No characters on screen sent to an Ncurses pad

Question

This should work Can anyone tell me why I see no typed output on the screen?

#include <stdio.h>
#include <stdlib.h>
#include <curses.h>


int nRows;
int nCols;

WINDOW  *myPad;


int main(void)
{

  initscr();

  getmaxyx(stdscr, nRows, nCols);

  myPad = newpad(nRows, nCols);


  while (1)
  {
    waddch(myPad, wgetch(myPad));
    prefresh(myPad, 0, 0, 0, 0, nRows, nCols);
  }

  return EXIT_SUCCESS;
}

I have no idea ... other similar examples work. Could this be an Ubuntu issue?

18.04.3 latest patches of today.

Answer 1

After calling initscr, the current position in stdscr is 0,0. Your program then asks for the position and uses it as the size of a pad:

getyx(stdscr, nRows, nCols);

myPad = newpad(nRows, nCols);

A pad with zero lines and zero columns will not show much on the screen.

In the altered question, there are still two problems:

• the input is buffered (use cbreak to change that)
• there is a missing refresh before the loop (to ensure that stdscr is displayed).

Here is a diff showing what might be done to fix those problems:

> diff -u foo.c.orig foo.c
--- foo.c.orig  2019-08-21 19:24:24.000000000 -0400
+++ foo.c       2019-08-21 19:30:46.202769968 -0400
@@ -13,12 +13,14 @@
 {
 
   initscr();
+  cbreak();
+  noecho();
 
   getmaxyx(stdscr, nRows, nCols);
 
   myPad = newpad(nRows, nCols);
 
-
+  refresh();
   while (1)
   {
     waddch(myPad, wgetch(myPad));