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<H1 class="no-header">new_pair 3x 2024-03-16 ncurses 6.5 Library calls</H1>
<PRE>
<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>
</PRE><H2><a name="h2-NAME">NAME</a></H2><PRE>
<STRONG>alloc_pair</STRONG>, <STRONG>find_pair</STRONG>, <STRONG>free_pair</STRONG> - dynamically allocate <EM>curses</EM> color
pairs
</PRE><H2><a name="h2-SYNOPSIS">SYNOPSIS</a></H2><PRE>
<STRONG>#include</STRONG> <STRONG><curses.h></STRONG>
<STRONG>int</STRONG> <STRONG>alloc_pair(int</STRONG> <EM>fg</EM><STRONG>,</STRONG> <STRONG>int</STRONG> <EM>bg</EM><STRONG>);</STRONG>
<STRONG>int</STRONG> <STRONG>find_pair(int</STRONG> <EM>fg</EM><STRONG>,</STRONG> <STRONG>int</STRONG> <EM>bg</EM><STRONG>);</STRONG>
<STRONG>int</STRONG> <STRONG>free_pair(int</STRONG> <EM>pair</EM><STRONG>);</STRONG>
</PRE><H2><a name="h2-DESCRIPTION">DESCRIPTION</a></H2><PRE>
These functions are an extension to the <EM>curses</EM> 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:
<STRONG>o</STRONG> While almost all terminals allow setting the color <EM>attributes</EM>
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.
<STRONG>o</STRONG> Color pairs are the <EM>curses</EM> library's way of managing a color
palette on a terminal. If the library does not keep track of the
<EM>combinations</EM> of colors which are displayed, it will be inefficient.
<STRONG>o</STRONG> 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:
<STRONG>COLORS</STRONG> <EM>*</EM> <STRONG>COLORS</STRONG>
<STRONG>o</STRONG> Terminals which support <EM>default</EM> <EM>colors</EM> distinct from "ANSI colors"
add to the possible combinations, producing this total:
<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>
<STRONG>o</STRONG> 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.
</PRE><H3><a name="h3-alloc_pair">alloc_pair</a></H3><PRE>
The <STRONG>alloc_pair</STRONG> function accepts parameters for foreground and
background color, and checks if that color combination is already
associated with a color pair.
<STRONG>o</STRONG> If the combination already exists, <STRONG>alloc_pair</STRONG> returns the existing
pair.
<STRONG>o</STRONG> If the combination does not exist, <STRONG>alloc_pair</STRONG> allocates a new color
pair and returns that.
<STRONG>o</STRONG> If the table fills up, <STRONG>alloc_pair</STRONG> discards the least-recently
allocated entry using <STRONG>free_pair</STRONG> 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 <STRONG>pairs</STRONG>
capability. The table is shared with <STRONG>init_pair</STRONG>; in fact <STRONG>alloc_pair</STRONG>
calls <STRONG>init_pair</STRONG> after updating the <EM>ncurses</EM> library's fast index to the
colors versus color pairs.
</PRE><H3><a name="h3-find_pair">find_pair</a></H3><PRE>
The <STRONG>find_pair</STRONG> 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.
</PRE><H3><a name="h3-free_pair">free_pair</a></H3><PRE>
Marks the given color pair as unused, i.e., like color pair 0.
</PRE><H2><a name="h2-RETURN-VALUE">RETURN VALUE</a></H2><PRE>
The <STRONG>alloc_pair</STRONG> function returns a color pair number in the range 1
through <STRONG>COLOR_PAIRS</STRONG>-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 <STRONG>find_pair</STRONG> function returns a color pair number if the given color
combination has been associated with a color pair, or -1 if not.
Likewise, <STRONG>free_pair</STRONG> returns <STRONG>OK</STRONG> unless it encounters an error updating
the fast index or if no such color pair is in use.
</PRE><H2><a name="h2-PORTABILITY">PORTABILITY</a></H2><PRE>
These routines are specific to <EM>ncurses</EM>. They were not supported on
Version 7, BSD or System V implementations. It is recommended that any
code depending on them be conditioned using <STRONG>NCURSES_VERSION</STRONG>.
</PRE><H2><a name="h2-AUTHORS">AUTHORS</a></H2><PRE>
Thomas Dickey
</PRE><H2><a name="h2-SEE-ALSO">SEE ALSO</a></H2><PRE>
<STRONG><A HREF="curs_color.3x.html">curs_color(3x)</A></STRONG>
ncurses 6.5 2024-03-16 <STRONG><A HREF="new_pair.3x.html">new_pair(3x)</A></STRONG>
</PRE>
<div class="nav">
<ul>
<li><a href="#h2-NAME">NAME</a></li>
<li><a href="#h2-SYNOPSIS">SYNOPSIS</a></li>
<li><a href="#h2-DESCRIPTION">DESCRIPTION</a>
<ul>
<li><a href="#h3-alloc_pair">alloc_pair</a></li>
<li><a href="#h3-find_pair">find_pair</a></li>
<li><a href="#h3-free_pair">free_pair</a></li>
</ul>
</li>
<li><a href="#h2-RETURN-VALUE">RETURN VALUE</a></li>
<li><a href="#h2-PORTABILITY">PORTABILITY</a></li>
<li><a href="#h2-AUTHORS">AUTHORS</a></li>
<li><a href="#h2-SEE-ALSO">SEE ALSO</a></li>
</ul>
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