#include <curses.h>int start_color(void);int init_pair(short pair, short f, short b);int init_color(short color, short r, short g, short b);bool has_colors(void);bool can_change_color(void);int color_content(short color, short *r, short *g, short *b);int pair_content(short pair, short *f, short *b);int COLOR_PAIR(int n);PAIR_NUMBER(attrs);
Overviewcurses supports color attributes on terminals with that capability.
To use these routines start_color must be called, usually right after
initscr. Colors are always used in pairs (referred to as color-
pairs). A color-pair consists of a foreground color (for characters)
and a background color (for the blank field on which the characters
are displayed). A programmer initializes a color-pair with the
routine init_pair. After it has been initialized, COLOR_PAIR(n) can
be used to convert the pair to a video attribute.
If a terminal is capable of redefining colors, the programmer can use
the routine init_color to change the definition of a color. The
routines has_colors and can_change_color return TRUE or FALSE,
depending on whether the terminal has color capabilities and whether
the programmer can change the colors. The routine color_content
allows a programmer to extract the amounts of red, green, and blue
components in an initialized color. The routine pair_content allows
a programmer to find out how a given color-pair is currently defined.
The curses library combines these inputs to produce the actual
foreground and background colors shown on the screen:
· per-character video attributes (e.g., via waddch),
· the window attribute (e.g., by wattrset), and
· the background character (e.g., wbkgdset).
Per-character and window attributes are usually set by a parameter
containing video attributes including a color pair value. Some
functions such as wattr_set use a separate parameter which is the
color pair number.
The background character is a special case: it includes a character
value, just as if it were passed to waddch.
The curses library does the actual work of combining these color
pairs in an internal function called from waddch:
· If the parameter passed to waddch is blank, and it uses the
special color pair 0,
· curses next checks the window attribute.
· If the window attribute does not use color pair 0, curses
uses the color pair from the window attribute.
· Otherwise, curses uses the background character.
· If the parameter passed to waddch is not blank, or it does not
use the special color pair 0, curses prefers the color pair from
the parameter, if it is nonzero. Otherwise, it tries the window
attribute next, and finally the background character.
Some curses functions such as wprintw call waddch. Those do not
combine its parameter with a color pair. Consequently those calls
use only the window attribute or the background character.
The start_color 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 initscr. start_color does this:
· It initializes two global variables, COLORS and COLOR_PAIRS
(respectively defining the maximum number of colors and color-
pairs the terminal can support).
· It initializes the special color pair 0 to the default foreground
and background colors. No other color pairs are initialized.
· It restores the colors on the terminal to the values they had
when the terminal was just turned on.
· If the terminal supports the initc (initialize_color) capability,
start_color 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 hls (hue_lightness_saturation)
capability is set). The table is initialized first for eight
basic colors (black, red, green, yellow, blue, magenta, cyan, and
white), and after that (if the terminal supports more than eight
colors) the components are initialized to 1000.
start_color does not attempt to set the terminal's color palette
to match its built-in table. An application may use init_color
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 legal, and may result in a runtime error:
· COLORS corresponds to the terminal database's max_colors
capability, which is typically a signed 16-bit integer (see
· color values are expected to be in the range 0 to COLORS-1,
inclusive (including 0 and COLORS-1).
· a special color value -1 is used in certain extended functions to
denote the default color (see use_default_colors).
· COLOR_PAIRS corresponds to the terminal database's max_pairs
capability, which is typically a signed 16-bit integer (see
· legal color pair values are in the range 1 to COLOR_PAIRS-1,
· color pair 0 is special; it denotes “no color”.
Color pair 0 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.
The init_pair 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
· The first argument must be a legal color pair value. If default
colors are used (see use_default_colors) the upper limit is
adjusted to allow for extra pairs which use a default color in
foreground and/or background.
· The second and third arguments must be legal 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
As an extension, ncurses allows you to set color pair 0 via the
assume_default_colors routine, or to specify the use of default
colors (color number -1) if you first invoke the use_default_colors
The init_color 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). The first argument must be a legal color value; default
colors are not allowed here. (See the section Colors for the default
color index.) Each of the last three arguments must be a value in
the range 0 through 1000. When init_color is used, all occurrences
of that color on the screen immediately change to the new definition.
The has_colors routine requires no arguments. It returns TRUE if the
terminal can manipulate colors; otherwise, it returns FALSE. 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.
The can_change_color routine requires no arguments. It returns TRUE
if the terminal supports colors and can change their definitions;
other, it returns FALSE. This routine facilitates writing terminal-
The color_content 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
shorts for storing the information about the amounts of red, green,
and blue components in the given color. The first argument must be a
legal color value, i.e., 0 through COLORS-1, inclusive. The values
that are stored at the addresses pointed to by the last three
arguments are in the range 0 (no component) through 1000 (maximum
amount of component), inclusive.
The pair_content 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 shorts for storing the
foreground and the background color numbers. The first argument must
be a legal color value, i.e., in the range 1 through COLOR_PAIRS-1,
inclusive. The values that are stored at the addresses pointed to by
the second and third arguments are in the range 0 through COLORS,
PAIR_NUMBER(attrs) extracts the color value from its attrs parameter
and returns it as a color pair number. Its inverse COLOR_PAIR(n)
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 attr_set (which pass the
color pair as a separate parameter) rather than the legacy functions
such as attrset.
In <curses.h> the following macros are defined. These are the
standard colors (ISO-6429). curses also assumes that COLOR_BLACK is
the default background color for all terminals.
The routines can_change_color and has_colors return TRUE or FALSE.
All other routines return the integer ERR upon failure and an OK
(SVr4 specifies only “an integer value other than ERR”) upon
X/Open defines no error conditions. This implementation will return
ERR on attempts to use color values outside the range 0 to COLORS-1
(except for the default colors extension), or use color pairs outside
the range 0 to COLOR_PAIRS-1. Color values used in init_color must
be in the range 0 to 1000. An error is returned from all functions
if the terminal has not been initialized. An error is returned from
secondary functions such as init_pair if start_color was not called.
returns an error if the terminal does not support this
feature, e.g., if the initialize_color capability is absent
from the terminal description.
returns an error if the color table cannot be allocated.
In the ncurses implementation, there is a separate color activation
flag, color palette, color pairs table, and associated COLORS and
COLOR_PAIRS counts for each screen; the start_color 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.
Note that 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
Several caveats apply on 386 and 486 machines with VGA-compatible
· COLOR_YELLOW is actually brown. To get yellow, use COLOR_YELLOW
combined with the A_BOLD attribute.
· 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).
· Color RGB values are not settable.
This implementation satisfies XSI Curses's minimum maximums for
COLORS and COLOR_PAIRS.
The init_pair routine accepts negative values of foreground and
background color to support the use_default_colors extension, but
only if that routine has been first invoked.
The assumption that COLOR_BLACK is the default background color for
all terminals can be modified using the assume_default_colors
This implementation checks the pointers, e.g., for the values
returned by color_content and pair_content, and will treat those as
optional parameters when null.
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