Manual Pages  — curs_getch

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

SYNOPSIS DESCRIPTION Reading Characters Keypad Mode Ungetting Characters Predefined Key Codes Testing Key Codes RETURN VALUE NOTES EXTENSIONS PORTABILITY SEE ALSO

#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); 

 wgetch gathers a key stroke 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 stroke; for alphanumeric and punctuation keys, this value corresponds to the character encoding used by the terminal. Use of the control key as a modifier 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) has been called, this happens after one character is read. If  nocbreak(3X) has been called, it occurs when the next newline is read. If  halfdelay(3X) has been called, curses waits until a character is typed 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 following rules.

»	If c matches the terminal's erase character, 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 enabled (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 has been moved or modified since the last call to  wrefresh(3X), curses calls  wrefresh.

If c is a carriage return and nl(3X) has been called,  wgetch returns the character code for line feed instead.

To curses, 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) are treated as function keys. (In curses, the term function key includes but is not limited to keycaps engraved with F1, PF1, and so on.) If the window is in keypad mode, these produce a numeric code corresponding to the KEY_ symbols listed in subsection Predefined Key Codes below; otherwise, they transmit a sequence of codes typically starting with the escape character, and which must be collected with multiple  wgetch calls.

»	The  curses.h header file declares many predefined function keys whose names begin with KEY_; these object-like macros have 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 values outside the range of eight-bit 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 character ESC. This fact implies that curses cannot know whether the terminal has sent an ESC key stroke or the beginning of a function key's character sequence without waiting to see if, and how soon, further input arrives. When curses reads such an ambiguous character, it sets a timer. If the remainder of the sequence does not arrive within the designated time,  wgetch returns the prefix character; otherwise, it returns the function key code corresponding to the unique sequence defined by the terminal. Consequently, a user of a curses application may experience a delay after pressing ESC while curses disambiguates the input; see section EXTENSIONS below. If the window is in no time-out mode, the timer does not expire; it is an infinite (or very large) value. See  notimeout(3X). Because function key sequences usually begin with an escape character, the terminal may appear to hang in no time-out mode after the user has pressed ESC. Generally, further typing awakens curses.

 ungetch places c into the input queue to be returned by the next call to  wgetch. A single input queue serves all windows.

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  term info capability names for the keys, and were standardized before the IBM PC/AT keyboard layout achieved a dominant position in industry.

Many keyboards feature a nine-key directional pad.

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 disabled, when  ncurses handles a  SIGWINCH signal; see  initscr(3X) and  resizeterm(3X).
»	wgetch returns  KEY_MOUSE to indicate that a mouse event is pending collection; see  curs_mouse(3X). Receipt of this code requires a window's keypad mode to be enabled, because to interpret mouse input (as with with  xterm(1)'s mouse prototocol),  ncurses must read an escape sequence, as with a function key.

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).

Except for  has_key, these functions return OK on success and ERR on failure.

Functions taking a  WINDOW pointer argument fail if the pointer is NULL.

Functions prefixed with mv first perform cursor movement and fail if the position (y, x) is outside the window boundaries.

 wgetch also fails if

»	its timeout expires without any data arriving, or
»	execution was interrupted by a signal, in which case  errno is set to  EINTR.

 ungetch fails if there is no more room in the input queue.

 has_key returns TRUE or FALSE.

curses discourages assignment of the ESC key to a discrete function by the programmer because the library requires a delay while it awaits the potential remainder of a terminal escape sequence.

Some key strokes are indistinguishable from control characters; for example,  KEY_ENTER may be the same as ^M, and  KEY_BACKSPACE may be the same as ^H or ^?. Consult the terminal's  term info entry to determine whether this is the case; see  infocmp(1). Some curses implementations, including  ncurses, honor the  term info key definitions; others treat such control 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, and is reliably recognized only if the window's keypad mode is enabled.

»	The  term info  key_enter (kent) capability describes the character (sequence) sent by the Enter key of a terminal's numeric (or similar) keypad.
»	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 keyboard differently.

»	It usually produces a control code for carriage return (^M) or line feed (^J).
»	Depending on the terminal mode (raw, cbreak, or cooked), 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 function-key-rich keyboard of the AT&T 7300 (also known variously as the 3B1, Safari 4, and UNIX PC), a 1985 machine. Today's computer keyboards are based 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), and  KEY_F(n) for 1 ≤ n ≤ 12.

 getch,  mvgetch, and  mvwgetch may be implemented as macros.

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 function key character sequence from a series of key strokes beginning with ESC typed by the user; see  curs_variables(3X).

 has_key was designed for  ncurses(3X), and is not found in SVr4 curses, 4.4BSD curses, or any other previous curses implementation.

Applications employing  ncurses extensions should condition their use on the visibility of the  NCURSES_VERSION preprocessor macro.

X/Open Curses, Issue 4 describes  getch,  wgetch,  mvgetch,  mvwgetch, and  ungetch. It specifies no error conditions for them.

 wgetch reads only single-byte characters.

The echo behavior of these functions on input of KEY_ or backspace characters was not specified in the SVr4 documentation. This description is adapted from X/Open Curses.

The behavior of  wgetch in the presence of signal handlers is unspecified in the SVr4 documentation and X/Open Curses. In historical curses implementations, it varied depending on whether the operating system's dispatch of a signal to a handler interrupting a read(2) call in progress, and also (in some implementations) whether an input timeout or non-blocking mode has been set. Programmers concerned about portability should be prepared for either of two cases: (a) signal receipt does not interrupt  wgetch; or (b) signal receipt interrupts  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  term info capabilities, but no higher-level functions use the feature. The implementation 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.