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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 buffer 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 c); /* extension */ int has_key(int c); DESCRIPTION Reading Characters wgetch gathers a key event 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 event; for alphanumeric and punctuation keys, the space bar, and (usually) the Backspace, Tab, Return, and Escape keys, this value corresponds to the character encoding used by the terminal. Use of the control key as a modi- fier, by holding it down while pressing and releasing another key, 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) or raw(3X) has been called, this happens after curses reads one key event. If nocbreak(3X) or noraw(3X) has been called, it occurs when curses reads a newline. (Because the terminal's canonical or "cooked" mode is line-buffered, multiple wgetch calls may then be necessary to empty the input queue.) If halfdelay(3X) has been called, curses waits until input is available or the specified delay elapses. If echo(3X) has been called, and the window is not a pad, curses writes the returned character c to the window (at the cursor position) per the follow- ing rules. * If c matches the terminal's erase character (see erasechar(3X)), and the cursor is not at the window's leftmost column, 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 en- abled (see below), KEY_LEFT and KEY_BACKSPACE are handled the same way. * curses writes any other c to the window, as with wechochar(3X). * If the window win has been moved or modified since the last call to wrefresh(3X), curses calls wrefresh on it. If c is a carriage return and nl(3X) has been called, wgetch returns the character code for line feed instead. Keypad Mode Call keypad(3X) on a window to configure keypad mode when reading input from it. In keypad mode, curses treats 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) as function keys. (In curses, the term "function key" includes but is not limited to keycaps engraved with "F1", "PF1", and so on.) If a window is in keypad mode, wgetch translates these key strokes to a numeric code cor- responding to the KEY_ symbols listed in subsection "Key Codes" below. If the window is not in keypad mode, the input queue populates with the char- acters of the function key's escape sequence, which the application must collect individually with multiple wgetch calls. * The curses.h header file declares many function keys whose names begin with KEY_; these object-like macros have integer values outside the range of eight-bit character codes. * In ncurses, user-defined function keys are configured with define_key(3X); they have no names, but are also expected to have inte- ger values outside the range of eight-bit character 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 charac- ter ESC. This fact implies that curses cannot distinguish a user's press of the escape key (assuming it sends ESC) from the beginning of a function key's character sequence without waiting to see if, and how soon, further input arrives. * If the escape sequence matches a string capability defining a function key for the terminal type (such as key_home (khome) or key_up (kuu1)), wgetch returns the function key code corresponding to the unique se- quence defined by the terminal. * If the escape sequence matches no function keys defined for the termi- nal type, call wgetch repeatedly to obtain the codes of the individual characters of the sequence, in the order they occurred in the input. * If wgetch cannot decide the validity of the input as a function key be- cause it has not read enough characters to disambiguate it, the func- tion waits until it has this information or the escape delay elapses. Configure the escape delay with the global variable ESCDELAY, an exten- sion (see section "EXTENSIONS" below), or the environment variable of the same name (see section "ENVIRONMENT" of ncurses(3X)), also an ex- tension. Consequently, a user of a curses application that employs keypad mode may experience a pause or "hang" after pressing the escape key while curses collects sufficient characters to disambiguate the input. If the window is in "no time-out" mode, the escape delay is effectively infinite; see notimeout(3X). In the event of such a pause, further typing "awakens" curses. Ungetting Characters ungetch places c into the input queue to be returned by the next call to wgetch. A single input queue serves all windows associated with the screen. Key Codes The header file curses.h defines the following function key codes. * Except for the special case of KEY_RESIZE, a window's keypad mode must be enabled for wgetch to read these codes from it. * 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 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 Many keyboards feature a nine-key directional pad. +------+------+-------+ | A1 | up | A3 | +------+------+-------+ | left | B2 | right | +------+------+-------+ | C1 | down | C3 | +------+------+-------+ Two of the symbols in the list above do not correspond to a physical key. * wgetch returns KEY_RESIZE, even if the window's keypad mode is dis- abled, if ncurses has handled a SIGWINCH signal since wgetch was called; see initscr(3X) and resizeterm(3X). * wgetch returns KEY_MOUSE to indicate that a mouse event is pending col- lection; see curs_mouse(3X). Receipt of this code requires a window's keypad mode to be enabled, because to interpret mouse input (as with xterm(1)'s mouse protocol), ncurses must read an escape sequence, as with a function key. Testing Key Codes In ncurses, has_key returns a Boolean value indicating whether the terminal type recognizes its parameter as a key code value. See also define_key(3X) and key_defined(3X). RETURN VALUE wgetch returns a key code identifying the key event as described above, which may include KEY_RESIZE or KEY_MOUSE indicating non-key events, or ERR on failure. wgetch fails if its timeout expires without any data arriving, which cannot happen if nodelay(3X) is in effect on the window. In ncurses, wgetch also fails if * the curses screen has not been initialized, * (for functions taking a WINDOW pointer argument) win is a null pointer, or * execution was interrupted by a signal, in which case the library sets errno to EINTR. Functions prefixed with "mv" first perform cursor movement and fail if the position (y, x) is outside the window boundaries. ungetch returns OK on success and ERR on failure. In ncurses, ungetch fails if * the curses screen has not been initialized, or * there is no more room in the input queue. has_key returns TRUE or FALSE. NOTES getch, mvgetch, and mvwgetch may be implemented as macros. curses discourages assignment of the ESC key to a discrete function by the programmer because the library requires a delay while it awaits the poten- tial remainder of a terminal escape sequence. Some key strokes are indistinguishable from control characters; for exam- ple, KEY_ENTER may be the same as ^M, and KEY_BACKSPACE may be the same as ^H or ^?. Consult the terminfo entry for the terminal type to determine whether this is the case; see infocmp(1). Some curses implementations, in- cluding ncurses, honor the terminfo key definitions; others treat such con- trol 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. * The terminfo key_enter (kent) capability describes the character (se- quence) sent by the Enter key of a terminal's numeric (or similar) key- pad. * "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 key- board differently. * It usually produces a control code for carriage return (^M) or line feed (^J). * Depending on the terminal mode (raw, cbreak, or canonical), 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 key- board of the AT&T 7300 (also known variously as the "3B1", "Safari 4", and "UNIX PC"), a 1985 machine rich in function keys. Today's computer key- boards are based on that of the IBM PC/AT 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), KEY_A1, KEY_A3, KEY_B2, KEY_C1, KEY_C3, and KEY_F(n) for 1 <= n <= 12. 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 func- tion key character sequence from a series of key strokes beginning with ESC typed by the user; see curs_variables(3X). has_key is an ncurses extension, 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. Except as noted in section "EXTENSIONS" above, X/Open Curses Issue 4 de- scribes these functions. It specifies no error conditions for them. SVr4 describes a successful return value only as "an integer value other than ERR". wgetch reads only single-byte characters. The echo behavior of these functions on input of KEY_ or backspace charac- ters is not documented in SVr4 curses. The behavior of wgetch in the presence of signal handlers is not documented in SVr4 curses and is unspecified by X/Open Curses. In historical curses implementations, it varied depending on whether the operating system's dis- patch of a signal to a handler interrupted a read(2) call in progress, and also (in some implementations) whether an input timeout or non-blocking mode had been set. A portable curses application prepares for two cases: (a) signal receipt does not interrupt wgetch; and (b) signal receipt inter- rupts 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 terminfo capabilities, but no higher-level functions use the feature. The implemen- tation 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. HISTORY 4BSD (1980) introduced wgetch and its variants. SVr3 (1987) added ungetch. ncurses 1.9.9g (1996) furnished the has_key extension. SEE ALSO 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/> curs_get_wch(3X) describes comparable functions of the ncurses library in its wide-character configuration (ncursesw). 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) ncurses 6.6 2025-11-11 curs_getch(3X)
NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | NOTES | EXTENSIONS | PORTABILITY | HISTORY | SEE ALSO
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