bkgd(3NCURSES)

💖 bkgd(3NCURSES) — bestie edition 💖

okay so this is a library call page from the 3NCURSES manual, and it's all about bkgdset, wbkgdset, bkgd, wbkgd, and getbkgd — the girlies that manipulate the background of a curses window of characters. yes ma'am. let's get into it 🎀

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✨ NAME ✨

bkgdset, wbkgdset, bkgd, wbkgd, getbkgd — manipulate background of a curses window of characters 🦋

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🌸 SYNOPSIS 🌸

#include <curses.h>

int bkgd(chtype ch);
int wbkgd(WINDOW *win, chtype ch);

void bkgdset(chtype ch);
void wbkgdset(WINDOW *win, chtype ch);

chtype getbkgd(WINDOW *win);

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💅 DESCRIPTION 💅

okay so every single curses window has a background character property, right? in the library's non-wide-character configuration, that property is a curses character (chtype) that combines a set of attributes (and, if colors are enabled, a color pair identifier) with a character code. when curses erases (parts of) a window, it replaces the erased cells with that background character. periodt.

curses also uses the background character when writing characters to a populated window. the way that it works:

• The attribute part of the background character combines with all non-blank character cells in the window, as populated by the waddch(3NCURSES) and winsch(3NCURSES) families of functions (and those that call them).
• 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 moves with it through any scrolling and insert/delete line/character operations. lowkey it's glued to the cell fr fr. 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. iconic.

🫶 bkgd, wbkgd

bkgd and wbkgd set the background property of stdscr or the specified window and then apply this setting to every character cell in that window. so it's not just vibes for the future, it's a whole glow-up of what's already there.

• The rendition of every character in the window changes to the new background rendition.
• 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 the following procedure to each cell in the window, whether or not it is blank. no cell gets skipped bestie, everybody eats.

• 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.
• 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.
• 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.
• 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 (for example, if it is a control character), ncurses retains the existing background character, except for one special case: ncurses treats a background character code of zero (0) as a space. like, zero is doing a space cosplay, we support her.

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

🧚 bkgdset, wbkgdset

bkgdset and wbkgdset manipulate the background of the applicable window, without updating the character cells as bkgd and wbkgd do; only future writes reflect the updated background. so like, this is the "setting the vibe for what's coming next" girlie, not the "redo the whole room right now" girlie. both are valid. 🙈

⭐ getbkgd

getbkgd returns the given window's background character, attributes, and color pair as a chtype. she's the reader, she's the observer, she just tells you what's there. 👑

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🎀 RETURN VALUE 🎀

bkgdset and wbkgdset do not return a value. they're void, they're mysterious, they give nothing back and that's their right.

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

• the curses screen has not been initialized, or
• win is NULL.

getbkgd's return value is as described above.

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🌈 NOTES 🌈

Unusually, there is no wgetbkgd function; getbkgd behaves as one would expect wgetbkgd to, accepting a WINDOW pointer argument. not me looking for wgetbkgd... she simply does not exist bestie, getbkgd is doing both jobs and honestly? main character energy.

bkgd and bkgdset may be implemented as macros. so don't be weird about them, they might not be real functions, iykyk.

X/Open Curses mentions that the character part of the background must be a single-byte value. ncurses, like SVr4 curses, checks to ensure that it is, and retains the existing background character if the check fails. so if you hand it something too big, nothing happens, the old background just stays. no drama, no error, just vibes preserved. ✨

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🦋 PORTABILITY 🦋

X/Open Curses Issue 4 describes these functions. It indicates that bkgd, wbkgd, and getbkgd return ERR on failure (in the case of the last, this value is cast to chtype), but specifies no error conditions for them. so like... they can fail, but nobody says when. iconic behavior honestly.

SVr4 documentation says that bkgd and wbkgd return OK "or a non-negative integer if immedok() is set", referring to the return value from wrefresh, which in SVr4 returns a count of characters written to the window if its immedok property is set; in ncurses, it does not. so yeah, don't count on that one.

Neither X/Open Curses nor the SVr4 manual pages detail how the rendition of characters in the window updates when bkgd or wbkgd changes the background character. ncurses, like SVr4 curses, does not (in its non-wide-character configuration) store the background and window attribute contributions to each character cell separately. so the internals are lowkey just merged together and we move on. 💅

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💜 HISTORY 💜

SVr3.1 (1987) introduced these functions. a vintage release, a classic, the original girlie. 💖

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🍓 SEE ALSO 🍓

bkgrnd(3NCURSES) describes the corresponding functions in the wide configuration of ncurses. so if you need the wide-character version, that's your page bestie.

ncurses(3NCURSES), addch(3NCURSES), attr(3NCURSES)

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ngl, bkgd is the quiet one in the group chat but she's holding the whole window's aesthetic together. treat her right. 🫶

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and that's the whole page, bestie!! 💖✨ this was ncurses 6.6, dated 2025-08-23, and it's the bkgd(3NCURSES) page. mwah. go make your windows pretty. 🎀💅👑