curs_getch(3) Library calls curs_getch(3)
NAME
getch, wgetch, mvgetch, mvwgetch, ungetch, has_key - get (or push back)
characters from curses terminal keyboard
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 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.
o 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.
o curses writes any other c to the window, as with wechochar(3X).
o 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.
Keypad Mode
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.
o 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.
o 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.
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.
Predefined Key Codes
The header file curses.h defines the following function key codes.
o Except for the special case of KEY_RESIZE, a window's keypad mode
must be enabled for wgetch to read these codes from it.
o Not all of these are necessarily supported on any particular
terminal.
o 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 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) 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.
o 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).
o 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.
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
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
o its timeout expires without any data arriving, or
o 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.
NOTES
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 terminfo entry to determine
whether this is the case; see infocmp(1). Some curses implementations,
including ncurses, honor the terminfo 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.
o The terminfo key_enter (kent) capability describes the character
(sequence) sent by the Enter key of a terminal's numeric (or
similar) keypad.
o "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.
o It usually produces a control code for carriage return (^M) or line
feed (^J).
o 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.
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
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.
PORTABILITY
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
terminfo 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.
SEE ALSO
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)
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/>
ncurses 6.5 2024-04-20 curs_getch(3)
ncurses 6.5 - Generated Wed May 1 12:56:00 CDT 2024