get_wch(3NCURSES) Library calls get_wch(3NCURSES)
NAME
get_wch, wget_wch, mvget_wch, mvwget_wch, unget_wch - get (or push back)
a wide character from curses terminal keyboard buffer
SYNOPSIS
#include <curses.h>
int get_wch(wint_t * wch);
int wget_wch(WINDOW * win, wint_t * wch);
int mvget_wch(int y, int x, wint_t * wch);
int mvwget_wch(WINDOW * win, int y, int x, wint_t * wch);
int unget_wch(const wchar_t wc);
DESCRIPTION
Reading Characters
wget_wch gathers a key event from the terminal keyboard associated with
a curses window win, returning OK if a wide character is read,
KEY_CODE_YES if a function key is read, and ERR if no key event is
available. ncurses(3NCURSES) describes the variants of this function.
When input is pending, wget_wch stores an integer identifying the key
event in wch; for alphanumeric and punctuation keys, this value corre-
sponds to the character encoding used by the terminal. Use of the con-
trol key as a modifier, 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 subsections “Keypad
Mode” and “Predefined Key Codes” in getch(3NCURSES).
If no input is pending, then if the no-delay flag is set in the window
(see nodelay(3NCURSES)), the function returns ERR; otherwise, curses
waits until the terminal has input. If cbreak(3NCURSES) or
raw(3NCURSES) has been called, this happens after one character is read.
If nocbreak(3NCURSES) or noraw(3NCURSES) has been called, it occurs when
the next newline is read. (Because the terminal's canonical or “cooked”
mode is line-buffered, multiple wget_wch calls may then be necessary to
empty the input queue.) If halfdelay(3NCURSES) has been called, curses
waits until input is available or the specified delay elapses.
If echo(3NCURSES) has been called, and the window is not a pad, curses
writes the wide character from the input queue to the window (at the
cursor position) per the following rules.
• If the wide character matches the terminal's erase character (see
erasewchar(3NCURSES)), the cursor moves leftward one position and
the new position is erased as if wmove(3NCURSES) and then
wdelch(3NCURSES) 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 wide character to the window, as with
wecho_wchar(3NCURSES).
• If the window win has been moved or modified since the last call to
wrefresh(3NCURSES), curses calls wrefresh on it.
If the wide character is a carriage return and nl(3NCURSES) has been
called, wget_wch stores the wide character code for line feed in wch in-
stead.
Ungetting Characters
unget_wch places wc into the input queue to be retrieved by the next
call to wget_wch. A single input queue serves all windows associated
with the screen.
RETURN VALUE
wget_wch returns OK when it reads a wide character, KEY_CODE_YES when it
reads a function key code, and ERR on failure. wget_wch fails if
• its timeout expires without any data arriving, or
• execution was interrupted by a signal, in which case errno is set to
EINTR.
Functions taking a WINDOW pointer argument fail if win is a null
pointer.
Functions prefixed with “mv” first perform cursor movement and fail if
the position (y, x) is outside the window boundaries.
unget_wch returns OK on success and ERR if there is no more room in the
input queue.
NOTES
See the “NOTES” section of wgetch(3NCURSES).
All of these functions except wget_wch and unget_wch may be implemented
as macros.
Unlike wgetch(3NCURSES), wget_wch and its variants store the value of
the input character in an additional wch parameter instead of the return
value.
Unlike ungetch, unget_wch cannot distinguish function key codes from
conventional character codes. An application can overcome this limita-
tion by pushing function key codes with ungetch and subsequently check-
ing the return value of wget_wch for a match with KEY_CODE_YES.
EXTENSIONS
See the “EXTENSIONS” section of wgetch(3NCURSES).
PORTABILITY
Applications employing ncurses extensions should condition their use on
the visibility of the NCURSES_VERSION preprocessor macro.
X/Open Curses Issue 4 describes these functions. It specifies no error
conditions for them.
See the “PORTABILITY” section of wgetch(3NCURSES) regarding the interac-
tion of wget_wch with signal handlers.
HISTORY
X/Open Curses Issue 4 (1995) initially specified these functions. The
System V Interface Definition Version 4 of the same year specified func-
tions named wgetwch (with its variants) ungetwch. These were later ad-
ditions to SVr4.x, not appearing in the first SVr4 (1989). They differ
from X/Open's later wget_wch and unget_wch in that wgetwch takes no wch
argument, but returns the (wide) key code as an int (with no provision
for distinguishing a character code from a function key code); and
ungetwch takes a non-const int argument.
SEE ALSO
getch(3NCURSES) describes comparable functions of the ncurses library in
its non-wide-character configuration.
ncurses(3NCURSES), add_wch(3NCURSES), inopts(3NCURSES), move(3NCURSES),
refresh(3NCURSES)
ncurses 6.5 2025-02-15 get_wch(3NCURSES)
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