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<H1 class="no-header">curs_color 3x 2024-04-20 ncurses 6.5 Library calls</H1>
<PRE>
<STRONG><A HREF="curs_color.3x.html">curs_color(3x)</A></STRONG> Library calls <STRONG><A HREF="curs_color.3x.html">curs_color(3x)</A></STRONG>
</PRE><H2><a name="h2-NAME">NAME</a></H2><PRE>
<STRONG>start_color</STRONG>, <STRONG>has_colors</STRONG>, <STRONG>can_change_color</STRONG>, <STRONG>init_pair</STRONG>, <STRONG>init_color</STRONG>,
<STRONG>init_extended_pair</STRONG>, <STRONG>init_extended_color</STRONG>, <STRONG>color_content</STRONG>, <STRONG>pair_content</STRONG>,
<STRONG>extended_color_content</STRONG>, <STRONG>extended_pair_content</STRONG>, <STRONG>reset_color_pairs</STRONG>,
<STRONG>COLOR_PAIR</STRONG>, <STRONG>PAIR_NUMBER</STRONG>, <STRONG>COLORS</STRONG>, <STRONG>COLOR_PAIRS</STRONG>, <STRONG>COLOR_BLACK</STRONG>, <STRONG>COLOR_RED</STRONG>,
<STRONG>COLOR_GREEN</STRONG>, <STRONG>COLOR_YELLOW</STRONG>, <STRONG>COLOR_BLUE</STRONG>, <STRONG>COLOR_MAGENTA</STRONG>, <STRONG>COLOR_CYAN</STRONG>,
<STRONG>COLOR_WHITE</STRONG> - manipulate terminal colors with <EM>curses</EM>
</PRE><H2><a name="h2-SYNOPSIS">SYNOPSIS</a></H2><PRE>
<STRONG>#include</STRONG> <STRONG><curses.h></STRONG>
<EM>/*</EM> <EM>variables</EM> <EM>*/</EM>
<STRONG>int</STRONG> <STRONG>COLOR_PAIRS;</STRONG>
<STRONG>int</STRONG> <STRONG>COLORS;</STRONG>
<STRONG>int</STRONG> <STRONG>start_color(void);</STRONG>
<STRONG>bool</STRONG> <STRONG>has_colors(void);</STRONG>
<STRONG>bool</STRONG> <STRONG>can_change_color(void);</STRONG>
<STRONG>int</STRONG> <STRONG>init_pair(short</STRONG> <EM>pair</EM><STRONG>,</STRONG> <STRONG>short</STRONG> <EM>f</EM><STRONG>,</STRONG> <STRONG>short</STRONG> <EM>b</EM><STRONG>);</STRONG>
<STRONG>int</STRONG> <STRONG>init_color(short</STRONG> <EM>color</EM><STRONG>,</STRONG> <STRONG>short</STRONG> <EM>r</EM><STRONG>,</STRONG> <STRONG>short</STRONG> <EM>g</EM><STRONG>,</STRONG> <STRONG>short</STRONG> <EM>b</EM><STRONG>);</STRONG>
<EM>/*</EM> <EM>extensions</EM> <EM>*/</EM>
<STRONG>int</STRONG> <STRONG>init_extended_pair(int</STRONG> <EM>pair</EM><STRONG>,</STRONG> <STRONG>int</STRONG> <EM>f</EM><STRONG>,</STRONG> <STRONG>int</STRONG> <EM>b</EM><STRONG>);</STRONG>
<STRONG>int</STRONG> <STRONG>init_extended_color(int</STRONG> <EM>color</EM><STRONG>,</STRONG> <STRONG>int</STRONG> <EM>r</EM><STRONG>,</STRONG> <STRONG>int</STRONG> <EM>g</EM><STRONG>,</STRONG> <STRONG>int</STRONG> <EM>b</EM><STRONG>);</STRONG>
<STRONG>int</STRONG> <STRONG>color_content(short</STRONG> <EM>color</EM><STRONG>,</STRONG> <STRONG>short</STRONG> <STRONG>*</STRONG><EM>r</EM><STRONG>,</STRONG> <STRONG>short</STRONG> <STRONG>*</STRONG><EM>g</EM><STRONG>,</STRONG> <STRONG>short</STRONG> <STRONG>*</STRONG><EM>b</EM><STRONG>);</STRONG>
<STRONG>int</STRONG> <STRONG>pair_content(short</STRONG> <EM>pair</EM><STRONG>,</STRONG> <STRONG>short</STRONG> <STRONG>*</STRONG><EM>f</EM><STRONG>,</STRONG> <STRONG>short</STRONG> <STRONG>*</STRONG><EM>b</EM><STRONG>);</STRONG>
<EM>/*</EM> <EM>extensions</EM> <EM>*/</EM>
<STRONG>int</STRONG> <STRONG>extended_color_content(int</STRONG> <EM>color</EM><STRONG>,</STRONG> <STRONG>int</STRONG> <STRONG>*</STRONG><EM>r</EM><STRONG>,</STRONG> <STRONG>int</STRONG> <STRONG>*</STRONG><EM>g</EM><STRONG>,</STRONG> <STRONG>int</STRONG> <STRONG>*</STRONG><EM>b</EM><STRONG>);</STRONG>
<STRONG>int</STRONG> <STRONG>extended_pair_content(int</STRONG> <EM>pair</EM><STRONG>,</STRONG> <STRONG>int</STRONG> <STRONG>*</STRONG><EM>f</EM><STRONG>,</STRONG> <STRONG>int</STRONG> <STRONG>*</STRONG><EM>b</EM><STRONG>);</STRONG>
<EM>/*</EM> <EM>extension</EM> <EM>*/</EM>
<STRONG>void</STRONG> <STRONG>reset_color_pairs(void);</STRONG>
<STRONG>int</STRONG> <STRONG>COLOR_PAIR(int</STRONG> <EM>n</EM><STRONG>);</STRONG>
<STRONG>PAIR_NUMBER(int</STRONG> <EM>attr</EM><STRONG>);</STRONG>
</PRE><H2><a name="h2-DESCRIPTION">DESCRIPTION</a></H2><PRE>
</PRE><H3><a name="h3-Overview">Overview</a></H3><PRE>
<EM>curses</EM> supports color attributes on terminals with that capability.
Call <STRONG>start_color</STRONG> (typically right after <STRONG><A HREF="curs_initscr.3x.html">initscr(3x)</A></STRONG>) to enable this
feature. Colors are always used in pairs. A <EM>color</EM> <EM>pair</EM> couples a
foreground color for characters with a background color for the blank
field on which characters are rendered. <STRONG>init_pair</STRONG> initializes a color
pair. The macro <STRONG>COLOR_PAIR</STRONG>(<EM>n</EM>) can then convert the pair to a video
attribute.
If a terminal has the relevant capability, <STRONG>init_color</STRONG> permits
(re)definition of a color. <STRONG>has_colors</STRONG> and <STRONG>can_change_color</STRONG> return <STRONG>TRUE</STRONG>
or <STRONG>FALSE</STRONG>, depending on whether the terminal has color capability and
whether the programmer can change the colors. <STRONG>color_content</STRONG> permits
extraction of the red, green, and blue components of an initialized
color. <STRONG>pair_content</STRONG> permits discovery of a color pair's current
definition.
</PRE><H3><a name="h3-Rendering">Rendering</a></H3><PRE>
<EM>curses</EM> combines the following data to render a character cell. Any of
them can include color information.
<STRONG>o</STRONG> <EM>curses</EM> character attributes, as from <STRONG><A HREF="curs_addch.3x.html">waddch(3x)</A></STRONG> or <STRONG><A HREF="curs_add_wch.3x.html">wadd_wch(3x)</A></STRONG>
<STRONG>o</STRONG> window attributes, as from <STRONG><A HREF="curs_attr.3x.html">wattrset(3x)</A></STRONG> or <STRONG><A HREF="curs_attr.3x.html">wattr_set(3x)</A></STRONG>
<STRONG>o</STRONG> window background character attributes, as from <STRONG><A HREF="curs_bkgd.3x.html">wbkgdset(3x)</A></STRONG> or
<STRONG><A HREF="curs_bkgrnd.3x.html">wbkgrndset(3x)</A></STRONG>
Per-character and window attributes are usually set through a function
parameter containing attributes including a color pair value. Some
functions, such as <STRONG>wattr_set</STRONG>, use a separate color pair number
parameter.
The background character is a special case: it includes a character
code, just as if it were passed to <STRONG>waddch</STRONG>.
The <EM>curses</EM> library does the actual work of combining these color pairs
in an internal function called from <STRONG>waddch</STRONG>:
<STRONG>o</STRONG> If the parameter passed to <STRONG>waddch</STRONG> is <EM>blank</EM>, and it uses the special
color pair 0,
<STRONG>o</STRONG> <EM>curses</EM> next checks the window attribute.
<STRONG>o</STRONG> If the window attribute does not use color pair 0, <EM>curses</EM> uses
the color pair from the window attribute.
<STRONG>o</STRONG> Otherwise, <EM>curses</EM> uses the background character.
<STRONG>o</STRONG> If the parameter passed to <STRONG>waddch</STRONG> is <EM>not</EM> <EM>blank</EM>, or it does not use
the special color pair 0, <EM>curses</EM> prefers the color pair from the
parameter, if it is nonzero. Otherwise, it tries the window
attribute next, and finally the background character.
Some <EM>curses</EM> functions such as <STRONG>wprintw</STRONG> call <STRONG>waddch</STRONG>. Those do not
combine its parameter with a color pair. Consequently those calls use
only the window attribute or the background character.
</PRE><H2><a name="h2-CONSTANTS">CONSTANTS</a></H2><PRE>
In <STRONG><curses.h></STRONG> the following macros are defined. These are the standard
colors (ISO-6429). <EM>curses</EM> also assumes that <STRONG>COLOR_BLACK</STRONG> is the default
background color for all terminals.
<STRONG>COLOR_BLACK</STRONG>
<STRONG>COLOR_RED</STRONG>
<STRONG>COLOR_GREEN</STRONG>
<STRONG>COLOR_YELLOW</STRONG>
<STRONG>COLOR_BLUE</STRONG>
<STRONG>COLOR_MAGENTA</STRONG>
<STRONG>COLOR_CYAN</STRONG>
<STRONG>COLOR_WHITE</STRONG>
Some terminals support more than the eight (8) "ANSI" colors. There
are no standard names for those additional colors.
</PRE><H2><a name="h2-VARIABLES">VARIABLES</a></H2><PRE>
</PRE><H3><a name="h3-COLORS">COLORS</a></H3><PRE>
is initialized by <STRONG>start_color</STRONG> to the maximum number of colors the
terminal can support.
</PRE><H3><a name="h3-COLOR_PAIRS">COLOR_PAIRS</a></H3><PRE>
is initialized by <STRONG>start_color</STRONG> to the maximum number of color pairs the
terminal can support. Often, its value is the product <STRONG>COLORS</STRONG> x <STRONG>COLORS</STRONG>,
but this is not always true.
<STRONG>o</STRONG> A few terminals use the HLS color space (see <STRONG>start_color</STRONG> below),
ignoring this rule; and
<STRONG>o</STRONG> terminals supporting a large number of colors are limited to the
number of color pairs that a <EM>signed</EM> <EM>short</EM> value can represent.
</PRE><H2><a name="h2-FUNCTIONS">FUNCTIONS</a></H2><PRE>
</PRE><H3><a name="h3-start_color">start_color</a></H3><PRE>
The <STRONG>start_color</STRONG> routine requires no arguments. It must be called if
the programmer wants to use colors, and before any other color
manipulation routine is called. It is good practice to call this
routine right after <STRONG>initscr</STRONG>. <STRONG>start_color</STRONG> does this:
<STRONG>o</STRONG> It initializes two global variables, <STRONG>COLORS</STRONG> and <STRONG>COLOR_PAIRS</STRONG>
(respectively defining the maximum number of colors and color pairs
the terminal can support).
<STRONG>o</STRONG> It initializes the special color pair <STRONG>0</STRONG> to the default foreground
and background colors. No other color pairs are initialized.
<STRONG>o</STRONG> It restores the colors on the terminal to the values they had when
the terminal was just turned on.
<STRONG>o</STRONG> If the terminal supports the <STRONG>initc</STRONG> (<STRONG>initialize_color</STRONG>) capability,
<STRONG>start_color</STRONG> initializes its internal table representing the red,
green, and blue components of the color palette.
The components depend on whether the terminal uses CGA (aka "ANSI")
or HLS (i.e., the <STRONG>hls</STRONG> (<STRONG>hue_lightness_saturation</STRONG>) capability is
set). The table is initialized first for eight basic colors
(black, red, green, yellow, blue, magenta, cyan, and white), using
weights that depend upon the CGA/HLS choice. For "ANSI" colors the
weights are <STRONG>680</STRONG> or <STRONG>0</STRONG> depending on whether the corresponding red,
green, or blue component is used or not. That permits using <STRONG>1000</STRONG>
to represent bold/bright colors. After the initial eight colors
(if the terminal supports more than eight colors) the components
are initialized using the same pattern, but with weights of <STRONG>1000</STRONG>.
SVr4 uses a similar scheme, but uses <STRONG>1000</STRONG> for the components of the
initial eight colors.
<STRONG>start_color</STRONG> does not attempt to set the terminal's color palette to
match its built-in table. An application may use <STRONG>init_color</STRONG> to
alter the internal table along with the terminal's color.
These limits apply to color values and color pairs. Values outside
these limits are not valid, and may result in a runtime error:
<STRONG>o</STRONG> <STRONG>COLORS</STRONG> corresponds to the terminal database's <STRONG>max_colors</STRONG>
capability, (see <STRONG><A HREF="terminfo.5.html">terminfo(5)</A></STRONG>).
<STRONG>o</STRONG> color values are expected to be in the range <STRONG>0</STRONG> to <STRONG>COLORS-1</STRONG>,
inclusive (including <STRONG>0</STRONG> and <STRONG>COLORS-1</STRONG>).
<STRONG>o</STRONG> a special color value <STRONG>-1</STRONG> is used in certain extended functions to
denote the <EM>default</EM> <EM>color</EM> (see <STRONG><A HREF="default_colors.3x.html">use_default_colors(3x)</A></STRONG>).
<STRONG>o</STRONG> <STRONG>COLOR_PAIRS</STRONG> corresponds to the terminal database's <STRONG>max_pairs</STRONG>
capability, (see <STRONG><A HREF="terminfo.5.html">terminfo(5)</A></STRONG>).
<STRONG>o</STRONG> valid color pair values are in the range <STRONG>1</STRONG> to <STRONG>COLOR_PAIRS-1</STRONG>,
inclusive.
<STRONG>o</STRONG> color pair <STRONG>0</STRONG> is special; it denotes "no color".
Color pair <STRONG>0</STRONG> is assumed to be white on black, but is actually
whatever the terminal implements before color is initialized. It
cannot be modified by the application.
</PRE><H3><a name="h3-has_colors">has_colors</a></H3><PRE>
The <STRONG>has_colors</STRONG> routine requires no arguments. It returns <STRONG>TRUE</STRONG> if the
terminal can manipulate colors; otherwise, it returns <STRONG>FALSE</STRONG>. This
routine facilitates writing terminal-independent programs. For
example, a programmer can use it to decide whether to use color or some
other video attribute.
</PRE><H3><a name="h3-can_change_color">can_change_color</a></H3><PRE>
The <STRONG>can_change_color</STRONG> routine requires no arguments. It returns <STRONG>TRUE</STRONG> if
the terminal supports colors and can change their definitions; other,
it returns <STRONG>FALSE</STRONG>. This routine facilitates writing terminal-
independent programs.
</PRE><H3><a name="h3-init_pair">init_pair</a></H3><PRE>
The <STRONG>init_pair</STRONG> routine changes the definition of a color pair. It takes
three arguments: the number of the color pair to be changed, the
foreground color number, and the background color number. For portable
applications:
<STRONG>o</STRONG> The first argument must be a valid color pair value. If default
colors are used (see <STRONG><A HREF="default_colors.3x.html">use_default_colors(3x)</A></STRONG>) the upper limit is
adjusted to allow for extra pairs which use a default color in
foreground and/or background.
<STRONG>o</STRONG> The second and third arguments must be valid color values.
If the color pair was previously initialized, the screen is refreshed
and all occurrences of that color pair are changed to the new
definition.
As an extension, <EM>ncurses</EM> allows you to set color pair <STRONG>0</STRONG> via the
<STRONG><A HREF="default_colors.3x.html">assume_default_colors(3x)</A></STRONG> routine, or to specify the use of default
colors (color number <STRONG>-1</STRONG>) if you first invoke the <STRONG><A HREF="default_colors.3x.html">use_default_colors(3x)</A></STRONG>
routine.
</PRE><H3><a name="h3-init_extended_pair">init_extended_pair</a></H3><PRE>
Because <STRONG>init_pair</STRONG> uses signed <STRONG>short</STRONG>s for its parameters, that limits
color pairs and color-values to 32767 on modern hardware. The
extension <STRONG>init_extended_pair</STRONG> uses <STRONG>int</STRONG>s for the color pair and color-
value, allowing a larger number of colors to be supported.
</PRE><H3><a name="h3-init_color">init_color</a></H3><PRE>
The <STRONG>init_color</STRONG> routine changes the definition of a color. It takes
four arguments: the number of the color to be changed followed by three
RGB values (for the amounts of red, green, and blue components).
<STRONG>o</STRONG> The first argument must be a valid color value; default colors are
not allowed here. (See the section <STRONG>Colors</STRONG> for the default color
index.)
<STRONG>o</STRONG> Each of the last three arguments must be a value in the range <STRONG>0</STRONG>
through <STRONG>1000</STRONG>.
When <STRONG>init_color</STRONG> is used, all occurrences of that color on the screen
immediately change to the new definition.
</PRE><H3><a name="h3-init_extended_color">init_extended_color</a></H3><PRE>
Because <STRONG>init_color</STRONG> uses signed <STRONG>short</STRONG>s for its parameters, that limits
color-values and their red, green, and blue components to 32767 on
modern hardware. The extension <STRONG>init_extended_color</STRONG> uses <STRONG>int</STRONG>s for the
color value and for setting the red, green, and blue components,
allowing a larger number of colors to be supported.
</PRE><H3><a name="h3-color_content">color_content</a></H3><PRE>
The <STRONG>color_content</STRONG> routine gives programmers a way to find the intensity
of the red, green, and blue (RGB) components in a color. It requires
four arguments: the color number, and three addresses of <STRONG>short</STRONG>s for
storing the information about the amounts of red, green, and blue
components in the given color.
<STRONG>o</STRONG> The first argument must be a valid color value, i.e., <STRONG>0</STRONG> through
<STRONG>COLORS-1</STRONG>, inclusive.
<STRONG>o</STRONG> The values that are stored at the addresses pointed to by the last
three arguments are in the range <STRONG>0</STRONG> (no component) through <STRONG>1000</STRONG>
(maximum amount of component), inclusive.
</PRE><H3><a name="h3-extended_color_content">extended_color_content</a></H3><PRE>
Because <STRONG>color_content</STRONG> uses signed <STRONG>short</STRONG>s for its parameters, that
limits color-values and their red, green, and blue components to 32767
on modern hardware. The extension <STRONG>extended_color_content</STRONG> uses <STRONG>int</STRONG>s for
the color value and for returning the red, green, and blue components,
allowing a larger number of colors to be supported.
</PRE><H3><a name="h3-pair_content">pair_content</a></H3><PRE>
The <STRONG>pair_content</STRONG> routine allows programmers to find out what colors a
given color pair consists of. It requires three arguments: the color
pair number, and two addresses of <STRONG>short</STRONG>s for storing the foreground and
the background color numbers.
<STRONG>o</STRONG> The first argument must be a valid color value, i.e., in the range
<STRONG>1</STRONG> through <STRONG>COLOR_PAIRS-1</STRONG>, inclusive.
<STRONG>o</STRONG> The values that are stored at the addresses pointed to by the
second and third arguments are in the range <STRONG>0</STRONG> through <STRONG>COLORS</STRONG>,
inclusive.
</PRE><H3><a name="h3-extended_pair_content">extended_pair_content</a></H3><PRE>
Because <STRONG>pair_content</STRONG> uses signed <STRONG>short</STRONG>s for its parameters, that limits
color pair and color-values to 32767 on modern hardware. The extension
<STRONG>extended_pair_content</STRONG> uses <STRONG>int</STRONG>s for the color pair and for returning
the foreground and background colors, allowing a larger number of
colors to be supported.
</PRE><H3><a name="h3-reset_color_pairs">reset_color_pairs</a></H3><PRE>
The extension <STRONG>reset_color_pairs</STRONG> tells <EM>ncurses</EM> to discard all of the
color pair information which was set with <STRONG>init_pair</STRONG>. It also touches
the current- and standard-screens, allowing an application to switch
color palettes rapidly.
</PRE><H3><a name="h3-COLOR_PAIR">COLOR_PAIR</a></H3><PRE>
<STRONG>COLOR_PAIR(</STRONG><EM>n</EM><STRONG>)</STRONG> converts a color pair number to an attribute. Attributes
can hold color pairs in the range 0 to 255. If you need a color pair
larger than that, you must use functions such as <STRONG>attr_set</STRONG> (which pass
the color pair as a separate parameter) rather than the legacy
functions such as <STRONG>attrset</STRONG>.
</PRE><H3><a name="h3-PAIR_NUMBER">PAIR_NUMBER</a></H3><PRE>
<STRONG>PAIR_NUMBER(</STRONG><EM>attr</EM>) extracts the color information from its <EM>attr</EM>
parameter and returns it as a color pair number; it is the inverse
operation of <STRONG>COLOR_PAIR</STRONG>.
</PRE><H2><a name="h2-RETURN-VALUE">RETURN VALUE</a></H2><PRE>
The routines <STRONG>can_change_color</STRONG> and <STRONG>has_colors</STRONG> return <STRONG>TRUE</STRONG> or <STRONG>FALSE</STRONG>.
All other routines return the integer <STRONG>ERR</STRONG> upon failure and an <STRONG>OK</STRONG> (SVr4
specifies only "an integer value other than <STRONG>ERR</STRONG>") upon successful
completion.
X/Open defines no error conditions. SVr4 does document some error
conditions which apply in general:
<STRONG>o</STRONG> This implementation will return <STRONG>ERR</STRONG> on attempts to use color values
outside the range <STRONG>0</STRONG> to <STRONG>COLORS</STRONG>-1 (except for the default colors
extension), or use color pairs outside the range <STRONG>0</STRONG> to
<STRONG>COLOR_PAIRS-1</STRONG>.
Color values used in <STRONG>init_color</STRONG> must be in the range <STRONG>0</STRONG> to <STRONG>1000</STRONG>.
An error is returned from all functions if the terminal has not
been initialized.
An error is returned from secondary functions such as <STRONG>init_pair</STRONG> if
<STRONG>start_color</STRONG> was not called.
<STRONG>o</STRONG> SVr4 does much the same, except that it returns <STRONG>ERR</STRONG> from
<STRONG>pair_content</STRONG> if the pair was not initialized using <STRONG>init_pairs</STRONG> and
it returns <STRONG>ERR</STRONG> from <STRONG>color_content</STRONG> if the terminal does not support
changing colors.
This implementation does not return <STRONG>ERR</STRONG> for either case.
Specific functions make additional checks:
<STRONG>init_color</STRONG>
returns an error if the terminal does not support this feature,
e.g., if the <STRONG>initialize_color</STRONG> capability is absent from the
terminal description.
<STRONG>start_color</STRONG>
returns an error if the color table cannot be allocated.
</PRE><H2><a name="h2-NOTES">NOTES</a></H2><PRE>
In the <EM>ncurses</EM> implementation, there is a separate color activation
flag, color palette, color pairs table, and associated <STRONG>COLORS</STRONG> and
<STRONG>COLOR_PAIRS</STRONG> counts for each screen; the <STRONG>start_color</STRONG> function only
affects the current screen. The SVr4/XSI interface is not really
designed with this in mind, and historical implementations may use a
single shared color palette.
Setting an implicit background color via a color pair affects only
character cells that a character write operation explicitly touches.
To change the background color used when parts of a window are blanked
by erasing or scrolling operations, see <STRONG><A HREF="curs_bkgd.3x.html">curs_bkgd(3x)</A></STRONG>.
Several caveats apply on older x86 machines (e.g., i386, i486) with
VGA-compatible graphics:
<STRONG>o</STRONG> COLOR_YELLOW is actually brown. To get yellow, use COLOR_YELLOW
combined with the <STRONG>A_BOLD</STRONG> attribute.
<STRONG>o</STRONG> The A_BLINK attribute should in theory cause the background to go
bright. This often fails to work, and even some cards for which it
mostly works (such as the Paradise and compatibles) do the wrong
thing when you try to set a bright "yellow" background (you get a
blinking yellow foreground instead).
<STRONG>o</STRONG> Color RGB values are not settable.
</PRE><H2><a name="h2-EXTENSIONS">EXTENSIONS</a></H2><PRE>
The functions marked as extensions were designed for <STRONG><A HREF="ncurses.3x.html">ncurses(3x)</A></STRONG>, and
are not found in SVr4 <EM>curses</EM>, 4.4BSD <EM>curses</EM>, or any other previous
curses implementation.
</PRE><H2><a name="h2-PORTABILITY">PORTABILITY</a></H2><PRE>
Applications employing <EM>ncurses</EM> extensions should condition their use on
the visibility of the <STRONG>NCURSES_VERSION</STRONG> preprocessor macro.
This implementation satisfies X/Open Curses's minimum maximums for
<STRONG>COLORS</STRONG> and <STRONG>COLOR_PAIRS</STRONG>.
The <STRONG>init_pair</STRONG> routine accepts negative values of foreground and
background color to support the <STRONG><A HREF="default_colors.3x.html">use_default_colors(3x)</A></STRONG> extension, but
only if that routine has been first invoked.
The assumption that <STRONG>COLOR_BLACK</STRONG> is the default background color for all
terminals can be modified using the <STRONG><A HREF="default_colors.3x.html">assume_default_colors(3x)</A></STRONG>
extension.
This implementation checks the pointers, e.g., for the values returned
by <STRONG>color_content</STRONG> and <STRONG>pair_content</STRONG>, and will treat those as optional
parameters when null.
X/Open Curses does not specify a limit for the number of colors and
color pairs which a terminal can support. However, in its use of <STRONG>short</STRONG>
for the parameters, it carries over SVr4's implementation detail for
the compiled terminfo database, which uses signed 16-bit numbers. This
implementation provides extended versions of those functions which use
<STRONG>short</STRONG> parameters, allowing applications to use larger color- and pair-
numbers.
The <STRONG>reset_color_pairs</STRONG> function is an extension of <EM>ncurses</EM>.
</PRE><H2><a name="h2-HISTORY">HISTORY</a></H2><PRE>
SVr3.2 introduced color support to curses in 1987.
SVr4 made internal changes, e.g., moving the storage for the color
state from <STRONG>SP</STRONG> (the <EM>SCREEN</EM> structure) to <STRONG>cur_term</STRONG> (the <EM>TERMINAL</EM>
structure), but provided the same set of library functions.
SVr4 curses limits the number of color pairs to 64, reserving color
pair zero (0) as the terminal's initial uncolored state. This limit
arises because the color pair information is a bitfield in the <STRONG>chtype</STRONG>
data type (denoted by <STRONG>A_COLOR</STRONG>).
Other implementations of curses had different limits:
<STRONG>o</STRONG> PCCurses (1987-1990) provided for only eight (8) colors.
<STRONG>o</STRONG> PDCurses (1992-present) inherited the 8-color limitation from
PCCurses, but changed this to 256 in version 2.5 (2001), along with
changing <STRONG>chtype</STRONG> from 16-bits to 32-bits.
<STRONG>o</STRONG> X/Open Curses (1992-present) added a new structure <STRONG>cchar_t</STRONG> to store
the character, attributes and color pair values, allowing increased
range of color pairs. Both color pairs and color-values used a
signed <STRONG>short</STRONG>, limiting values to 15 bits.
<STRONG>o</STRONG> <EM>ncurses</EM> (1992-present) uses eight bits for <STRONG>A_COLOR</STRONG> in <STRONG>chtype</STRONG>
values.
Version 5.3 provided a wide-character interface (2002), but left
color pairs as part of the attributes-field.
Since version 6 (2015), ncurses uses a separate <STRONG>int</STRONG> for color pairs
in the <STRONG>cchar_t</STRONG> values. When those color pair values fit in 8 bits,
ncurses allows color pairs to be manipulated via the functions
using <STRONG>chtype</STRONG> values.
<STRONG>o</STRONG> NetBSD curses used 6 bits from 2000 (when colors were first
supported) until 2004. At that point, NetBSD changed to use 10
bits. As of 2021, that size is unchanged. Like <EM>ncurses</EM> before
version 6, the NetBSD color pair information is stored in the
attributes field of <STRONG>cchar_t</STRONG>, limiting the number of color pairs by
the size of the bitfield.
</PRE><H2><a name="h2-SEE-ALSO">SEE ALSO</a></H2><PRE>
<STRONG><A HREF="ncurses.3x.html">curses(3x)</A></STRONG>, <STRONG><A HREF="curs_attr.3x.html">curs_attr(3x)</A></STRONG>, <STRONG><A HREF="curs_initscr.3x.html">curs_initscr(3x)</A></STRONG>, <STRONG><A HREF="curs_variables.3x.html">curs_variables(3x)</A></STRONG>,
<STRONG><A HREF="default_colors.3x.html">default_colors(3x)</A></STRONG>
ncurses 6.5 2024-04-20 <STRONG><A HREF="curs_color.3x.html">curs_color(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-Overview">Overview</a></li>
<li><a href="#h3-Rendering">Rendering</a></li>
</ul>
</li>
<li><a href="#h2-CONSTANTS">CONSTANTS</a></li>
<li><a href="#h2-VARIABLES">VARIABLES</a>
<ul>
<li><a href="#h3-COLORS">COLORS</a></li>
<li><a href="#h3-COLOR_PAIRS">COLOR_PAIRS</a></li>
</ul>
</li>
<li><a href="#h2-FUNCTIONS">FUNCTIONS</a>
<ul>
<li><a href="#h3-start_color">start_color</a></li>
<li><a href="#h3-has_colors">has_colors</a></li>
<li><a href="#h3-can_change_color">can_change_color</a></li>
<li><a href="#h3-init_pair">init_pair</a></li>
<li><a href="#h3-init_extended_pair">init_extended_pair</a></li>
<li><a href="#h3-init_color">init_color</a></li>
<li><a href="#h3-init_extended_color">init_extended_color</a></li>
<li><a href="#h3-color_content">color_content</a></li>
<li><a href="#h3-extended_color_content">extended_color_content</a></li>
<li><a href="#h3-pair_content">pair_content</a></li>
<li><a href="#h3-extended_pair_content">extended_pair_content</a></li>
<li><a href="#h3-reset_color_pairs">reset_color_pairs</a></li>
<li><a href="#h3-COLOR_PAIR">COLOR_PAIR</a></li>
<li><a href="#h3-PAIR_NUMBER">PAIR_NUMBER</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-EXTENSIONS">EXTENSIONS</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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