NAME

SYNOPSIS

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

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

/* extensions */
void reset_color_pairs(void);

int COLOR_PAIR(int n);
PAIR_NUMBER(attrs);

DESCRIPTION

CONSTANTS

      COLOR_BLACK
      COLOR_RED
      COLOR_GREEN
      COLOR_YELLOW
      COLOR_BLUE
      COLOR_MAGENTA
      COLOR_CYAN
      COLOR_WHITE

Some terminals support more than the eight (8) “ANSI” colors. There are no standard names for those additional colors.

VARIABLES

FUNCTIONS

RETURN VALUE

All other routines return the integer ERR upon failure and an OK (SVr4 specifies only “an integer value other than ERR”) upon successful completion.

X/Open defines no error conditions. SVr4 does document some error conditions which apply in general:

•

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.

•

SVr4 does much the same, except that it returns ERR from pair_content if the pair was not initialized using init_pairs and it returns ERR from color_content if the terminal does not support changing colors.

This implementation does not return ERR for either case.

Specific functions make additional checks:

NOTES

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 curs_bkgd(3X).

Several caveats apply on older x86 machines (e.g., i386, i486) with VGA-compatible graphics:

• 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.

HISTORY

SVr4 made internal changes, e.g., moving the storage for the color state from SP (the SCREEN structure) to cur_term (the TERMINAL 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 chtype data type (denoted by A_COLOR).

Other implementations of curses had different limits:

• PCCurses (1987-1990) provided for only eight (8) colors.
• PDCurses (1992-present) inherited the 8-color limitation from PCCurses, but changed this to 256 in version 2.5 (2001), along with changing chtype from 16-bits to 32-bits.
• X/Open Curses (1992-present) added a new structure cchar_t to store the character, attributes and color-pair values, allowing increased range of color-pairs. Both color-pairs and color-values used a signed short, limiting values to 15 bits.
• ncurses (1992-present) uses eight bits for A_COLOR in chtype 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 int for color-pairs in the cchar_t values. When those color-pair values fit in 8 bits, ncurses allows color-pairs to be manipulated via the functions using chtype values.

•

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 ncurses before version 6, the NetBSD color-pair information is stored in the attributes field of cchar_t, limiting the number of color-pairs by the size of the bitfield.

PORTABILITY

The init_pair routine accepts negative values of foreground and background color to support the use_default_colors(3X) 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(3X) extension.

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.

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 short 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 short parameters, allowing applications to use larger color- and pair-numbers.

The reset_color_pairs function is an extension of ncurses.

SEE ALSO