curs_variables(3X)

NAME
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

SYNOPSIS
#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;

DESCRIPTION
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.

CONSTANTS

  TRUE, FALSE
The curses library defines TRUE and FALSE to represent the values of the Boolean data type.

  ERR, OK
curses and terminfo functions frequently return these constant integral values indicating failure and success, respectively.

  CCHARW_MAX
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.

DATA TYPES

  bool
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.

  chtype
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).

  SCREEN
curses manages a terminal device with this structure type; see initscr(3X).

  WINDOW
curses represents rectangular portions of the terminal screen with the WINDOW structure type; see subsection “Overview” of ncurses(3X).

VARIABLES

  curscr, newscr, stdscr
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.

  COLORS
Once a curses screen is initialized, COLORS contains the number of colors supported by the terminal; see curs_color(3X).

  COLOR_PAIRS
Once a curses screen is initialized, COLOR_PAIRS contains the number of color pairs supported by the terminal; see curs_color(3X).

  COLS, LINES
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.

  ESCDELAY
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.

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

NOTES
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.

EXTENSIONS
The CCHARW_MAX constant, and ESCDELAY, TABSIZE, and newscr variables, are extensions, the first of these originating in ncurses.

PORTABILITY
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. SVr4 initially sets TABSIZE from the terminal description's init_tabs (it) capability. After that, it can be altered by applications using SVr4 curses. 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). 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). 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. AIX treats ESCDELAY's value as counting fifths of milliseconds. AIX's default ESCDELAY equals 0.1 seconds. 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.

SEE ALSO
[UAX #29] “Unicode Standard Annex #29: Unicode Text Segmentation” (https://unicode.org/reports/tr29/)

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)