new_pair(3x) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | PORTABILITY | SEE ALSO | AUTHOR | COLOPHON

new_pair(3X)                                                new_pair(3X)

NAME         top

       alloc_pair, find_pair, free_pair - new curses color-pair
       functions

SYNOPSIS         top

       #include <curses.h>

       int alloc_pair(int fg, int bg);
       int find_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
           inefficient.

       •   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 application).

           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.

   alloc_pair
       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.

   find_pair
       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.

   free_pair
       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

       curs_color(3X).

AUTHOR         top

       Thomas Dickey.

COLOPHON         top

       This page is part of the ncurses (new curses) project.
       Information about the project can be found at 
       ⟨https://www.gnu.org/software/ncurses/ncurses.html⟩.  If you have
       a bug report for this manual page, send it to
       bug-ncurses-request@gnu.org.  This page was obtained from the
       project's upstream Git mirror of the CVS repository
       ⟨https://github.com/mirror/ncurses.git⟩ on 2023-12-22.  (At that
       time, the date of the most recent commit that was found in the
       repository was 2023-03-12.)  If you discover any rendering
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       is a better or more up-to-date source for the page, or you have
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       (which is not part of the original manual page), send a mail to
       man-pages@man7.org

                                                            new_pair(3X)