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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 in- stead 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 stan- dards, each of which also defined a Boolean data type. The curses li- brary 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 exam- ple, 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 exam- ple, 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 sup- ported 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 es- cape 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 pro- gram 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 li- braries, most of these variables reside in the former. 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 opera- tions like clearing and redrawing a screen containing garbage". Nei- ther 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 applica- tions 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) capa- bility for computing hardware tabs (that is, tab stops on the phys- ical 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 6.5 2024-04-13 curs_variables(3X)