man/curs_getch.3x

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.\" $Id: curs_getch.3x,v 1.87 2024/04/20 19:18:18 tom Exp $
.TH curs_getch 3X 2024-04-20 "ncurses @NCURSES_MAJOR@.@NCURSES_MINOR@" "Library calls"
.ie \n(.g \{\
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..
.SH NAME
\fB\%getch\fP,
\fB\%wgetch\fP,
\fB\%mvgetch\fP,
\fB\%mvwgetch\fP,
\fB\%ungetch\fP,
\fB\%has_key\fP \-
get (or push back) characters from \fIcurses\fR terminal keyboard
.SH SYNOPSIS
.nf
.B #include <curses.h>
.PP
.B int getch(void);
.B int wgetch(WINDOW *\fIwin\fP);
.B int mvgetch(int \fIy\fP, int \fIx\fP);
.B int mvwgetch(WINDOW *\fIwin\fP, int \fIy\fP, int \fIx\fP);
.PP
.B int ungetch(int \fIc\fP);
.PP
.\" XXX: Move has_key into its own page like define_key and key_defined?
\fI/* extension */\fP
.B int has_key(int \fIc\fP);
.fi
.SH DESCRIPTION
.SS "Reading Characters"
.B \%wgetch
gathers a key stroke from the terminal keyboard associated with a
.I curses
window
.IR win .
\fB\%ncurses\fP(3X) describes the variants of this function.
.PP
When input is pending,
.B \%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
.I win
is in keypad mode;
see subsection \*(``Keypad Mode\*('' below.
.PP
If no input is pending,
then if the no-delay flag is set in the window
(see \fB\%nodelay\fP(3X)),
the function returns
.BR ERR ;
otherwise,
.I curses
waits until the terminal has input.
If \fB\%cbreak\fP(3X)
has been called,
this happens after one character is read.
If \fB\%nocbreak\fP(3X)
has been called,
it occurs when the next newline is read.
If \fB\%halfdelay\fP(3X)
has been called,
.I curses
waits until a character is typed or the specified delay elapses.
.PP
If \fB\%echo\fP(3X) has been called,
and the window is not a pad,
.I curses
writes the returned character
.I c
to the window
(at the cursor position)
per the following rules.
.bP
If
.I c
matches the terminal's erase character,
the cursor moves leftward one position
and the new position is erased
as if \fB\%wmove\fP(3X) and then \fB\%wdelch\fP(3X) were called.
When the window's keypad mode is enabled
(see below),
.B \%KEY_LEFT
and
.B \%KEY_BACKSPACE
are handled the same way.
.bP
.I curses
writes any other
.I c
to the window,
as with \fB\%wechochar\fP(3X).
.bP
If the window has been moved or modified since the last call to
\fB\%wrefresh\fP(3X),
.I curses
calls
.BR \%wrefresh .
.PP
If
.I c
is a carriage return and \fBnl\fP(3X) has been called,
.B \%wgetch
returns the character code for line feed instead.
.SS "Keypad Mode"
To
.IR curses ,
key strokes not from the alphabetic section of the keyboard
(those corresponding to the ECMA-6 character set\(emsee
\fIascii\fP(7)\(emoptionally modified by either the control or shift
keys)
are treated as
.I function
keys.
(In
.IR 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
.B 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
.B \%wgetch
calls.
.bP
The
.I \%curses.h
header file declares many
.I "predefined function keys"
whose names begin with
.BR KEY_ ;
these object-like macros have values outside the range of eight-bit
character codes.
.bP
In
.IR \%ncurses ,
.I "user-defined function keys"
are configured with \fB\%define_key\fP(3X);
they have no names,
but are also expected to have values outside the range of eight-bit
codes.
.PP
A variable intended to hold a function key code must thus be of type
.I short
or larger.
.PP
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
.I 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
.I curses
reads such an ambiguous character,
it sets a timer.
If the remainder of the sequence does not arrive within the designated
time,
.B \%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
.I curses
application may experience a delay after pressing ESC while
.I 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 \fB\%notimeout\fP(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\*(''
.IR curses .
.SS "Ungetting Characters"
.B \%ungetch
places
.I c
into the input queue to be returned by the next call to
.BR \%wgetch .
A single input queue serves all windows.
.SS "Predefined Key Codes"
The header file
.I \%curses.h
defines the following function key codes.
.bP
Except for the special case of
.BR \%KEY_RESIZE ,
a window's keypad mode must be enabled for
.B \%wgetch
to read these codes from it.
.bP
Not all of these are necessarily supported on any particular terminal.
.bP
The naming convention may seem obscure,
with some apparent misspellings
(such as \*(``RSUME\*('' for \*(``resume\*('');
the names correspond to the
.I \%term\%info
capability names for the keys,
and were standardized before the IBM PC/AT keyboard layout achieved a
dominant position in industry.
.PP
.RS
.\" XXX: Move this list into ncurses(3X), rather than duplicating it in
.\" get_wch(3X) or having that page cross reference this one?
.TS
Lb Lb
Lb Lx.
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	T{
Function keys; space for 64 keys is reserved
T}
KEY_F(\fIn\fP)	T{
Function key \fIn\fP where 0 \(<= \fIn\fP \(<= 63
T}
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
.TE
.RE
.PP
Many keyboards feature a nine-key directional pad.
.PP
.RS
.TS
allbox center;
C C C.
A1	up	A3
left	B2	right
C1	down	C3
.TE
.RE
.sp
Two of the symbols in the list above do
.I not
correspond to a physical key.
.bP
.B \%wgetch
returns
.BR \%KEY_RESIZE ,
even if the window's keypad mode is disabled,
when
.I \%ncurses
handles a
.B \%SIGWINCH
signal;
see \fB\%initscr\fP(3X) and \fB\%resizeterm\fP(3X).
.bP
.B \%wgetch
returns
.B \%KEY_MOUSE
to indicate that a mouse event is pending collection;
see \fB\%curs_mouse\fP(3X).
Receipt of this code requires a window's keypad mode to be enabled,
because to interpret mouse input
(as with with \fI\%xterm\fP(1)'s mouse prototocol),
.I \%ncurses
must read an escape sequence,
as with a function key.
.SS "Testing Key Codes"
In
.IR \%ncurses ,
.B \%has_key
returns a Boolean value indicating whether the terminal type recognizes
its parameter as a key code value.
See also
\fB\%define_key\fP(3X) and \fB\%key_defined\fP(3X).
.SH RETURN VALUE
Except for
.BR \%has_key ,
these functions return
.B OK
on success and
.B ERR
on failure.
.PP
Functions taking a
.I \%WINDOW
pointer argument fail if the pointer is
.BR NULL .
.PP
Functions prefixed with \*(``mv\*('' first perform cursor movement and
fail if the position
.RI ( y ,
.IR x )
is outside the window boundaries.
.PP
.B \%wgetch
also fails if
.bP
its timeout expires without any data arriving,
or
.bP
execution was interrupted by a signal,
in which case
.B \%errno
is set to
.BR \%EINTR .
.PP
.B \%ungetch
fails if there is no more room in the input queue.
.PP
.B \%has_key
returns
.B TRUE
or
.BR FALSE .
.SH NOTES
.I 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.
.PP
Some key strokes are indistinguishable from control characters;
for example,
.B \%KEY_ENTER
may be the same as
.BR \*^M ,
.\" as with att630 or pccon+keys
and
.B \%KEY_BACKSPACE
may be the same as
.B \*^H
.\" as with att505 or vt52-basic
or
.BR \*^? .
.\" as with pccon+keys or vt320
Consult the terminal's
.I \%term\%info
entry to determine whether this is the case;
see \fB\%infocmp\fP(1).
Some
.I curses
implementations,
including
.IR \%ncurses ,
honor the
.I \%term\%info
key definitions;
others treat such control characters specially.
.PP
.I curses
distinguishes the Enter keys in the alphabetic and numeric keypad
sections of a keyboard because (most) terminals do.
.B \%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.
.bP
The
.I \%term\%info
.B \%key_enter
.RB ( kent )
capability describes the character (sequence) sent by the Enter key of
a terminal's numeric
(or similar)
keypad.
.bP
\*(``Enter or send\*('' is X/Open Curses's description of this key.
.PP
.I curses
treats the Enter or Return key in the
.I alphabetic
section of the keyboard differently.
.bP
It usually produces a control code for carriage return
.RB ( \*^M )
or line feed
.RB ( \*^J ).
.bP
Depending on the terminal mode
(raw,
cbreak,
or
\*(``cooked\*(''),
and whether \fB\%nl\fP(3X) or \fB\%nonl\fP(3X) has been called,
.B \%wgetch
may return either a carriage return or line feed upon an Enter or Return
key stroke.
.PP
Use of
.B \%wgetch
with \fB\%echo\fP(3X) and neither \fB\%cbreak\fP(3X) nor \fB\%raw\fP(3X)
is not well-defined.
.PP
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
.I curses
application can expect such a keyboard to transmit key codes
.BR \%KEY_UP ,
.BR \%KEY_DOWN ,
.BR \%KEY_LEFT ,
.BR \%KEY_RIGHT ,
.BR \%KEY_HOME ,
.BR \%KEY_END ,
.B \%KEY_PPAGE
(Page Up),
.B \%KEY_NPAGE
(Page Down),
.B \%KEY_IC
(Insert),
.B \%KEY_DC
(Delete),
and
.BI \%KEY_F( n )
for 1 \(<=
.I n
\(<= 12.
.PP
.BR \%getch ,
.BR \%mvgetch ,
and
.B \%mvwgetch
may be implemented as macros.
.SH EXTENSIONS
In
.IR \%ncurses ,
when a window's \*(``no time-out\*('' mode is
.I not
set,
the
.B \%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
\fB\%curs_variables\fP(3X).
.PP
\fB\%has_key\fP was designed for \fB\%ncurses\fP(3X),
and is not found in SVr4
.IR curses ,
4.4BSD
.IR curses ,
or any other previous curses implementation.
.SH PORTABILITY
Applications employing
.I \%ncurses
extensions should condition their use on the visibility of the
.B \%NCURSES_VERSION
preprocessor macro.
.PP
X/Open Curses,
Issue 4 describes
\fB\%getch\fP,
\fB\%wgetch\fP,
\fB\%mvgetch\fP,
\fB\%mvwgetch\fP,
and
\fB\%ungetch\fP.
It specifies no error conditions for them.
.PP
.B \%wgetch
reads only single-byte characters.
.PP
The echo behavior of these functions on input of
.B KEY_
or backspace characters was not specified in the SVr4 documentation.
This description is adapted from X/Open Curses.
.PP
The behavior of
.B \%wgetch
in the presence of signal handlers is unspecified in the SVr4
documentation and X/Open Curses.
In historical
.I curses
implementations,
it varied depending on whether the operating system's dispatch of a
signal to a handler interrupting a \fIread\fP(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
.BR \%wgetch ;
or
(b) signal receipt interrupts
.B \%wgetch
and causes it to return
.B ERR
with
.B \%errno
set to
.BR \%EINTR .
.PP
.B \%KEY_MOUSE
is mentioned in X/Open Curses,
along with a few related
.I \%term\%info
capabilities,
but no higher-level functions use the feature.
The implementation in
.I \%ncurses
is an extension.
.PP
.B \%KEY_RESIZE
and
.B \%has_key
are extensions first implemented for
.IR \%ncurses .
By 2022,
.I \%PDCurses
.\" https://web.archive.org/web/20220117232009/https://pdcurses.org/docs/MANUAL.html
and
NetBSD
.I curses
.\" https://web.archive.org/web/20200923185647/https://man.netbsd.org/curses_input.3
had added them along with
.BR \%KEY_MOUSE .
.SH SEE ALSO
\fB\%curs_get_wch\fP(3X) describes comparable functions of the
.I \%ncurses
library in its wide-character configuration
.RI ( \%ncursesw ).
.PP
\fB\%curses\fP(3X),
\fB\%curs_addch\fP(3X),
\fB\%curs_inopts\fP(3X),
\fB\%curs_mouse\fP(3X),
\fB\%curs_move\fP(3X),
\fB\%curs_outopts\fP(3X),
\fB\%curs_refresh\fP(3X),
\fB\%curs_variables\fP(3X),
\fB\%resizeterm\fP(3X),
\fB\%ascii\fP(7)
.PP
ECMA-6 \*(``7-bit coded Character Set\*(''
\%<https://\*:ecma\-international\*:.org/\
\*:publications\-and\-standards/\*:standards/\*:ecma\-6/>
.PP
ECMA-48 \*(``Control Functions for Coded Character Sets\*(''
\%<https://\*:ecma\-international\*:.org/\
\*:publications\-and\-standards/\*:standards/\*:ecma\-48/>