# curs_getch 3x 2024-04-20 ncurses 6.4 Library calls

    curs_getch(3x)                   Library calls                  curs_getch(3x)

## 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
                  KEY_UP          Arrow keys
                  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 term-
           info 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 6.4                       2024-04-20                    curs_getch(3x)