NCURSES Programming HOWTO

Pradeep Padala

p_padala@yahoo.com

v1.7.1, 2002-06-25

Revision History
Revision 1.7.12002-06-25Revised by: ppadala
Added a README file for building and instructions for building from source.
Revision 1.72002-06-25Revised by: ppadala
Added "Other formats" section and made lot of fancy changes to the programs. Inlining of programs is gone.
Revision 1.6.12002-02-24Revised by: ppadala
Removed the old Changelog section, cleaned the makefiles
Revision 1.62002-02-16Revised by: ppadala
Corrected lot of spelling mistakes, added ACS variables section
Revision 1.52002-01-05Revised by: ppadala
Changed structure to present proper TOC
Revision 1.3.12001-07-26Revised by: ppadala
Corrected maintainers paragraph, Corrected stable release number
Revision 1.32001-07-24Revised by: ppadala
Added copyright notice(LDP license) to main document, Put copyright notice (GPL) for programs as well, Corrected printw_example.
Revision 1.22001-06-05Revised by: ppadala
Incorporated ravi's changes. Mainly to introduction, menu, form, justforfun sections
Revision 1.12001-05-22Revised by: ppadala
Added "a word about window" section, Added scanw_example.

Table of Contents
1. Introduction
1.1. What is NCURSES?
1.2. What we can do with NCURSES
1.3. Where to get it
1.4. Purpose/Scope of the document
1.5. About the Programs
1.6. Other Formats of the document
1.7. Credits
1.8. Wish List
1.9. Copyright
2. The Hello World Program
2.1. Compiling With the Ncurses Library
2.2. Dissection
3. The Gory Details
4. Initialization
4.1. About Initialization functions like raw() etc...
4.2. raw() and cbreak()
4.3. echo() and noecho()
4.4. keypad()
4.5. halfdelay()
4.6. Miscellaneous Initialization functions
4.7. An Example
5. A Word about Windows
6. About output functions like printw()
6.1. addch() class of functions
6.2. mvaddch(), waddch() and mvwaddch()
6.3. printw() class of functions
6.4. addstr() class of functions
6.5. A word of caution
7. About input functions like scanw()
7.1. getch() class of functions
7.2. scanw() class of functions
7.3. getstr() class of functions
7.4. Some examples
8. Attributes
8.1. The details
8.2. attron() vs attrset()
8.3. attr_get()
8.4. attr_ functions
8.5. wattr functions
8.6. chgat() functions
9. All about window functions
9.1. The basics
9.2. Let there be a Window !!!
9.3. Explanation
9.4. The other stuff in the example
9.5. Other Border functions
10. All about color
10.1. The basics
10.2. Changing Color Definitions
10.3. Color Content
11. Key management. How to read function keys, arrow keys etc..
11.1. The Basics
11.2. A Simple Key Usage example
12. Interfacing with the mouse
12.1. The Basics
12.2. Getting the events
12.3. Putting it all Together
12.4. Miscellaneous Functions
13. Screen Manipulation
13.1. getyx() functions
13.2. Screen Dumping
13.3. Window Dumping
14. Miscellaneous features
14.1. curs_set()
14.2. Temporarily Leaving Curses mode
14.3. ACS_ variables
15. Other libraries
16. Panel Library
16.1. The Basics
16.2. Compiling With the Panels Library
16.3. Panel Window Browsing
16.4. Using User Pointers
16.5. Moving and Resizing Panels
16.6. Hiding and Showing Panels
16.7. panel_above() and panel_below() Functions
17. Menus Library
17.1. The Basics
17.2. Compiling With the Menu Library
17.3. Menu Driver: The work horse of the menu system
17.4. Menu Windows
17.5. Scrolling Menus
17.6. Multi Columnar Menus
17.7. Multi Valued Menus
17.8. Menu Options
17.9. The useful User Pointer
18. Forms Library
18.1. The Basics
18.2. Compiling With the Forms Library
18.3. Playing with Fields
18.4. Form Windows
18.5. Field Validation
18.6. Form Driver: The work horse of the forms system
19. Tools and Widget Libraries
19.1. CDK (Curses Development Kit)
19.2. The dialog
19.3. Perl Curses Modules CURSES::FORM and CURSES::WIDGETS
20. Just For Fun !!!
20.1. The Game of Life
20.2. Magic Square
20.3. Towers of Hanoi
20.4. Queens Puzzle
20.5. Shuffle
20.6. Typing Tutor

1. Introduction

In the olden days of teletype terminals, terminals were away from computers and were connected to them through serial cables. The terminals could be configured by sending a series of bytes to each of them. All the capabilities (such as moving the cursor to a new location, erasing part of the screen, scrolling the screen, changing modes, changing appearance, colors, brightness, blinking, underlining, reverse video etc.) of terminals could be accessed through these series of bytes which are usually called escape sequences because they start with an escape(0x1B) character. Even today, with proper emulation, we can send escape sequences to the emulator and achieve the same effect on the terminal window.

Suppose you wanted to print a line in color. Try typing this on your console.

echo "^[[0;31;40mIn Color"

The first character is an escape character, which looks like two characters ^ and [. To be able to print that you have to press CTRL+V and then the ESC key. All the others are normal printable characters. You should be able to see the string "In Color" in red. It stays that way and to revert back to the original mode type this.

echo "^[[0;37;40m"

Now, what do those magic characters mean? Difficult to comprehend? They might even be different for different terminals. So the designers of UNIX invented a mechanism named termcap. It is a file that lists all the capabilities of a particular terminal, along with the escape sequences needed to achieve a particular effect. In the later years, this was replaced by terminfo. Without delving too much into details, the concept of the mechanism is to allow application programs query the terminfo database and obtain the control characters to be sent to the terminal or terminal emulator.


1.1. What is NCURSES?

You might be wondering, what the import of all this technical gibberish is. In the above scenario, every application program is supposed to query the terminfo and do the necessary stuff(sending control characters etc.). It soon became difficult to manage this complexity and this gave birth to 'CURSES'. Curses is a pun on the name "cursor optimization". The Curses library forms a wrapper over working with raw terminal codes, and provides highly flexible and efficient API (Application Programming Interface). It provides functions to move the cursor, create windows, produce colors, play with mouse etc. The Application programs need not worry about the underlying terminal capabilities.

So what is NCURSES? NCURSES is a clone of the original System V Release 4.0 (SVr4) curses. It is a freely distributable library, fully compatible with older version of curses. In short, it is a library of functions that manages an application's display on character-cell terminals. In the remainder of the document, the terms curses and ncurses are used interchangeably.

The ncurses package was originated by Pavel Curtis. The original maintainer of this package is Zeyd Ben-Halim . Eric S. Raymond wrote many of the new features in versions after 1.8.1. Jürgen Pfeifer wrote all of the menu and forms code as well as the Ada95 binding. Ongoing work is being done by Thomas Dickey and Jürgen Pfeifer. Florian La Roche acts as the maintainer for the Free Software Foundation, which holds the copyright on ncurses. Contact the current maintainers at bug-ncurses@gnu.org.


1.3. Where to get it

All right, now that you know what you can do with ncurses, you must be rearing to get started. Ncurses is usually shipped with your installation. In case you don't have the library or want to compile it on your own, read on.

Compiling the package

Ncurses can be obtained from ftp://ftp.gnu.org/pub/gnu/ncurses/ncurses.tar.gz or any of the ftp sites mentioned in http://www.gnu.org/order/ftp.html. The latest stable release is 5.2 20001021.

Read the README and INSTALL files for details on to how to install it. It usually involves the following operations.

    tar zxvf ncurses<version>.tar.gz  # unzip and untar the archive
    cd ncurses<version>               # cd to the directory
    ./configure                             # configure the build according to your 
                                            # environment
    make                                    # make it
    su root                                 # become root
    make install                            # install it

Using the RPM

Ncurses RPM can be found and downloaded from http://rpmfind.net . The RPM can be installed with the following command after becoming root.

    rpm -i <downloaded rpm>

1.5. About the Programs

All the programs in the document are available in zipped form here. Unzip and untar it. The directory structure looks like this.

ncurses
   |
   |----> JustForFun     -- just for fun programs
   |----> basics         -- basic programs
   |----> demo           -- output files go into this directory after make
   |          |
   |          |----> exe -- exe files of all example programs
   |----> forms          -- programs related to form library
   |----> menus          -- programs related to menus library
   |----> panels         -- programs related to panels library
   |----> Makefile       -- the top level Makefile
   |----> README         -- the top level README file. contains instructions
   |----> COPYING        -- copyright notice

The individual directories contain the following files.

Description of files in each directory
--------------------------------------
JustForFun
    |
    |----> hanoi.c   -- The Towers of Hanoi Solver
    |----> life.c    -- The Game of Life demo
    |----> magic.c   -- An Odd Order Magic Square builder 
    |----> queens.c  -- The famous N-Queens Solver
    |----> shuffle.c -- A fun game, if you have time to kill
    |----> tt.c      -- A very trivial typing tutor

  basics
    |
    |----> acs_vars.c            -- ACS_ variables example
    |----> hello_world.c         -- Simple "Hello World" Program
    |----> init_func_example.c   -- Initialization functions example
    |----> key_code.c            -- Shows the scan code of the key pressed
    |----> mouse_menu.c          -- A menu accessible by mouse
    |----> other_border.c        -- Shows usage of other border functions apa
    |                               -- rt from box()
    |----> printw_example.c      -- A very simple printw() example
    |----> scanw_example.c       -- A very simple getstr() example
    |----> simple_attr.c         -- A program that can print a c file with 
    |                               -- comments in attribute
    |----> simple_color.c        -- A simple example demonstrating colors
    |----> simple_key.c          -- A menu accessible with keyboard UP, DOWN 
    |                               -- arrows
    |----> temp_leave.c          -- Demonstrates temporarily leaving curses mode
    |----> win_border.c          -- Shows Creation of windows and borders
    |----> with_chgat.c          -- chgat() usage example

  forms 
    |
    |----> form_attrib.c     -- Usage of field attributes
    |----> form_options.c    -- Usage of field options
    |----> form_simple.c     -- A simple form example
    |----> form_win.c        -- Demo of windows associated with forms

  menus 
    |
    |----> menu_attrib.c     -- Usage of menu attributes
    |----> menu_item_data.c  -- Usage of item_name() etc.. functions
    |----> menu_multi_column.c    -- Creates multi columnar menus
    |----> menu_scroll.c     -- Demonstrates scrolling capability of menus
    |----> menu_simple.c     -- A simple menu accessed by arrow keys
    |----> menu_toggle.c     -- Creates multi valued menus and explains
    |                           -- REQ_TOGGLE_ITEM
    |----> menu_userptr.c    -- Usage of user pointer
    |----> menu_win.c        -- Demo of windows associated with menus

  panels 
    |
    |----> panel_browse.c    -- Panel browsing through tab. Usage of user 
    |                           -- pointer
    |----> panel_hide.c      -- Hiding and Un hiding of panels
    |----> panel_resize.c    -- Moving and resizing of panels
    |----> panel_simple.c    -- A simple panel example

There is a top level Makefile included in the main directory. It builds all the files and puts the ready-to-use exes in demo/exe directory. You can also do selective make by going into the corresponding directory. Each directory contains a README file explaining the purpose of each c file in the directory.

For every example I have given the path name for the file relative to the ncurses directory.

If you prefer you can browse individual programs at http://tldp.org/HOWTO/NCURSES-Programming-HOWTO/ncurses_programs/

All the programs are released under GPL and you can use them for any thing you like.


1.7. Credits

I thank Sharath and Emre Akbas for helping me with few sections. The introduction was initially written by sharath. I rewrote it with few excerpts taken from his initial work. Emre helped in writing printw and scanw sections.

Then comes Ravi Parimi, my dearest friend, who has been on this project before even one line was written. He constantly bombarded me with suggestions and patiently reviewed the whole text. He also checked each program on Linux and Solaris. See his notes to check on your problems.


1.8. Wish List

This is the wish list, in the order of priority. If you have a wish or you want to work on completing the wish, mail me.

  • Add examples to last parts of forms section. (I am working on it)

  • Prepare a Demo showing all the programs and allow the user to browse through description of each program. Let the user compile and see the program in action. A dialog based interface is preferred. (My friend N.N.Ashok is working on it)

  • Add debug info. _tracef, _tracemouse stuff.

  • Accessing termcap, terminfo using functions provided by ncurses package.

  • Working on two terminals simultaneously.

  • Add things in miscellaneous section.


1.9. Copyright

Copyright (c) 2001 by Pradeep Padala. This document may be distributed under the terms set forth in the LDP license at linuxdoc.org/COPYRIGHT.html.

This HOWTO is free documentation; you can redistribute it and/or modify it under the terms of the LDP license. This document is distributed in the hope that it will be useful, but without any warranty; without even the implied warranty of merchantability or fitness for a particular purpose. See the LDP license for more details.


2. The Hello World Program

Welcome to the world of curses. Before we plunge into the library and look into its various features, bells and whistles, let's write a simple program and say hello to the world.


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.


3. The Gory Details

Now that we have seen how to write a simple curses program let's get into the details. There are many functions that help customize what you see on screen and many features which can be put to full use.

Here we go...


4. Initialization

We now know that to initialize curses system the function initscr() has to be called. There are functions which can be called after this initialization to customize our curses session. We may ask the curses system to set the terminal in raw mode or initialize color or initialize the mouse etc.. Let's discuss some of the functions that are normally called immediately after initscr();


5. A Word about Windows

Before we plunge into the myriad ncurses functions, let me clear few things about windows. Windows are explained in detail in following sections

A Window is an imaginary screen defined by curses system. A window does not mean a bordered window which you usually see on Win9X platforms. When curses is initialized, it creates a default window named stdscr which represents your 80x25 (or the size of window in which you are running) screen. If you are doing simple tasks like printing few strings, reading input etc., you can safely use this single window for all of your purposes. You can also create windows and call functions which explicitly work on the specified window.

For example, if you call

    printw("Hi There !!!");
    refresh();

It prints the string on stdscr at the present cursor position. Similarly the call to refresh(), works on stdscr only.

Say you have created windows then you have to call a function with a 'w' added to the usual function.

    wprintw(win, "Hi There !!!");
    wrefresh(win);

As you will see in the rest of the document, naming of functions follow the same convention. For each function there usually are three more functions.

    printw(string);        /* Print on stdscr at present cursor position */
    mvprintw(y, x, string);/* Move to (y, x) then print string     */
    wprintw(win, string);  /* Print on window win at present cursor position */
                           /* in the window */
    mvwprintw(win, y, x, string);   /* Move to (y, x) relative to window */
                                    /* co-ordinates and then print         */

Usually the w-less functions are macros which expand to corresponding w-function with stdscr as the window parameter.


6. About output functions like printw()

I guess you can't wait any more to see some action. Back to our odyssey of curses functions. Now that curses is initialized, let's interact with world.

There are three classes of functions which you can use to do output on screen.

  1. addch() class: Print single character with attributes

  2. printw() class: Print formatted output similar to printf()

  3. addstr() class: Print strings

These functions can be used interchangeably and it's a matter of style as to which class is used. Let's see each one in detail.


6.1. addch() class of functions

These functions put a single character into the current cursor location and advance the position of the cursor. You can give the character to be printed but they usually are used to print a character with some attributes. Attributes are explained in detail in later sections of the document. If a character is associated with an attribute(bold, reverse video etc.), when curses prints the character, it is printed in that attribute.

In order to combine a character with some attributes, you have two options:

  • By OR'ing a single character with the desired attribute macros. These attribute macros could be found in the header file ncurses.h. For example, you want to print a character ch(of type char) bold and underlined, you would call addch() as below.
        addch(ch | A_BOLD | A_UNDERLINE);

  • By using functions like attrset(),attron(),attroff(). These functions are explained in the Attributes section. Briefly, they manipulate the current attributes of the given window. Once set, the character printed in the window are associated with the attributes until it is turned off.

Additionally, curses provides some special characters for character-based graphics. You can draw tables, horizontal or vertical lines, etc. You can find all avaliable characters in the header file ncurses.h. Try looking for macros beginning with ACS_ in this file.


6.3. printw() class of functions

These functions are similar to printf() with the added capability of printing at any position on the screen.


7. About input functions like scanw()

Well, printing without taking input, is boring. Let's see functions which allow us to get input from user. These functions also can be divided into three categories.

  1. getch() class: Get a character

  2. scanw() class: Get formatted input

  3. getstr() class: Get strings


8. Attributes

We have seen an example of how attributes can be used to print characters with some special effects. Attributes, when set prudently, can present information in an easy, understandable manner. The following program takes a C file as input and prints the file with comments in bold. Scan through the code.

Don't worry about all those initialization and other crap. Concentrate on the while loop. It reads each character in the file and searches for the pattern /*. Once it spots the pattern, it switches the BOLD attribute on with attron() . When we get the pattern */ it is switched off by attroff() .

The above program also introduces us to two useful functions getyx() and move(). The first function gets the co-ordinates of the present cursor into the variables y, x. Since getyx() is a macro we don't have to pass pointers to variables. The function move() moves the cursor to the co-ordinates given to it.

The above program is really a simple one which doesn't do much. On these lines one could write a more useful program which reads a C file, parses it and prints it in different colors. One could even extend it to other languages as well.


8.1. The details

Let's get into more details of attributes. The functions attron(), attroff(), attrset() , and their sister functions attr_get() etc.. can be used to switch attributes on/off , get attributes and produce a colorful display.

The functions attron and attroff take a bit-mask of attributes and switch them on or off, respectively. The following video attributes, which are defined in <curses.h> can be passed to these functions.

    
    A_NORMAL        Normal display (no highlight)
    A_STANDOUT      Best highlighting mode of the terminal.
    A_UNDERLINE     Underlining
    A_REVERSE       Reverse video
    A_BLINK         Blinking
    A_DIM           Half bright
    A_BOLD          Extra bright or bold
    A_PROTECT       Protected mode
    A_INVIS         Invisible or blank mode
    A_ALTCHARSET    Alternate character set
    A_CHARTEXT      Bit-mask to extract a character
    COLOR_PAIR(n)   Color-pair number n 
    

The last one is the most colorful one :-) Colors are explained in the next sections.

We can OR(|) any number of above attributes to get a combined effect. If you wanted reverse video with blinking characters you can use

    attron(A_REVERSE | A_BLINK);

8.6. chgat() functions

The function chgat() is listed in the end of the man page curs_attr. It actually is a useful one. This function can be used to set attributes for a group of characters without moving. I mean it !!! without moving the cursor :-) It changes the attributes of a given number of characters starting at the current cursor location.

We can give -1 as the character count to update till end of line. If you want to change attributes of characters from current position to end of line, just use this.

    chgat(-1, A_REVERSE, 0, NULL);

This function is useful when changing attributes for characters that are already on the screen. Move to the character from which you want to change and change the attribute.

Other functions wchgat(), mvchgat(), wchgat() behave similarly except that the w functions operate on the particular window. The mv functions first move the cursor then perform the work given to them. Actually chgat is a macro which is replaced by a wchgat() with stdscr as the window. Most of the "w-less" functions are macros.

This example also introduces us to the color world of curses. Colors will be explained in detail later. Use 0 for no color.


9. All about window functions

Windows form the most important concept in curses. You have seen the standard window stdscr above where all the functions implicitly operated on this window. Now to make design even a simplest GUI, you need to resort to windows. The main reason you may want to use windows is to manipulate parts of the screen separately, for better efficiency, by updating only the windows that need to be changed and for a better design. I would say the last reason is the most important in going for windows. You should always strive for a better and easy-to-manage design in your programs. If you are writing big, complex GUIs this is of pivotal importance before you start doing anything.


9.2. Let there be a Window !!!

What fun is it, if a window is created and we can't see it. So the fun part begins by displaying the window. The function box() can be used to draw a border around the window. Let's explore these functions in more detail in this example.

Example 7. Window Border example

#include <ncurses.h>


WINDOW *create_newwin(int height, int width, int starty, int startx);
void destroy_win(WINDOW *local_win);

int main(int argc, char *argv[])
{	WINDOW *my_win;
	int startx, starty, width, height;
	int ch;

	initscr();			/* Start curses mode 		*/
	cbreak();			/* Line buffering disabled, Pass on
					 * everty thing to me 		*/
	keypad(stdscr, TRUE);		/* I need that nifty F1 	*/

	height = 3;
	width = 10;
	starty = (LINES - height) / 2;	/* Calculating for a center placement */
	startx = (COLS - width) / 2;	/* of the window		*/
	printw("Press F1 to exit");
	refresh();
	my_win = create_newwin(height, width, starty, startx);

	while((ch = getch()) != KEY_F(1))
	{	switch(ch)
		{	case KEY_LEFT:
				destroy_win(my_win);
				my_win = create_newwin(height, width, starty,--startx);
				break;
			case KEY_RIGHT:
				destroy_win(my_win);
				my_win = create_newwin(height, width, starty,++startx);
				break;
			case KEY_UP:
				destroy_win(my_win);
				my_win = create_newwin(height, width, --starty,startx);
				break;
			case KEY_DOWN:
				destroy_win(my_win);
				my_win = create_newwin(height, width, ++starty,startx);
				break;	
		}
	}
		
	endwin();			/* End curses mode		  */
	return 0;
}

WINDOW *create_newwin(int height, int width, int starty, int startx)
{	WINDOW *local_win;

	local_win = newwin(height, width, starty, startx);
	box(local_win, 0 , 0);		/* 0, 0 gives default characters 
					 * for the vertical and horizontal
					 * lines			*/
	wrefresh(local_win);		/* Show that box 		*/

	return local_win;
}

void destroy_win(WINDOW *local_win)
{	
	/* box(local_win, ' ', ' '); : This won't produce the desired
	 * result of erasing the window. It will leave it's four corners 
	 * and so an ugly remnant of window. 
	 */
	wborder(local_win, ' ', ' ', ' ',' ',' ',' ',' ',' ');
	/* The parameters taken are 
	 * 1. win: the window on which to operate
	 * 2. ls: character to be used for the left side of the window 
	 * 3. rs: character to be used for the right side of the window 
	 * 4. ts: character to be used for the top side of the window 
	 * 5. bs: character to be used for the bottom side of the window 
	 * 6. tl: character to be used for the top left corner of the window 
	 * 7. tr: character to be used for the top right corner of the window 
	 * 8. bl: character to be used for the bottom left corner of the window 
	 * 9. br: character to be used for the bottom right corner of the window
	 */
	wrefresh(local_win);
	delwin(local_win);
}

9.5. Other Border functions

Above program is grossly inefficient in that with each press of a key, a window is destroyed and another is created. So let's write a more efficient program which uses other border related functions.

The following program uses mvhline() and mvvline() to achieve similar effect. These two functions are simple. They create a horizontal or vertical line of the specified length at the specified position.

Example 8. More border functions

#include <ncurses.h>

typedef struct _win_border_struct {
	chtype 	ls, rs, ts, bs, 
	 	tl, tr, bl, br;
}WIN_BORDER;

typedef struct _WIN_struct {

	int startx, starty;
	int height, width;
	WIN_BORDER border;
}WIN;

void init_win_params(WIN *p_win);
void print_win_params(WIN *p_win);
void create_box(WIN *win, int bool);

int main(int argc, char *argv[])
{	WIN win;
	int ch;

	initscr();			/* Start curses mode 		*/
	start_color();			/* Start the color functionality */
	cbreak();			/* Line buffering disabled, Pass on
					 * everty thing to me 		*/
	keypad(stdscr, TRUE);		/* I need that nifty F1 	*/
	noecho();
	init_pair(1, COLOR_CYAN, COLOR_BLACK);

	/* Initialize the window parameters */
	init_win_params(&win);
	print_win_params(&win);

	attron(COLOR_PAIR(1));
	printw("Press F1 to exit");
	refresh();
	attroff(COLOR_PAIR(1));
	
	create_box(&win, TRUE);
	while((ch = getch()) != KEY_F(1))
	{	switch(ch)
		{	case KEY_LEFT:
				create_box(&win, FALSE);
				--win.startx;
				create_box(&win, TRUE);
				break;
			case KEY_RIGHT:
				create_box(&win, FALSE);
				++win.startx;
				create_box(&win, TRUE);
				break;
			case KEY_UP:
				create_box(&win, FALSE);
				--win.starty;
				create_box(&win, TRUE);
				break;
			case KEY_DOWN:
				create_box(&win, FALSE);
				++win.starty;
				create_box(&win, TRUE);
				break;	
		}
	}
	endwin();			/* End curses mode		  */
	return 0;
}
void init_win_params(WIN *p_win)
{
	p_win->height = 3;
	p_win->width = 10;
	p_win->starty = (LINES - p_win->height)/2;	
	p_win->startx = (COLS - p_win->width)/2;

	p_win->border.ls = '|';
	p_win->border.rs = '|';
	p_win->border.ts = '-';
	p_win->border.bs = '-';
	p_win->border.tl = '+';
	p_win->border.tr = '+';
	p_win->border.bl = '+';
	p_win->border.br = '+';

}
void print_win_params(WIN *p_win)
{
#ifdef _DEBUG
	mvprintw(25, 0, "%d %d %d %d", p_win->startx, p_win->starty, 
				p_win->width, p_win->height);
	refresh();
#endif
}
void create_box(WIN *p_win, int bool)
{	int i, j;
	int x, y, w, h;

	x = p_win->startx;
	y = p_win->starty;
	w = p_win->width;
	h = p_win->height;

	if(bool == TRUE)
	{	mvaddch(y, x, p_win->border.tl);
		mvaddch(y, x + w, p_win->border.tr);
		mvaddch(y + h, x, p_win->border.bl);
		mvaddch(y + h, x + w, p_win->border.br);
		mvhline(y, x + 1, p_win->border.ts, w - 1);
		mvhline(y + h, x + 1, p_win->border.bs, w - 1);
		mvvline(y + 1, x, p_win->border.ls, h - 1);
		mvvline(y + 1, x + w, p_win->border.rs, h - 1);

	}
	else
		for(j = y; j <= y + h; ++j)
			for(i = x; i <= x + w; ++i)
				mvaddch(j, i, ' ');
				
	refresh();

}

10. All about color

10.1. The basics

Life seems dull with no colors. Curses has a nice mechanism to handle colors. Let's get into the thick of the things with a small program.

As you can see, to start using color, you should first call the function start_color(). After that you can use color capabilities of your terminals by various functions. To find out whether terminal has color capabilities or not, you can use has_colors() function, which returns FALSE if the terminal does not support color.

Curses initializes all the colors supported by terminal when start_color() is called. These can be accessed by the define constants like COLOR_BLACK etc. Now to actually start using colors, you have to define pairs. Colors are always used in pairs. That means you have to use the function init_pair() to define the foreground and background for the pair number you give. After that that pair number can be used as a normal attribute with COLOR_PAIR()function. This may seem to be cumbersome at first. But this elegant solution allows us to manage color pairs very easily. To appreciate it, you have to look into the the source code of "dialog", a utility for displaying dialog boxes from shell scripts. The developers have defined foreground and background combinations for all the colors they might need and initialized at the beginning. This makes it very easy to set attributes just by accessing a pair which we already have defined as a constant.

The following colors are defined in curses.h. You can use these as parameters for various color functions.
        COLOR_BLACK   0
        COLOR_RED     1
        COLOR_GREEN   2
        COLOR_YELLOW  3
        COLOR_BLUE    4
        COLOR_MAGENTA 5
        COLOR_CYAN    6
        COLOR_WHITE   7


11. Key management. How to read function keys, arrow keys etc..

11.1. The Basics

No GUI is complete without a strong user interface and to interact with the user, a curses program should be sensitive to key presses or the mouse actions done by the user. Let's deal with the keys first.

As you have seen in almost all of the above examples, it's very easy to get key input from the user. A simple way of getting key presses is to use getch() function. The cbreak mode should be enabled to read keys when you are interested in reading individual key hits rather than complete lines of text (which usually end with a carriage return). keypad should be enabled to get the Functions keys, arrow keys etc. See the initialization section for details.

getch() returns an integer corresponding to the key pressed. If it is a normal character, the integer value will be equivalent to the character. Otherwise it returns a number which can be matched with the constants defined in curses.h. For example if the user presses F1, the integer returned is 265. This can be checked using the macro KEY_F() defined in curses.h. This makes reading keys portable and easy to manage.

For example, if you call getch() like this

    int ch;

    ch = getch();

getch() will wait for the user to press a key, (unless you specified a timeout) and when user presses a key, the corresponding integer is returned. Then you can check the value returned with the constants defined in curses.h to match against the keys you want.

The following code piece will do that job.

    if(ch == KEY_LEFT)
        printw("Left arrow is pressed\n");

Let's write a small program which creates a menu which can be navigated by up and down arrows.


11.2. A Simple Key Usage example

Example 10. A Simple Key Usage example

#include <stdio.h>
#include <ncurses.h>

#define WIDTH 30
#define HEIGHT 10 

int startx = 0;
int starty = 0;

char *choices[] = { 
			"Choice 1",
			"Choice 2",
			"Choice 3",
			"Choice 4",
			"Exit",
		  };
int n_choices = sizeof(choices) / sizeof(char *);
void print_menu(WINDOW *menu_win, int highlight);

int main()
{	WINDOW *menu_win;
	int highlight = 1;
	int choice = 0;
	int c;

	initscr();
	clear();
	noecho();
	cbreak();	/* Line buffering disabled. pass on everything */
	startx = (80 - WIDTH) / 2;
	starty = (24 - HEIGHT) / 2;
		
	menu_win = newwin(HEIGHT, WIDTH, starty, startx);
	keypad(menu_win, TRUE);
	mvprintw(0, 0, "Use arrow keys to go up and down, Press enter to select a choice");
	refresh();
	print_menu(menu_win, highlight);
	while(1)
	{	c = wgetch(menu_win);
		switch(c)
		{	case KEY_UP:
				if(highlight == 1)
					highlight = n_choices;
				else
					--highlight;
				break;
			case KEY_DOWN:
				if(highlight == n_choices)
					highlight = 1;
				else 
					++highlight;
				break;
			case 10:
				choice = highlight;
				break;
			default:
				mvprintw(24, 0, "Charcter pressed is = %3d Hopefully it can be printed as '%c'", c, c);
				refresh();
				break;
		}
		print_menu(menu_win, highlight);
		if(choice != 0)	/* User did a choice come out of the infinite loop */
			break;
	}	
	mvprintw(23, 0, "You chose choice %d with choice string %s\n", choice, choices[choice - 1]);
	clrtoeol();
	refresh();
	endwin();
	return 0;
}


void print_menu(WINDOW *menu_win, int highlight)
{
	int x, y, i;	

	x = 2;
	y = 2;
	box(menu_win, 0, 0);
	for(i = 0; i < n_choices; ++i)
	{	if(highlight == i + 1) /* High light the present choice */
		{	wattron(menu_win, A_REVERSE); 
			mvwprintw(menu_win, y, x, "%s", choices[i]);
			wattroff(menu_win, A_REVERSE);
		}
		else
			mvwprintw(menu_win, y, x, "%s", choices[i]);
		++y;
	}
	wrefresh(menu_win);
}

12. Interfacing with the mouse

Now that you have seen how to get keys, lets do the same thing from mouse. Usually each UI allows the user to interact with both keyboard and mouse.


12.1. The Basics

Before you do any thing else, the events you want to receive have to be enabled with mousemask().

    mousemask(  mmask_t newmask,    /* The events you want to listen to */
                mmask_t *oldmask)    /* The old events mask                */

The first parameter to above function is a bit mask of events you would like to listen. By default, all the events are turned off. The bit mask ALL_MOUSE_EVENTS can be used to get all the events.

The following are all the event masks:

    Name            Description
       ---------------------------------------------------------------------
       BUTTON1_PRESSED          mouse button 1 down
       BUTTON1_RELEASED         mouse button 1 up
       BUTTON1_CLICKED          mouse button 1 clicked
       BUTTON1_DOUBLE_CLICKED   mouse button 1 double clicked
       BUTTON1_TRIPLE_CLICKED   mouse button 1 triple clicked
       BUTTON2_PRESSED          mouse button 2 down
       BUTTON2_RELEASED         mouse button 2 up
       BUTTON2_CLICKED          mouse button 2 clicked
       BUTTON2_DOUBLE_CLICKED   mouse button 2 double clicked
       BUTTON2_TRIPLE_CLICKED   mouse button 2 triple clicked
       BUTTON3_PRESSED          mouse button 3 down
       BUTTON3_RELEASED         mouse button 3 up
       BUTTON3_CLICKED          mouse button 3 clicked
       BUTTON3_DOUBLE_CLICKED   mouse button 3 double clicked
       BUTTON3_TRIPLE_CLICKED   mouse button 3 triple clicked
       BUTTON4_PRESSED          mouse button 4 down
       BUTTON4_RELEASED         mouse button 4 up
       BUTTON4_CLICKED          mouse button 4 clicked
       BUTTON4_DOUBLE_CLICKED   mouse button 4 double clicked
       BUTTON4_TRIPLE_CLICKED   mouse button 4 triple clicked
       BUTTON_SHIFT             shift was down during button state change
       BUTTON_CTRL              control was down during button state change
       BUTTON_ALT               alt was down during button state change
       ALL_MOUSE_EVENTS         report all button state changes
       REPORT_MOUSE_POSITION    report mouse movement

12.3. Putting it all Together

That's pretty much interfacing with mouse. Let's create the same menu and enable mouse interaction. To make things simpler, key handling is removed.

Example 11. Access the menu with mouse !!!

#include <ncurses.h>

#define WIDTH 30
#define HEIGHT 10 

int startx = 0;
int starty = 0;

char *choices[] = { 	"Choice 1",
			"Choice 2",
			"Choice 3",
			"Choice 4",
			"Exit",
		  };

int n_choices = sizeof(choices) / sizeof(char *);

void print_menu(WINDOW *menu_win, int highlight);
void report_choice(int mouse_x, int mouse_y, int *p_choice);

int main()
{	int c, choice = 0;
	WINDOW *menu_win;
	MEVENT event;

	/* Initialize curses */
	initscr();
	clear();
	noecho();
	cbreak();	//Line buffering disabled. pass on everything

	/* Try to put the window in the middle of screen */
	startx = (80 - WIDTH) / 2;
	starty = (24 - HEIGHT) / 2;
	
	attron(A_REVERSE);
	mvprintw(23, 1, "Click on Exit to quit (Works best in a virtual console)");
	refresh();
	attroff(A_REVERSE);

	/* Print the menu for the first time */
	menu_win = newwin(HEIGHT, WIDTH, starty, startx);
	print_menu(menu_win, 1);
	/* Get all the mouse events */
	mousemask(ALL_MOUSE_EVENTS, NULL);
	
	while(1)
	{	c = wgetch(menu_win);
		switch(c)
		{	case KEY_MOUSE:
			if(getmouse(&event) == OK)
			{	/* When the user clicks left mouse button */
				if(event.bstate & BUTTON1_PRESSED)
				{	report_choice(event.x + 1, event.y + 1, &choice);
					if(choice == -1) //Exit chosen
						goto end;
					mvprintw(22, 1, "Choice made is : %d String Chosen is \"%10s\"", choice, choices[choice - 1]);
					refresh(); 
				}
			}
			print_menu(menu_win, choice);
			break;
		}
	}		
end:
	endwin();
	return 0;
}


void print_menu(WINDOW *menu_win, int highlight)
{
	int x, y, i;	

	x = 2;
	y = 2;
	box(menu_win, 0, 0);
	for(i = 0; i < n_choices; ++i)
	{	if(highlight == i + 1)
		{	wattron(menu_win, A_REVERSE); 
			mvwprintw(menu_win, y, x, "%s", choices[i]);
			wattroff(menu_win, A_REVERSE);
		}
		else
			mvwprintw(menu_win, y, x, "%s", choices[i]);
		++y;
	}
	wrefresh(menu_win);
}

/* Report the choice according to mouse position */
void report_choice(int mouse_x, int mouse_y, int *p_choice)
{	int i,j, choice;

	i = startx + 2;
	j = starty + 3;
	
	for(choice = 0; choice < n_choices; ++choice)
		if(mouse_y == j + choice && mouse_x >= i && mouse_x <= i + strlen(choices[choice]))
		{	if(choice == n_choices - 1)
				*p_choice = -1;		
			else
				*p_choice = choice + 1;	
			break;
		}
}

13. Screen Manipulation

In this section, we will look into some functions, which allow us to manage the screen efficiently and to write some fancy programs. This is especially important in writing games.


14. Miscellaneous features

Now you know enough features to write a good curses program, with all bells and whistles. There are some miscellaneous functions which are useful in various cases. Let's go headlong into some of those.


14.3. ACS_ variables

If you have ever programmed in DOS, you know about those nifty characters in extended character set. They are printable only on some terminals. NCURSES functions like box() use these characters. All these variables start with ACS meaning alternative character set. You might have noticed me using these characters in some of the programs above. Here's an example showing all the characters.

Example 13. ACS Variables Example

#include <ncurses.h>

int main()
{
        initscr();

        printw("Upper left corner           "); addch(ACS_ULCORNER); printw("\n"); 
        printw("Lower left corner           "); addch(ACS_LLCORNER); printw("\n");
        printw("Lower right corner          "); addch(ACS_LRCORNER); printw("\n");
        printw("Tee pointing right          "); addch(ACS_LTEE); printw("\n");
        printw("Tee pointing left           "); addch(ACS_RTEE); printw("\n");
        printw("Tee pointing up             "); addch(ACS_BTEE); printw("\n");
        printw("Tee pointing down           "); addch(ACS_TTEE); printw("\n");
        printw("Horizontal line             "); addch(ACS_HLINE); printw("\n");
        printw("Vertical line               "); addch(ACS_VLINE); printw("\n");
        printw("Large Plus or cross over    "); addch(ACS_PLUS); printw("\n");
        printw("Scan Line 1                 "); addch(ACS_S1); printw("\n");
        printw("Scan Line 3                 "); addch(ACS_S3); printw("\n");
        printw("Scan Line 7                 "); addch(ACS_S7); printw("\n");
        printw("Scan Line 9                 "); addch(ACS_S9); printw("\n");
        printw("Diamond                     "); addch(ACS_DIAMOND); printw("\n");
        printw("Checker board (stipple)     "); addch(ACS_CKBOARD); printw("\n");
        printw("Degree Symbol               "); addch(ACS_DEGREE); printw("\n");
        printw("Plus/Minus Symbol           "); addch(ACS_PLMINUS); printw("\n");
        printw("Bullet                      "); addch(ACS_BULLET); printw("\n");
        printw("Arrow Pointing Left         "); addch(ACS_LARROW); printw("\n");
        printw("Arrow Pointing Right        "); addch(ACS_RARROW); printw("\n");
        printw("Arrow Pointing Down         "); addch(ACS_DARROW); printw("\n");
        printw("Arrow Pointing Up           "); addch(ACS_UARROW); printw("\n");
        printw("Board of squares            "); addch(ACS_BOARD); printw("\n");
        printw("Lantern Symbol              "); addch(ACS_LANTERN); printw("\n");
        printw("Solid Square Block          "); addch(ACS_BLOCK); printw("\n");
        printw("Less/Equal sign             "); addch(ACS_LEQUAL); printw("\n");
        printw("Greater/Equal sign          "); addch(ACS_GEQUAL); printw("\n");
        printw("Pi                          "); addch(ACS_PI); printw("\n");
        printw("Not equal                   "); addch(ACS_NEQUAL); printw("\n");
        printw("UK pound sign               "); addch(ACS_STERLING); printw("\n");

        refresh();
        getch();
        endwin();

	return 0;
}

15. Other libraries

Apart from the curses library, there are few text mode libraries, which provide more functionality and a lot of features. The following sections explain three standard libraries which are usually distributed along with curses.


16. Panel Library

Now that you are proficient in curses, you wanted to do some thing big. You created a lot of overlapping windows to give a professional windows-type look. Unfortunately, it soon becomes difficult to manage these. The multiple refreshes, updates plunge you into a nightmare. The overlapping windows create blotches, whenever you forget to refresh the windows in the proper order.

Don't despair. There's an elegant solution provided in panels library. In the words of developers of ncurses

When your interface design is such that windows may dive deeper into the visibility stack or pop to the top at runtime, the resulting book-keeping can be tedious and difficult to get right. Hence the panels library.

If you have lot of overlapping windows, then panels library is the way to go. It obviates the need of doing series of wnoutrefresh(), doupdate() and relieves the burden of doing it correctly(bottom up). The library maintains information about the order of windows, their overlapping and update the screen properly. So why wait? Let's take a close peek into panels.


16.1. The Basics

Panel object is a window that is implicitly treated as part of a deck including all other panel objects. The deck is treated as a stack with the top panel being completely visible and the other panels may or may not be obscured according to their positions. So the basic idea is to create a stack of overlapping panels and use panels library to display them correctly. There is a function similar to refresh() which, when called , displays panels in the correct order. Functions are provided to hide or show panels, move panels, change its size etc.. The overlapping problem is managed by the panels library during all the calls to these functions.

The general flow of a panel program goes like this:

  1. Create the windows (with newwin()) to be attached to the panels.

  2. Create panels with the chosen visibility order. Stack them up according to the desired visibility. The function new_panel() is used to created panels.

  3. Call update_panels() to write the panels to the virtual screen in correct visibility order. Do a doupdate() to show it on the screen.

  4. Mainpulate the panels with show_panel(), hide_panel(), move_panel() etc. Make use of helper functions like panel_hidden() and panel_window(). Make use of user pointer to store custom data for a panel. Use the functions set_panel_userptr() and panel_userptr() to set and get the user pointer for a panel.

  5. When you are done with the panel use del_panel() to delete the panel.

Let's make the concepts clear, with some programs. The following is a simple program which creates 3 overlapping panels and shows them on the screen.


16.3. Panel Window Browsing

A slightly complicated example is given below. This program creates 3 windows which can be cycled through using tab. Have a look at the code.

Example 15. Panel Window Browsing Example

#include <panel.h>

#define NLINES 10
#define NCOLS 40

void init_wins(WINDOW **wins, int n);
void win_show(WINDOW *win, char *label, int label_color);
void print_in_middle(WINDOW *win, int starty, int startx, int width, char *string, chtype color);

int main()
{	WINDOW *my_wins[3];
	PANEL  *my_panels[3];
	PANEL  *top;
	int ch;

	/* Initialize curses */
	initscr();
	start_color();
	cbreak();
	noecho();
	keypad(stdscr, TRUE);

	/* Initialize all the colors */
	init_pair(1, COLOR_RED, COLOR_BLACK);
	init_pair(2, COLOR_GREEN, COLOR_BLACK);
	init_pair(3, COLOR_BLUE, COLOR_BLACK);
	init_pair(4, COLOR_CYAN, COLOR_BLACK);

	init_wins(my_wins, 3);
	
	/* Attach a panel to each window */ 	/* Order is bottom up */
	my_panels[0] = new_panel(my_wins[0]); 	/* Push 0, order: stdscr-0 */
	my_panels[1] = new_panel(my_wins[1]); 	/* Push 1, order: stdscr-0-1 */
	my_panels[2] = new_panel(my_wins[2]); 	/* Push 2, order: stdscr-0-1-2 */

	/* Set up the user pointers to the next panel */
	set_panel_userptr(my_panels[0], my_panels[1]);
	set_panel_userptr(my_panels[1], my_panels[2]);
	set_panel_userptr(my_panels[2], my_panels[0]);

	/* Update the stacking order. 2nd panel will be on top */
	update_panels();

	/* Show it on the screen */
	attron(COLOR_PAIR(4));
	mvprintw(LINES - 2, 0, "Use tab to browse through the windows (F1 to Exit)");
	attroff(COLOR_PAIR(4));
	doupdate();

	top = my_panels[2];
	while((ch = getch()) != KEY_F(1))
	{	switch(ch)
		{	case 9:
				top = (PANEL *)panel_userptr(top);
				top_panel(top);
				break;
		}
		update_panels();
		doupdate();
	}
	endwin();
	return 0;
}

/* Put all the windows */
void init_wins(WINDOW **wins, int n)
{	int x, y, i;
	char label[80];

	y = 2;
	x = 10;
	for(i = 0; i < n; ++i)
	{	wins[i] = newwin(NLINES, NCOLS, y, x);
		sprintf(label, "Window Number %d", i + 1);
		win_show(wins[i], label, i + 1);
		y += 3;
		x += 7;
	}
}

/* Show the window with a border and a label */
void win_show(WINDOW *win, char *label, int label_color)
{	int startx, starty, height, width;

	getbegyx(win, starty, startx);
	getmaxyx(win, height, width);

	box(win, 0, 0);
	mvwaddch(win, 2, 0, ACS_LTEE); 
	mvwhline(win, 2, 1, ACS_HLINE, width - 2); 
	mvwaddch(win, 2, width - 1, ACS_RTEE); 
	
	print_in_middle(win, 1, 0, width, label, COLOR_PAIR(label_color));
}

void print_in_middle(WINDOW *win, int starty, int startx, int width, char *string, chtype color)
{	int length, x, y;
	float temp;

	if(win == NULL)
		win = stdscr;
	getyx(win, y, x);
	if(startx != 0)
		x = startx;
	if(starty != 0)
		y = starty;
	if(width == 0)
		width = 80;

	length = strlen(string);
	temp = (width - length)/ 2;
	x = startx + (int)temp;
	wattron(win, color);
	mvwprintw(win, y, x, "%s", string);
	wattroff(win, color);
	refresh();
}

16.5. Moving and Resizing Panels

The function move_panel() can be used to move a panel to the desired location. It does not change the position of the panel in the stack. Make sure that you use move_panel() instead mvwin() on the window associated with the panel.

Resizing a panel is slightly complex. There is no straight forward function just to resize the window associated with a panel. A solution to resize a panel is to create a new window with the desired sizes, change the window associated with the panel using replace_panel(). Don't forget to delete the old window. The window associated with a panel can be found by using the function panel_window().

The following program shows these concepts, in supposedly simple program. You can cycle through the window with <TAB> as usual. To resize or move the active panel press 'r' for resize 'm' for moving. Then use arrow keys to resize or move it to the desired way and press enter to end your resizing or moving. This example makes use of user data to get the required data to do the operations.

Example 16. Panel Moving and Resizing example

#include <panel.h>

typedef struct _PANEL_DATA {
	int x, y, w, h;
	char label[80]; 
	int label_color;
	PANEL *next;
}PANEL_DATA;

#define NLINES 10
#define NCOLS 40

void init_wins(WINDOW **wins, int n);
void win_show(WINDOW *win, char *label, int label_color);
void print_in_middle(WINDOW *win, int starty, int startx, int width, char *string, chtype color);
void set_user_ptrs(PANEL **panels, int n);

int main()
{	WINDOW *my_wins[3];
	PANEL  *my_panels[3];
	PANEL_DATA  *top;
	PANEL *stack_top;
	WINDOW *temp_win, *old_win;
	int ch;
	int newx, newy, neww, newh;
	int size = FALSE, move = FALSE;

	/* Initialize curses */
	initscr();
	start_color();
	cbreak();
	noecho();
	keypad(stdscr, TRUE);

	/* Initialize all the colors */
	init_pair(1, COLOR_RED, COLOR_BLACK);
	init_pair(2, COLOR_GREEN, COLOR_BLACK);
	init_pair(3, COLOR_BLUE, COLOR_BLACK);
	init_pair(4, COLOR_CYAN, COLOR_BLACK);

	init_wins(my_wins, 3);
	
	/* Attach a panel to each window */ 	/* Order is bottom up */
	my_panels[0] = new_panel(my_wins[0]); 	/* Push 0, order: stdscr-0 */
	my_panels[1] = new_panel(my_wins[1]); 	/* Push 1, order: stdscr-0-1 */
	my_panels[2] = new_panel(my_wins[2]); 	/* Push 2, order: stdscr-0-1-2 */

	set_user_ptrs(my_panels, 3);
	/* Update the stacking order. 2nd panel will be on top */
	update_panels();

	/* Show it on the screen */
	attron(COLOR_PAIR(4));
	mvprintw(LINES - 3, 0, "Use 'm' for moving, 'r' for resizing");
	mvprintw(LINES - 2, 0, "Use tab to browse through the windows (F1 to Exit)");
	attroff(COLOR_PAIR(4));
	doupdate();

	stack_top = my_panels[2];
	top = (PANEL_DATA *)panel_userptr(stack_top);
	newx = top->x;
	newy = top->y;
	neww = top->w;
	newh = top->h;
	while((ch = getch()) != KEY_F(1))
	{	switch(ch)
		{	case 9:		/* Tab */
				top = (PANEL_DATA *)panel_userptr(stack_top);
				top_panel(top->next);
				stack_top = top->next;
				top = (PANEL_DATA *)panel_userptr(stack_top);
				newx = top->x;
				newy = top->y;
				neww = top->w;
				newh = top->h;
				break;
			case 'r':	/* Re-Size*/
				size = TRUE;
				attron(COLOR_PAIR(4));
				mvprintw(LINES - 4, 0, "Entered Resizing :Use Arrow Keys to resize and press <ENTER> to end resizing");
				refresh();
				attroff(COLOR_PAIR(4));
				break;
			case 'm':	/* Move */
				attron(COLOR_PAIR(4));
				mvprintw(LINES - 4, 0, "Entered Moving: Use Arrow Keys to Move and press <ENTER> to end moving");
				refresh();
				attroff(COLOR_PAIR(4));
				move = TRUE;
				break;
			case KEY_LEFT:
				if(size == TRUE)
				{	--newx;
					++neww;
				}
				if(move == TRUE)
					--newx;
				break;
			case KEY_RIGHT:
				if(size == TRUE)
				{	++newx;
					--neww;
				}
				if(move == TRUE)
					++newx;
				break;
			case KEY_UP:
				if(size == TRUE)
				{	--newy;
					++newh;
				}
				if(move == TRUE)
					--newy;
				break;
			case KEY_DOWN:
				if(size == TRUE)
				{	++newy;
					--newh;
				}
				if(move == TRUE)
					++newy;
				break;
			case 10:	/* Enter */
				move(LINES - 4, 0);
				clrtoeol();
				refresh();
				if(size == TRUE)
				{	old_win = panel_window(stack_top);
					temp_win = newwin(newh, neww, newy, newx);
					replace_panel(stack_top, temp_win);
					win_show(temp_win, top->label, top->label_color); 
					delwin(old_win);
					size = FALSE;
				}
				if(move == TRUE)
				{	move_panel(stack_top, newy, newx);
					move = FALSE;
				}
				break;
			
		}
		attron(COLOR_PAIR(4));
		mvprintw(LINES - 3, 0, "Use 'm' for moving, 'r' for resizing");
	    	mvprintw(LINES - 2, 0, "Use tab to browse through the windows (F1 to Exit)");
	    	attroff(COLOR_PAIR(4));
	        refresh();	
		update_panels();
		doupdate();
	}
	endwin();
	return 0;
}

/* Put all the windows */
void init_wins(WINDOW **wins, int n)
{	int x, y, i;
	char label[80];

	y = 2;
	x = 10;
	for(i = 0; i < n; ++i)
	{	wins[i] = newwin(NLINES, NCOLS, y, x);
		sprintf(label, "Window Number %d", i + 1);
		win_show(wins[i], label, i + 1);
		y += 3;
		x += 7;
	}
}

/* Set the PANEL_DATA structures for individual panels */
void set_user_ptrs(PANEL **panels, int n)
{	PANEL_DATA *ptrs;
	WINDOW *win;
	int x, y, w, h, i;
	char temp[80];
	
	ptrs = (PANEL_DATA *)calloc(n, sizeof(PANEL_DATA));

	for(i = 0;i < n; ++i)
	{	win = panel_window(panels[i]);
		getbegyx(win, y, x);
		getmaxyx(win, h, w);
		ptrs[i].x = x;
		ptrs[i].y = y;
		ptrs[i].w = w;
		ptrs[i].h = h;
		sprintf(temp, "Window Number %d", i + 1);
		strcpy(ptrs[i].label, temp);
		ptrs[i].label_color = i + 1;
		if(i + 1 == n)
			ptrs[i].next = panels[0];
		else
			ptrs[i].next = panels[i + 1];
		set_panel_userptr(panels[i], &ptrs[i]);
	}
}

/* Show the window with a border and a label */
void win_show(WINDOW *win, char *label, int label_color)
{	int startx, starty, height, width;

	getbegyx(win, starty, startx);
	getmaxyx(win, height, width);

	box(win, 0, 0);
	mvwaddch(win, 2, 0, ACS_LTEE); 
	mvwhline(win, 2, 1, ACS_HLINE, width - 2); 
	mvwaddch(win, 2, width - 1, ACS_RTEE); 
	
	print_in_middle(win, 1, 0, width, label, COLOR_PAIR(label_color));
}

void print_in_middle(WINDOW *win, int starty, int startx, int width, char *string, chtype color)
{	int length, x, y;
	float temp;

	if(win == NULL)
		win = stdscr;
	getyx(win, y, x);
	if(startx != 0)
		x = startx;
	if(starty != 0)
		y = starty;
	if(width == 0)
		width = 80;

	length = strlen(string);
	temp = (width - length)/ 2;
	x = startx + (int)temp;
	wattron(win, color);
	mvwprintw(win, y, x, "%s", string);
	wattroff(win, color);
	refresh();
}

Concentrate on the main while loop. Once it finds out the type of key pressed, it takes appropriate action. If 'r' is pressed resizing mode is started. After this the new sizes are updated as the user presses the arrow keys. When the user presses <ENTER> present selection ends and panel is resized by using the concept explained. While in resizing mode the program doesn't show how the window is getting resized. It's left as an exercise to the reader to print a dotted border while it gets resized to a new position.

When the user presses 'm' the move mode starts. This is a bit simpler than resizing. As the arrow keys are pressed the new position is updated and pressing of <ENTER> causes the panel to be moved by calling the function move_panel().

In this program the user data which is represented as PANEL_DATA, plays very important role in finding the associated information with a panel. As written in the comments, the PANEL_DATA stores the panel sizes, label, label color and a pointer to the next panel in the cycle.


16.6. Hiding and Showing Panels

A Panel can be hidden by using the function hide_panel(). This function merely removes it form the stack of panels, thus hiding it on the screen once you do update_panels() and doupdate(). It doesn't destroy the PANEL structure associated with the hidden panel. It can be shown again by using the show_panel() function.

The following program shows the hiding of panels. Press 'a' or 'b' or 'c' to show or hide first, second and third windows respectively. It uses a user data with a small variable hide, which keeps track of whether the window is hidden or not. For some reason the function panel_hidden() which tells whether a panel is hidden or not is not working. A bug report was also presented by Michael Andres here

Example 17. Panel Hiding and Showing example

#include <panel.h>

typedef struct _PANEL_DATA {
	int hide;	/* TRUE if panel is hidden */
}PANEL_DATA;

#define NLINES 10
#define NCOLS 40

void init_wins(WINDOW **wins, int n);
void win_show(WINDOW *win, char *label, int label_color);
void print_in_middle(WINDOW *win, int starty, int startx, int width, char *string, chtype color);

int main()
{	WINDOW *my_wins[3];
	PANEL  *my_panels[3];
	PANEL_DATA panel_datas[3];
	PANEL_DATA *temp;
	int ch;

	/* Initialize curses */
	initscr();
	start_color();
	cbreak();
	noecho();
	keypad(stdscr, TRUE);

	/* Initialize all the colors */
	init_pair(1, COLOR_RED, COLOR_BLACK);
	init_pair(2, COLOR_GREEN, COLOR_BLACK);
	init_pair(3, COLOR_BLUE, COLOR_BLACK);
	init_pair(4, COLOR_CYAN, COLOR_BLACK);

	init_wins(my_wins, 3);
	
	/* Attach a panel to each window */ 	/* Order is bottom up */
	my_panels[0] = new_panel(my_wins[0]); 	/* Push 0, order: stdscr-0 */
	my_panels[1] = new_panel(my_wins[1]); 	/* Push 1, order: stdscr-0-1 */
	my_panels[2] = new_panel(my_wins[2]); 	/* Push 2, order: stdscr-0-1-2 */

	/* Initialize panel datas saying that nothing is hidden */
	panel_datas[0].hide = FALSE;
	panel_datas[1].hide = FALSE;
	panel_datas[2].hide = FALSE;

	set_panel_userptr(my_panels[0], &panel_datas[0]);
	set_panel_userptr(my_panels[1], &panel_datas[1]);
	set_panel_userptr(my_panels[2], &panel_datas[2]);

	/* Update the stacking order. 2nd panel will be on top */
	update_panels();

	/* Show it on the screen */
	attron(COLOR_PAIR(4));
	mvprintw(LINES - 3, 0, "Show or Hide a window with 'a'(first window)  'b'(Second Window)  'c'(Third Window)");
	mvprintw(LINES - 2, 0, "F1 to Exit");

	attroff(COLOR_PAIR(4));
	doupdate();
	
	while((ch = getch()) != KEY_F(1))
	{	switch(ch)
		{	case 'a':			
				temp = (PANEL_DATA *)panel_userptr(my_panels[0]);
				if(temp->hide == FALSE)
				{	hide_panel(my_panels[0]);
					temp->hide = TRUE;
				}
				else
				{	show_panel(my_panels[0]);
					temp->hide = FALSE;
				}
				break;
			case 'b':
				temp = (PANEL_DATA *)panel_userptr(my_panels[1]);
				if(temp->hide == FALSE)
				{	hide_panel(my_panels[1]);
					temp->hide = TRUE;
				}
				else
				{	show_panel(my_panels[1]);
					temp->hide = FALSE;
				}
				break;
			case 'c':
				temp = (PANEL_DATA *)panel_userptr(my_panels[2]);
				if(temp->hide == FALSE)
				{	hide_panel(my_panels[2]);
					temp->hide = TRUE;
				}
				else
				{	show_panel(my_panels[2]);
					temp->hide = FALSE;
				}
				break;
		}
		update_panels();
		doupdate();
	}
	endwin();
	return 0;
}

/* Put all the windows */
void init_wins(WINDOW **wins, int n)
{	int x, y, i;
	char label[80];

	y = 2;
	x = 10;
	for(i = 0; i < n; ++i)
	{	wins[i] = newwin(NLINES, NCOLS, y, x);
		sprintf(label, "Window Number %d", i + 1);
		win_show(wins[i], label, i + 1);
		y += 3;
		x += 7;
	}
}

/* Show the window with a border and a label */
void win_show(WINDOW *win, char *label, int label_color)
{	int startx, starty, height, width;

	getbegyx(win, starty, startx);
	getmaxyx(win, height, width);

	box(win, 0, 0);
	mvwaddch(win, 2, 0, ACS_LTEE); 
	mvwhline(win, 2, 1, ACS_HLINE, width - 2); 
	mvwaddch(win, 2, width - 1, ACS_RTEE); 
	
	print_in_middle(win, 1, 0, width, label, COLOR_PAIR(label_color));
}

void print_in_middle(WINDOW *win, int starty, int startx, int width, char *string, chtype color)
{	int length, x, y;
	float temp;

	if(win == NULL)
		win = stdscr;
	getyx(win, y, x);
	if(startx != 0)
		x = startx;
	if(starty != 0)
		y = starty;
	if(width == 0)
		width = 80;

	length = strlen(string);
	temp = (width - length)/ 2;
	x = startx + (int)temp;
	wattron(win, color);
	mvwprintw(win, y, x, "%s", string);
	wattroff(win, color);
	refresh();
}

17. Menus Library

The menus library provides a nice extension to basic curses, through which you can create menus. It provides a set of functions to create menus. But they have to be customized to give a nicer look, with colors etc. Let's get into the details.

A menu is a screen display that assists the user to choose some subset of a given set of items. To put it simple, a menu is a collection of items from which one or more items can be chosen. Some readers might not be aware of multiple item selection capability. Menu library provides functionality to write menus from which the user can chose more than one item as the preferred choice. This is dealt with in a later section. Now it is time for some rudiments.


17.2. Compiling With the Menu Library

To use menu library functions, you have to include menu.h and to link the program with menu library the flag -lmenu should be added along with -lncurses in that order.

    #include <menu.h>
    .
    .
    .

    compile and link: gcc <program file> -lmenu -lncurses

This program demonstrates the basic concepts involved in creating a menu using menus library. First we create the items using new_item() and then attach them to the menu with new_menu() function. After posting the menu and refreshing the screen, the main processing loop starts. It reads user input and takes corresponding action. The function menu_driver() is the main work horse of the menu system. The second parameter to this function tells what's to be done with the menu. According to the parameter, menu_driver() does the corresponding task. The value can be either a menu navigational request, an ascii character, or a KEY_MOUSE special key associated with a mouse event.

The menu_driver accepts following navigational requests.

     REQ_LEFT_ITEM         Move left to an item.
     REQ_RIGHT_ITEM      Move right to an item.
     REQ_UP_ITEM         Move up to an item.
     REQ_DOWN_ITEM       Move down to an item.
     REQ_SCR_ULINE       Scroll up a line.
     REQ_SCR_DLINE          Scroll down a line.
     REQ_SCR_DPAGE          Scroll down a page.
     REQ_SCR_UPAGE         Scroll up a page.
     REQ_FIRST_ITEM     Move to the first item.
     REQ_LAST_ITEM         Move to the last item.
     REQ_NEXT_ITEM         Move to the next item.
     REQ_PREV_ITEM         Move to the previous item. 
     REQ_TOGGLE_ITEM     Select/deselect an item.
     REQ_CLEAR_PATTERN     Clear the menu pattern buffer.
     REQ_BACK_PATTERN      Delete the previous character from the pattern buffer.
     REQ_NEXT_MATCH     Move to the next item matching the pattern match.
     REQ_PREV_MATCH     Move to the previous item matching the pattern match.

Don't get overwhelmed by the number of options. We will see them slowly one after another. The options of interest in this example are REQ_UP_ITEM and REQ_DOWN_ITEM. These two options when passed to menu_driver, menu driver updates the current item to one item up or down respectively.