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  set‐
       ting  of cbreak, this is after one character (cbreak mode), or af‐
       ter 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  charac‐
       ter  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 re‐
       turned 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 en‐
           able 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 corre‐
           spond 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 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_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 insert 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
                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 de‐
           tected (see initscr(3X) and resizeterm(3X)).  This code is re‐
           turned 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 en‐
           abled, because (e.g., with xterm(1) 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 termi‐
       nal type recognizes a key with that value.

       The library also supports these extensions:

          define_key
               defines a key-code for a given string (see de‐
               fine_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 time‐
               out 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 func‐
       tion 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 charac‐
       ter 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, Is‐
       sue 4.  They read single-byte characters only.  The standard spec‐
       ifies that they return ERR on failure, but specifies no error con‐
       ditions.

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

       The behavior of getch and friends in the presence of handled sig‐
       nals is unspecified in the SVr4 and XSI Curses documentation.  Un‐
       der 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 fea‐
       ture.  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 ei‐
       ther 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), re‐
       sizeterm(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.  Informa‐
       tion 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
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       ⟨https://github.com/mirror/ncurses.git⟩ on 2025-02-02.  (At that
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                                                           curs_getch(3X)