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new_pair 3x

new_pair(3x)                                                      new_pair(3x)




NAME

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


SYNOPSIS

       #include <curses.h>

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


DESCRIPTION

       These functions are an extension to the curses library.  They permit an
       application to dynamically  allocate  a  color  pair  using  the  fore-
       ground/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:

       o   While almost all terminals allow setting the color attributes inde-
           pendently, 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.

       o   Color  pairs  are the curses library's way of managing a color pal-
           ette on a terminal.  If the library does not keep track of the com-
           binations of colors which are displayed, it will be inefficient.

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

             COLORS * COLORS

       o   Terminals  which support default colors distinct from "ANSI colors"
           add to the possible combinations, producing this total:

             ( COLORS + 1 ) * ( COLORS + 1 )

       o   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 appli-
           cation).

           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  back-
       ground  color,  and checks if that color combination is already associ-
       ated with a color pair.

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

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

       o   If the table fills up, alloc_pair discards the least-recently allo-
           cated 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 capa-
       bility.   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.  Oth-
       erwise it returns -1.


free_pair

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


RETURN VALUE

       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

       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

       init_pair(3x).


AUTHOR

       Thomas Dickey.



                                                                  new_pair(3x)