# curs_variables 3x 2025-01-18 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.

## 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, 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 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

           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 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   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

           [UAX  #29]  "Unicode  Standard  Annex  #29:  Unicode Text Segmentation"
           <https://unicode.org/reports/tr29/>

           getcchar(3x) further discusses CCHARW_MAX.

           curses(3x),   curs_color(3x),    curs_opaque(3x),    curs_terminfo(3x),
           curs_threads(3x), term_variables(3x), terminfo(5)

    ncurses 6.5                       2025-01-18                curs_variables(3x)