6. About output functions like printw()

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.

6.2. mvaddch(), waddch() and mvwaddch()

mvaddch() is used to move the cursor to a given point, and then print. Thus, the calls:

move(row,col); /* moves the cursor to rowth row and colth column */ addch(ch);

can be replaced by

mvaddch(row,col,ch);

waddch() is similar to addch(), except that it adds a character into the given window. (Note that addch() adds a character into the window stdscr.)

In a similar fashion mvwaddch() function is used to add a character into the given window at the given coordinates.

Now, we are familiar with the basic output function addch(). But, if we want to print a string, it would be very annoying to print it character by character. Fortunately, ncurses provides printf-like or puts-like functions.

6.3. printw() class of functions

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

#include <ncurses.h>			/* ncurses.h includes stdio.h */  
#include <string.h> 
 
int main()
{
 char mesg[]="Just a string";		/* message to be appeared on the screen */
 int row,col;				/* to store the number of rows and *
					 * the number of colums of the screen */
 initscr();				/* start the curses mode */
 getmaxyx(stdscr,row,col);		/* get the number of rows and columns */
 mvprintw(row/2,(col-strlen(mesg))/2,"%s",mesg);
                                	/* print the message at the center of the screen */
 mvprintw(row-2,0,"This screen has %d rows and %d columns\n",row,col);
 printw("Try resizing your window(if possible) and then run this program again");
 refresh();
 getch();
 endwin();

 return 0;
}

6.4. addstr() class of functions

addstr() is used to put a character string into a given window. This function is similar to calling addch() once for each character in a given string. This is true for all output functions. There are other functions from this family such as mvaddstr(),mvwaddstr() and waddstr(), which obey the naming convention of curses.(e.g. mvaddstr() is similar to the respective calls move() and then addstr().) Another function of this family is addnstr(), which takes an integer parameter(say n) additionally. This function puts at most n characters into the screen. If n is negative, then the entire string will be added.

6.5. A word of caution

All these functions take y co-ordinate first and then x in their arguments. A common mistake by beginners is to pass x,y in that order. If you are doing too many manipulations of (y,x) co-ordinates, think of dividing the screen into windows and manipulate each one separately. Windows are explained in the windows section.