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curses_variables(3NCURSES) Library calls curses_variables(3NCURSES)


bool, chtype, cchar_t, attr_t, WINDOW, TRUE, FALSE, ERR, OK, COLORS, COLOR_PAIRS, COLS, ESCDELAY, LINES, TABSIZE, curscr, newscr, stdscr - curses data types, constants, and global variables


#include <curses.h>
/* data types */
typedef /* ... */ bool;
typedef /* ... */ chtype;
typedef /* ... */ cchar_t;
typedef /* ... */ attr_t;
typedef /* ... */ WINDOW;
/* constants */
const bool TRUE;
const bool FALSE;
const /* ... */ ERR;
const /* ... */ OK;
/* variables */
int COLS;
int LINES;
WINDOW * curscr;
WINDOW * newscr;
WINDOW * stdscr;


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.


X/Open Issue 4 curses (1996) preceded the ISO C99 and ISO C++98 standards, each of which also defined a Boolean data type. The curses library requires an integral type bool and constants TRUE and FALSE to store its two possible values.


curses and terminfo routines frequently return these constant integral values indicating failure and success, respectively.


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).

cchar_t, attr_t

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).


Once curses is initialized, COLOR_PAIRS contains the number of color pairs supported by the terminal. Often, its value is the product COLORS × COLORS, but this is not always true.

  • A few terminals use HLS colors, ignoring this rule; and
  • terminals supporting a large number of colors are limited by the number of color pairs that a signed short value can represent.


Once curses is initialized, COLORS contains the number of colors supported by the terminal.


Once curses is initialized, COLS contains the screen's width in character cells; that is, the number of columns.


For curses to distinguish an escape character corresponding to a user's press of an “Escape” key on the input device from one included in a control sequence used by a cursor movement or function key, the library waits to see if another key event occurs after the escape character. ESCDELAY stores this interval in milliseconds.


Once curses is initialized, LINES contains the screen's height in character cells; that is, the number of lines.


The curses library converts a tab character to this number of spaces as it adds a tab to a window; see curs_addch(3X).


curses records updates to the terminal screen in a WINDOW structure 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 structure 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 curses is initialized, it creates a WINDOW structure named stdscr. It is the same size as the terminal screen and is the default window used by routines that do not take a parameter identifying one. Many curses functions use this window.


Either initscr(3X) or newterm(3X) initializes curses.

If ncurses is configured to provide separate curses and terminfo libraries, most of these variables reside in the curses library.


The X/Open Curses standard documents all of the foregoing types and symbols except for newscr, TABSIZE, and ESCDELAY.

X/Open Curses describes curscr only as “an internal data structure”; SVID 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, this window is used as a working area for combining the standard screen stdscr with any other windows which the application may have created with newwin(3X). When the updated newscr is complete, curses updates curscr to match newscr.

TABSIZE is a feature of SVr4 curses.

  • SVr4 initially sets TABSIZE from the terminal description's init_tabs capability. After that, it can be altered by applications using SVr4 curses.
  • SVr4 curses uses the value of TABSIZE to compute the position of tab stops when updating both the virtual screen with addch(3X) and the physical screen with mvcur(3X).
  • ncurses uses the value of TABSIZE only to update the virtual screen. It uses the terminal description's “it” (init_tabs) capability for computing hardware tabs (that is, tab stops on the physical screen).
  • 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 capability and the TABSIZE variable only for updating the virtual screen.

ESCDELAY is a feature of AIX curses.

  • In AIX, the units for ESCDELAY are fifths of milliseconds.
  • The default value for AIX's ESCDELAY equals 0.1 seconds.
  • AIX also enforces a limit of 10,000 seconds for ESCDELAY; ncurses does not enforce any upper limit.

ncurses has long used ESCDELAY with units 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.


curses(3X), curs_opaque(3X), curs_terminfo(3X), curs_threads(3X), term_variables(3X), terminfo(5)

[UAX #29] “Unicode Standard Annex #29: Unicode Text Segmentation”; <>

2023-10-07 ncurses 6.4