korson@hubcap.clemson.edu (Timothy Korson) (02/15/90)
Reading ESC Char and the Arrow Keys from Keyboard:
Problem:
I want to be able to read the ESC char (^[) and also the escape
sequence for the arrow keys (eg. ^[[D for Left) from the keyboard.
Is there any elegant solution to this problem?
I tried the following method and would not call it an elegant solution
because it won't work in all cases. Here is my solution :
I used System V curses library functions "nodelay" and "getch" that are
explained below (excerpts from man pages) :
nodelay (win, bf) This option causes wgetch() to be a
non-blocking call. If no input is
ready, wgetch() will return ERR. If dis-
abled, wgetch() will hang until a key is
pressed.
getch() A character is read from the terminal
associated with the window. In NODELAY
mode, if there is no input waiting, the
value ERR is returned. In DELAY mode,
the program will hang until the system
passes text through to the program.
Depending on the setting of cbreak(),
this will be after one character (CBREAK
mode), or after the first newline (NOC-
BREAK mode). In HALF-DELAY mode, the
program will hang until a character is
typed or the specified timeout has been
reached. Unless noecho() has been set,
the character will also be echoed into
the designated window.
If keypad (win, TRUE) has been called,
and a function key is pressed, the token
for that function key will be returned
instead of the raw characters. (See
keypad() under Input Options Setting.)
Possible function keys are defined in
<curses.h> with integers beginning with
0401, whose names begin with KEY_. If a
character is received that could be the
beginning of a function key (such as
escape), curses will set a timer. If
the remainder of the sequence is not
received within the designated time, the
character will be passed through, other-
wise the function key value will be
returned. For this reason, on many ter-
minals, there will be a delay after a
user presses the escape key before the
escape is returned to the program. (Use
by a programmer of the escape key for a
single character routine is discouraged.
Also see notimeout() below.)
The following program illustrates my approach. It is necessary to compile
this program with System V C-compiler since some of the above functions are
defined only in System V library. On my Sun system I used the
following command to make a.out:
/usr/5bin/cc filename.c -lcurses -ltermlib
/*---------- The program begins here ----------*/
#include <curses.h>
#define ESC '\033'
main ()
{
int in, in1;
/* initialise curses setup */
initscr();
cbreak ();
noecho ();
move (3,3);
in = getch ();
if (in == ESC) {
nodelay (stdscr, 1); /* NODELAY mode ON */
in1 = getch (); /* returns ERR or garbage */
nodelay (stdscr, 0); /* NODELAY mode OFF */
if (in1 == ERR)
printw ("ESC \n");
else {
in1 = getch (); /* returns 1st char after ESC */
if (in1 = '[') {
in1 = getch (); /* returns 2nd char after ESC */
if (in1 == 'D')
printw ("LEFT ARROW %d \n",in1);
} else
printf("NONE");
}
}
refresh();
sleep(1);
endwin();
}
/*---------- The program ends here ----------*/
The above program reads the ESC and Left Arrow keys correctly when I work on
the console. But it won't work correctly when I remote login and type
the ESC / Arrow keys (because of transmission delay???).
Another weird thing : The getch() issued to read a char, if any, after the
ESC char should return the input char ('[' for Left arrow) if one is present.
Instead it returns garbage and the second getch() after the ESC char returns
the actual char that is present after the ESC ('[').