NAME¶

start_color, has_colors, can_change_color, init_pair, init_color, init_extended_pair, init_extended_color, color_content, pair_content, extended_color_content, extended_pair_content, reset_color_pairs, COLOR_PAIR, PAIR_NUMBER, COLORS, COLOR_PAIRS, COLOR_BLACK, COLOR_RED, COLOR_GREEN, COLOR_YELLOW, COLOR_BLUE, COLOR_MAGENTA, COLOR_CYAN, COLOR_WHITE, A_COLOR - manipulate terminal colors with curses

SYNOPSIS¶

#include <ncursesw/curses.h>

/* variables */
int COLOR_PAIRS;
int COLORS;

int start_color(void);

bool has_colors(void);
bool can_change_color(void);

int init_pair(short pair, short f, short b);
int init_color(short index, short r, short g, short b);
/* extensions */
int init_extended_pair(int pair, int f, int b);
int init_extended_color(int index, int r, int g, int b);

int color_content(short index, short *r, short *g, short *b);
int pair_content(short pair, short *f, short *b);
/* extensions */
int extended_color_content(int index, int *r, int *g, int *b);
int extended_pair_content(int pair, int *f, int *b);

/* extension */
void reset_color_pairs(void);

/* macros */
int COLOR_PAIR(int n);
PAIR_NUMBER(int attr);
COLOR_BLACK
COLOR_RED
COLOR_GREEN
COLOR_YELLOW
COLOR_BLUE
COLOR_MAGENTA
COLOR_CYAN
COLOR_WHITE
A_COLOR

DESCRIPTION¶

curses supports color rendering on terminals with applicable capabilities. Once the library has initialized the terminal, has_colors tells an application whether that terminal type has color capability. If it does, calling start_color enables the feature. (See section “NOTES” below regarding ripoffline(3NCURSES).)

When applying colors to a curses window, the library manages them in pairs. A color pair couples a foreground color applied to the visible strokes of a glyph with a background color for the field in the character cell within which the glyph appears. Configure at least one color pair to use the color feature. init_pair initializes a color pair identifier, whose value you select, from a pair of color indices, foreground and background. Each index represents a color. X/Open Curses standardizes, and a curses library predefines, a small set of color indices; see section “CONSTANTS” below. The macro COLOR_PAIR(n) converts a pair n thus initialized to the value required to encode it in a chtype or attr_t. Another macro, PAIR_NUMBER(n) conversely extracts a color pair identifier from variables of those data types. pair_content permits discovery of a color pair's current definition. color_content extracts the red, green, and blue components of the color using the given index.

can_change_color tells an application whether the terminal type permits (re)definition of a color. If it does, you can call init_color to update the specified color index to use red, green, and blue components of your choice.

Subsection “Color Handling” of terminfo(5) describes the capabilities that terminal types use to manage color.

Passing a curses function a color index outside the range 0 to COLORS-1, or a color pair identifier outside the range 0 to COLOR_PAIRS-1 may result in a runtime error. COLORS corresponds to the terminal type's max_colors (colors) capability, and COLOR_PAIRS to max_pairs (pairs). ncurses permits specification of a color index of -1 in certain extended functions to select a default color; see use_default_colors(3NCURSES).

Color pair 0 is special; it denotes “no color”, meaning the terminal's (typically monochrome) power-up default fore- and background.

For each screen, ncurses maintains a color palette that maps color indices into a color space. curses supports RGB (red, green, blue) and HLS (hue, lightness, saturation) color spaces. A terminal type uses one or the other. RGB is the default; the hue_lightness_saturation (hls) capability indicates the alternative.

CONSTANTS¶

ISO 6429 and ECMA-48 define eight standard colors (also known as “ANSI” colors). curses.h defines object-like macros COLOR_BLACK, COLOR_RED, COLOR_GREEN, COLOR_YELLOW, COLOR_BLUE, COLOR_MAGENTA, COLOR_CYAN, and COLOR_WHITE accordingly. curses assumes that COLOR_BLACK is the default background color for all terminals. ncurses offers an extension to override that assumption; see assume_default_colors(3NCURSES). Some terminals support additional colors that lack standard names.

A_COLOR is a bit mask that, when bitwise “and”-ed with a chtype, extracts its color pair identifier.

VARIABLES¶

FUNCTIONS¶

MACROS¶

X/Open Curses mandates the provision of two function-like macros. They have no application in the wide-character API of curses.

RETURN VALUE¶

can_change_color and has_colors return TRUE or FALSE. The other functions return OK on success and ERR on failure.

In ncurses, color manipulation functions returning an int recognize several error conditions.

• All return ERR if the screen has not been initialized; see initscr(3NCURSES) or newterm(3NCURSES).
• All except start_color return ERR if start_color has not been called, or itself returned ERR.
• start_color returns ERR if it cannot allocate memory for its color pair table.
• init_color returns ERR if the terminal type does not support assignable color values; that is, if the initialize_color (initc) capability is absent from its description.
• init_color returns ERR if any of its r, g, b arguments is outside the range 0-1000 inclusive.
• init_pair, init_color, init_extended_pair, init_extended_color, color_content, pair_content, extended_color_content, and extended_pair_content return ERR on attempts to use

NOTES¶

X/Open Curses says nothing about how the standard colors are to be configured in a color space. ncurses initializes a screen's color palette such that, in the RGB color space, each channel of the eight standard colors has a value of either 680 or 0. If the terminal type supports at least 16 colors, this configuration aids an application to support a terminal type with only one typeface to simulate bold text with “bright” colors. With appropriate configuration of the bright color pairs by the application, increasing nonzero channel values to 1000, this scheme suffices to approximate the 16 colors of IBM CGA text mode video and the power-up configuration of the DEC VT525. SVr4 curses instead assigns values of 1000 to the nonzero color channel values of the eight standard colors.

Setting a background color via a color pair identifier 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 bkgd(3NCURSES) (wide-character API users: bkgrnd(3NCURSES)).

Windows created by ripoffline(3NCURSES) do not inherit color pair configuration applied to stdscr; they must be configured independently.

In ncurses, init_pair accepts negative foreground and background color arguments to support its use_default_colors(3NCURSES) extension, but only after the latter function has been called.

The assumption that COLOR_BLACK is the terminal's default background color can be overridden using ncurses's assume_default_colors(3NCURSES) extension.

In ncurses, each pointer passed to color_content and pair_content can be null, in which case the library ignores it, permitting the application to disregard unnecessary information.

In ncurses, each screen has a color activation flag, color palette, color pair table, and associated COLORS and COLOR_PAIRS values; start_color affects only the current screen. The SVr4 curses interface, standardizes by X/Open Curses, was not designed with distinguishable screens clearly in mind; historical implementations may use a single shared color palette for all screens the library manages.

Several caveats apply to emulation of the CGA/EGA/VGA video of IBM PC-compatible machines of the 80486 era and earlier.

• COLOR_YELLOW was frequently converted, in the analog domain, to a shade of brown if the intensity bit was not set. To get yellow on such devices, one would combine COLOR_YELLOW with the A_BOLD attribute.
• The A_BLINK attribute should in theory make the background bright. This often fails to work, and even VGA controllers for which it mostly works, such as those from 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 configurable on these devices (in text mode).

EXTENSIONS¶

The functions marked as extensions originated in ncurses, and are not found in SVr4 curses, 4.4BSD curses, or any other previous curses implementation.

PORTABILITY¶

Applications employing ncurses extensions should condition their use on the visibility of the NCURSES_VERSION preprocessor macro.

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

ncurses satisfies X/Open Curses's minimum maximums for COLORS and COLOR_PAIRS.

ncurses does not refresh the screen if init_pair is used to no effect on an existing color pair.

X/Open Curses does not specify a limit for the number of color indices and color pair identifiers a terminal can support. However, in its use of short for the parameters, it carries over SVr4's implementation detail for the compiled terminfo database, which uses signed 16-bit numbers. ncurses provides extended versions of the functions using int parameters, allowing applications to use larger index and pair identifiers.

SVr4 curses returns ERR from pair_content if its pair argument was not initialized using init_pairs, and from color_content if the terminal does not support changing colors. ncurses does neither.

HISTORY¶

SVr3.2 (1988) introduced color support to curses with all of the symbols in the synopsis above except those marked as extensions. It reserved color pair 0 as the terminal's initial, “uncolored” state, and limited the number of possible color pairs to 64, because the color pair datum was encoded in six bits of a chtype.

SVr4 (1989) made only internal changes, such as moving the storage of color state from the SCREEN structure (pointed to by SP) to the TERMINAL structure (pointed to by cur_term).

Other curses implementations impose different limits on the number of color indices and color pairs.

• PCCurses (1987-1990) provided for only 8 color indices (and therefore permitted at most 8×8 = 64 color pairs).
• PDCurses (1992-present) initially inherited the 8-color limitation from PCCurses, but increased it to 256 in version 2.5 (2001), and widened its chtype from 16 to 32 bits.
• X/Open Curses (1992-present) specified a new integral type, attr_t, storing rendering attributes (see attr_on(3NCURSES)) and a color pair identifier, and a new structure type, cchar_t, to store a sequence of wide character codes separately from the character cell's attributed and color pair, allowing an increased range of color pairs. The standard specifies attr_t as a short, limiting portable values to 15 bits; negative values are invalid in System V.
• ncurses (1992-present), in its non-wide-character configuration, uses 8 bits of chtype for the color pair identifier.

Version 5.3 (2002) introduced a wide-character interface, but encoded the color pair identifier with attributes in the character type.

Since version 6 (2015), ncurses uses a separate int for the color pair identifier in a cchar_t, adding extension functions to manage the wider type. When a color pair identifier fits in 8 bits, ncurses permits manipulation of color pair identifiers with functions taking chtype arguments, even when a curses window uses wide-character cells.

•

NetBSD curses used 6 bits for the color pair identifier from 2000 (when it first added color support) until 2004. At that point, NetBSD widened the color pair identifier to use 9 bits. As of 2025, that size is unchanged. Like ncurses before version 6, the NetBSD color pair identifier is stored in the attributes field of cchar_t, limiting the number of color pairs.

ncurses 6.1 (2018) introduced init_extended_pair, init_extended_color, extended_pair_content, extended_color_content, and reset_color_pairs.

SEE ALSO¶

ncurses(3NCURSES), attr(3NCURSES), initscr(3NCURSES), curses_variables(3NCURSES), default_colors(3NCURSES)