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<H1 class="no-header">curs_variables 3x 2025-08-23 ncurses 6.6 Library calls</H1>
<PRE>
<STRONG><A HREF="curs_variables.3x.html">curs_variables(3x)</A></STRONG> Library calls <STRONG><A HREF="curs_variables.3x.html">curs_variables(3x)</A></STRONG>
</PRE><H2><a name="h2-NAME">NAME</a></H2><PRE>
<EM>bool</EM>, <EM>chtype</EM>, <EM>cchar</EM><STRONG>_</STRONG><EM>t</EM>, <EM>attr</EM><STRONG>_</STRONG><EM>t</EM>, <EM>SCREEN</EM>, <EM>WINDOW</EM>, <STRONG>TRUE</STRONG>, <STRONG>FALSE</STRONG>, <STRONG>ERR</STRONG>, <STRONG>OK</STRONG>,
<STRONG>CCHARW_MAX</STRONG>, <STRONG>curscr</STRONG>, <STRONG>newscr</STRONG>, <STRONG>stdscr</STRONG>, <STRONG>COLORS</STRONG>, <STRONG>COLOR_PAIRS</STRONG>, <STRONG>COLS</STRONG>, <STRONG>LINES</STRONG>,
<STRONG>ESCDELAY</STRONG>, <STRONG>TABSIZE</STRONG> - <EM>curses</EM> data types, constants, and global variables
</PRE><H2><a name="h2-SYNOPSIS">SYNOPSIS</a></H2><PRE>
<STRONG>#include</STRONG> <STRONG><curses.h></STRONG>
<EM>/*</EM> <EM>data</EM> <EM>types</EM> <EM>*/</EM>
<STRONG>typedef</STRONG> <EM>/*</EM> <STRONG>...</STRONG> <EM>*/</EM> <STRONG>bool;</STRONG>
<STRONG>typedef</STRONG> <EM>/*</EM> <STRONG>...</STRONG> <EM>*/</EM> <STRONG>chtype;</STRONG>
<STRONG>typedef</STRONG> <EM>/*</EM> <STRONG>...</STRONG> <EM>*/</EM> <STRONG>cchar_t;</STRONG>
<STRONG>typedef</STRONG> <EM>/*</EM> <STRONG>...</STRONG> <EM>*/</EM> <STRONG>attr_t;</STRONG>
<STRONG>typedef</STRONG> <EM>/*</EM> <STRONG>...</STRONG> <EM>*/</EM> <STRONG>SCREEN;</STRONG>
<STRONG>typedef</STRONG> <EM>/*</EM> <STRONG>...</STRONG> <EM>*/</EM> <STRONG>WINDOW;</STRONG>
<EM>/*</EM> <EM>constants</EM> <EM>*/</EM>
<STRONG>const</STRONG> <STRONG>bool</STRONG> <STRONG>TRUE;</STRONG>
<STRONG>const</STRONG> <STRONG>bool</STRONG> <STRONG>FALSE;</STRONG>
<STRONG>const</STRONG> <EM>/*</EM> <STRONG>...</STRONG> <EM>*/</EM> <STRONG>ERR;</STRONG>
<STRONG>const</STRONG> <EM>/*</EM> <STRONG>...</STRONG> <EM>*/</EM> <STRONG>OK;</STRONG>
<EM>/*</EM> <EM>extension</EM> <EM>*/</EM>
<STRONG>const</STRONG> <EM>/*</EM> <STRONG>...</STRONG> <EM>*/</EM> <STRONG>CCHARW_MAX;</STRONG>
<EM>/*</EM> <EM>variables</EM> <EM>*/</EM>
<STRONG>int</STRONG> <STRONG>COLORS;</STRONG>
<STRONG>int</STRONG> <STRONG>COLOR_PAIRS;</STRONG>
<STRONG>int</STRONG> <STRONG>COLS;</STRONG>
<STRONG>int</STRONG> <STRONG>LINES;</STRONG>
<STRONG>WINDOW</STRONG> <STRONG>*</STRONG> <STRONG>curscr;</STRONG>
<STRONG>WINDOW</STRONG> <STRONG>*</STRONG> <STRONG>stdscr;</STRONG>
<EM>/*</EM> <EM>extensions</EM> <EM>*/</EM>
<STRONG>int</STRONG> <STRONG>ESCDELAY;</STRONG>
<STRONG>int</STRONG> <STRONG>TABSIZE;</STRONG>
<STRONG>WINDOW</STRONG> <STRONG>*</STRONG> <STRONG>newscr;</STRONG>
</PRE><H2><a name="h2-DESCRIPTION">DESCRIPTION</a></H2><PRE>
This page summarizes data types, constants, and variables provided by
the <EM>curses</EM> library. Locate further discussion in <STRONG><A HREF="ncurses.3x.html">curses(3x)</A></STRONG>.
Depending on <EM>ncurses</EM>'s build-time configuration, the variables may
instead be macros (see <STRONG><A HREF="curs_threads.3x.html">curs_threads(3x)</A></STRONG> and <STRONG><A HREF="curs_opaque.3x.html">curs_opaque(3x)</A></STRONG>) that
provide read-only access to the library's state. In either case,
applications should treat them as read-only to avoid confusing the
library.
</PRE><H2><a name="h2-CONSTANTS">CONSTANTS</a></H2><PRE>
</PRE><H3><a name="h3-TRUE_FALSE">TRUE, FALSE</a></H3><PRE>
The <EM>curses</EM> library defines <STRONG>TRUE</STRONG> and <STRONG>FALSE</STRONG> to represent the values of
the Boolean data type.
</PRE><H3><a name="h3-ERR_OK">ERR, OK</a></H3><PRE>
<EM>curses</EM> and <EM>terminfo</EM> functions frequently return these constant integral
values indicating failure and success, respectively.
</PRE><H3><a name="h3-CCHARW_MAX">CCHARW_MAX</a></H3><PRE>
This integral value, an <EM>ncurses</EM> extension, indicates the maximum number
of <EM>wchar</EM><STRONG>_</STRONG><EM>t</EM> wide characters that can be stored in a <EM>curses</EM> complex
character <EM>cchar</EM><STRONG>_</STRONG><EM>t</EM>.
</PRE><H2><a name="h2-DATA-TYPES">DATA TYPES</a></H2><PRE>
</PRE><H3><a name="h3-bool"><EM>bool</EM></a></H3><PRE>
<EM>curses</EM> defines an integral type <EM>bool</EM>. X/Open Issue 4 <EM>curses</EM> (1996)
preceded the ISO C99 and ISO C++98 standards, each of which also
defined a Boolean data type of the same name.
<EM>ncurses</EM>'s configure script attempts to discover the data type used by
the system's C and C++ compilers, to reuse them as its own <EM>bool</EM>.
</PRE><H3><a name="h3-chtype"><EM>chtype</EM></a></H3><PRE>
The <EM>chtype</EM> integral type combines a ("narrow", 8-bit) character with
attributes encoding the character's <EM>rendition</EM>, such as the styling of
its typeface and/or foreground and background colors. See, for
example, <STRONG><A HREF="curs_addch.3x.html">addch(3x)</A></STRONG>, <STRONG><A HREF="curs_attr.3x.html">attron(3x)</A></STRONG>, and <STRONG><A HREF="curs_inch.3x.html">inch(3x)</A></STRONG>.
</PRE><H3><a name="h3-cchar_t_attr_t"><EM>cchar_t,</EM> attr_t</a></H3><PRE>
<EM>chtype</EM> is too small for the standard C library's wide-character type,
<EM>wchar</EM><STRONG>_</STRONG><EM>t</EM>. <EM>cchar</EM><STRONG>_</STRONG><EM>t</EM> is a type that can accommodate an <EM>attr</EM><STRONG>_</STRONG><EM>t</EM> and enough
wide characters to store what Unicode terms a <EM>grapheme</EM> <EM>cluster</EM> (a
"user-perceived character" [UAX #29], which may nevertheless require
several character encoding units to represent). <EM>attr</EM><STRONG>_</STRONG><EM>t</EM> is an integral
type storing "wide" attributes that apply to <EM>cchar</EM><STRONG>_</STRONG><EM>t</EM>s. See, for
example, <STRONG><A HREF="curs_add_wch.3x.html">add_wch(3x)</A></STRONG>, <STRONG><A HREF="curs_attr.3x.html">attr_on(3x)</A></STRONG>, and <STRONG><A HREF="curs_in_wch.3x.html">in_wch(3x)</A></STRONG>.
</PRE><H3><a name="h3-SCREEN"><EM>SCREEN</EM></a></H3><PRE>
<EM>curses</EM> manages a terminal device with this structure type; see
<STRONG><A HREF="curs_initscr.3x.html">initscr(3x)</A></STRONG>.
</PRE><H3><a name="h3-WINDOW"><EM>WINDOW</EM></a></H3><PRE>
<EM>curses</EM> represents rectangular portions of the terminal screen with the
<EM>WINDOW</EM> structure type; see subsection "Overview" of <STRONG><A HREF="ncurses.3x.html">ncurses(3x)</A></STRONG>.
</PRE><H2><a name="h2-VARIABLES">VARIABLES</a></H2><PRE>
</PRE><H3><a name="h3-curscr_newscr_stdscr">curscr, newscr, stdscr</a></H3><PRE>
When a <EM>curses</EM> application calls <STRONG><A HREF="curs_initscr.3x.html">initscr(3x)</A></STRONG> or <STRONG><A HREF="curs_initscr.3x.html">newterm(3x)</A></STRONG>, the library
creates a window named <STRONG>stdscr</STRONG> that is the same size as the terminal
screen, (minus any lines reserved by <STRONG><A HREF="curs_kernel.3x.html">ripoffline(3x)</A></STRONG> or <STRONG><A HREF="curs_slk.3x.html">slk_init(3x)</A></STRONG>)
and is the implicit window used by functions that interact with a
window but do not take a parameter identifying one; many <EM>curses</EM>
functions use it. An application need not use <STRONG>stdscr</STRONG>; it might prefer
to tile the display into multiple windows instead.
The library records updates to the terminal screen in a window named
<STRONG>curscr</STRONG>. This object is referred to as the "physical screen" in
<STRONG><A HREF="curs_refresh.3x.html">curs_refresh(3x)</A></STRONG> and <STRONG><A HREF="curs_outopts.3x.html">curs_outopts(3x)</A></STRONG>.
<EM>ncurses</EM> collects pending updates to the terminal screen in a window
named <STRONG>newscr</STRONG>. This object is referred to as the "virtual screen" in
the <STRONG><A HREF="curs_kernel.3x.html">curs_kernel(3x)</A></STRONG>, <STRONG><A HREF="curs_refresh.3x.html">curs_refresh(3x)</A></STRONG>, and <STRONG><A HREF="curs_outopts.3x.html">curs_outopts(3x)</A></STRONG>. When the
screen is refreshed, <EM>curses</EM> determines a minimal set of updates using
the terminal's capabilities to make <STRONG>curscr</STRONG> look like <STRONG>newscr</STRONG>.
</PRE><H3><a name="h3-COLORS">COLORS</a></H3><PRE>
Once a <EM>curses</EM> screen is initialized, <STRONG>COLORS</STRONG> contains the number of
colors supported by the terminal; see <STRONG><A HREF="curs_color.3x.html">curs_color(3x)</A></STRONG>.
</PRE><H3><a name="h3-COLOR_PAIRS">COLOR_PAIRS</a></H3><PRE>
Once a <EM>curses</EM> screen is initialized, <STRONG>COLOR_PAIRS</STRONG> contains the number of
color pairs supported by the terminal; see <STRONG><A HREF="curs_color.3x.html">curs_color(3x)</A></STRONG>.
</PRE><H3><a name="h3-COLS_LINES">COLS, LINES</a></H3><PRE>
Once a <EM>curses</EM> screen is initialized, <STRONG>COLS</STRONG> and <STRONG>LINES</STRONG> contain its width
and height in character cells, respectively; that is, the number of
columns and lines.
</PRE><H3><a name="h3-ESCDELAY">ESCDELAY</a></H3><PRE>
When reading key strokes from a window in keypad mode, <EM>curses</EM>
distinguishes the ESC character resulting from a user's press of the
"Escape" key on the input device from one beginning an escape sequence
(commonly produced by function keys), by waiting after receiving the
escape character to see if further characters are available on the
input stream within a short interval. <STRONG>ESCDELAY</STRONG> stores this interval in
milliseconds.
If <STRONG><A HREF="curs_inopts.3x.html">keypad(3x)</A></STRONG> is disabled for the <EM>curses</EM> window receiving input, a
program must disambiguate escape sequences itself.
</PRE><H3><a name="h3-TABSIZE">TABSIZE</a></H3><PRE>
The <EM>curses</EM> library converts a tab character to this number of spaces as
it adds a tab to a window; see <STRONG><A HREF="curs_addch.3x.html">curs_addch(3x)</A></STRONG>.
</PRE><H2><a name="h2-NOTES">NOTES</a></H2><PRE>
Initialize a <EM>curses</EM> screen with either <STRONG><A HREF="curs_initscr.3x.html">initscr(3x)</A></STRONG> or <STRONG><A HREF="curs_initscr.3x.html">newterm(3x)</A></STRONG>.
If <EM>ncurses</EM> is configured to provide separate <EM>curses</EM> and <EM>tinfo</EM>
libraries, most of these symbols reside in the former. Both use the
<STRONG>bool</STRONG> data type.
</PRE><H2><a name="h2-EXTENSIONS">EXTENSIONS</a></H2><PRE>
The <STRONG>CCHARW_MAX</STRONG> constant, and <STRONG>ESCDELAY</STRONG>, <STRONG>TABSIZE</STRONG>, and <STRONG>newscr</STRONG> variables,
are extensions, the first of these originating in <EM>ncurses</EM>.
</PRE><H2><a name="h2-PORTABILITY">PORTABILITY</a></H2><PRE>
Applications employing <EM>ncurses</EM> extensions should condition their use on
the visibility of the <STRONG>NCURSES_VERSION</STRONG> preprocessor macro.
The X/Open Curses standard documents all of the foregoing types and
symbols except for <STRONG>CCHARW_MAX</STRONG>, <STRONG>newscr</STRONG>, <STRONG>TABSIZE</STRONG>, and <STRONG>ESCDELAY</STRONG>.
X/Open Curses describes <STRONG>curscr</STRONG> only as "an internal data structure";
SVr4 gave more details, noting its use "for certain low-level
operations like clearing and redrawing a screen containing garbage".
Neither specified its interaction with the rest of the interface beyond
use as an argument to <STRONG><A HREF="curs_outopts.3x.html">clearok(3x)</A></STRONG> and <STRONG><A HREF="curs_refresh.3x.html">wrefresh(3x)</A></STRONG>.
<STRONG>newscr</STRONG> is a feature of SVr4 <EM>curses</EM>. When refreshing the screen, it is
used as a working area for combining the standard window <STRONG>stdscr</STRONG> with
any others the application may have created with <STRONG><A HREF="curs_window.3x.html">newwin(3x)</A></STRONG>. When the
update of <STRONG>newscr</STRONG> is complete, <EM>curses</EM> modifies <STRONG>curscr</STRONG> to match <STRONG>newscr</STRONG>.
<STRONG>TABSIZE</STRONG> is a feature of SVr4 <EM>curses</EM>.
<STRONG>o</STRONG> SVr4 initially sets <STRONG>TABSIZE</STRONG> from the terminal description's
<STRONG>init_tabs</STRONG> (<STRONG>it</STRONG>) capability. After that, it can be altered by
applications using SVr4 <EM>curses</EM>.
<STRONG>o</STRONG> SVr4 <EM>curses</EM> uses <STRONG>TABSIZE</STRONG>'s value to compute the position of tab
stops when updating both the virtual screen with <STRONG><A HREF="curs_addch.3x.html">addch(3x)</A></STRONG> and the
physical screen with <STRONG><A HREF="curs_terminfo.3x.html">mvcur(3x)</A></STRONG>.
<STRONG>o</STRONG> In <EM>ncurses</EM>, <STRONG>TABSIZE</STRONG>'s value affects only the virtual screen. The
library uses the terminal type description's <STRONG>init_tabs</STRONG> (<STRONG>it</STRONG>)
capability to compute hardware tabs (that is, tab stops on the
physical screen).
<STRONG>o</STRONG> Other implementations differ. For instance, NetBSD <EM>curses</EM> allows
<STRONG>TABSIZE</STRONG> to be set through an environment variable. <EM>ncurses</EM> does
not.
NetBSD <EM>curses</EM> does not support hardware tabs; it uses the <STRONG>init_tabs</STRONG>
(<STRONG>it</STRONG>) capability and the <STRONG>TABSIZE</STRONG> variable only to update the virtual
screen.
<STRONG>ESCDELAY</STRONG> is a feature of AIX <EM>curses</EM>.
<STRONG>o</STRONG> AIX treats <STRONG>ESCDELAY</STRONG>'s value as counting <EM>fifths</EM> of milliseconds.
<STRONG>o</STRONG> AIX's default <STRONG>ESCDELAY</STRONG> equals 0.1 seconds.
<STRONG>o</STRONG> AIX also enforces a limit of 10,000 seconds for <STRONG>ESCDELAY</STRONG>; <EM>ncurses</EM>
does not enforce an upper limit.
<EM>ncurses</EM> has long interpreted <STRONG>ESCDELAY</STRONG> as a count of milliseconds,
making it impossible to be completely compatible with AIX.
Consequently, most users have decided either to override the value, or
to rely upon its default.
</PRE><H2><a name="h2-SEE-ALSO">SEE ALSO</a></H2><PRE>
[UAX #29] "Unicode Standard Annex #29: Unicode Text Segmentation"
<STRONG><A HREF="curs_getcchar.3x.html">getcchar(3x)</A></STRONG> further discusses the <EM>ncurses</EM> extension <STRONG>CCHARW_MAX</STRONG>.
<STRONG><A HREF="ncurses.3x.html">curses(3x)</A></STRONG>, <STRONG><A HREF="curs_color.3x.html">curs_color(3x)</A></STRONG>, <STRONG><A HREF="curs_opaque.3x.html">curs_opaque(3x)</A></STRONG>, <STRONG><A HREF="curs_terminfo.3x.html">curs_terminfo(3x)</A></STRONG>,
<STRONG><A HREF="curs_threads.3x.html">curs_threads(3x)</A></STRONG>, <STRONG><A HREF="term_variables.3x.html">term_variables(3x)</A></STRONG>, <STRONG><A HREF="terminfo.5.html">terminfo(5)</A></STRONG>
ncurses 6.6 2025-08-23 <STRONG><A HREF="curs_variables.3x.html">curs_variables(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></li>
<li><a href="#h2-CONSTANTS">CONSTANTS</a>
<ul>
<li><a href="#h3-TRUE_FALSE">TRUE, FALSE</a></li>
<li><a href="#h3-ERR_OK">ERR, OK</a></li>
<li><a href="#h3-CCHARW_MAX">CCHARW_MAX</a></li>
</ul>
</li>
<li><a href="#h2-DATA-TYPES">DATA TYPES</a>
<ul>
<li><a href="#h3-bool">bool</a></li>
<li><a href="#h3-chtype">chtype</a></li>
<li><a href="#h3-cchar_t_attr_t">cchar_t, attr_t</a></li>
<li><a href="#h3-SCREEN">SCREEN</a></li>
<li><a href="#h3-WINDOW">WINDOW</a></li>
</ul>
</li>
<li><a href="#h2-VARIABLES">VARIABLES</a>
<ul>
<li><a href="#h3-curscr_newscr_stdscr">curscr, newscr, stdscr</a></li>
<li><a href="#h3-COLORS">COLORS</a></li>
<li><a href="#h3-COLOR_PAIRS">COLOR_PAIRS</a></li>
<li><a href="#h3-COLS_LINES">COLS, LINES</a></li>
<li><a href="#h3-ESCDELAY">ESCDELAY</a></li>
<li><a href="#h3-TABSIZE">TABSIZE</a></li>
</ul>
</li>
<li><a href="#h2-NOTES">NOTES</a></li>
<li><a href="#h2-EXTENSIONS">EXTENSIONS</a></li>
<li><a href="#h2-PORTABILITY">PORTABILITY</a></li>
<li><a href="#h2-SEE-ALSO">SEE ALSO</a></li>
</ul>
</div>
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