getch not working without initscr

Question

I gone through the Documentation of NCURSES. I am not getting that if I use getch without initscr then why this program is not working. Is there any other approach to get arrow keys input without clearing screen (that initscr do).

#include <ncurses.h>
#include <unistd.h>
int main()
{
    int ch;
    //initscr();
    //raw();
    //keypad(stdscr, TRUE);
    //noecho();

    while(1)
    {
        ch = getch();
        switch(ch)
        {
            case KEY_UP: 
                printw("\nUp Arrow");
                break;
            case KEY_DOWN: 
                printw("\nDown Arrow");
                break;
            case KEY_LEFT: 
                printw("\nLeft Arrow");
                break;
            case KEY_RIGHT: 
                printw("\nRight Arrow");
                break;
        }

        if(ch == KEY_UP)
            break;
    }
    //endwin();
}

Answer 1

Alternatively you may use change the terminal attribute through tcsetattr in termios. If you cycle between the canonical mode (requires new line for the process to begin) and non-canonocal mode (Keypress is more than enough).

The following program works as follows - THe process waits for user input. If up arrow key is pressed, it prints 'Arrow key pressed' and exits. If something else is pressed, it waits for the user to press Enter and then prints the user inpu. Exits after the inut is printed.

#include <termios.h>
#include <unistd.h>
#include <fcntl.h>
#include <stdio.h>
int main()
{
  struct termios oldt, newt;
  char ch, command[20];
  int oldf;

  tcgetattr(STDIN_FILENO, &oldt);
  newt = oldt;
  newt.c_lflag &= ~(ICANON | ECHO);
  tcsetattr(STDIN_FILENO, TCSANOW, &newt);
  oldf = fcntl(STDIN_FILENO, F_GETFL, 0);
  fcntl(STDIN_FILENO, F_SETFL, oldf | O_NONBLOCK);

  while(1)
  {
    ch = getchar();
    if (ch == '\033')
    { printf("Arrow key\n"); ch=-1; break;}
    else if(ch == -1) // by default the function returns -1, as it is non blocking
    {
      continue;
    }
    else
    {
      break;
    }

  }
  tcsetattr(STDIN_FILENO, TCSANOW, &oldt);
  fcntl(STDIN_FILENO, F_SETFL, oldf);
  if(ch != EOF)
  {
    ungetc(ch,stdin);ith
    putchar(ch);
    scanf("%s",command);
    printf("\n%s\n",command);

    return 1;
  }

  return 0;
}