# curs_getch 3x 2025-03-15 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.

           o   If  the  escape  sequence  matches  a  string capability defining a
               function key for the terminal type (such  as  key_home  (khome)  or
               key_up  (kuu1)), wgetch returns the function key code corresponding
               to the unique sequence defined by the terminal.

           o   If the escape sequence matches no function  keys  defined  for  the
               terminal  type,  wgetch  returns the code of the last (most recent)
               character it has read.

           o   If wgetch cannot decide the validity of the input as a function key
               because  it  has not read enough characters to disambiguate it, the
               function waits until it has this information or the  escape  delay,
               configured  by  the  global  variable  ESCDELAY  (an extension; see
               section "EXTENSIONS" below) or the environment variable of the same
               name (see section "ENVIRONMENT" of ncurses(3x)), also an extension,
               elapses.

           Consequently, a user of a curses application that employs  keypad  mode
           may  experience a pause or "hang" after the escape key is pressed while
           curses collects sufficient characters to disambiguate  the  input.   If
           the  window  is  in "no time-out" mode, the escape delay is effectively
           infinite; see notimeout(3x).  In the event of  such  a  pause,  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.

## HISTORY

           4BSD (1980) introduced wgetch and its variants.

           ncurses 1.9.9g (1996) added has_key.

## 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                       2025-03-15                    curs_getch(3x)