getch(3x) — Linux manual page


curs_getch(3X)                                                curs_getch(3X)

NAME         top

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

SYNOPSIS         top

       #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         top

   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

       ·   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_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:

                               │ A1  up  A3   │
                               │left B2  right │
                               │ C1  down C3   │
       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(3X)).  This code is returned
           whether or not keypad has been enabled.

       ·   KEY_MOUSE is returned for mouse-events (see curs_mouse(3X)).
           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:

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

               checks if there is a key-code defined for a given string (see

RETURN VALUE         top

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

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

               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         top

       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_PPAGE, and function keys 1 through 12.  The Ins key is usually
       mapped to KEY_IC.

PORTABILITY         top

       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

SEE ALSO         top

       curses(3X), curs_inopts(3X), curs_outopts(3X), curs_mouse(3X),
       curs_move(3X), curs_refresh(3X), curs_variables(3X), resizeterm(3X).

       Comparable functions in the wide-character (ncursesw) library are
       described in curs_get_wch(3X).

COLOPHON         top

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