6. Output functionsI 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.
addch() class: Print single character with attributes printw() class: Print formatted output similar to printf() 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 functionsThese 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
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 functionsThese functions are similar to printf() with
the added capability of printing at any position on the screen. 6.3.1. printw() and mvprintwThese two functions work much like printf().
mvprintw() can be used to move the cursor to a
position and then print. If you want to move the cursor first and then print
using printw() function, use
move() first and then use
printw() though I see no point why one should
avoid using mvprintw(), you have the
flexibility to manipulate. 6.3.2. wprintw() and mvwprintwThese two functions are similar to above two except that they print in the
corresponding window given as argument. 6.3.3. vwprintw()This function is similar to vprintf(). This can
be used when variable number of arguments are to be printed. 6.3.4. A Simple printw exampleExample 3. A Simple printw example #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;
} |
Above program demonstrates how easy it is to use printw. You just feed the coordinates and the message to be appeared
on the screen, then it does what you want. The above program introduces us to a new function
getmaxyx(), a macro defined in
ncurses.h. It gives the number of columns and
the number of rows in a given window.
getmaxyx() does this by updating the variables
given to it. Since getmaxyx() is not a function
we don't pass pointers to it, we just give two integer variables. 6.4. addstr() class of functionsaddstr() 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 cautionAll 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. |
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