# curs_variables 3x 2025-08-23 ncurses 6.6 Library calls

    curs_variables(3x)               Library calls              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.

           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.

## SEE ALSO

           [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 6.6                       2025-08-23                curs_variables(3x)