curs_getch 3x 2024-05-18 ncurses 6.5 Library calls

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


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


       #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);


Reading Characters

       wgetch gathers a key event from the terminal keyboard associated with a
       curses   window  win.   ncurses(3x)  describes  the  variants  of  this

       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"

       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 input is available or the specified delay

       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 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  they  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

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

       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_UP          Arrow keys
              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

       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 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).


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

       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.


       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  "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

       Use  of  wgetch with echo(3x) and neither cbreak(3x) nor raw(3x) is not

       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
       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.


       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, and is  not  found  in  SVr4  curses,
       4.4BSD curses, or any other previous curses implementation.


       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 interrupted a  read(2)  call
       in  progress,  and  also  (in  some  implementations)  whether an input
       timeout or non-blocking mode had 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


       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"  <

       ECMA-48   "Control   Functions  for  Coded  Character  Sets"  <https://>

ncurses 6.5                       2024-05-18                    curs_getch(3x)