https://invisible-island.net/ncurses/man/


curs_getch 3x 2024-03-23 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 ch);

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


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 ch to the window (at the  cursor  position)  per
       the following rules.

       o   If  ch  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 ch 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 ch is a carriage return and nl(3x) has been called,  wgetch  returns
       the character code for newline (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 ch 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

       The keypad is arranged as follows.

                                   +-----+------+-------+
                                   | A1  |  up  |  A3   |
                                   +-----+------+-------+
                                   |left |  B2  | right |
                                   +-----+------+-------+
                                   | C1  | down |  C3   |
                                   +-----+------+-------+
       Two of these symbols do not correspond to a real key.

       o   wgetch returns KEY_RESIZE (even if  the  window's  keypad  mode  is
           disabled) when ncurses detects the 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 takes a key code value from  the  above  list,  and
       returns  a  Boolean  value indicating the terminal's recognition of it.
       See also define_key(3x) and key_defined(3x).


RETURN VALUE

       wgetch returns ERR if

       o   the WINDOW pointer is NULL, or

       o   its timeout expires without any data arriving, or

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

       Functions  with  a  "mv"  prefix  first  perform  cursor movement using
       wmove(3x) and fail if the position is outside the window, or (for "mvw"
       functions) if the win parameter is a null pointer.

       ungetch  returns  OK on success and ERR 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, 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 terminal's keypad Enter key.

       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 on the IBM PC/AT keyboard 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 interrupts a read(2) call in
       progress  or  not,  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

       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)

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

       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                       2024-03-23                    curs_getch(3x)