - %d", ch, ch);    // prints out the char and it's int code

It's kind of bold but it explains alot. Good luck !

getch () function returns two keycodes for arrow keys (and some other special keys), as mentioned in the comment by FatalError. It returns either 0 (0x00) or 224 (0xE0) first, and then returns a code identifying the key that was pressed.

For the arrow keys, it returns 224 first followed by 72 (up), 80 (down), 75 (left) and 77 (right). If the num-pad arrow keys (with NumLock off) are pressed, getch () returns 0 first instead of 224.

Please note that getch () is not standardized in any way, and these codes might vary from compiler to compiler. These codes are returned by MinGW and Visual C++ on Windows.

A handy program to see the action of getch () for various keys is:

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

int main ()
{
    int ch;

    while ((ch = _getch()) != 27) /* 27 = Esc key */
    {
        printf("%d", ch);
        if (ch == 0 || ch == 224)
            printf (", %d", _getch ()); 
        printf("\n");
    }

    printf("ESC %d\n", ch);

    return (0);
}

This works for MinGW and Visual C++. These compilers use the name _getch () instead of getch () to indicate that it is a non-standard function.

So, you may do something like:

ch = _getch ();
if (ch == 0 || ch == 224)
{
    switch (_getch ())
    {
        case 72:
            /* Code for up arrow handling */
            break;

        case 80:
            /* Code for down arrow handling */
            break;

        /* ... etc ... */
    }
}

By pressing one arrow key getch will push three values into the buffer:

• '\033'
• '['
• 'A', 'B', 'C' or 'D'

So the code will be something like this:

if (getch() == '\033') { // if the first value is esc
    getch(); // skip the [
    switch(getch()) { // the real value
        case 'A':
            // code for arrow up
            break;
        case 'B':
            // code for arrow down
            break;
        case 'C':
            // code for arrow right
            break;
        case 'D':
            // code for arrow left
            break;
    }
}