# curs_bkgrnd 3x 2025-02-15 ncurses 6.5 Library calls

    curs_bkgrnd(3x)                  Library calls                 curs_bkgrnd(3x)

## NAME

           bkgrnd,   wbkgrnd,   bkgrndset,  wbkgrndset,  getbkgrnd,  wgetbkgrnd  -
           manipulate background of a curses window of wide characters

## SYNOPSIS

           #include <curses.h>

           int bkgrnd(const cchar_t *wch);
           int wbkgrnd(WINDOW *win, const cchar_t *wch);

           void bkgrndset(const cchar_t *wch);
           void wbkgrndset(WINDOW *win, const cchar_t *wch);

           int getbkgrnd(cchar_t *wch);
           int wgetbkgrnd(WINDOW *win, cchar_t *wch);

## DESCRIPTION

           Every curses  window  has  a  background  character  property:  in  the
           library's   wide  configuration,  it  is  a  curses  complex  character
           (cchar_t) that combines  a  set  of  attributes  (and,  if  colors  are
           enabled,  a color pair identifier) with a character code.  When erasing
           (parts of)  a  window,  curses  replaces  the  erased  cells  with  the
           background character.

           curses  also uses the background character when writing characters to a
           populated window.

           o   The attribute part of the background character  combines  with  all
               non-blank  character  cells  in  the  window,  as  populated by the
               wadd_wch(3x) and wins_wch(3x) families of functions (and those that
               call them).

           o   Both  the character code and attributes of the background character
               combine with blank character cells in the window.

           The background character's set of attributes becomes a property of  the
           character cell and move with it through any scrolling and insert/delete
           line/character operations.  To the  extent  possible  on  the  terminal
           type, curses displays the attributes of the background character as the
           graphic rendition of a character cell on the display.

### bkgrnd, wbkgrnd

           bkgrnd and wbkgrnd  set  the  background  property  of  stdscr  or  the
           specified window and then apply this setting to every character cell in
           that window.

           o   The rendition of every character in the window changes to  the  new
               background rendition.

           o   Wherever the former background character appears, it changes to the
               new background character.

           ncurses updates the rendition of each character cell by  comparing  the
           character, non-color attributes, and color pair selection.  The library
           applies to following procedure to each cell in the window,  whether  or
           not it is blank.

           o   ncurses  first  compares  the  cell's  character  to the previously
               specified background character; if they match, ncurses  writes  the
               new background character to the cell.

           o   ncurses then checks whether the cell uses color; that is, its color
               pair value is nonzero.  If not, it simply replaces  the  attributes
               and  color  pair  in  the  cell  with those from the new background
               character.

           o   If the cell uses color, and its background color  matches  that  of
               the  current window background, ncurses removes attributes that may
               have come from the current background and adds those from  the  new
               background.   It  finishes  by setting the cell's background to use
               the new window background color.

           o   If the cell uses color, and its background  color  does  not  match
               that  of  the  current  window background, ncurses updates only the
               non-color attributes, first removing those that may have come  from
               the  current  background,  and  then adding attributes from the new
               background.

           If the new background's character is non-spacing,  ncurses  reuses  the
           old background character, except for one special case: ncurses treats a
           background character code of zero (0) as a space.

           If the terminal does not support  color,  or  if  color  has  not  been
           initialized  with  start_color(3x),  ncurses ignores the new background
           character's color pair selection.

### bkgrndset, wbkgrndset

           bkgrndset and wbkgrndset manipulate the background  of  the  applicable
           window,  without updating the character cells as bkgrnd and wbkgrnd do;
           only future writes reflect the updated background.

### getbkgrnd, wgetbkgrnd

           getbkgrnd and wgetbkgrnd respectively  obtain  stdscr's  or  the  given
           window's background character, attributes, and color pair, and store it
           in their wch argument.

## RETURN VALUE

           bkgrndset and wbkgrndset do not return a value.

           Functions returning an int return ERR upon failure and OK upon success.
           In ncurses, failure occurs if

           o   the curses screen has not been initialized,

           o   win is NULL, or

           o   wch is NULL.

## NOTES

           bkgrnd, bkgrndset, and getbkgrnd may be implemented as macros.

           Unlike  their  counterparts  in  the non-wide configuration of ncurses,
           getbkgrnd and wgetbkgrnd store the background character in a modifiable
           cchar_t parameter, rather than supplying it as the return value.

## PORTABILITY

           X/Open Curses Issue 4 describes these functions.  It specifies no error
           conditions for them.

           X/Open Curses does not provide details of how the rendition is updated.
           ncurses  follows  the approach used in SVr4 curses's non-wide functions
           for manipulating the window background.

## HISTORY

           X/Open Curses Issue 4 (1995) initially specified these functions.

## SEE ALSO

           curs_bkgd(3x) describes the corresponding  functions  in  the  non-wide
           configuration of ncurses.

           curses(3x), curs_add_wch(3x), curs_attr(3x)

    ncurses 6.5                       2025-02-15                   curs_bkgrnd(3x)