# curs_getch 3x 2025-02-15 ncurses 6.5 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 buffer

## 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 event 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
           event; for alphanumeric and punctuation keys, this value corresponds to
           the character encoding used by the terminal.  Use of the control key as
           a  modifier,  by  holding  it down while pressing and releasing another
           key, 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)  or  raw(3x)  has  been
           called,  this  happens after one character is read.  If nocbreak(3x) or
           noraw(3x) has been called, it occurs when the  next  newline  is  read.
           (Because  the  terminal's  canonical or "cooked" mode is line-buffered,
           multiple wgetch calls may then be necessary to empty the input  queue.)
           If halfdelay(3x) has been called, curses waits until input is available
           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  (see  erasechar(3x)),
               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 win has been moved or modified since the last call to
               wrefresh(3x), curses calls wrefresh on it.

           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 distinguish
           a  user's  press  of  the  escape  key (assuming it sends ESC) from 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  the  escape  key  is
           pressed  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 ESC, the terminal may
           appear  to  hang  in no time-out mode after the user presses the escape
           key.  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 associated with the
           screen.

### 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, if ncurses has handled a SIGWINCH signal since wgetch was
               called; 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 xterm(1)'s mouse protocol),  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

           wgetch returns a key code identifying the key event as described above,
           which may include KEY_RESIZE or KEY_MOUSE indicating non-key events, or
           ERR on failure.  wgetch 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 returns OK on success and ERR on  failure.   ungetch  fails  if
           there is no more room in the input queue.

           has_key returns TRUE or FALSE.

           Functions  taking  a  WINDOW  pointer  argument  fail  if win is a null
           pointer.

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

## NOTES

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

           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 terminfo entry for the terminal type 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,
           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 canonical), 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
           keyboard of the AT&T 7300 (also known variously as the  "3B1",  "Safari
           4",  and  "UNIX  PC"),  a  1985 machine rich in function keys.  Today's
           computer keyboards are based on 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), KEY_A1, KEY_A3, KEY_B2, KEY_C1, KEY_C3, and KEY_F(n) for 1 <=
           n <= 12.

## 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 is an ncurses extension, 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.

           Except as noted in section "EXTENSIONS" above,  X/Open  Curses  Issue 4
           describes these functions.  It specifies no error conditions for them.

           SVr4  describes  a  successful  return  value only as "an integer value
           other than ERR".

           wgetch reads only single-byte characters.

           The echo behavior of these functions on  input  of  KEY_  or  backspace
           characters is not documented in SVr4 curses.

           The  behavior  of  wgetch  in  the  presence  of signal handlers is not
           documented in SVr4 curses and is  unspecified  by  X/Open  Curses.   In
           historical  curses  implementations, it varied depending on whether the
           operating system's dispatch of a signal  to  a  handler  interrupted  a
           read(2) call in progress, and also (in some implementations) whether an
           input timeout or non-blocking mode had been  set.   A  portable  curses
           application  prepares  for  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

           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/>

           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)

    ncurses 6.5                       2025-02-15                    curs_getch(3x)