Welcome to the world of curses. Before we plunge into the library and look into
its various features, let's write a simple program and say
hello to the world.
2.1. Compiling With the NCURSES Library
To use ncurses library functions, you have to include ncurses.h in your
programs. To link the
program with ncurses the flag -lncurses should be added.
#include <ncurses.h>
.
.
.
compile and link: gcc <program file> -lncurses |
Example 1. The Hello World !!! Program
#include <ncurses.h>
int main()
{
initscr(); /* Start curses mode */
printw("Hello World !!!"); /* Print Hello World */
refresh(); /* Print it on to the real screen */
getch(); /* Wait for user input */
endwin(); /* End curses mode */
return 0;
} |
2.2. Dissection
The above program prints "Hello World !!!" to the screen and exits. This
program shows how to initialize curses and do screen manipulation and
end curses mode. Let's dissect it line by line.
2.2.1. About initscr()
The function initscr() initializes the terminal in curses mode. In some
implementations, it clears the screen and presents a blank screen. To do any
screen manipulation using curses package this has to be called first. This
function initializes the curses system and allocates memory for our present
window (called stdscr) and some other data-structures. Under extreme
cases this function might fail due to insufficient memory to allocate memory
for curses library's data structures.
After this is done, we can do a variety of initializations to customize
our curses settings. These details will be explained later .
2.2.2. The mysterious refresh()
The next line printw prints the string "Hello World !!!" on to the screen. This
function is analogous to normal printf in all respects except that it prints
the data on a window called stdscr at the current (y,x) co-ordinates. Since our
present co-ordinates are at 0,0 the string is printed at the left hand corner
of the window.
This brings us to that mysterious refresh(). Well, when we called printw
the data is actually written to an imaginary window, which is not updated
on the screen yet. The job of printw 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 do a refresh once all his screen update
is done. refresh() 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 printw() class of
functions. I still forget to add it sometimes :-)
2.2.3. About endwin()
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
curses sub-system and its data structures and puts the terminal in normal
mode. This function must be called after you are done with the curses mode.