To use ncurses library functions, you have to load the
curses) module into the program.
Here is the Hello World program.
#!/usr/bin/guile !# (use-modules (ncurses curses)) (define stdscr (initscr)) (addstr stdscr "Hello World!!!") (refresh stdscr) (getch stdscr) (endwin)
The first line of the example,
#!/usr/bin/guile, gives the
location of where Guile is installed on my system. This may differ on
The above program prints “Hello World!!!” to the screen, waits for the user to press any key, and then exits. This program shows how to initialize curses and do screen manipulation and end curses mode. Let’s dissect it line by line.
initscr initializes the terminal in curses mode.
It clears the screen and presents a blank screen. To do any screen
manipulation using the curses package, this has to be called first.
This function initializes the curses system and allocates memory for
screen handling and some other data structures. It returns a SMOB
that represents the default window: the window that represents the
entire screen. By convention, this window is denoted
the standard screen. Under extreme cases, this function might
fail due to insufficient memory to allocate memory for curses
library’s data structures.
initscr returns a
#<window> that contains
necessary information about the curses screen. The
that is returned must be stored until the program is finished with the
curses library. If that
#<window> is garbage collected, the
curses library cannot continue.
After this is done, we can do a variety of initializations to customize our curses settings
The next line
addstr prints the string “Hello World!!!” on to
the screen. This function prints the data on a window called
stdscr at the current
(y, x) coordinates. Since our
present coordinates are at 0,0 the string is printed at the top,
left-hand corner of the window.
This brings us to the mysterious
(refresh stdscr). Well, when
addstr, the data is actually written to an imaginary
window, which is not updated on the screen yet. The job of
addstr is to update a few flags and data structures and write
the data to a buffer corresponding to
stdscr. In order to show
it on the screen, we need to call
refresh and tell the curses
system to dump the contents on the screen.
The philosophy behind all this is to allow the programmer to do
multiple updates on the imaginary screen or windows and to do a
refresh once all the screen update is done.
checks the window and updates only the portion which has been
changed. This improves performance and offers greater flexibility,
too. But, it is sometimes frustrating to beginners. A common mistake
committed by beginners is to forget to call
refresh after they
did some update through
And finally, don’t forget to end the curses mode. Otherwise your
terminal might behave strangely after the program quits.
endwin frees the memory taken by the curses sub-system and its
data structures and puts the terminal in normal mode. This function
must be called after you are done with curses mode.