https://invisible-island.net/ncurses/man/
curs_variables(3x) Library calls curs_variables(3x)
bool, chtype, cchar_t, attr_t, SCREEN, WINDOW, TRUE, FALSE, ERR, OK,
CCHARW_MAX, curscr, newscr, stdscr, COLORS, COLOR_PAIRS, COLS, LINES,
ESCDELAY, TABSIZE - curses data types, constants, and global variables
#include <curses.h>
/* data types */
typedef /* ... */ bool;
typedef /* ... */ chtype;
typedef /* ... */ cchar_t;
typedef /* ... */ attr_t;
typedef /* ... */ SCREEN;
typedef /* ... */ WINDOW;
/* constants */
const bool TRUE;
const bool FALSE;
const /* ... */ ERR;
const /* ... */ OK;
/* extension */
const /* ... */ CCHARW_MAX;
/* variables */
int COLORS;
int COLOR_PAIRS;
int COLS;
int LINES;
WINDOW * curscr;
WINDOW * stdscr;
/* extensions */
int ESCDELAY;
int TABSIZE;
WINDOW * newscr;
This page summarizes data types, constants, and variables provided by
the curses library. Locate further discussion in curses(3x).
Depending on ncurses's build-time configuration, the variables may
instead be macros (see curs_threads(3x) and curs_opaque(3x)) 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.
The curses library defines TRUE and FALSE to represent the values of
the Boolean data type.
curses and terminfo functions frequently return these constant integral
values indicating failure and success, respectively.
This integral value, an ncurses extension, indicates the maximum number
of wchar_t wide characters that can be stored in a curses complex
character cchar_t.
curses defines an integral type bool. X/Open Issue 4 curses (1996)
preceded the ISO C99 and ISO C++98 standards, each of which also
defined a Boolean data type of the same name.
ncurses's configure script attempts to discover the data type used by
the system's C and C++ compilers, to reuse them as its own bool.
The chtype integral type combines a ("narrow", 8-bit) character with
attributes encoding the character's rendition, such as the styling of
its typeface and/or foreground and background colors. See, for
example, addch(3x), attron(3x), and inch(3x).
chtype is too small for the standard C library's wide-character type,
wchar_t. cchar_t is a type that can accommodate an attr_t and enough
wide characters to store what Unicode terms a grapheme cluster (a
"user-perceived character" [UAX #29], which may nevertheless require
several character encoding units to represent). attr_t is an integral
type storing "wide" attributes that apply to cchar_ts. See, for
example, add_wch(3x), attr_on(3x), and in_wch(3x).
curses manages a terminal device with this structure type; see
initscr(3x).
curses represents rectangular portions of the terminal screen with the
WINDOW structure type; see subsection "Overview" of ncurses(3x).
When a curses application calls initscr(3x) or newterm(3x), the library
creates a window named stdscr that is the same size as the terminal
screen, (minus any lines reserved by ripoffline(3x) or slk_init(3x))
and is the implicit window used by functions that interact with a
window but do not take a parameter identifying one; many curses
functions use it. An application need not use stdscr; it might prefer
to tile the display into multiple windows instead.
The library records updates to the terminal screen in a window named
curscr. This object is referred to as the "physical screen" in
curs_refresh(3x) and curs_outopts(3x).
ncurses collects pending updates to the terminal screen in a window
named newscr. This object is referred to as the "virtual screen" in
the curs_kernel(3x), curs_refresh(3x), and curs_outopts(3x). When the
screen is refreshed, curses determines a minimal set of updates using
the terminal's capabilities to make curscr look like newscr.
Once a curses screen is initialized, COLORS contains the number of
colors supported by the terminal; see curs_color(3x).
Once a curses screen is initialized, COLOR_PAIRS contains the number of
color pairs supported by the terminal; see curs_color(3x).
Once a curses screen is initialized, COLS and LINES contain its width
and height in character cells, respectively; that is, the number of
columns and lines.
When reading key strokes from a window in keypad mode, curses
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. ESCDELAY stores this interval in
milliseconds.
If keypad(3x) is disabled for the curses window receiving input, a
program must disambiguate escape sequences itself.
The curses library converts a tab character to this number of spaces as
it adds a tab to a window; see curs_addch(3x).
Initialize a curses screen with either initscr(3x) or newterm(3x).
If ncurses is configured to provide separate curses and tinfo
libraries, most of these symbols reside in the former. Both use the
bool data type.
The CCHARW_MAX constant, and ESCDELAY, TABSIZE, and newscr variables,
are extensions, the first of these originating in ncurses.
Applications employing ncurses extensions should condition their use on
the visibility of the NCURSES_VERSION preprocessor macro.
The X/Open Curses standard documents all of the foregoing types and
symbols except for CCHARW_MAX, newscr, TABSIZE, and ESCDELAY.
X/Open Curses describes curscr 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 clearok(3x) and wrefresh(3x).
newscr is a feature of SVr4 curses. When refreshing the screen, it is
used as a working area for combining the standard window stdscr with
any others the application may have created with newwin(3x). When the
update of newscr is complete, curses modifies curscr to match newscr.
TABSIZE is a feature of SVr4 curses.
o SVr4 initially sets TABSIZE from the terminal description's
init_tabs (it) capability. After that, it can be altered by
applications using SVr4 curses.
o SVr4 curses uses TABSIZE's value to compute the position of tab
stops when updating both the virtual screen with addch(3x) and the
physical screen with mvcur(3x).
o In ncurses, TABSIZE's value affects only the virtual screen. The
library uses the terminal type description's init_tabs (it)
capability to compute hardware tabs (that is, tab stops on the
physical screen).
o Other implementations differ. For instance, NetBSD curses allows
TABSIZE to be set through an environment variable. ncurses does
not.
NetBSD curses does not support hardware tabs; it uses the init_tabs
(it) capability and the TABSIZE variable only to update the virtual
screen.
ESCDELAY is a feature of AIX curses.
o AIX treats ESCDELAY's value as counting fifths of milliseconds.
o AIX's default ESCDELAY equals 0.1 seconds.
o AIX also enforces a limit of 10,000 seconds for ESCDELAY; ncurses
does not enforce an upper limit.
ncurses has long interpreted ESCDELAY 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.
[UAX #29] "Unicode Standard Annex #29: Unicode Text Segmentation"
getcchar(3x) further discusses the ncurses extension CCHARW_MAX.
curses(3x), curs_color(3x), curs_opaque(3x), curs_terminfo(3x),
curs_threads(3x), term_variables(3x), terminfo(5)
ncurses 6.5 2025-08-23 curs_variables(3x)