Provided by: ncurses-doc_6.1+20181013-2ubuntu2_all bug

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);
       int has_key(int ch);

DESCRIPTION

   Reading characters
       The getch, wgetch, mvgetch and mvwgetch, routines read a character from  the  window.   In
       no-delay  mode,  if  no  input  is waiting, the value ERR is returned.  In delay mode, the
       program waits until the system passes text through  to  the  program.   Depending  on  the
       setting  of  cbreak, this is after one character (cbreak mode), or after the first newline
       (nocbreak mode).  In half-delay mode, the program waits until a character is typed or  the
       specified timeout has been reached.

       If  echo  is  enabled, and the window is not a pad, then the character will also be echoed
       into the designated window according to the following rules:

       ·   If the character is the current erase character, left arrow, or backspace, the  cursor
           is moved one space to the left and that screen position is erased as if delch had been
           called.

       ·   If the character value is any other KEY_ define, the user is alerted with a beep call.

       ·   If the character is a carriage-return, and if nl is enabled, it  is  translated  to  a
           line-feed after echoing.

       ·   Otherwise the character is simply output to the screen.

       If  the  window  is  not  a  pad, and it has been moved or modified since the last call to
       wrefresh, wrefresh will be called before another character is read.

   Keypad mode
       If keypad is TRUE, and a function key is pressed, the  token  for  that  function  key  is
       returned instead of the raw characters:

       ·   The  predefined  function  keys are listed in <curses.h> as macros with values outside
           the range of 8-bit characters.  Their names begin with KEY_.

       ·   Other (user-defined) function keys which may be defined using define_key(3X)  have  no
           names, but also are expected to have values outside the range of 8-bit characters.

       Thus, a variable intended to hold the return value of a function key must be of short size
       or larger.

       When a character that could be the beginning of a function  key  is  received  (which,  on
       modern  terminals,  means  an escape character), curses sets a timer.  If the remainder of
       the sequence does not come in within the designated time, the character is passed through;
       otherwise, the function key value is returned.  For this reason, many terminals experience
       a delay between the time a user presses the escape key and the escape is returned  to  the
       program.

       In   ncurses,   the   timer   normally   expires   after   the   value  in  ESCDELAY  (see
       curs_variables(3X)).  If notimeout is TRUE, the timer does not expire; it is  an  infinite
       (or  very large) value.  Because function keys usually begin with an escape character, the
       terminal may appear to hang in notimeout mode after pressing the escape key until  another
       key is pressed.

   Ungetting characters
       The ungetch routine places ch back onto the input queue to be returned by the next call to
       wgetch.  There is just one input queue for all windows.

   Predefined key-codes
       The following special keys are defined in <curses.h>.

       ·   Except for the special case KEY_RESIZE, it is necessary to enable keypad for getch  to
           return these codes.

       ·   Not all of these are necessarily supported on any particular terminal.

       ·   The  naming  convention  may  seem  obscure,  with some apparent misspellings (such as
           "RSUME" for "resume").  The names correspond to the long terminfo capability names for
           the keys, and were defined long ago, in the 1980s.

                            Name            Key name
                            ─────────────────────────────────────────────────
                            KEY_BREAK       Break key
                            KEY_DOWN        The four arrow keys ...
                            KEY_UP
                            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)        For 0 ≤ n ≤ 63
                            KEY_DL          Delete line
                            KEY_IL          Insert line
                            KEY_DC          Delete character
                            KEY_IC          Insert char or enter insert mode
                            KEY_EIC         Exit insert char mode
                            KEY_CLEAR       Clear screen
                            KEY_EOS         Clear to end of screen
                            KEY_EOL         Clear to end of line
                            KEY_SF          Scroll 1 line forward
                            KEY_SR          Scroll 1 line backward (reverse)
                            KEY_NPAGE       Next page
                            KEY_PPAGE       Previous page
                            KEY_STAB        Set tab
                            KEY_CTAB        Clear tab
                            KEY_CATAB       Clear all tabs
                            KEY_ENTER       Enter or send
                            KEY_SRESET      Soft (partial) reset
                            KEY_RESET       Reset or hard reset
                            KEY_PRINT       Print or copy
                            KEY_LL          Home down or 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 read
                            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_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 char key
                            KEY_SDL         Shifted delete line key
                            KEY_SELECT      Select 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 input key
                            KEY_SLEFT       Shifted left arrow key
                            KEY_SMESSAGE    Shifted message key
                            KEY_SMOVE       Shifted move key
                            KEY_SNEXT       Shifted next key
                            KEY_SOPTIONS    Shifted options key
                            KEY_SPREVIOUS   Shifted prev key
                            KEY_SPRINT      Shifted print key
                            KEY_SREDO       Shifted redo key
                            KEY_SREPLACE    Shifted replace key
                            KEY_SRIGHT      Shifted right arrow
                            KEY_SRSUME      Shifted resume key
                            KEY_SSAVE       Shifted save key
                            KEY_SSUSPEND    Shifted suspend key
                            KEY_SUNDO       Shifted undo key
                            KEY_SUSPEND     Suspend key
                            KEY_UNDO        Undo key

       Keypad is arranged like this:

                                         ┌─────┬──────┬───────┐
                                         │ A1upA3   │
                                         ├─────┼──────┼───────┤
                                         │leftB2right │
                                         ├─────┼──────┼───────┤
                                         │ C1downC3   │
                                         └─────┴──────┴───────┘
       A few of these predefined values do not correspond to a real key:

       ·   KEY_RESIZE is returned when the SIGWINCH signal has been detected (see initscr(3X) and
           resizeterm(3NCURSES)).  This code is returned whether or not keypad has been enabled.

       ·   KEY_MOUSE  is  returned for mouse-events (see mouse(3NCURSES)).  This code relies upon
           whether  or  not  keypad(3X)  has  been  enabled,  because  (e.g.,  with  xterm  mouse
           prototocol) ncurses must read escape sequences, just like a function key.

   Testing key-codes
       The  has_key routine takes a key-code value from the above list, and returns TRUE or FALSE
       according to whether the current terminal type recognizes a key with that value.

       The library also supports these extensions:

          define_key
               defines a key-code for a given string (see define_key(3X)).

          key_defined
               checks if there is a key-code defined for a given string (see key_defined(3X)).

RETURN VALUE

       All routines return the integer ERR upon failure and an integer value other than  ERR  (OK
       in the case of ungetch) upon successful completion.

          ungetch
               returns ERR if there is no more room in the FIFO.

          wgetch
               returns  ERR  if  the  window  pointer  is null, or if its timeout expires without
               having any data, or if the execution was interrupted by a signal  (errno  will  be
               set to EINTR).

       Functions  with  a  "mv" prefix first perform a cursor movement using wmove, and return an
       error if the position is outside the window, or if the window pointer is null.

NOTES

       Use of the escape key by a programmer for a single character function is  discouraged,  as
       it  will  cause  a  delay  of up to one second while the keypad code looks for a following
       function-key sequence.

       Some keys may be the same as commonly used control keys, e.g., KEY_ENTER versus control/M,
       KEY_BACKSPACE  versus  control/H.   Some  curses  implementations  may differ according to
       whether they treat these control keys specially (and ignore  the  terminfo),  or  use  the
       terminfo definitions.  Ncurses uses the terminfo definition.  If it says that KEY_ENTER is
       control/M, getch will return KEY_ENTER when you press control/M.

       Generally, KEY_ENTER denotes the character(s) sent by the Enter key on the numeric keypad:

       ·   the terminal description lists the most useful keys,

       ·   the Enter key on the regular  keyboard  is  already  handled  by  the  standard  ASCII
           characters for carriage-return and line-feed,

       ·   depending  on  whether nl or nonl was called, pressing "Enter" on the regular keyboard
           may return either a carriage-return or line-feed, and finally

       ·   "Enter or send" is the standard description for this key.

       When using getch, wgetch, mvgetch, or mvwgetch, nocbreak mode  (nocbreak)  and  echo  mode
       (echo) should not be used at the same time.  Depending on the state of the tty driver when
       each character is typed, the program may produce undesirable results.

       Note that getch, mvgetch, and mvwgetch may be macros.

       Historically, the set of keypad macros was largely defined by the extremely  function-key-
       rich  keyboard of the AT&T 7300, aka 3B1, aka Safari 4.  Modern personal computers usually
       have only a small subset of these.  IBM PC-style consoles typically  support  little  more
       than  KEY_UP,  KEY_DOWN, KEY_LEFT, KEY_RIGHT, KEY_HOME, KEY_END, KEY_NPAGE, KEY_PPAGE, and
       function keys 1 through 12.  The Ins key is usually mapped to KEY_IC.

PORTABILITY

       The *get* functions are described in the XSI Curses standard, Issue 4.  They read  single-
       byte  characters  only.   The  standard  specifies  that  they  return ERR on failure, but
       specifies no error conditions.

       The echo behavior of these functions on input of KEY_  or  backspace  characters  was  not
       specified  in  the  SVr4  documentation.   This description is adopted from the XSI Curses
       standard.

       The behavior of getch and friends in the presence of handled signals is unspecified in the
       SVr4  and  XSI  Curses  documentation.  Under historical curses implementations, it varied
       depending on whether the operating  system's  implementation  of  handled  signal  receipt
       interrupts a read(2) call in progress or not, and also (in some implementations) depending
       on whether an input timeout or non-blocking mode has been set.

       KEY_MOUSE is mentioned in XSI Curses, along with a few related terminfo capabilities,  but
       no higher-level functions use the feature.  The implementation in ncurses is an extension.

       KEY_RESIZE  is an extension first implemented for ncurses.  NetBSD curses later added this
       extension.

       Programmers concerned about portability should be prepared for either of  two  cases:  (a)
       signal receipt does not interrupt getch; (b) signal receipt interrupts getch and causes it
       to return ERR with errno set to EINTR.

       The has_key function is unique to ncurses.   We  recommend  that  any  code  using  it  be
       conditionalized on the NCURSES_VERSION feature macro.

SEE ALSO

       ncurses(3NCURSES),  inopts(3NCURSES),  outopts(3NCURSES), mouse(3NCURSES), move(3NCURSES),
       refresh(3NCURSES), curses_variables(3NCURSES), resizeterm(3NCURSES).

       Comparable  functions  in  the  wide-character  (ncursesw)  library   are   described   in
       get_wch(3NCURSES).

                                                                                  getch(3NCURSES)