curs_getch(3x) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | NOTES | PORTABILITY | SEE ALSO | COLOPHON

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);

       /* extension */
       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
           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:

                             ┌─────┬──────┬───────┐
                             │ 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:

          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         top

       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         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_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         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
       macro.

SEE ALSO         top

       curses(3X), curs_inopts(3X), curs_mouse(3X), curs_move(3X),
       curs_outopts(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

       This page is part of the ncurses (new curses) project.
       Information about the project can be found at 
       ⟨https://www.gnu.org/software/ncurses/ncurses.html⟩.  If you have
       a bug report for this manual page, send it to
       bug-ncurses-request@gnu.org.  This page was obtained from the
       project's upstream Git mirror of the CVS repository
       ⟨git://ncurses.scripts.mit.edu/ncurses.git⟩ on 2021-08-27.  (At
       that time, the date of the most recent commit that was found in
       the repository was 2021-05-23.)  If you discover any rendering
       problems in this HTML version of the page, or you believe there
       is a better or more up-to-date source for the page, or you have
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       (which is not part of the original manual page), send a mail to
       man-pages@man7.org

                                                          curs_getch(3X)