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.


17.3. Menu Driver: The work horse of the menu system

As you have seen in the above example, menu_driver plays an important role in updating the menu. It is very important to understand various options it takes and what they do. As explained above, the second parameter to menu_driver() can be either a navigational request, a printable character or a KEY_MOUSE key. Let's dissect the different navigational requests.

Each of the above requests will be explained in the following lines with several examples whenever appropriate.


17.4. Menu Windows

Every menu created is associated with a window and a sub window. The menu window displays any title or border associated with the menu. The menu sub window displays the menu items currently available for selection. But we didn't specify any window or sub window in the simple example. When a window is not specified, stdscr is taken as the main window, and then menu system calculates the sub window size required for the display of items. Then items are displayed in the calculated sub window. So let's play with these windows and display a menu with a border and a title.

Example 19. Menu Windows Usage example

#include <menu.h>

#define ARRAY_SIZE(a) (sizeof(a) / sizeof(a[0]))
#define CTRLD 	4

char *choices[] = {
                        "Choice 1",
                        "Choice 2",
                        "Choice 3",
                        "Choice 4",
                        "Exit",
                        (char *)NULL,
                  };
void print_in_middle(WINDOW *win, int starty, int startx, int width, char *string, chtype color);

int main()
{	ITEM **my_items;
	int c;				
	MENU *my_menu;
        WINDOW *my_menu_win;
        int n_choices, i;
	
	/* Initialize curses */
	initscr();
	start_color();
        cbreak();
        noecho();
	keypad(stdscr, TRUE);
	init_pair(1, COLOR_RED, COLOR_BLACK);

	/* Create items */
        n_choices = ARRAY_SIZE(choices);
        my_items = (ITEM **)calloc(n_choices, sizeof(ITEM *));
        for(i = 0; i < n_choices; ++i)
                my_items[i] = new_item(choices[i], choices[i]);

	/* Crate menu */
	my_menu = new_menu((ITEM **)my_items);

	/* Create the window to be associated with the menu */
        my_menu_win = newwin(10, 40, 4, 4);
        keypad(my_menu_win, TRUE);
     
	/* Set main window and sub window */
        set_menu_win(my_menu, my_menu_win);
        set_menu_sub(my_menu, derwin(my_menu_win, 6, 38, 3, 1));

	/* Set menu mark to the string " * " */
        set_menu_mark(my_menu, " * ");

	/* Print a border around the main window and print a title */
        box(my_menu_win, 0, 0);
	print_in_middle(my_menu_win, 1, 0, 40, "My Menu", COLOR_PAIR(1));
	mvwaddch(my_menu_win, 2, 0, ACS_LTEE);
	mvwhline(my_menu_win, 2, 1, ACS_HLINE, 38);
	mvwaddch(my_menu_win, 2, 39, ACS_RTEE);
	mvprintw(LINES - 2, 0, "F1 to exit");
	refresh();
        
	/* Post the menu */
	post_menu(my_menu);
	wrefresh(my_menu_win);

	while((c = wgetch(my_menu_win)) != KEY_F(1))
	{       switch(c)
	        {	case KEY_DOWN:
				menu_driver(my_menu, REQ_DOWN_ITEM);
				break;
			case KEY_UP:
				menu_driver(my_menu, REQ_UP_ITEM);
				break;
		}
                wrefresh(my_menu_win);
	}	

	/* Unpost and free all the memory taken up */
        unpost_menu(my_menu);
        free_menu(my_menu);
        for(i = 0; i < n_choices; ++i)
                free_item(my_items[i]);
	endwin();
}

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();
}

This example creates a menu with a title, border, a fancy line separating title and the items. As you can see, in order to attach a window to a menu the function set_menu_win() has to be used. Then we attach the sub window also. This displays the items in the sub window. You can also set the mark string which gets displayed to the left of the selected item with set_menu_mark().


17.5. Scrolling Menus

If the sub window given for a window is not big enough to show all the items, then the menu will be scrollable. When you are on the last item in the present list, if you send REQ_DOWN_ITEM, it gets translated into REQ_SCR_DLINE and the menu scrolls by one item. You can manually give REQ_SCR_ operations to do scrolling. Let's see how it can be done.

Example 20. Scrolling Menus example

#include <curses.h>
#include <menu.h>

#define ARRAY_SIZE(a) (sizeof(a) / sizeof(a[0]))
#define CTRLD 	4

char *choices[] = {
                        "Choice 1",
                        "Choice 2",
                        "Choice 3",
                        "Choice 4",
			"Choice 5",
			"Choice 6",
			"Choice 7",
			"Choice 8",
			"Choice 9",
			"Choice 10",
                        "Exit",
                        (char *)NULL,
                  };
void print_in_middle(WINDOW *win, int starty, int startx, int width, char *string, chtype color);

int main()
{	ITEM **my_items;
	int c;				
	MENU *my_menu;
        WINDOW *my_menu_win;
        int n_choices, i;
	
	/* Initialize curses */
	initscr();
	start_color();
        cbreak();
        noecho();
	keypad(stdscr, TRUE);
	init_pair(1, COLOR_RED, COLOR_BLACK);
	init_pair(2, COLOR_CYAN, COLOR_BLACK);

	/* Create items */
        n_choices = ARRAY_SIZE(choices);
        my_items = (ITEM **)calloc(n_choices, sizeof(ITEM *));
        for(i = 0; i < n_choices; ++i)
                my_items[i] = new_item(choices[i], choices[i]);

	/* Crate menu */
	my_menu = new_menu((ITEM **)my_items);

	/* Create the window to be associated with the menu */
        my_menu_win = newwin(10, 40, 4, 4);
        keypad(my_menu_win, TRUE);
     
	/* Set main window and sub window */
        set_menu_win(my_menu, my_menu_win);
        set_menu_sub(my_menu, derwin(my_menu_win, 6, 38, 3, 1));
	set_menu_format(my_menu, 5, 1);
			
	/* Set menu mark to the string " * " */
        set_menu_mark(my_menu, " * ");

	/* Print a border around the main window and print a title */
        box(my_menu_win, 0, 0);
	print_in_middle(my_menu_win, 1, 0, 40, "My Menu", COLOR_PAIR(1));
	mvwaddch(my_menu_win, 2, 0, ACS_LTEE);
	mvwhline(my_menu_win, 2, 1, ACS_HLINE, 38);
	mvwaddch(my_menu_win, 2, 39, ACS_RTEE);
        
	/* Post the menu */
	post_menu(my_menu);
	wrefresh(my_menu_win);
	
	attron(COLOR_PAIR(2));
	mvprintw(LINES - 2, 0, "Use PageUp and PageDown to scoll down or up a page of items");
	mvprintw(LINES - 1, 0, "Arrow Keys to navigate (F1 to Exit)");
	attroff(COLOR_PAIR(2));
	refresh();

	while((c = wgetch(my_menu_win)) != KEY_F(1))
	{       switch(c)
	        {	case KEY_DOWN:
				menu_driver(my_menu, REQ_DOWN_ITEM);
				break;
			case KEY_UP:
				menu_driver(my_menu, REQ_UP_ITEM);
				break;
			case KEY_NPAGE:
				menu_driver(my_menu, REQ_SCR_DPAGE);
				break;
			case KEY_PPAGE:
				menu_driver(my_menu, REQ_SCR_UPAGE);
				break;
		}
                wrefresh(my_menu_win);
	}	

	/* Unpost and free all the memory taken up */
        unpost_menu(my_menu);
        free_menu(my_menu);
        for(i = 0; i < n_choices; ++i)
                free_item(my_items[i]);
	endwin();
}

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();
}

This program is self-explanatory. In this example the number of choices has been increased to ten, which is larger than our sub window size which can hold 6 items. This message has to be explicitly conveyed to the menu system with the function set_menu_format(). In here we specify the number of rows and columns we want to be displayed for a single page. We can specify any number of items to be shown, in the rows variables, if it is less than the height of the sub window. If the key pressed by the user is a PAGE UP or PAGE DOWN, the menu is scrolled a page due to the requests (REQ_SCR_DPAGE and REQ_SCR_UPAGE) given to menu_driver().


17.6. Multi Columnar Menus

In the above example you have seen how to use the function set_menu_format(). I didn't mention what the cols variable (third parameter) does. Well, If your sub window is wide enough, you can opt to display more than one item per row. This can be specified in the cols variable. To make things simpler, the following example doesn't show descriptions for the items.

Example 21. Milt Columnar Menus Example

#include <curses.h>
#include <menu.h>

#define ARRAY_SIZE(a) (sizeof(a) / sizeof(a[0]))
#define CTRLD 	4

char *choices[] = {
                        "Choice 1", "Choice 2", "Choice 3", "Choice 4", "Choice 5",
			"Choice 6", "Choice 7", "Choice 8", "Choice 9", "Choice 10",
			"Choice 11", "Choice 12", "Choice 13", "Choice 14", "Choice 15",
			"Choice 16", "Choice 17", "Choice 18", "Choice 19", "Choice 20",
                        "Exit",
                        (char *)NULL,
                  };

int main()
{	ITEM **my_items;
	int c;				
	MENU *my_menu;
        WINDOW *my_menu_win;
        int n_choices, i;
	
	/* Initialize curses */
	initscr();
	start_color();
        cbreak();
        noecho();
	keypad(stdscr, TRUE);
	init_pair(1, COLOR_RED, COLOR_BLACK);
	init_pair(2, COLOR_CYAN, COLOR_BLACK);

	/* Create items */
        n_choices = ARRAY_SIZE(choices);
        my_items = (ITEM **)calloc(n_choices, sizeof(ITEM *));
        for(i = 0; i < n_choices; ++i)
                my_items[i] = new_item(choices[i], choices[i]);

	/* Crate menu */
	my_menu = new_menu((ITEM **)my_items);

	/* Set menu option not to show the description */
	menu_opts_off(my_menu, O_SHOWDESC);

	/* Create the window to be associated with the menu */
        my_menu_win = newwin(10, 70, 4, 4);
        keypad(my_menu_win, TRUE);
     
	/* Set main window and sub window */
        set_menu_win(my_menu, my_menu_win);
        set_menu_sub(my_menu, derwin(my_menu_win, 6, 68, 3, 1));
	set_menu_format(my_menu, 5, 3);
	set_menu_mark(my_menu, " * ");

	/* Print a border around the main window and print a title */
        box(my_menu_win, 0, 0);
	
	attron(COLOR_PAIR(2));
	mvprintw(LINES - 3, 0, "Use PageUp and PageDown to scroll");
	mvprintw(LINES - 2, 0, "Use Arrow Keys to navigate (F1 to Exit)");
	attroff(COLOR_PAIR(2));
	refresh();

	/* Post the menu */
	post_menu(my_menu);
	wrefresh(my_menu_win);
	
	while((c = wgetch(my_menu_win)) != KEY_F(1))
	{       switch(c)
	        {	case KEY_DOWN:
				menu_driver(my_menu, REQ_DOWN_ITEM);
				break;
			case KEY_UP:
				menu_driver(my_menu, REQ_UP_ITEM);
				break;
			case KEY_LEFT:
				menu_driver(my_menu, REQ_LEFT_ITEM);
				break;
			case KEY_RIGHT:
				menu_driver(my_menu, REQ_RIGHT_ITEM);
				break;
			case KEY_NPAGE:
				menu_driver(my_menu, REQ_SCR_DPAGE);
				break;
			case KEY_PPAGE:
				menu_driver(my_menu, REQ_SCR_UPAGE);
				break;
		}
                wrefresh(my_menu_win);
	}	

	/* Unpost and free all the memory taken up */
        unpost_menu(my_menu);
        free_menu(my_menu);
        for(i = 0; i < n_choices; ++i)
                free_item(my_items[i]);
	endwin();
}

Watch the function call to set_menu_format(). It specifies the number of columns to be 3, thus displaying 3 items per row. We have also switched off the showing descriptions with the function menu_opts_off(). There are couple of functions set_menu_opts(), menu_opts_on() and menu_opts() which can be used to manipulate menu options. The following menu options can be specified.

       O_ONEVALUE
            Only one item can be selected for this menu.

       O_SHOWDESC
            Display  the  item  descriptions  when  the  menu  is
            posted.

       O_ROWMAJOR
            Display the menu in row-major order.

       O_IGNORECASE
            Ignore the case when pattern-matching.

       O_SHOWMATCH
            Move the cursor to within the item  name  while  pat­
            tern-matching.

       O_NONCYCLIC
            Don't   wrap   around  next-item  and  previous-item,
            requests to the other end of the menu.

All options are on by default. You can switch specific attributes on or off with menu_opts_on() and menu_opts_off() functions. You can also use set_menu_opts() to directly specify the options. The argument to this function should be a OR ed value of some of those above constants. The function menu_opts() can be used to find out a menu's present options.


17.7. Multi Valued Menus

You might be wondering what if you switch off the option O_ONEVALUE. Then the menu becomes multi-valued. That means you can select more than one item. This brings us to the request REQ_TOGGLE_ITEM. Let's see it in action.

Example 22. Multi Valued Menus example

#include <curses.h>
#include <menu.h>

#define ARRAY_SIZE(a) (sizeof(a) / sizeof(a[0]))
#define CTRLD 	4

char *choices[] = {
                        "Choice 1",
                        "Choice 2",
                        "Choice 3",
                        "Choice 4",
			"Choice 5",
			"Choice 6",
			"Choice 7",
                        "Exit",
                  };

int main()
{	ITEM **my_items;
	int c;				
	MENU *my_menu;
        int n_choices, i;
	ITEM *cur_item;
	
	/* Initialize curses */	
	initscr();
        cbreak();
        noecho();
	keypad(stdscr, TRUE);

	/* Initialize items */
        n_choices = ARRAY_SIZE(choices);
        my_items = (ITEM **)calloc(n_choices + 1, sizeof(ITEM *));
        for(i = 0; i < n_choices; ++i)
                my_items[i] = new_item(choices[i], choices[i]);
	my_items[n_choices] = (ITEM *)NULL;

	my_menu = new_menu((ITEM **)my_items);

	/* Make the menu multi valued */
	menu_opts_off(my_menu, O_ONEVALUE);

	mvprintw(LINES - 3, 0, "Use <SPACE> to select or unselect an item.");
	mvprintw(LINES - 2, 0, "<ENTER> to see presently selected items(F1 to Exit)");
	post_menu(my_menu);
	refresh();

	while((c = getch()) != KEY_F(1))
	{       switch(c)
	        {	case KEY_DOWN:
				menu_driver(my_menu, REQ_DOWN_ITEM);
				break;
			case KEY_UP:
				menu_driver(my_menu, REQ_UP_ITEM);
				break;
			case ' ':
				menu_driver(my_menu, REQ_TOGGLE_ITEM);
				break;
			case 10:	/* Enter */
			{	char temp[200];
				ITEM **items;

				items = menu_items(my_menu);
				temp[0] = '\0';
				for(i = 0; i < item_count(my_menu); ++i)
					if(item_value(items[i]) == TRUE)
					{	strcat(temp, item_name(items[i]));
						strcat(temp, " ");
					}
				move(20, 0);
				clrtoeol();
				mvprintw(20, 0, temp);
				refresh();
			}
			break;
		}
	}	

	free_item(my_items[0]);
        free_item(my_items[1]);
	free_menu(my_menu);
	endwin();
}
	

Whew, A lot of new functions. Let's take them one after another. Firstly, the REQ_TOGGLE_ITEM. In a multi-valued menu, the user should be allowed to select or un select more than one item. The request REQ_TOGGLE_ITEM toggles the present selection. In this case when space is pressed REQ_TOGGLE_ITEM request is sent to menu_driver to achieve the result.

Now when the user presses <ENTER> we show the items he presently selected. First we find out the items associated with the menu using the function menu_items(). Then we loop through the items to find out if the item is selected or not. The function item_value() returns TRUE if an item is selected. The function item_count() returns the number of items in the menu. The item name can be found with item_name(). You can also find the description associated with an item using item_description().


17.8. Menu Options

Well, by this time you must be itching for some difference in your menu, with lots of functionality. I know. You want Colors !!!. You want to create nice menus similar to those text mode dos games. The functions set_menu_fore() and set_menu_back() can be used to change the attribute of the selected item and unselected item. The names are misleading. They don't change menu's foreground or background which would have been useless.

The function set_menu_grey() can be used to set the display attribute for the non-selectable items in the menu. This brings us to the interesting option for an item the one and only O_SELECTABLE. We can turn it off by the function item_opts_off() and after that that item is not selectable. It's like a grayed item in those fancy windows menus. Let's put these concepts in practice with this example

Example 23. Menu Options example

#include <menu.h>

#define ARRAY_SIZE(a) (sizeof(a) / sizeof(a[0]))
#define CTRLD 	4

char *choices[] = {
                        "Choice 1",
                        "Choice 2",
                        "Choice 3",
                        "Choice 4",
			"Choice 5",
			"Choice 6",
			"Choice 7",
                        "Exit",
                  };

int main()
{	ITEM **my_items;
	int c;				
	MENU *my_menu;
        int n_choices, i;
	ITEM *cur_item;
	
	/* Initialize curses */	
	initscr();
	start_color();
        cbreak();
        noecho();
	keypad(stdscr, TRUE);
	init_pair(1, COLOR_RED, COLOR_BLACK);
	init_pair(2, COLOR_GREEN, COLOR_BLACK);
	init_pair(3, COLOR_MAGENTA, COLOR_BLACK);

	/* Initialize items */
        n_choices = ARRAY_SIZE(choices);
        my_items = (ITEM **)calloc(n_choices + 1, sizeof(ITEM *));
        for(i = 0; i < n_choices; ++i)
                my_items[i] = new_item(choices[i], choices[i]);
	my_items[n_choices] = (ITEM *)NULL;
	item_opts_off(my_items[3], O_SELECTABLE);
	item_opts_off(my_items[6], O_SELECTABLE);

	/* Create menu */
	my_menu = new_menu((ITEM **)my_items);

	/* Set fore ground and back ground of the menu */
	set_menu_fore(my_menu, COLOR_PAIR(1) | A_REVERSE);
	set_menu_back(my_menu, COLOR_PAIR(2));
	set_menu_grey(my_menu, COLOR_PAIR(3));

	/* Post the menu */
	mvprintw(LINES - 3, 0, "Press <ENTER> to see the option selected");
	mvprintw(LINES - 2, 0, "Up and Down arrow keys to naviage (F1 to Exit)");
	post_menu(my_menu);
	refresh();

	while((c = getch()) != KEY_F(1))
	{       switch(c)
	        {	case KEY_DOWN:
				menu_driver(my_menu, REQ_DOWN_ITEM);
				break;
			case KEY_UP:
				menu_driver(my_menu, REQ_UP_ITEM);
				break;
			case 10: /* Enter */
				move(20, 0);
				clrtoeol();
				mvprintw(20, 0, "Item selected is : %s", 
						item_name(current_item(my_menu)));
				pos_menu_cursor(my_menu);
				break;
		}
	}	
	unpost_menu(my_menu);
	for(i = 0; i < n_choices; ++i)
		free_item(my_items[i]);
	free_menu(my_menu);
	endwin();
}
	

17.9. The useful User Pointer

We can associate a user pointer with each item in the menu. It works the same way as user pointer in panels. It's not touched by menu system. You can store any thing you like in that. I usually use it to store the function to be executed when the menu option is chosen (It's selected and may be the user pressed <ENTER>);

Example 24. Menu User Pointer Usage

#include <curses.h>
#include <menu.h>

#define ARRAY_SIZE(a) (sizeof(a) / sizeof(a[0]))
#define CTRLD 	4

char *choices[] = {
                        "Choice 1",
                        "Choice 2",
                        "Choice 3",
                        "Choice 4",
			"Choice 5",
			"Choice 6",
			"Choice 7",
                        "Exit",
                  };
void func(char *name);

int main()
{	ITEM **my_items;
	int c;				
	MENU *my_menu;
        int n_choices, i;
	ITEM *cur_item;
	
	/* Initialize curses */	
	initscr();
	start_color();
        cbreak();
        noecho();
	keypad(stdscr, TRUE);
	init_pair(1, COLOR_RED, COLOR_BLACK);
	init_pair(2, COLOR_GREEN, COLOR_BLACK);
	init_pair(3, COLOR_MAGENTA, COLOR_BLACK);

	/* Initialize items */
        n_choices = ARRAY_SIZE(choices);
        my_items = (ITEM **)calloc(n_choices + 1, sizeof(ITEM *));
        for(i = 0; i < n_choices; ++i)
	{       my_items[i] = new_item(choices[i], choices[i]);
		/* Set the user pointer */
		set_item_userptr(my_items[i], func);
	}
	my_items[n_choices] = (ITEM *)NULL;

	/* Create menu */
	my_menu = new_menu((ITEM **)my_items);

	/* Post the menu */
	mvprintw(LINES - 3, 0, "Press <ENTER> to see the option selected");
	mvprintw(LINES - 2, 0, "Up and Down arrow keys to naviage (F1 to Exit)");
	post_menu(my_menu);
	refresh();

	while((c = getch()) != KEY_F(1))
	{       switch(c)
	        {	case KEY_DOWN:
				menu_driver(my_menu, REQ_DOWN_ITEM);
				break;
			case KEY_UP:
				menu_driver(my_menu, REQ_UP_ITEM);
				break;
			case 10: /* Enter */
			{	ITEM *cur;
				void (*p)(char *);

				cur = current_item(my_menu);
				p = item_userptr(cur);
				p((char *)item_name(cur));
				pos_menu_cursor(my_menu);
				break;
			}
			break;
		}
	}	
	unpost_menu(my_menu);
	for(i = 0; i < n_choices; ++i)
		free_item(my_items[i]);
	free_menu(my_menu);
	endwin();
}

void func(char *name)
{	move(20, 0);
	clrtoeol();
	mvprintw(20, 0, "Item selected is : %s", name);
}	

18. Forms Library

Well. If you have seen those forms on web pages which take input from users and do various kinds of things, you might be wondering how would any one create such forms in text mode display. It's quite difficult to write those nifty forms in plain ncurses. Forms library tries to provide a basic frame work to build and maintain forms with ease. It has lot of features(functions) which manage validation, dynamic expansion of fields etc.. Let's see it in full flow.

A form is a collection of fields; each field can be either a label(static text) or a data-entry location. The forms also library provides functions to divide forms into multiple pages.


18.2. Compiling With the Forms Library

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

    #include <form.h>
    .
    .
    .

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

Above example is pretty straight forward. It creates two fields with new_field(). new_field() takes height, width, starty, startx, number of offscreen rows and number of additional working buffers. The fifth argument number of offscreen rows specifies how much of the field to be shown. If it is zero, the entire field is always displayed otherwise the form will be scrollable when the user accesses not displayed parts of the field. The forms library allocates one buffer per field to store the data user enters. Using the last parameter to new_field() we can specify it to allocate some additional buffers. These can be used for any purpose you like.

After creating the fields, back ground attribute of both of them is set to an underscore with set_field_back(). The AUTOSKIP option is turned off using field_opts_off(). If this option is turned on, focus will move to the next field in the form once the active field is filled up completely.

After attaching the fields to the form, it is posted. Here on, user inputs are processed in the while loop, by making corresponding requests to form_driver. The details of all the requests to the form_driver() are explained later.


18.3. Playing with Fields

Each form field is associated with a lot of attributes. They can be manipulated to get the required effect and to have fun !!!. So why wait?


18.3.1. Fetching Size and Location of Field

The parameters we have given at the time of creation of a field can be retrieved with field_info(). It returns height, width, starty, startx, number of offscreen rows, and number of additional buffers into the parameters given to it. It is a sort of inverse of new_field().

int field_info(     FIELD *field,              /* field from which to fetch */
                    int *height, *int width,   /* field size */ 
                    int *top, int *left,       /* upper left corner */
                    int *offscreen,            /* number of offscreen rows */
                    int *nbuf);                /* number of working buffers */

18.3.4. Field Display Attributes

As you have seen, in the above example, display attribute for the fields can be set with set_field_fore() and setfield_back(). These functions set foreground and background attribute of the fields. You can also specify a pad character which will be filled in the unfilled portion of the field. The pad character is set with a call to set_field_pad(). Default pad value is a space. The functions field_fore(), field_back, field_pad() can be used to query the present foreground, background attributes and pad character for the field. The following list gives the usage of functions.


int set_field_fore(FIELD *field,        /* field to alter */
                   chtype attr);        /* attribute to set */ 

chtype field_fore(FIELD *field);        /* field to query */
                                        /* returns foreground attribute */

int set_field_back(FIELD *field,        /* field to alter */
                   chtype attr);        /* attribute to set */ 

chtype field_back(FIELD *field);        /* field to query */
                                        /* returns background attribute */

int set_field_pad(FIELD *field,         /* field to alter */
                  int pad);             /* pad character to set */ 

chtype field_pad(FIELD *field);         /* field to query */  
                                        /* returns present pad character */

Though above functions seem quite simple, using colors with set_field_fore() may be frustrating in the beginning. Let me first explain about foreground and background attributes of a field. The foreground attribute is associated with the character. That means a character in the field is printed with the attribute you have set with set_field_fore(). Background attribute is the attribute used to fill background of field, whether any character is there or not. So what about colors? Since colors are always defined in pairs, what is the right way to display colored fields? Here's an example clarifying color attributes.

Example 26. Form Attributes example

#include <form.h>

int main()
{	FIELD *field[3];
	FORM  *my_form;
	int ch;
	
	/* Initialize curses */
	initscr();
	start_color();
	cbreak();
	noecho();
	keypad(stdscr, TRUE);

	/* Initialize few color pairs */
	init_pair(1, COLOR_WHITE, COLOR_BLUE);
	init_pair(2, COLOR_WHITE, COLOR_BLUE);

	/* Initialize the fields */
	field[0] = new_field(1, 10, 4, 18, 0, 0);
	field[1] = new_field(1, 10, 6, 18, 0, 0);
	field[2] = NULL;

	/* Set field options */
	set_field_fore(field[0], COLOR_PAIR(1));/* Put the field with blue background */
	set_field_back(field[0], COLOR_PAIR(2));/* and white foreground (characters */
						/* are printed in white 	*/
	field_opts_off(field[0], O_AUTOSKIP);  	/* Don't go to next field when this */
						/* Field is filled up 		*/
	set_field_back(field[1], A_UNDERLINE); 
	field_opts_off(field[1], O_AUTOSKIP);

	/* Create the form and post it */
	my_form = new_form(field);
	post_form(my_form);
	refresh();
	
	set_current_field(my_form, field[0]); /* Set focus to the colored field */
	mvprintw(4, 10, "Value 1:");
	mvprintw(6, 10, "Value 2:");
	mvprintw(LINES - 2, 0, "Use UP, DOWN arrow keys to switch between fields");
	refresh();

	/* Loop through to get user requests */
	while((ch = getch()) != KEY_F(1))
	{	switch(ch)
		{	case KEY_DOWN:
				/* Go to next field */
				form_driver(my_form, REQ_NEXT_FIELD);
				/* Go to the end of the present buffer */
				/* Leaves nicely at the last character */
				form_driver(my_form, REQ_END_LINE);
				break;
			case KEY_UP:
				/* Go to previous field */
				form_driver(my_form, REQ_PREV_FIELD);
				form_driver(my_form, REQ_END_LINE);
				break;
			default:
				/* If this is a normal character, it gets */
				/* Printed				  */	
				form_driver(my_form, ch);
				break;
		}
	}

	/* Un post form and free the memory */
	unpost_form(my_form);
	free_form(my_form);
	free_field(field[0]);
	free_field(field[1]); 

	endwin();
	return 0;
}

Play with the color pairs and try to understand the foreground and background attributes. In my programs using color attributes, I usually set only the background with set_field_back(). Curses simply doesn't allow defining individual color attributes.


18.3.5. Field Option Bits

There is also a large collection of field option bits you can set to control various aspects of forms processing. You can manipulate them with these functions:

int set_field_opts(FIELD *field,          /* field to alter */
                   int attr);             /* attribute to set */ 

int field_opts_on(FIELD *field,           /* field to alter */
                  int attr);              /* attributes to turn on */ 

int field_opts_off(FIELD *field,          /* field to alter */
                  int attr);              /* attributes to turn off */ 

int field_opts(FIELD *field);             /* field to query */ 

The function set_field_opts() can be used to directly set attributes of a field or you can choose to switch a few attributes on and off with field_opts_on() and field_opts_off() selectively. Anytime you can query the attributes of a field with field_opts(). The following is the list of available options. By default, all options are on.

O_VISIBLE

Controls whether the field is visible on the screen. Can be used during form processing to hide or pop up fields depending on the value of parent fields.

O_ACTIVE

Controls whether the field is active during forms processing (i.e. visited by form navigation keys). Can be used to make labels or derived fields with buffer values alterable by the forms application, not the user.

O_PUBLIC

Controls whether data is displayed during field entry. If this option is turned off on a field, the library will accept and edit data in that field, but it will not be displayed and the visible field cursor will not move. You can turn off the O_PUBLIC bit to define password fields.

O_EDIT

Controls whether the field's data can be modified. When this option is off, all editing requests except REQ_PREV_CHOICE and REQ_NEXT_CHOICEwill fail. Such read-only fields may be useful for help messages.

O_WRAP

Controls word-wrapping in multi-line fields. Normally, when any character of a (blank-separated) word reaches the end of the current line, the entire word is wrapped to the next line (assuming there is one). When this option is off, the word will be split across the line break.

O_BLANK

Controls field blanking. When this option is on, entering a character at the first field position erases the entire field (except for the just-entered character).

O_AUTOSKIP

Controls automatic skip to next field when this one fills. Normally, when the forms user tries to type more data into a field than will fit, the editing location jumps to next field. When this option is off, the user's cursor will hang at the end of the field. This option is ignored in dynamic fields that have not reached their size limit.

O_NULLOK

Controls whether validation is applied to blank fields. Normally, it is not; the user can leave a field blank without invoking the usual validation check on exit. If this option is off on a field, exit from it will invoke a validation check.

O_PASSOK

Controls whether validation occurs on every exit, or only after the field is modified. Normally the latter is true. Setting O_PASSOK may be useful if your field's validation function may change during forms processing.

O_STATIC

Controls whether the field is fixed to its initial dimensions. If you turn this off, the field becomes dynamic and will stretch to fit entered data.

A field's options cannot be changed while the field is currently selected. However, options may be changed on posted fields that are not current.

The option values are bit-masks and can be composed with logical-or in the obvious way. You have seen the usage of switching off O_AUTOSKIP option. The following example clarifies usage of some more options. Other options are explained where appropriate.

Example 27. Field Options Usage example

#include <form.h>

#define STARTX 15
#define STARTY 4
#define WIDTH 25

#define N_FIELDS 3

int main()
{	FIELD *field[N_FIELDS];
	FORM  *my_form;
	int ch, i;
	
	/* Initialize curses */
	initscr();
	cbreak();
	noecho();
	keypad(stdscr, TRUE);

	/* Initialize the fields */
	for(i = 0; i < N_FIELDS - 1; ++i)
		field[i] = new_field(1, WIDTH, STARTY + i * 2, STARTX, 0, 0);
	field[N_FIELDS - 1] = NULL;

	/* Set field options */
	set_field_back(field[1], A_UNDERLINE); 	/* Print a line for the option 	*/
	
	field_opts_off(field[0], O_ACTIVE); /* This field is a static label */
	field_opts_off(field[1], O_PUBLIC); /* This filed is like a password field*/
	field_opts_off(field[1], O_AUTOSKIP); /* To avoid entering the same field */
					      /* after last character is entered */
	
	/* Create the form and post it */
	my_form = new_form(field);
	post_form(my_form);
	refresh();
	
	set_field_just(field[0], JUSTIFY_CENTER); /* Center Justification */
	set_field_buffer(field[0], 0, "This is a static Field"); 
						  /* Initialize the field  */
	mvprintw(STARTY, STARTX - 10, "Field 1:");
	mvprintw(STARTY + 2, STARTX - 10, "Field 2:");
	refresh();

	/* Loop through to get user requests */
	while((ch = getch()) != KEY_F(1))
	{	switch(ch)
		{	case KEY_DOWN:
				/* Go to next field */
				form_driver(my_form, REQ_NEXT_FIELD);
				/* Go to the end of the present buffer */
				/* Leaves nicely at the last character */
				form_driver(my_form, REQ_END_LINE);
				break;
			case KEY_UP:
				/* Go to previous field */
				form_driver(my_form, REQ_PREV_FIELD);
				form_driver(my_form, REQ_END_LINE);
				break;
			default:
				/* If this is a normal character, it gets */
				/* Printed				  */	
				form_driver(my_form, ch);
				break;
		}
	}

	/* Un post form and free the memory */
	unpost_form(my_form);
	free_form(my_form);
	free_field(field[0]);
	free_field(field[1]); 

	endwin();
	return 0;
}

This example, though useless, shows the usage of options. If used properly, they can present information very effectively in a form. The second field being not O_PUBLIC, does not show the characters you are typing.


18.3.7. Field User Pointer

Every field structure contains one pointer that can be used by the user for various purposes. It is not touched by forms library and can be used for any purpose by the user. The following functions set and fetch user pointer.

int set_field_userptr(FIELD *field,   
           char *userptr);      /* the user pointer you wish to associate */
                                /* with the field    */

char *field_userptr(FIELD *field);      /* fetch user pointer of the field */

18.3.8. Variable-Sized Fields

If you want a dynamically changing field with variable width, this is the feature you want to put to full use. This will allow the user to enter more data than the original size of the field and let the field grow. According to the field orientation it will scroll horizontally or vertically to incorporate the new data.

To make a field dynamically growable, the option O_STATIC should be turned off. This can be done with a
    field_opts_off(field_pointer, O_STATIC);

But it's usually not advisable to allow a field to grow infinitely. You can set a maximum limit to the growth of the field with
int set_max_field(FIELD *field,    /* Field on which to operate */
                  int max_growth); /* maximum growth allowed for the field */

The field info for a dynamically growable field can be retrieved by
int dynamic_field_info( FIELD *field,     /* Field on which to operate */
            int   *prows,     /* number of rows will be filled in this */
            int   *pcols,     /* number of columns will be filled in this*/
            int   *pmax)      /* maximum allowable growth will be filled */
                              /* in this */
Though field_info work as usual, it is advisable to use this function to get the proper attributes of a dynamically growable field.

Recall the library routine new_field; a new field created with height set to one will be defined to be a one line field. A new field created with height greater than one will be defined to be a multi line field.

A one line field with O_STATIC turned off (dynamically growable field) will contain a single fixed row, but the number of columns can increase if the user enters more data than the initial field will hold. The number of columns displayed will remain fixed and the additional data will scroll horizontally.

A multi line field with O_STATIC turned off (dynamically growable field) will contain a fixed number of columns, but the number of rows can increase if the user enters more data than the initial field will hold. The number of rows displayed will remain fixed and the additional data will scroll vertically.

The above two paragraphs pretty much describe a dynamically growable field's behavior. The way other parts of forms library behaves is described below:

  1. The field option O_AUTOSKIP will be ignored if the option O_STATIC is off and there is no maximum growth specified for the field. Currently, O_AUTOSKIP generates an automatic REQ_NEXT_FIELD form driver request when the user types in the last character position of a field. On a growable field with no maximum growth specified, there is no last character position. If a maximum growth is specified, the O_AUTOSKIP option will work as normal if the field has grown to its maximum size.

  2. The field justification will be ignored if the option O_STATIC is off. Currently, set_field_just can be used to JUSTIFY_LEFT, JUSTIFY_RIGHT, JUSTIFY_CENTER the contents of a one line field. A growable one line field will, by definition, grow and scroll horizontally and may contain more data than can be justified. The return from field_just will be unchanged.

  3. The overloaded form driver request REQ_NEW_LINE will operate the same way regardless of the O_NL_OVERLOAD form option if the field option O_STATIC is off and there is no maximum growth specified for the field. Currently, if the form option O_NL_OVERLOAD is on, REQ_NEW_LINE implicitly generates a REQ_NEXT_FIELD if called from the last line of a field. If a field can grow without bound, there is no last line, so REQ_NEW_LINE will never implicitly generate a REQ_NEXT_FIELD. If a maximum growth limit is specified and the O_NL_OVERLOAD form option is on, REQ_NEW_LINE will only implicitly generate REQ_NEXT_FIELD if the field has grown to its maximum size and the user is on the last line.

  4. The library call dup_field will work as usual; it will duplicate the field, including the current buffer size and contents of the field being duplicated. Any specified maximum growth will also be duplicated.

  5. The library call link_field will work as usual; it will duplicate all field attributes and share buffers with the field being linked. If the O_STATIC field option is subsequently changed by a field sharing buffers, how the system reacts to an attempt to enter more data into the field than the buffer will currently hold will depend on the setting of the option in the current field.

  6. The library call field_info will work as usual; the variable nrow will contain the value of the original call to new_field. The user should use dynamic_field_info, described above, to query the current size of the buffer.

Some of the above points make sense only after explaining form driver. We will be looking into that in next few sections.


18.4. Form Windows

The form windows concept is pretty much similar to menu windows. Every form is associated with a main window and a sub window. The form main window displays any title or border associated or whatever the user wishes. Then the sub window contains all the fields and displays them according to their position. This gives the flexibility of manipulating fancy form displaying very easily.

Since this is pretty much similar to menu windows, I am providing an example with out much explanation. The functions are similar and they work the same way.

Example 28. Form Windows Example

#include <form.h>

void print_in_middle(WINDOW *win, int starty, int startx, int width, char *string, chtype color);

int main()
{
	FIELD *field[3];
	FORM  *my_form;
	WINDOW *my_form_win;
	int ch, rows, cols;
	
	/* Initialize curses */
	initscr();
	start_color();
	cbreak();
	noecho();
	keypad(stdscr, TRUE);

	/* Initialize few color pairs */
   	init_pair(1, COLOR_RED, COLOR_BLACK);

	/* Initialize the fields */
	field[0] = new_field(1, 10, 6, 1, 0, 0);
	field[1] = new_field(1, 10, 8, 1, 0, 0);
	field[2] = NULL;

	/* Set field options */
	set_field_back(field[0], A_UNDERLINE);
	field_opts_off(field[0], O_AUTOSKIP); /* Don't go to next field when this */
					      /* Field is filled up 		*/
	set_field_back(field[1], A_UNDERLINE); 
	field_opts_off(field[1], O_AUTOSKIP);
	
	/* Create the form and post it */
	my_form = new_form(field);
	
	/* Calculate the area required for the form */
	scale_form(my_form, &rows, &cols);

	/* Create the window to be associated with the form */
        my_form_win = newwin(rows + 4, cols + 4, 4, 4);
        keypad(my_form_win, TRUE);

	/* Set main window and sub window */
        set_form_win(my_form, my_form_win);
        set_form_sub(my_form, derwin(my_form_win, rows, cols, 2, 2));

	/* Print a border around the main window and print a title */
        box(my_form_win, 0, 0);
	print_in_middle(my_form_win, 1, 0, cols + 4, "My Form", COLOR_PAIR(1));
	
	post_form(my_form);
	wrefresh(my_form_win);

	mvprintw(LINES - 2, 0, "Use UP, DOWN arrow keys to switch between fields");
	refresh();

	/* Loop through to get user requests */
	while((ch = wgetch(my_form_win)) != KEY_F(1))
	{	switch(ch)
		{	case KEY_DOWN:
				/* Go to next field */
				form_driver(my_form, REQ_NEXT_FIELD);
				/* Go to the end of the present buffer */
				/* Leaves nicely at the last character */
				form_driver(my_form, REQ_END_LINE);
				break;
			case KEY_UP:
				/* Go to previous field */
				form_driver(my_form, REQ_PREV_FIELD);
				form_driver(my_form, REQ_END_LINE);
				break;
			default:
				/* If this is a normal character, it gets */
				/* Printed				  */	
				form_driver(my_form, ch);
				break;
		}
	}

	/* Un post form and free the memory */
	unpost_form(my_form);
	free_form(my_form);
	free_field(field[0]);
	free_field(field[1]); 

	endwin();
	return 0;
}

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();
}

18.5. Field Validation

By default, a field will accept any data input by the user. It is possible to attach validation to the field. Then any attempt by the user to leave the field, while it contains data that doesn't match the validation type will fail. Some validation types also have a character-validity check for each time a character is entered in the field.

Validation can be attached to a field with the following function.
int set_field_type(FIELD *field,          /* field to alter */
                   FIELDTYPE *ftype,      /* type to associate */
                   ...);                  /* additional arguments*/
Once set, the validation type for a field can be queried with
FIELDTYPE *field_type(FIELD *field);      /* field to query */

The form driver validates the data in a field only when data is entered by the end-user. Validation does not occur when

The following are the pre-defined validation types. You can also specify custom validation, though it's a bit tricky and cumbersome.

TYPE_ALPHA

This field type accepts alphabetic data; no blanks, no digits, no special characters (this is checked at character-entry time). It is set up with:

int set_field_type(FIELD *field,          /* field to alter */
                   TYPE_ALPHA,            /* type to associate */
                   int width);            /* maximum width of field */

The width argument sets a minimum width of data. The user has to enter at-least width number of characters before he can leave the field. Typically you'll want to set this to the field width; if it's greater than the field width, the validation check will always fail. A minimum width of zero makes field completion optional.

TYPE_ALNUM

This field type accepts alphabetic data and digits; no blanks, no special characters (this is checked at character-entry time). It is set up with:

int set_field_type(FIELD *field,          /* field to alter */
                   TYPE_ALNUM,            /* type to associate */
                   int width);            /* maximum width of field */

The width argument sets a minimum width of data. As with TYPE_ALPHA, typically you'll want to set this to the field width; if it's greater than the field width, the validation check will always fail. A minimum width of zero makes field completion optional.

TYPE_ENUM

This type allows you to restrict a field's values to be among a specified set of string values (for example, the two-letter postal codes for U.S. states). It is set up with:

int set_field_type(FIELD *field,          /* field to alter */
                   TYPE_ENUM,             /* type to associate */
                   char **valuelist;      /* list of possible values */
                   int checkcase;         /* case-sensitive? */
                   int checkunique);      /* must specify uniquely? */

The valuelist parameter must point at a NULL-terminated list of valid strings. The checkcase argument, if true, makes comparison with the string case-sensitive.

When the user exits a TYPE_ENUM field, the validation procedure tries to complete the data in the buffer to a valid entry. If a complete choice string has been entered, it is of course valid. But it is also possible to enter a prefix of a valid string and have it completed for you.

By default, if you enter such a prefix and it matches more than one value in the string list, the prefix will be completed to the first matching value. But the checkunique argument, if true, requires prefix matches to be unique in order to be valid.

The REQ_NEXT_CHOICE and REQ_PREV_CHOICE input requests can be particularly useful with these fields.

TYPE_INTEGER

This field type accepts an integer. It is set up as follows:

int set_field_type(FIELD *field,          /* field to alter */
                   TYPE_INTEGER,          /* type to associate */
                   int padding,           /* # places to zero-pad to */
                   int vmin, int vmax);   /* valid range */

Valid characters consist of an optional leading minus and digits. The range check is performed on exit. If the range maximum is less than or equal to the minimum, the range is ignored.

If the value passes its range check, it is padded with as many leading zero digits as necessary to meet the padding argument.

A TYPE_INTEGER value buffer can conveniently be interpreted with the C library function atoi(3).

TYPE_NUMERIC

This field type accepts a decimal number. It is set up as follows:

int set_field_type(FIELD *field,          /* field to alter */
                   TYPE_NUMERIC,          /* type to associate */
                   int padding,           /* # places of precision */
                   int vmin, int vmax);   /* valid range */

Valid characters consist of an optional leading minus and digits. possibly including a decimal point. The range check is performed on exit. If the range maximum is less than or equal to the minimum, the range is ignored.

If the value passes its range check, it is padded with as many trailing zero digits as necessary to meet the padding argument.

A TYPE_NUMERIC value buffer can conveniently be interpreted with the C library function atof(3).

TYPE_REGEXP

This field type accepts data matching a regular expression. It is set up as follows:

int set_field_type(FIELD *field,          /* field to alter */
                   TYPE_REGEXP,           /* type to associate */
                   char *regexp);         /* expression to match */

The syntax for regular expressions is that of regcomp(3). The check for regular-expression match is performed on exit.


18.6. Form Driver: The work horse of the forms system

As in the menu system, form_driver() plays a very important role in forms system. All types of requests to forms system should be funneled through form_driver().

int form_driver(FORM *form,     /* form on which to operate     */
                int request)    /* form request code         */

As you have seen some of the examples above, you have to be in a loop looking for user input and then decide whether it's a field data or a form request. The form requests are then passed to form_driver() to do the work.

The requests roughly can be divided into following categories. Different requests and their usage is explained below:


18.6.2. Inter-Field Navigation Requests

These requests handle navigation between fields on the same page.

These requests treat the list of fields on a page as cyclic; that is, REQ_NEXT_FIELD from the last field goes to the first, and REQ_PREV_FIELD from the first field goes to the last. The order of the fields for these (and the REQ_FIRST_FIELD and REQ_LAST_FIELD requests) is simply the order of the field pointers in the form array (as set up by new_form() or set_form_fields()

It is also possible to traverse the fields as if they had been sorted in screen-position order, so the sequence goes left-to-right and top-to-bottom. To do this, use the second group of four sorted-movement requests.

Finally, it is possible to move between fields using visual directions up, down, right, and left. To accomplish this, use the third group of four requests. Note, however, that the position of a form for purposes of these requests is its upper-left corner.

For example, suppose you have a multi-line field B, and two single-line fields A and C on the same line with B, with A to the left of B and C to the right of B. A REQ_MOVE_RIGHT from A will go to B only if A, B, and C all share the same first line; otherwise it will skip over B to C.


18.6.5. Editing Requests

When you pass the forms driver an ASCII character, it is treated as a request to add the character to the field's data buffer. Whether this is an insertion or a replacement depends on the field's edit mode (insertion is the default.

The following requests support editing the field and changing the edit mode:

The behavior of the REQ_NEW_LINE and REQ_DEL_PREV requests is complicated and partly controlled by a pair of forms options. The special cases are triggered when the cursor is at the beginning of a field, or on the last line of the field.

First, we consider REQ_NEW_LINE:

The normal behavior of REQ_NEW_LINE in insert mode is to break the current line at the position of the edit cursor, inserting the portion of the current line after the cursor as a new line following the current and moving the cursor to the beginning of that new line (you may think of this as inserting a newline in the field buffer).

The normal behavior of REQ_NEW_LINE in overlay mode is to clear the current line from the position of the edit cursor to end of line. The cursor is then moved to the beginning of the next line.

However, REQ_NEW_LINE at the beginning of a field, or on the last line of a field, instead does a REQ_NEXT_FIELD. O_NL_OVERLOAD option is off, this special action is disabled.

Now, let us consider REQ_DEL_PREV:

The normal behavior of REQ_DEL_PREV is to delete the previous character. If insert mode is on, and the cursor is at the start of a line, and the text on that line will fit on the previous one, it instead appends the contents of the current line to the previous one and deletes the current line (you may think of this as deleting a newline from the field buffer).

However, REQ_DEL_PREV at the beginning of a field is instead treated as a REQ_PREV_FIELD.

If the O_BS_OVERLOAD option is off, this special action is disabled and the forms driver just returns E_REQUEST_DENIED.


19. Tools and Widget Libraries

Now that you have seen the capabilities of ncurses and its sister libraries, you are rolling your sleeves up and gearing for a project that heavily manipulates screen. But wait.. It can be pretty difficult to write and maintain complex GUI widgets in plain ncurses or even with the additional libraries. There are some ready-to-use tools and widget libraries that can be used instead of writing your own widgets. You can use some of them, get ideas from the code, or even extend them.


19.1. CDK (Curses Development Kit)

In the author's words

CDK stands for 'Curses Development Kit' and it currently contains 21 ready to use widgets which facilitate the speedy development of full screen curses programs.

The kit provides some useful widgets, which can be used in your programs directly. It's pretty well written and the documentation is very good. The examples in the examples directory can be a good place to start for beginners. The CDK can be downloaded from http://www.vexus.ca/release/cdk.tar.gz . Follow the instructions in README file to install it.


19.1.1. Widget List

The following is the list of widgets provided with cdk and their description.

Widget Type           Quick Description
===========================================================================
Alphalist             Allows a user to select from a list of words, with
                      the ability to narrow the search list by typing in a
                      few characters of the desired word.
Buttonbox             This creates a multiple button widget. 
Calendar              Creates a little simple calendar widget.
Dialog                Prompts the user with a message, and the user
                      can pick an answer from the buttons provided.
Entry                 Allows the user to enter various types of information.
File Selector         A file selector built from Cdk base widgets. This
                      example shows how to create more complicated widgets
                      using the Cdk widget library.
Graph                 Draws a graph.
Histogram             Draws a histogram.
Item List             Creates a pop up field which allows the user to select
                      one of several choices in a small field. Very useful
                      for things like days of the week or month names.
Label                 Displays messages in a pop up box, or the label can be
                      considered part of the screen.
Marquee               Displays a message in a scrolling marquee.
Matrix                Creates a complex matrix with lots of options.
Menu                  Creates a pull-down menu interface.
Multiple Line Entry   A multiple line entry field. Very useful
                      for long fields. (like a description
                      field)
Radio List            Creates a radio button list.
Scale                 Creates a numeric scale. Used for allowing a user to
                      pick a numeric value and restrict them to a range of 
                      values.
Scrolling List        Creates a scrolling list/menu list.
Scrolling Window      Creates a scrolling log file viewer. Can add 
                      information into the window while its running. 
                      A good widget for displaying the progress of
                      something. (akin to a console window)
Selection List        Creates a multiple option selection list.
Slider                Akin to the scale widget, this widget provides a
                      visual slide bar to represent the numeric value.
Template              Creates a entry field with character sensitive 
                      positions. Used for pre-formatted fields like
                      dates and phone numbers.
Viewer                This is a file/information viewer. Very useful
                      when you need to display loads of information.
===========================================================================

19.2. The dialog

Long long ago, in September 1994, when few people knew linux, Jeff Tranter wrote an article on dialog in Linux Journal. He starts the article with these words..

Linux is based on the Unix operating system, but also features a number of unique and useful kernel features and application programs that often go beyond what is available under Unix. One little-known gem is "dialog", a utility for creating professional-looking dialog boxes from within shell scripts. This article presents a tutorial introduction to the dialog utility, and shows examples of how and where it can be used

As he explains, dialog is a real gem in making professional-looking dialog boxes with ease. It creates a variety of dialog boxes, menus, check lists etc.. It is usually installed by default. If not, you can find it at ibiblio linux archive.

The above-mentioned article gives a very good overview of its uses and capabilites. The man page has more details. It can be used in variety of situations. One good example is building of linux kernel in text mode. Linux kernel uses a modified version of dialog tailored for its needs.

dialog was initially designed to be used with shell scripts. If you want to use its functionality in a c program, then you can use libdialog. The documentation regarding this is sparse. Definitive reference is the dialog.h header file which comes with the library. You may need to hack here and there to get the required output. The source is easily customizable. I have used it on a number of occasions by modifying the code.


19.3. Perl Curses Modules CURSES::FORM and CURSES::WIDGETS

The perl module Curses, Curses::Form and Curses::Widgets give access to curses from perl. If you have curses and basic perl is installed, you can get these modules from CPAN All Modules page. Get the three zipped modules in the Curses category. Once installed you can use these modules from perl scripts like any other module. For more information on perl modules see perlmod man page. The above modules come with good documentation and they have some demo scripts to test the functionality. Though the widgets provided are very rudimentary, these modules provide good access to curses library from perl.

For more information see man pages Curses(3) , Curses::Form(3) and Curses::Widgets(3). These pages are installed only when the above modules are acquired and installed.


20. Just For Fun !!!

This section contains few programs written by me just for fun. They don't signify a better programming practice or the best way of using ncurses. They are provided here so as to allow beginners to get ideas and add more programs to this section. If you have written a couple of nice, simple programs in curses and want them to included here, contact me.


20.1. The Game of Life

Game of life is a wonder of math. In Paul Callahan's words

The Game of Life (or simply Life) is not a game in the conventional sense. There
are no players, and no winning or losing. Once the "pieces" are placed in the
starting position, the rules determine everything that happens later.
Nevertheless, Life is full of surprises! In most cases, it is impossible to look
at a starting position (or pattern) and see what will happen in the future. The
only way to find out is to follow the rules of the game.

This program starts with a simple inverted U pattern and shows how wonderful life works. There is a lot of room for improvement in the program. You can let the user enter pattern of his choice or even take input from a file. You can also change rules and play with a lot of variations. Search on google for interesting information on game of life.

File Path: JustForFun/life.c