new_pair(3X)                                                    new_pair(3X)

NAME         top

       alloc_pair, free_pair - new curses color-pair functions

SYNOPSIS         top

       #include <curses.h>

       int alloc_pair(int fg, int bg);
       int free_pair(int pair);

DESCRIPTION         top

       These functions are an extension to the curses library.  They permit
       an application to dynamically allocate a color pair using the
       foreground/background colors rather than assign a fixed color pair
       number, and return an unused pair to the pool.

       The number of colors may be related to the number of possible color
       pairs for a given terminal, or it may not:

       ·   While almost all terminals allow setting the color attributes
           independently, it is unlikely that your terminal allows you to
           modify the attributes of a given character cell without rewriting
           it.  That is, the foreground and background colors are applied as
           a pair.

       ·   Color pairs are the curses library's way of managing a color
           palette on a terminal.  If the library does not keep track of the
           combinations of colors which are displayed, it will be

       ·   For simple terminal emulators with only a few dozen color
           combinations, it is convenient to use the maximum number of
           combinations as the limit on color pairs:

             COLORS * COLORS

       ·   Terminals which support default colors distinct from “ANSI
           colors” add to the possible combinations, producing this total:

             ( COLORS + 1 ) * ( COLORS + 1 )

       ·   An application might use up to a few dozen color pairs to
           implement a predefined color scheme.

           Beyond that lies in the realm of programs using the foreground
           and background colors for “ASCII art” (or some other non-textual

           Also beyond those few dozen pairs, the required size for a table
           to represent the combinations grows rapidly with an increasing
           number of colors.

           These functions allow a developer to let the screen library
           manage color pairs.

       The alloc_pair function accepts parameters for foreground and
       background color, and checks if that color combination is already
       associated with a color pair.

       ·   If the combination already exists, alloc_pair returns the
           existing pair.

       ·   If the combination does not exist, alloc_pair allocates a new
           color pair and returns that.

       ·   If the table fills up, alloc_pair discards the least-recently
           allocated entry using free_pair and allocates a new color pair.

       All of the color pairs are allocated from a table of possible color
       pairs.  The size of the table is determined by the terminfo pairs
       capability.  The table is shared with init_pair; in fact alloc_pair
       calls init_pair after updating the ncurses library's fast index to
       the colors versus color pairs.

       The find_pair function accepts parameters for foreground and
       background color, and checks if that color combination is already
       associated with a color pair, returning the pair number if it has
       been allocated.  Otherwise it returns -1.

       Marks the given color pair as unused, i.e., like color pair 0.

RETURN VALUE         top

       The alloc_pair function returns a color pair number in the range 1
       through COLOR_PAIRS-1, unless it encounters an error updating its
       fast index to the color pair values, preventing it from allocating a
       color pair.  In that case, it returns -1.

       The find_pair function returns a color pair number if the given color
       combination has been associated with a color pair, or -1 if not.

       Likewise, free_pair returns OK unless it encounters an error updating
       the fast index or if no such color pair is in use.

PORTABILITY         top

       These routines are specific to ncurses.  They were not supported on
       Version 7, BSD or System V implementations.  It is recommended that
       any code depending on them be conditioned using NCURSES_VERSION.

SEE ALSO         top


AUTHOR         top

       Thomas Dickey.

COLOPHON         top

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