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curs_getch(3)                   Library calls                  curs_getch(3)


NAME

       getch, wgetch, mvgetch, mvwgetch, ungetch, has_key - get (or push back)
       characters from curses terminal keyboard


SYNOPSIS

       #include <curses.h>

       int getch(void);
       int wgetch(WINDOW *win);
       int mvgetch(int y, int x);
       int mvwgetch(WINDOW *win, int y, int x);

       int ungetch(int c);

       /* extension */
       int has_key(int c);


DESCRIPTION

   Reading Characters
       wgetch gathers a key stroke from the terminal keyboard associated with
       a curses window win.  ncurses(3X) describes the variants of this
       function.

       When input is pending, wgetch returns an integer identifying the key
       stroke; for alphanumeric and punctuation keys, this value corresponds
       to the character encoding used by the terminal.  Use of the control key
       as a modifier often results in a distinct code.  The behavior of other
       keys depends on whether win is in keypad mode; see subsection "Keypad
       Mode" below.

       If no input is pending, then if the no-delay flag is set in the window
       (see nodelay(3X)), the function returns ERR; otherwise, curses waits
       until the terminal has input.  If cbreak(3X) has been called, this
       happens after one character is read.  If nocbreak(3X) has been called,
       it occurs when the next newline is read.  If halfdelay(3X) has been
       called, curses waits until a character is typed or the specified delay
       elapses.

       If echo(3X) has been called, and the window is not a pad, curses writes
       the returned character c to the window (at the cursor position) per the
       following rules.

       o   If c matches the terminal's erase character, the cursor moves
           leftward one position and the new position is erased as if
           wmove(3X) and then wdelch(3X) were called.  When the window's
           keypad mode is enabled (see below), KEY_LEFT and KEY_BACKSPACE are
           handled the same way.

       o   curses writes any other c to the window, as with wechochar(3X).

       o   If the window has been moved or modified since the last call to
           wrefresh(3X), curses calls wrefresh.

       If c is a carriage return and nl(3X) has been called, wgetch returns
       the character code for line feed instead.

   Keypad Mode
       To curses, key strokes not from the alphabetic section of the keyboard
       (those corresponding to the ECMA-6 character set--see
       ascii(7)--optionally modified by either the control or shift keys) are
       treated as function keys.  (In curses, the term "function key" includes
       but is not limited to keycaps engraved with "F1", "PF1", and so on.)
       If the window is in keypad mode, these produce a numeric code
       corresponding to the KEY_ symbols listed in subsection "Predefined Key
       Codes" below; otherwise, they transmit a sequence of codes typically
       starting with the escape character, and which must be collected with
       multiple wgetch calls.

       o   The curses.h header file declares many predefined function keys
           whose names begin with KEY_; these object-like macros have values
           outside the range of eight-bit character codes.

       o   In ncurses, user-defined function keys are configured with
           define_key(3X); they have no names, but are also expected to have
           values outside the range of eight-bit codes.

       A variable intended to hold a function key code must thus be of type
       short or larger.

       Most terminals one encounters follow the ECMA-48 standard insofar as
       their function keys produce character sequences prefixed with the
       escape character ESC.  This fact implies that curses cannot know
       whether the terminal has sent an ESC key stroke or the beginning of a
       function key's character sequence without waiting to see if, and how
       soon, further input arrives.  When curses reads such an ambiguous
       character, it sets a timer.  If the remainder of the sequence does not
       arrive within the designated time, wgetch returns the prefix character;
       otherwise, it returns the function key code corresponding to the unique
       sequence defined by the terminal.  Consequently, a user of a curses
       application may experience a delay after pressing ESC while curses
       disambiguates the input; see section "EXTENSIONS" below.  If the window
       is in "no time-out" mode, the timer does not expire; it is an infinite
       (or very large) value.  See notimeout(3X).  Because function key
       sequences usually begin with an escape character, the terminal may
       appear to hang in no time-out mode after the user has pressed ESC.
       Generally, further typing "awakens" curses.

   Ungetting Characters
       ungetch places c into the input queue to be returned by the next call
       to wgetch.  A single input queue serves all windows.

   Predefined Key Codes
       The header file curses.h defines the following function key codes.

       o   Except for the special case of KEY_RESIZE, a window's keypad mode
           must be enabled for wgetch to read these codes from it.

       o   Not all of these are necessarily supported on any particular
           terminal.

       o   The naming convention may seem obscure, with some apparent
           misspellings (such as "RSUME" for "resume"); the names correspond
           to the terminfo capability names for the keys, and were
           standardized before the IBM PC/AT keyboard layout achieved a
           dominant position in industry.


              Symbol          Key name
              =================================================================
              KEY_BREAK       Break key
              KEY_DOWN        Arrow keys
              KEY_UP
              KEY_LEFT
              KEY_RIGHT
              KEY_HOME        Home key (upward+left arrow)
              KEY_BACKSPACE   Backspace
              KEY_F0          Function keys; space for 64 keys is reserved
              KEY_F(n)        Function key n where 0 <= n <= 63
              KEY_DL          Delete line
              KEY_IL          Insert line
              KEY_DC          Delete character
              KEY_IC          Insert character/Enter insert mode
              KEY_EIC         Exit insert character mode
              KEY_CLEAR       Clear screen
              KEY_EOS         Clear to end of screen
              KEY_EOL         Clear to end of line
              KEY_SF          Scroll one line forward
              KEY_SR          Scroll one line backward (reverse)
              KEY_NPAGE       Next page/Page up
              KEY_PPAGE       Previous page/Page down
              KEY_STAB        Set tab
              KEY_CTAB        Clear tab
              KEY_CATAB       Clear all tabs
              KEY_ENTER       Enter/Send
              KEY_SRESET      Soft (partial) reset
              KEY_RESET       (Hard) reset
              KEY_PRINT       Print/Copy
              KEY_LL          Home down/Bottom (lower left)
              KEY_A1          Upper left of keypad
              KEY_A3          Upper right of keypad
              KEY_B2          Center of keypad
              KEY_C1          Lower left of keypad
              KEY_C3          Lower right of keypad
              KEY_BTAB        Back tab key
              KEY_BEG         Beg(inning) key
              KEY_CANCEL      Cancel key
              KEY_CLOSE       Close key
              KEY_COMMAND     Cmd (command) key
              KEY_COPY        Copy key
              KEY_CREATE      Create key
              KEY_END         End key
              KEY_EXIT        Exit key
              KEY_FIND        Find key
              KEY_HELP        Help key
              KEY_MARK        Mark key
              KEY_MESSAGE     Message key
              KEY_MOUSE       Mouse event occurred
              KEY_MOVE        Move key
              KEY_NEXT        Next object key
              KEY_OPEN        Open key
              KEY_OPTIONS     Options key
              KEY_PREVIOUS    Previous object key
              KEY_REDO        Redo key
              KEY_REFERENCE   Ref(erence) key
              KEY_REFRESH     Refresh key
              KEY_REPLACE     Replace key
              KEY_RESIZE      Screen resized
              KEY_RESTART     Restart key
              KEY_RESUME      Resume key
              KEY_SAVE        Save key
              KEY_SELECT      Select key
              KEY_SUSPEND     Suspend key
              KEY_UNDO        Undo key
              -----------------------------------------------------------------
              KEY_SBEG        Shifted beginning key
              KEY_SCANCEL     Shifted cancel key
              KEY_SCOMMAND    Shifted command key
              KEY_SCOPY       Shifted copy key
              KEY_SCREATE     Shifted create key
              KEY_SDC         Shifted delete character key
              KEY_SDL         Shifted delete line key
              KEY_SEND        Shifted end key
              KEY_SEOL        Shifted clear line key
              KEY_SEXIT       Shifted exit key
              KEY_SFIND       Shifted find key
              KEY_SHELP       Shifted help key
              KEY_SHOME       Shifted home key
              KEY_SIC         Shifted insert key
              KEY_SLEFT       Shifted left arrow key
              KEY_SMESSAGE    Shifted message key
              KEY_SMOVE       Shifted move key
              KEY_SNEXT       Shifted next object key
              KEY_SOPTIONS    Shifted options key
              KEY_SPREVIOUS   Shifted previous object key
              KEY_SPRINT      Shifted print key
              KEY_SREDO       Shifted redo key
              KEY_SREPLACE    Shifted replace key
              KEY_SRIGHT      Shifted right arrow key
              KEY_SRSUME      Shifted resume key
              KEY_SSAVE       Shifted save key
              KEY_SSUSPEND    Shifted suspend key
              KEY_SUNDO       Shifted undo key

       Many keyboards feature a nine-key directional pad.


                                   +-----+------+-------+
                                   | A1  |  up  |  A3   |
                                   +-----+------+-------+
                                   |left |  B2  | right |
                                   +-----+------+-------+
                                   | C1  | down |  C3   |
                                   +-----+------+-------+
       Two of the symbols in the list above do not correspond to a physical
       key.

       o   wgetch returns KEY_RESIZE, even if the window's keypad mode is
           disabled, when ncurses handles a SIGWINCH signal; see initscr(3X)
           and resizeterm(3X).

       o   wgetch returns KEY_MOUSE to indicate that a mouse event is pending
           collection; see curs_mouse(3X).  Receipt of this code requires a
           window's keypad mode to be enabled, because to interpret mouse
           input (as with with xterm(1)'s mouse prototocol), ncurses must read
           an escape sequence, as with a function key.

   Testing Key Codes
       In ncurses, has_key returns a Boolean value indicating whether the
       terminal type recognizes its parameter as a key code value.  See also
       define_key(3X) and key_defined(3X).


RETURN VALUE

       Except for has_key, these functions return OK on success and ERR on
       failure.

       Functions taking a WINDOW pointer argument fail if the pointer is NULL.

       Functions prefixed with "mv" first perform cursor movement and fail if
       the position (y, x) is outside the window boundaries.

       wgetch also fails if

       o   its timeout expires without any data arriving, or

       o   execution was interrupted by a signal, in which case errno is set
           to EINTR.

       ungetch fails if there is no more room in the input queue.

       has_key returns TRUE or FALSE.


NOTES

       curses discourages assignment of the ESC key to a discrete function by
       the programmer because the library requires a delay while it awaits the
       potential remainder of a terminal escape sequence.

       Some key strokes are indistinguishable from control characters; for
       example, KEY_ENTER may be the same as ^M, and KEY_BACKSPACE may be the
       same as ^H or ^?.  Consult the terminal's terminfo entry to determine
       whether this is the case; see infocmp(1).  Some curses implementations,
       including ncurses, honor the terminfo key definitions; others treat
       such control characters specially.

       curses distinguishes the Enter keys in the alphabetic and numeric
       keypad sections of a keyboard because (most) terminals do.  KEY_ENTER
       refers to the key on the numeric keypad and, like other function keys,
       and is reliably recognized only if the window's keypad mode is enabled.

       o   The terminfo key_enter (kent) capability describes the character
           (sequence) sent by the Enter key of a terminal's numeric (or
           similar) keypad.

       o   "Enter or send" is X/Open Curses's description of this key.

       curses treats the Enter or Return key in the alphabetic section of the
       keyboard differently.

       o   It usually produces a control code for carriage return (^M) or line
           feed (^J).

       o   Depending on the terminal mode (raw, cbreak, or "cooked"), and
           whether nl(3X) or nonl(3X) has been called, wgetch may return
           either a carriage return or line feed upon an Enter or Return key
           stroke.

       Use of wgetch with echo(3X) and neither cbreak(3X) nor raw(3X) is not
       well-defined.

       Historically, the list of key code macros above was influenced by the
       function-key-rich keyboard of the AT&T 7300 (also known variously as
       the "3B1", "Safari 4", and "UNIX PC"), a 1985 machine.  Today's
       computer keyboards are based that of the IBM PC/AT and tend to have
       fewer.  A curses application can expect such a keyboard to transmit key
       codes KEY_UP, KEY_DOWN, KEY_LEFT, KEY_RIGHT, KEY_HOME, KEY_END,
       KEY_PPAGE (Page Up), KEY_NPAGE (Page Down), KEY_IC (Insert), KEY_DC
       (Delete), and KEY_F(n) for 1 <= n <= 12.

       getch, mvgetch, and mvwgetch may be implemented as macros.


EXTENSIONS

       In ncurses, when a window's "no time-out" mode is not set, the ESCDELAY
       variable configures the duration of the timer used to disambiguate a
       function key character sequence from a series of key strokes beginning
       with ESC typed by the user; see curs_variables(3X).

       has_key was designed for ncurses(3X), and is not found in SVr4 curses,
       4.4BSD curses, or any other previous curses implementation.


PORTABILITY

       Applications employing ncurses extensions should condition their use on
       the visibility of the NCURSES_VERSION preprocessor macro.

       X/Open Curses, Issue 4 describes getch, wgetch, mvgetch, mvwgetch, and
       ungetch.  It specifies no error conditions for them.

       wgetch reads only single-byte characters.

       The echo behavior of these functions on input of KEY_ or backspace
       characters was not specified in the SVr4 documentation.  This
       description is adapted from X/Open Curses.

       The behavior of wgetch in the presence of signal handlers is
       unspecified in the SVr4 documentation and X/Open Curses.  In historical
       curses implementations, it varied depending on whether the operating
       system's dispatch of a signal to a handler interrupting a read(2) call
       in progress, and also (in some implementations) whether an input
       timeout or non-blocking mode has been set.  Programmers concerned about
       portability should be prepared for either of two cases: (a) signal
       receipt does not interrupt wgetch; or (b) signal receipt interrupts
       wgetch and causes it to return ERR with errno set to EINTR.

       KEY_MOUSE is mentioned in X/Open Curses, along with a few related
       terminfo capabilities, but no higher-level functions use the feature.
       The implementation in ncurses is an extension.

       KEY_RESIZE and has_key are extensions first implemented for ncurses.
       By 2022, PDCurses and NetBSD curses had added them along with
       KEY_MOUSE.


SEE ALSO

       curs_get_wch(3X) describes comparable functions of the ncurses library
       in its wide-character configuration (ncursesw).

       curses(3X), curs_addch(3X), curs_inopts(3X), curs_mouse(3X),
       curs_move(3X), curs_outopts(3X), curs_refresh(3X), curs_variables(3X),
       resizeterm(3X), ascii(7)

       ECMA-6 "7-bit coded Character Set" <https://ecma-international.org/
       publications-and-standards/standards/ecma-6/>

       ECMA-48 "Control Functions for Coded Character Sets" <https://
       ecma-international.org/publications-and-standards/standards/ecma-48/>

ncurses 6.5                       2024-04-20                    curs_getch(3)

ncurses 6.5 - Generated Wed May 1 12:56:00 CDT 2024
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