path: root/lib/libcurses/curs_getch.3

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.\" $Id: curs_getch.3,v 1.6 2023/10/17 09:52:08 nicm Exp $
.TH curs_getch 3 2023-08-19 "ncurses 6.4" "Library calls"
.na
.hy 0
.ie \n(.g .ds `` \(lq
.el       .ds `` ``
.ie \n(.g .ds '' \(rq
.el       .ds '' ''
.de bP
.ie n  .IP \(bu 4
.el    .IP \(bu 2
..
.SH NAME
\fBgetch\fP,
\fBwgetch\fP,
\fBmvgetch\fP,
\fBmvwgetch\fP,
\fBungetch\fP,
\fBhas_key\fP \- get (or push back) characters from \fBcurses\fP terminal keyboard
.ad
.hy
.SH SYNOPSIS
.B #include <curses.h>
.PP
.B int getch(void);
.br
.B int wgetch(WINDOW *\fIwin\fB);
.sp
.B int mvgetch(int \fIy\fB, int \fIx\fB);
.br
.B int mvwgetch(WINDOW *\fIwin\fB, int \fIy\fB, int \fIx\fB);
.sp
.B int ungetch(int \fIch\fB);
.sp
/* extension */
.br
.B int has_key(int \fIch\fB);
.br
.SH DESCRIPTION
.SS Reading characters
The \fBgetch\fP, \fBwgetch\fP, \fBmvgetch\fP and \fBmvwgetch\fP, routines read
a character from the window.
In no-delay mode, if no input is waiting, the value \fBERR\fP is returned.
In delay mode, the program waits until the system
passes text through to the program.
Depending on the setting of \fBcbreak\fP,
this is after one character (cbreak mode),
or after the first newline (nocbreak mode).
In half-delay mode,
the program waits until a character is typed or the
specified timeout has been reached.
.PP
If \fBecho\fP is enabled, and the window is not a pad,
then the character will also be echoed into the
designated window according to the following rules:
.bP
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 \fBdelch\fP had been called.
.bP
If the character value is any other \fBKEY_\fP define, the user is alerted
with a \fBbeep\fP call.
.bP
If the character is a carriage-return,
and if \fBnl\fP is enabled,
it is translated to a line-feed after echoing.
.bP
Otherwise the character is simply output to the screen.
.PP
If the window is not a pad, and it has been moved or modified since the last
call to \fBwrefresh\fP, \fBwrefresh\fP will be called before another character
is read.
.SS Keypad mode
If \fBkeypad\fP is \fBTRUE\fP, and a function key is pressed, the token for
that function key is returned instead of the raw characters:
.bP
The predefined function
keys are listed in \fB<curses.h>\fP as macros with values outside the range
of 8-bit characters.
Their names begin with \fBKEY_\fP.
.bP
Other (user-defined) function keys which may be defined
using \fBdefine_key\fP(3)
have no names, but also are expected to have values outside the range of
8-bit characters.
.PP
Thus, a variable
intended to hold the return value of a function key must be of short size or
larger.
.PP
When a character that could be the beginning of a function key is received
(which, on modern terminals, means an escape character),
\fBcurses\fP 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.
.PP
In \fBncurses\fP, the timer normally expires after
the value in \fBESCDELAY\fP (see \fBcurs_variables\fP(3)).
If \fBnotimeout\fP is \fBTRUE\fP, 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.
.SS Ungetting characters
The \fBungetch\fP routine places \fIch\fP back onto the input queue to be
returned by the next call to \fBwgetch\fP.
There is just one input queue for all windows.
.SS Predefined key-codes
The following special keys are defined in \fB<curses.h>\fP.
.bP
Except for the special case \fBKEY_RESIZE\fP,
it is necessary to enable \fBkeypad\fP for \fBgetch\fP to return these codes.
.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 long terminfo capability names for the keys,
and were defined long ago, in the 1980s.
.PP
.RS
.TS
tab(/) ;
l l .
\fBName\fP/\fBKey\fP \fBname\fP
_
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/T{
Function keys; space for 64 keys is reserved.
T}
KEY_F(\fIn\fP)/T{
For 0 \(<= \fIn\fP \(<= 63
T}
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
.TE
.RE
.PP
Keypad is arranged like this:
.PP
.RS
.TS
allbox tab(/) ;
c c c .
\fBA1\fP/\fBup\fP/\fBA3\fP
\fBleft\fP/\fBB2\fP/\fBright\fP
\fBC1\fP/\fBdown\fP/\fBC3\fP
.TE
.RE
.sp
A few of these predefined values do \fInot\fP correspond to a real key:
.bP
.B KEY_RESIZE
is returned when the \fBSIGWINCH\fP signal has been detected
(see \fBinitscr\fP(3) and \fBresizeterm\fP(3)).
This code is returned whether or not \fBkeypad\fP has been enabled.
.bP
.B KEY_MOUSE
is returned for mouse-events (see \fBcurs_mouse\fP(3)).
This code relies upon whether or not \fBkeypad\fP(3) has been enabled,
because (e.g., with \fBxterm\fP(1) mouse prototocol) ncurses must
read escape sequences,
just like a function key.
.SS Testing key-codes
The \fBhas_key\fP routine takes a key-code value from the above list, and
returns \fBTRUE\fP or \fBFALSE\fP according to whether
the current terminal type recognizes a key with that value.
.PP
The library also supports these extensions:
.RS 3
.TP 5
.B define_key
defines a key-code for a given string (see \fBdefine_key\fP(3)).
.TP 5
.B key_defined
checks if there is a key-code defined for a given
string (see \fBkey_defined\fP(3)).
.RE
.SH RETURN VALUE
All routines return the integer \fBERR\fP upon failure and an integer value
other than \fBERR\fP (\fBOK\fP in the case of \fBungetch\fP) upon successful
completion.
.RS 3
.TP 5
\fBungetch\fP
returns \fBERR\fP
if there is no more room in the FIFO.
.TP
\fBwgetch\fP
returns \fBERR\fP
if the window pointer is null, or
if its timeout expires without having any data, or
if the execution was interrupted by a signal (\fBerrno\fP will be set to
\fBEINTR\fP).
.RE
.PP
Functions with a \*(``mv\*('' prefix first perform a cursor movement using
\fBwmove\fP, and return an error if the position is outside the window,
or if the window pointer is null.
.SH NOTES
Use of the escape key by a programmer for a single character function is
discouraged, as it will cause a delay of up to one second while the
keypad code looks for a following function-key sequence.
.PP
Some keys may be the same as commonly used control
keys, e.g.,
\fBKEY_ENTER\fP versus control/M,
\fBKEY_BACKSPACE\fP 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.
\fBNcurses\fP uses the terminfo definition.
If it says that \fBKEY_ENTER\fP is control/M,
\fBgetch\fP will return \fBKEY_ENTER\fP
when you press control/M.
.PP
Generally, \fBKEY_ENTER\fP denotes the character(s) sent by the \fIEnter\fP
key on the numeric keypad:
.bP
the terminal description lists the most useful keys,
.bP
the \fIEnter\fP key on the regular keyboard is already handled by
the standard ASCII characters for carriage-return and line-feed,
.bP
depending on whether \fBnl\fP or \fBnonl\fP was called,
pressing \*(``Enter\*('' on the regular keyboard
may return either a carriage-return or line-feed, and finally
.bP
\*(``Enter or send\*('' is the standard description for this key.
.PP
When using \fBgetch\fP, \fBwgetch\fP, \fBmvgetch\fP, or
\fBmvwgetch\fP, nocbreak mode (\fBnocbreak\fP) and echo mode
(\fBecho\fP) should not be used at the same time.
Depending on the
state of the tty driver when each character is typed, the program may
produce undesirable results.
.PP
Note that \fBgetch\fP, \fBmvgetch\fP, and \fBmvwgetch\fP may be macros.
.PP
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 \fBKEY_UP\fP, \fBKEY_DOWN\fP,
\fBKEY_LEFT\fP, \fBKEY_RIGHT\fP, \fBKEY_HOME\fP, \fBKEY_END\fP,
\fBKEY_NPAGE\fP, \fBKEY_PPAGE\fP, and function keys 1 through 12.
The Ins key
is usually mapped to \fBKEY_IC\fP.
.SH PORTABILITY
The *get* functions are described in the XSI Curses standard, Issue 4.
They
read single-byte characters only.
The standard specifies that they return
\fBERR\fP on failure, but specifies no error conditions.
.PP
The echo behavior of these functions on input of \fBKEY_\fP or backspace
characters was not specified in the SVr4 documentation.
This description is
adopted from the XSI Curses standard.
.PP
The behavior of \fBgetch\fP and friends in the presence of handled signals is
unspecified in the SVr4 and XSI Curses documentation.
Under historical curses
implementations, it varied depending on whether the operating system's
implementation of handled signal receipt interrupts a \fBread\fP(2) call in
progress or not, and also (in some implementations) depending on whether an
input timeout or non-blocking mode has been set.
.PP
\fBKEY_MOUSE\fP is mentioned in XSI Curses, along with a few related
terminfo capabilities, but no higher-level functions use the feature.
The implementation in ncurses is an extension.
.PP
\fBKEY_RESIZE\fP is an extension first implemented for ncurses.
NetBSD curses later added this extension.
.PP
Programmers concerned about portability should be prepared for either of two
cases: (a) signal receipt does not interrupt \fBgetch\fP; (b) signal receipt
interrupts \fBgetch\fP and causes it to return \fBERR\fP with \fBerrno\fP set to
\fBEINTR\fP.
.PP
The \fBhas_key\fP function is unique to \fBncurses\fP.
We recommend that
any code using it be conditionalized on the \fBNCURSES_VERSION\fP feature macro.
.SH SEE ALSO
\fBcurses\fP(3),
\fBcurs_inopts\fP(3),
\fBcurs_mouse\fP(3),
\fBcurs_move\fP(3),
\fBcurs_outopts\fP(3),
\fBcurs_refresh\fP(3),
\fBcurs_variables\fP(3),
\fBresizeterm\fP(3).
.PP
Comparable functions in the wide-character (ncursesw) library are
described in
\fBcurs_get_wch\fP(3).