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.\" $Id: curs_variables.3x,v 1.65 2025/07/05 13:04:08 tom Exp $
.TH curs_variables 3X 2025-07-05 "ncurses 6.5" "Library calls"
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.SH NAME
\fI\%bool\fP,
\fI\%chtype\fP,
\fI\%cchar_t\fP,
\fI\%attr_t\fP,
\fI\%SCREEN\fP,
\fI\%WINDOW\fP,
\fB\%TRUE\fP,
\fB\%FALSE\fP,
\fB\%ERR\fP,
\fB\%OK\fP,
\fB\%CCHARW_MAX\fP,
\fB\%curscr\fP,
\fB\%newscr\fP,
\fB\%stdscr\fP,
\fB\%COLORS\fP,
\fB\%COLOR_PAIRS\fP,
\fB\%COLS\fP,
\fB\%LINES\fP,
\fB\%ESCDELAY\fP,
\fB\%TABSIZE\fP \-
\fIcurses\fR data types, constants, and global variables
.SH SYNOPSIS
.nf
\fB#include <curses.h>
.PP
\fI/* data types */
\fBtypedef \fI/*\fP .\|.\|. \fI*/\fP bool;
\fBtypedef \fI/*\fP .\|.\|. \fI*/\fP chtype;
\fBtypedef \fI/*\fP .\|.\|. \fI*/\fP cchar_t;
\fBtypedef \fI/*\fP .\|.\|. \fI*/\fP attr_t;
\fBtypedef \fI/*\fP .\|.\|. \fI*/\fP SCREEN;
\fBtypedef \fI/*\fP .\|.\|. \fI*/\fP WINDOW;
.PP
\fI/* constants */
\fBconst bool TRUE;
\fBconst bool FALSE;
.PP
\fBconst \fI/*\fP .\|.\|. \fI*/\fP ERR;
\fBconst \fI/*\fP .\|.\|. \fI*/\fP OK;
.PP
\fI/* extension */
\fBconst \fI/*\fP .\|.\|. \fI*/\fP CCHARW_MAX;
.PP
\fI/* variables */
\fBint COLORS;
\fBint COLOR_PAIRS;
\fBint COLS;
\fBint LINES;
\fBWINDOW * curscr;
\fBWINDOW * stdscr;
.PP
\fI/* extensions */
\fBint ESCDELAY;
\fBint TABSIZE;
\fBWINDOW * newscr;
.fi
.SH DESCRIPTION
This page summarizes data types,
constants,
and variables provided by the \fIcurses\fP library.
Locate further discussion in \fB\%curses\fP(3X).
.PP
Depending on \fI\%ncurses\fP's build-time configuration,
the variables may instead be
macros (see \fB\%curs_threads\fP(3X) and \fB\%curs_opaque\fP(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.
.SH CONSTANTS
.SS "TRUE, FALSE"
The \fIcurses\fP library defines \fBTRUE\fP and \fBFALSE\fP
to represent the values of the Boolean data type.
.SS "ERR, OK"
\fIcurses\fP and \fIterminfo\fP routines frequently return these
constant integral values indicating failure and success,
respectively.
.SS CCHARW_MAX
This integral value,
an
.I \%ncurses
extension,
contains the maximum number of
.I \%wchar_t
wide characters that can be stored in a
.I curses
complex character
.IR \%cchar_t "."
.SH "PREDEFINED TYPES"
.SS "\fIbool\fP"
X/Open Issue\ 4 \fIcurses\fP (1996) preceded the ISO C99 and ISO C++98
standards,
each of which also defined a Boolean data type.
The \fIcurses\fP library requires an integral type \fIbool\fP.
.PP
.IR \%ncurses 's
configure script attempts to discover the
data type used by the system's C and C++ compilers,
to reuse for the \fIcurses\fP \fIbool\fP.
.SS "\fIchtype\fP"
The \fI\%chtype\fP integral type combines a
(\*(``narrow\*('',
8-bit)
character with attributes encoding the character's \fIrendition\fP,
such as the styling of its typeface and/or foreground and background
colors.
See,
for example,
\fB\%addch\fP(3X),
\fB\%attron\fP(3X),
and
\fB\%inch\fP(3X).
.SS "\fIcchar_t\fP, \fIattr_t\fP"
\fI\%chtype\fP is too small for the standard C library's wide-character
type,
\fIwchar_t\fP.
\fI\%cchar_t\fP is a type that can accommodate an \fI\%attr_t\fP and
enough wide characters to store what Unicode terms a \fIgrapheme cluster\fP
(a \*(``user-perceived character\*('' [UAX #29],
which may nevertheless require several character encoding units to
represent).
\fI\%attr_t\fP is an integral type storing \*(``wide\*('' attributes that
apply to \fI\%cchar_t\fPs.
See,
for example,
\fB\%add_wch\fP(3X),
\fB\%attr_on\fP(3X),
and
\fB\%in_wch\fP(3X).
.SS "\fISCREEN\fP"
.I curses
manages a terminal device with this structure type;
see \fB\%initscr\fP(3X).
.SS "\fIWINDOW\fP"
.I curses
represents rectangular portions of the terminal screen with the
.I \%WINDOW
structure type;
see subsection \*(``Overview\*('' of \fB\%ncurses\fP(3X).
.SH "VARIABLES"
.SS "curscr, newscr, stdscr"
When a
.I curses
application calls
\fB\%initscr\fP(3X) or \fB\%newterm\fP(3X),
the library creates a window named
.B \%stdscr
that is the same size as the terminal screen,
(minus any lines reserved by
\fB\%ripoffline\fP(3X) or \fB\%slk_init\fP(3X))
and is the implicit window used by functions
that interact with a window
but do not take a parameter identifying one;
many
.I curses
functions use it.
An application need not use
.BR \%stdscr ";"
it might prefer to tile the display into multiple windows instead.
.PP
The library records updates to the terminal screen in a window named
\fB\%curscr\fP.
This object is referred to as the \*(``physical screen\*('' in
\fB\%curs_refresh\fP(3X) and
\fB\%curs_outopts\fP(3X).
.PP
\fI\%ncurses\fP collects pending updates to the terminal screen in a
window named \fB\%newscr\fP.
This object is referred to as the \*(``virtual screen\*('' in the
\fB\%curs_kernel\fP(3X),
\fB\%curs_refresh\fP(3X),
and
\fB\%curs_outopts\fP(3X).
When the screen is refreshed,
\fIcurses\fP determines a minimal set of updates using the terminal's
capabilities to make \fB\%curscr\fP look like \fB\%newscr\fP.
.SS COLORS
Once \fIcurses\fP is initialized,
\fB\%COLORS\fP
contains the number of colors supported by the terminal;
see \fB\%curs_color\fP(3X).
.SS COLOR_PAIRS
Once \fIcurses\fP is initialized,
\fB\%COLOR_PAIRS\fP
contains the number of color pairs supported by the terminal;
see \fB\%curs_color\fP(3X).
.SS "COLS, LINES"
Once \fIcurses\fP is initialized,
.B \%COLS
and
.B LINES
contain the screen's width and height in character cells,
respectively;
that is,
the number of columns and lines.
.SS ESCDELAY
When reading key strokes from a window in keypad mode,
.I 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.
.B \%ESCDELAY
stores this interval in milliseconds.
.PP
If \fB\%keypad\fP(3X) is disabled for the
.I curses
window receiving input,
a program must disambiguate escape sequences itself.
.SS TABSIZE
The \fIcurses\fP library converts a tab character to this number of
spaces as it adds a tab to a window;
see \fB\%curs_addch\fP(3X).
.SH NOTES
Either \fB\%initscr\fP(3X) or \fB\%newterm\fP(3X) initializes
\fIcurses\fP.
.PP
If
.I \%ncurses
is configured to provide separate
.I curses
and
.I \%tinfo
libraries,
most of these symbols reside in the former.
The
.B bool
data type
is used by both.
.SH EXTENSIONS
The
.B \%CCHARW_MAX
constant,
and
.BR \%ESCDELAY ","
.BR \%TABSIZE ","
and
.B \%newscr
variables,
are
extensions,
the first of these originating in
.\" Solaris xcurses calls it M_CCHAR_MAX.
.IR \%ncurses "."
.SH PORTABILITY
Applications employing
.I \%ncurses
extensions should condition their use on the visibility of the
.B \%NCURSES_VERSION
preprocessor macro.
.PP
The X/Open Curses standard documents all of the foregoing types and
symbols except for
.BR \%CCHARW_MAX ","
.BR \%newscr ","
.BR \%TABSIZE ","
and
.BR \%ESCDELAY "."
.PP
X/Open Curses describes \fB\%curscr\fP 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\*(''.
.\" SVID 4, Volume 3, p. 408
Neither specified its interaction with the rest of the interface beyond
use as an argument to \fB\%clearok\fP(3X) and \fB\%wrefresh\fP(3X).
.PP
\fB\%newscr\fP is a feature of SVr4 \fIcurses\fP.
When refreshing the screen,
it is used as a working area for combining the standard window
\fB\%stdscr\fP with any others the application may have created with
\fB\%newwin\fP(3X).
When the update of \fB\%newscr\fP is complete,
\fIcurses\fP modifies \fB\%curscr\fP to match \fB\%newscr\fP.
.PP
.B \%TABSIZE
is a feature of SVr4
.IR curses "."
.bP
SVr4 initially sets
.B \%TABSIZE
from the terminal description's
.B \%init_tabs
.RB ( it )
capability.
After that,
it can be altered by applications using SVr4
.IR curses "."
.bP
SVr4
.I curses
uses
.BR \%TABSIZE 's
value to compute the position of tab stops when updating both
the virtual screen with \fB\%addch\fP(3X) and
the physical screen with \fB\%mvcur\fP(3X).
.bP
In
.IR \%ncurses ","
.BR \%TABSIZE 's
value affects only the virtual screen.
The library uses the terminal type description's
.B \%init_tabs
.RB ( it )
capability to compute hardware tabs
(that is,
tab stops on the physical screen).
.bP
Other implementations differ.
For instance,
NetBSD
.I curses
allows
.B \%TABSIZE
to be set through an environment variable.
.I \%ncurses
does not.
.IP
NetBSD
.I curses
does not support hardware tabs;
it uses the
.B \%init_tabs
.RB ( it )
capability and the
.B \%TABSIZE
variable only to update the virtual screen.
.PP
.B \%ESCDELAY
is a feature of AIX
.IR curses "."
.bP
AIX treats
.BR \%ESCDELAY 's
value as counting
.I fifths
of milliseconds.
.bP
AIX's default
.B \%ESCDELAY
equals 0.1 seconds.
.bP
AIX also enforces a limit of 10,000 seconds for
.BR \%ESCDELAY ";"
.I \%ncurses
does not enforce an upper limit.
.PP
.I \%ncurses
has long interpreted
.B \%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.
.SH SEE ALSO
.UR https://\*:unicode\*:.org/\*:reports/\*:tr29/
[UAX #29] \*(``Unicode Standard Annex #29: Unicode Text
Segmentation\*(''
.UE
.PP
\fB\%getcchar\fP(3X)
further discusses the
.I \%ncurses
extension
.BR \%CCHARW_MAX "."
.PP
\fB\%curses\fP(3X),
\fB\%curs_color\fP(3X),
\fB\%curs_opaque\fP(3X),
\fB\%curs_terminfo\fP(3X),
\fB\%curs_threads\fP(3X),
\fB\%term_variables\fP(3X),
\fB\%terminfo\fP(5)