curs_variables(3) Library calls curs_variables(3)
NAME
bool, chtype, cchar_t, attr_t, SCREEN, WINDOW, TRUE, FALSE, ERR, OK,
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;
/* 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 routines frequently return these constant integral
values indicating failure and success, respectively.
PREDEFINED TYPES
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. The curses
library requires an integral type bool.
ncurses' configure script attempts to discover the data type used by
the system's C and C++ compilers, to reuse for the curses 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, stdscr, newscr
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 curses is initialized, it creates a window 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.
COLORS
Once curses is initialized, COLORS contains the number of colors
supported by the terminal; see curs_color(3X).
COLOR_PAIRS
Once curses is initialized, COLOR_PAIRS contains the number of color
pairs supported by the terminal; see curs_color(3X).
COLS, LINES
Once curses is initialized, COLS and LINES contain the screen's width
and height in character cells, respectively; that is, the number of
columns and lines.
ESCDELAY
For curses to distinguish the ESC character resulting from a user's
press of the "Escape" key on the input device from one beginning an
escape sequence (as commonly produced by function keys), it waits after
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
Either initscr(3X) or newterm(3X) initializes curses.
If ncurses is configured to provide separate curses and tinfo
libraries, most of these variables reside in the former.
PORTABILITY
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";
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 capability. After that, it can be altered by
applications using SVr4 curses.
o 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).
o 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).
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
capability and the TABSIZE variable only for updating the virtual
screen.
ESCDELAY is a feature of AIX curses.
o In AIX, the units for ESCDELAY are fifths of milliseconds.
o The default value for AIX's ESCDELAY equals 0.1 seconds.
o 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.
SEE ALSO
curses(3X), curs_color(3X), curs_opaque(3X), curs_terminfo(3X),
curs_threads(3X), term_variables(3X), terminfo(5)
[UAX #29] "Unicode Standard Annex #29: Unicode Text Segmentation";
<https://unicode.org/reports/tr29/>
ncurses 6.5 2024-04-13 curs_variables(3)
ncurses 6.5 - Generated Thu May 2 15:49:40 CDT 2024