# curs_variables 3x 2025-08-16 ncurses 6.5 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 routines frequently return these constant integral
           values indicating failure and success, respectively.

### CCHARW_MAX

           This integral value, an ncurses extension, contains the maximum  number
           of  wchar_t  wide  characters  that  can  be stored in a curses complex
           character cchar_t.

## DATA 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's 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, 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 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

           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

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

           If  ncurses  is  configured  to  provide  separate  curses  and   tinfo
           libraries,  most  of these symbols reside in the former.  The bool data
           type is used by both.

## 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"
           <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)

    ncurses 6.5                       2025-08-16                curs_variables(3x)