# curs_variables 3x 2024-01-05 ncurses 6.4 Library calls

    curs_variables(3x)               Library calls              curs_variables(3x)

## 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 an escape character corresponding to a user's
           press of an "Escape" key on the input device from  one  included  in  a
           control sequence used by a cursor movement or function key, the library
           waits to see if another key event occurs after  the  escape  character.
           ESCDELAY stores this interval in milliseconds.

### 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  terminfo
           libraries, most of these variables reside in the curses library.

## 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 6.4                       2024-01-05                curs_variables(3x)