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* Author: Thomas E. Dickey
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* @Id: new_pair.3x,v 1.26 2023/09/09 21:20:16 tom Exp @
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01//EN">
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<meta http-equiv="Content-Type" content="text/html; charset=us-ascii">
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<meta name="generator" content="Manpage converted by man2html - see https://invisible-island.net/scripts/readme.html#others_scripts">
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<TITLE>new_pair 3x 2023-09-09 ncurses 6.4 Library calls</TITLE>
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<link rel="author" href="mailto:bug-ncurses@gnu.org">
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<H1 class="no-header">new_pair 3x 2023-09-09 ncurses 6.4 Library calls</H1>
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<PRE>
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<STRONG><A HREF="new_pair.3x.html">new_pair(3x)</A></STRONG> Library calls <STRONG><A HREF="new_pair.3x.html">new_pair(3x)</A></STRONG>
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</PRE><H2><a name="h2-NAME">NAME</a></H2><PRE>
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<STRONG>alloc_pair</STRONG>, <STRONG>find_pair</STRONG>, <STRONG>free_pair</STRONG> - new curses color-pair functions
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</PRE><H2><a name="h2-SYNOPSIS">SYNOPSIS</a></H2><PRE>
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<STRONG>#include</STRONG> <STRONG><curses.h></STRONG>
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<STRONG>int</STRONG> <STRONG>alloc_pair(int</STRONG> <EM>fg</EM><STRONG>,</STRONG> <STRONG>int</STRONG> <EM>bg</EM><STRONG>);</STRONG>
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<STRONG>int</STRONG> <STRONG>find_pair(int</STRONG> <EM>fg</EM><STRONG>,</STRONG> <STRONG>int</STRONG> <EM>bg</EM><STRONG>);</STRONG>
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<STRONG>int</STRONG> <STRONG>free_pair(int</STRONG> <EM>pair</EM><STRONG>);</STRONG>
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</PRE><H2><a name="h2-DESCRIPTION">DESCRIPTION</a></H2><PRE>
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These functions are an extension to the curses library. They permit an
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application to dynamically allocate a color pair using the
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foreground/background colors rather than assign a fixed color pair
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number, and return an unused pair to the pool.
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The number of colors may be related to the number of possible color
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pairs for a given terminal, or it may not:
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<STRONG>o</STRONG> While almost all terminals allow setting the color <EM>attributes</EM>
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independently, it is unlikely that your terminal allows you to
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modify the attributes of a given character cell without rewriting
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it. That is, the foreground and background colors are applied as a
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pair.
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<STRONG>o</STRONG> Color pairs are the curses library's way of managing a color
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palette on a terminal. If the library does not keep track of the
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<EM>combinations</EM> of colors which are displayed, it will be inefficient.
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<STRONG>o</STRONG> For simple terminal emulators with only a few dozen color
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combinations, it is convenient to use the maximum number of
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combinations as the limit on color pairs:
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<STRONG>COLORS</STRONG> <EM>*</EM> <STRONG>COLORS</STRONG>
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<STRONG>o</STRONG> Terminals which support <EM>default</EM> <EM>colors</EM> distinct from "ANSI colors"
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add to the possible combinations, producing this total:
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<EM>(</EM> <STRONG>COLORS</STRONG> <EM>+</EM> <EM>1</EM> <EM>)</EM> <EM>*</EM> <EM>(</EM> <STRONG>COLORS</STRONG> <EM>+</EM> <EM>1</EM> <EM>)</EM>
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<STRONG>o</STRONG> An application might use up to a few dozen color pairs to implement
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a predefined color scheme.
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Beyond that lies in the realm of programs using the foreground and
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background colors for "ASCII art" (or some other non-textual
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application).
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Also beyond those few dozen pairs, the required size for a table to
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represent the combinations grows rapidly with an increasing number
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of colors.
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These functions allow a developer to let the screen library manage
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color pairs.
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</PRE><H3><a name="h3-alloc_pair">alloc_pair</a></H3><PRE>
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The <STRONG>alloc_pair</STRONG> function accepts parameters for foreground and
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background color, and checks if that color combination is already
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associated with a color pair.
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<STRONG>o</STRONG> If the combination already exists, <STRONG>alloc_pair</STRONG> returns the existing
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pair.
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<STRONG>o</STRONG> If the combination does not exist, <STRONG>alloc_pair</STRONG> allocates a new color
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pair and returns that.
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<STRONG>o</STRONG> If the table fills up, <STRONG>alloc_pair</STRONG> discards the least-recently
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allocated entry using <STRONG>free_pair</STRONG> and allocates a new color pair.
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All of the color pairs are allocated from a table of possible color
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pairs. The size of the table is determined by the terminfo <STRONG>pairs</STRONG>
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capability. The table is shared with <STRONG>init_pair</STRONG>; in fact <STRONG>alloc_pair</STRONG>
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calls <STRONG>init_pair</STRONG> after updating the ncurses library's fast index to the
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colors versus color pairs.
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</PRE><H3><a name="h3-find_pair">find_pair</a></H3><PRE>
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The <STRONG>find_pair</STRONG> function accepts parameters for foreground and background
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color, and checks if that color combination is already associated with
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a color pair, returning the pair number if it has been allocated.
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Otherwise it returns -1.
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</PRE><H3><a name="h3-free_pair">free_pair</a></H3><PRE>
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Marks the given color pair as unused, i.e., like color pair 0.
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</PRE><H2><a name="h2-RETURN-VALUE">RETURN VALUE</a></H2><PRE>
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The <STRONG>alloc_pair</STRONG> function returns a color pair number in the range 1
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through <STRONG>COLOR_PAIRS</STRONG>-1, unless it encounters an error updating its fast
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index to the color pair values, preventing it from allocating a color
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pair. In that case, it returns -1.
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The <STRONG>find_pair</STRONG> function returns a color pair number if the given color
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combination has been associated with a color pair, or -1 if not.
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Likewise, <STRONG>free_pair</STRONG> returns <STRONG>OK</STRONG> unless it encounters an error updating
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the fast index or if no such color pair is in use.
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</PRE><H2><a name="h2-PORTABILITY">PORTABILITY</a></H2><PRE>
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These routines are specific to ncurses. They were not supported on
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Version 7, BSD or System V implementations. It is recommended that any
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code depending on them be conditioned using NCURSES_VERSION.
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</PRE><H2><a name="h2-SEE-ALSO">SEE ALSO</a></H2><PRE>
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<STRONG><A HREF="curs_color.3x.html">curs_color(3x)</A></STRONG>.
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</PRE><H2><a name="h2-AUTHOR">AUTHOR</a></H2><PRE>
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Thomas Dickey.
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ncurses 6.4 2023-09-09 <STRONG><A HREF="new_pair.3x.html">new_pair(3x)</A></STRONG>
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</PRE>
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<div class="nav">
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<ul>
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<li><a href="#h2-NAME">NAME</a></li>
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<li><a href="#h2-SYNOPSIS">SYNOPSIS</a></li>
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<li><a href="#h2-DESCRIPTION">DESCRIPTION</a>
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<ul>
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<li><a href="#h3-alloc_pair">alloc_pair</a></li>
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<li><a href="#h3-find_pair">find_pair</a></li>
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<li><a href="#h3-free_pair">free_pair</a></li>
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</ul>
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</li>
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<li><a href="#h2-RETURN-VALUE">RETURN VALUE</a></li>
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<li><a href="#h2-PORTABILITY">PORTABILITY</a></li>
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<li><a href="#h2-SEE-ALSO">SEE ALSO</a></li>
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<li><a href="#h2-AUTHOR">AUTHOR</a></li>
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</ul>
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</div>
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