- This page summarizes variables provided by the curses library. A more
- complete description is given in the curses(3x) manual page.
+ 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.
+
+
+
+ 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 and constants TRUE and FALSE to
+ store its two possible values.
+
+
+
+ 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).
+
- Depending on the configuration, these may be actual variables, or
- macros (see curs_threads(3x) and curs_opaque(3x)) which provide read-
- only access to curses's state. In either case, applications should
- treat them as read-only to avoid confusing the library.
+
+ 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 graphemecluster (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).
- After initializing curses, this variable contains the number of color
- pairs which the terminal can support. Usually the number of color
- pairs will be the product COLORS*COLORS, however this is not always
- true:
+ Once curses is initialized, COLOR_PAIRS contains the number of color
+ pairs supported by the terminal. Often, its value is the product
+ COLORS x COLORS, but this is not always true.
- o a few terminals use HLS colors, which do not follow this rule
+ o A few terminals use HLS colors, ignoring this rule; and
o terminals supporting a large number of colors are limited by the
- number of color pairs that can be represented in a signedshort
- value.
+ number of color pairs that a signedshort value can represent.
- After initializing curses, this variable contains the number of colors
- which the terminal can support.
+ Once curses is initialized, COLORS contains the number of colors
+ supported by the terminal.
- After initializing curses, this variable contains the width of the
- screen, i.e., the number of columns.
+ Once curses is initialized, COLS contains the screen's width in
+ character cells; that is, the number of columns.
- This variable holds the number of milliseconds to wait after reading an
- escape character, to distinguish between an individual escape character
- entered on the keyboard from escape sequences sent by cursor- and func-
- tion-keys (see curses(3x).
+ 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.
- After initializing curses, this variable contains the height of the
- screen, i.e., the number of lines.
+ Once curses is initialized, LINES contains the screen's height in
+ character cells; that is, the number of lines.
- This variable holds the number of columns used by the curses library
- when converting a tab character to spaces as it adds the tab to a win-
- dow (see curs_addch(3x).
+ The curses library converts a tab character to this number of spaces as
+ it adds a tab to a window; see curs_addch(3x).
-
+ curses records updates to the terminal screen in a WINDOW structure
+ named curscr.
+ This object is referred to as the "physical screen" in curs_refresh(3x)
+ and curs_outopts(3x).
-
- Upon initializing curses, a default window called stdscr, which is the
- size of the terminal screen, is created. Many curses functions use
- this window.
+ 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 structure 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.
- The curses library is initialized using either initscr(3x), or
- newterm(3x).
+ Either initscr(3x) or newterm(3x) initializes curses.
- If curses is configured to use separate curses/terminfo libraries, most
- of these variables reside in the curses library.
+ If ncurses is configured to provide separate curses and terminfo
+ libraries, most of these variables reside in the curses library.
- ESCDELAY and TABSIZE are extensions, not provided in most other imple-
- mentations of curses.
+ 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";
+ SVID 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, this
+ window is used as a working area for combining the standard screen
+ stdscr with any other windows which the application may have created
+ with newwin(3x). When the updated newscr is complete, curses updates
+ 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.
- ESCDELAY is an extension in AIX 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 In AIX, the units for ESCDELAY are fifths of a millisecond.
+ oncurses 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 The default value for AIX's ESCDELAY is 0.1 seconds.
+ o Other implementations differ. For instance, NetBSD curses allows
+ TABSIZE to be set through an environment variable. ncurses does
+ not.
- o AIX also enforces a limit of 10,000 seconds for ESCDELAY; this im-
- plementation currently has no upper limit.
+ NetBSD curses does not support hardware tabs; it uses the init_tabs
+ capability and the TABSIZE variable only for updating the virtual
+ screen.
- This implementation has long used ESCDELAY with units of milliseconds,
- making it impossible to be completely compatible with AIX. Likewise,
- most users have either decided to override the value, or rely upon its
- default value.
+ 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.