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<H1 class="no-header">curs_bkgd 3x 2025-08-23 ncurses 6.6 Library calls</H1>
<PRE>
<STRONG><A HREF="curs_bkgd.3x.html">curs_bkgd(3x)</A></STRONG> Library calls <STRONG><A HREF="curs_bkgd.3x.html">curs_bkgd(3x)</A></STRONG>
</PRE><H2><a name="h2-NAME">NAME</a></H2><PRE>
<STRONG>bkgdset</STRONG>, <STRONG>wbkgdset</STRONG>, <STRONG>bkgd</STRONG>, <STRONG>wbkgd</STRONG>, <STRONG>getbkgd</STRONG> - manipulate background of a
<EM>curses</EM> window of characters
</PRE><H2><a name="h2-SYNOPSIS">SYNOPSIS</a></H2><PRE>
<STRONG>#include</STRONG> <STRONG><curses.h></STRONG>
<STRONG>int</STRONG> <STRONG>bkgd(chtype</STRONG> <EM>ch</EM><STRONG>);</STRONG>
<STRONG>int</STRONG> <STRONG>wbkgd(WINDOW</STRONG> <STRONG>*</STRONG><EM>win</EM><STRONG>,</STRONG> <STRONG>chtype</STRONG> <EM>ch</EM><STRONG>);</STRONG>
<STRONG>void</STRONG> <STRONG>bkgdset(chtype</STRONG> <EM>ch</EM><STRONG>);</STRONG>
<STRONG>void</STRONG> <STRONG>wbkgdset(WINDOW</STRONG> <STRONG>*</STRONG><EM>win</EM><STRONG>,</STRONG> <STRONG>chtype</STRONG> <EM>ch</EM><STRONG>);</STRONG>
<STRONG>chtype</STRONG> <STRONG>getbkgd(WINDOW</STRONG> <STRONG>*</STRONG><EM>win</EM><STRONG>);</STRONG>
</PRE><H2><a name="h2-DESCRIPTION">DESCRIPTION</a></H2><PRE>
Every <EM>curses</EM> window has a <EM>background</EM> <EM>character</EM> property: in the
library's non-wide-character configuration, it is a <EM>curses</EM> character
(<EM>chtype</EM>) 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, <EM>curses</EM> replaces the erased cells with the background
character.
<EM>curses</EM> also uses the background character when writing characters to a
populated window.
<STRONG>o</STRONG> The attribute part of the background character combines with all
non-blank character cells in the window, as populated by the
<STRONG><A HREF="curs_addch.3x.html">waddch(3x)</A></STRONG> and <STRONG><A HREF="curs_insch.3x.html">winsch(3x)</A></STRONG> families of functions (and those that
call them).
<STRONG>o</STRONG> 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, <EM>curses</EM> displays the attributes of the background character as the
graphic rendition of a character cell on the display.
</PRE><H3><a name="h3-bkgd_wbkgd">bkgd, wbkgd</a></H3><PRE>
<STRONG>bkgd</STRONG> and <STRONG>wbkgd</STRONG> set the background property of <STRONG>stdscr</STRONG> or the specified
window and then apply this setting to every character cell in that
window.
<STRONG>o</STRONG> The rendition of every character in the window changes to the new
background rendition.
<STRONG>o</STRONG> Wherever the former background character appears, it changes to the
new background character.
<EM>ncurses</EM> 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.
<STRONG>o</STRONG> <EM>ncurses</EM> first compares the cell's character to the previously
specified background character; if they match, <EM>ncurses</EM> writes the
new background character to the cell.
<STRONG>o</STRONG> <EM>ncurses</EM> 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.
<STRONG>o</STRONG> If the cell uses color, and its background color matches that of
the current window background, <EM>ncurses</EM> 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.
<STRONG>o</STRONG> If the cell uses color, and its background color does not match
that of the current window background, <EM>ncurses</EM> 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), <EM>ncurses</EM> retains the existing background
character, except for one special case: <EM>ncurses</EM> 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 <STRONG><A HREF="curs_color.3x.html">start_color(3x)</A></STRONG>, <EM>ncurses</EM> ignores the new background
character's color pair selection.
</PRE><H3><a name="h3-bkgdset_wbkgdset">bkgdset, wbkgdset</a></H3><PRE>
<STRONG>bkgdset</STRONG> and <STRONG>wbkgdset</STRONG> manipulate the background of the applicable
window, without updating the character cells as <STRONG>bkgd</STRONG> and <STRONG>wbkgd</STRONG> do; only
future writes reflect the updated background.
</PRE><H3><a name="h3-getbkgd">getbkgd</a></H3><PRE>
<STRONG>getbkgd</STRONG> returns the given window's background character, attributes,
and color pair as a <EM>chtype</EM>.
</PRE><H2><a name="h2-RETURN-VALUE">RETURN VALUE</a></H2><PRE>
<STRONG>bkgdset</STRONG> and <STRONG>wbkgdset</STRONG> do not return a value.
Functions returning an <EM>int</EM> return <STRONG>ERR</STRONG> upon failure and <STRONG>OK</STRONG> upon success.
In <EM>ncurses</EM>, failure occurs if
<STRONG>o</STRONG> the <EM>curses</EM> screen has not been initialized, or
<STRONG>o</STRONG> <EM>win</EM> is <EM>NULL</EM>.
<STRONG>getbkgd</STRONG>'s return value is as described above.
</PRE><H2><a name="h2-NOTES">NOTES</a></H2><PRE>
Unusually, there is no <STRONG>wgetbkgd</STRONG> function; <STRONG>getbkgd</STRONG> behaves as one would
expect <STRONG>wgetbkgd</STRONG> to, accepting a <EM>WINDOW</EM> pointer argument.
<STRONG>bkgd</STRONG> and <STRONG>bkgdset</STRONG> may be implemented as macros.
X/Open Curses mentions that the character part of the background must
be a single-byte value. <EM>ncurses</EM>, like SVr4 <EM>curses</EM>, checks to ensure
that it is, and retains the existing background character if the check
fails.
</PRE><H2><a name="h2-PORTABILITY">PORTABILITY</a></H2><PRE>
X/Open Curses Issue 4 describes these functions. It indicates that
<EM>bkgd</EM>, <EM>wbkgd</EM>, and <EM>getbkgd</EM> return <EM>ERR</EM> on failure (in the case of the
last, this value is cast to <EM>chtype</EM>), but specifies no error conditions
for them.
SVr4 documentation says that <EM>bkgd</EM> and <EM>wbkgd</EM> return <EM>OK</EM> "or a non-
negative integer if <EM>immedok()</EM> is set", referring to the return value
from <EM>wrefresh</EM>, which in SVr4 returns a count of characters written to
the window if its <EM>immedok</EM> property is set; in <EM>ncurses</EM>, it does not.
Neither X/Open Curses nor the SVr4 manual pages detail how the
rendition of characters in the window updates when <EM>bkgd</EM> or <EM>wbkgd</EM>
changes the background character. <EM>ncurses</EM>, like SVr4 <EM>curses</EM>, does not
(in its non-wide-character configuration) store the background and
window attribute contributions to each character cell separately.
</PRE><H2><a name="h2-HISTORY">HISTORY</a></H2><PRE>
SVr3.1 (1987) introduced these functions.
</PRE><H2><a name="h2-SEE-ALSO">SEE ALSO</a></H2><PRE>
<STRONG><A HREF="curs_bkgrnd.3x.html">curs_bkgrnd(3x)</A></STRONG> describes the corresponding functions in the wide
configuration of <EM>ncurses</EM>.
<STRONG><A HREF="ncurses.3x.html">curses(3x)</A></STRONG>, <STRONG><A HREF="curs_addch.3x.html">curs_addch(3x)</A></STRONG>, <STRONG><A HREF="curs_attr.3x.html">curs_attr(3x)</A></STRONG>
ncurses 6.6 2025-08-23 <STRONG><A HREF="curs_bkgd.3x.html">curs_bkgd(3x)</A></STRONG>
</PRE>
<div class="nav">
<ul>
<li><a href="#h2-NAME">NAME</a></li>
<li><a href="#h2-SYNOPSIS">SYNOPSIS</a></li>
<li><a href="#h2-DESCRIPTION">DESCRIPTION</a>
<ul>
<li><a href="#h3-bkgd_wbkgd">bkgd, wbkgd</a></li>
<li><a href="#h3-bkgdset_wbkgdset">bkgdset, wbkgdset</a></li>
<li><a href="#h3-getbkgd">getbkgd</a></li>
</ul>
</li>
<li><a href="#h2-RETURN-VALUE">RETURN VALUE</a></li>
<li><a href="#h2-NOTES">NOTES</a></li>
<li><a href="#h2-PORTABILITY">PORTABILITY</a></li>
<li><a href="#h2-HISTORY">HISTORY</a></li>
<li><a href="#h2-SEE-ALSO">SEE ALSO</a></li>
</ul>
</div>
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