Simple ncurses app not reacting to arrow keys

Question

I compiled this simple ncurses program and the up down keys are unresponsive. Any idea why this does not work?

I am using Fedora Linux 5.7.16-200.fc32.x86_64 the default terminal emulator is XTerm(351). I got no errors or warning building ncurses or making the app.

cc -o test test.c -lncurses

/* test.c */

#include <stdlib.h>
#include <stdio.h>
#include <curses.h>
 
int main(void) {
 
    WINDOW * mainwin, * childwin;
    int      ch;
 
 
    /*  Set the dimensions and initial
    position for our child window   */
 
    int      width = 23, height = 7;
    int      rows  = 25, cols   = 80;
    int      x = (cols - width)  / 2;
    int      y = (rows - height) / 2;
 
 
    /*  Initialize ncurses  */
 
    if ( (mainwin = initscr()) == NULL ) {
    fprintf(stderr, "Error initialising ncurses.\n");
    exit(EXIT_FAILURE);
    }
 
 
    /*  Switch of echoing and enable keypad (for arrow keys)  */
 
    noecho();
    keypad(mainwin, TRUE);
 
 
    /*  Make our child window, and add
    a border and some text to it.   */
 
    childwin = subwin(mainwin, height, width, y, x);
    box(childwin, 0, 0);
    mvwaddstr(childwin, 1, 4, "Move the window");
    mvwaddstr(childwin, 2, 2, "with the arrow keys");
    mvwaddstr(childwin, 3, 6, "or HOME/END");
    mvwaddstr(childwin, 5, 3, "Press 'q' to quit");
 
    refresh();
 
 
    /*  Loop until user hits 'q' to quit  */
 
    while ( (ch = getch()) != 'q' ) {
 
    switch ( ch ) {
 
    case KEY_UP:
        if ( y > 0 )
        --y;
        break;
 
    case KEY_DOWN:
        if ( y < (rows - height) )
        ++y;
        break;
 
    case KEY_LEFT:
        if ( x > 0 )
        --x;
        break;
 
    case KEY_RIGHT:
        if ( x < (cols - width) )
        ++x;
        break;
 
    case KEY_HOME:
        x = 0;
        y = 0;
        break;
 
    case KEY_END:
        x = (cols - width);
        y = (rows - height);
        break;
 
    }
 
    mvwin(childwin, y, x);
    }
 
 
    /*  Clean up after ourselves  */
 
    delwin(childwin);
    delwin(mainwin);
    endwin();
    refresh();
 
    return EXIT_SUCCESS;
}

Answer 1

The example doesn't repaint the child-window (so nothing seems to happen), and doesn't use cbreak (so nothing happens until you press Return (i.e., newline).

I did this change to see what it does:

> diff -u foo.c.orig foo.c
--- foo.c.orig  2020-08-30 06:00:47.000000000 -0400
+++ foo.c       2020-08-30 06:02:50.583242935 -0400
@@ -29,6 +29,7 @@
  
     /*  Switch of echoing and enable keypad (for arrow keys)  */
  
+    cbreak();
     noecho();
     keypad(mainwin, TRUE);
  
@@ -85,6 +86,7 @@
     }
  
     mvwin(childwin, y, x);
+    wrefresh(childwin);
     }

Some terminal descriptions may use the same character ControlJ for cursor-down (and get mapped into KEY_ENTER rather than KEY_DOWN—see source code). After allowing for the other two problems, you may be seeing that.