typeahead – curses input options
int halfdelay(int tenths);
int intrflush(WINDOW *win, bool bf);
int keypad(WINDOW *win, bool bf);
int meta(WINDOW *win, bool bf);
int nodelay(WINDOW *win, bool bf);
int notimeout(WINDOW *win, bool bf);
void timeout(int delay);
void wtimeout(WINDOW *win, int delay);
int typeahead(int fd);
Normally, the tty driver buffers typed characters until a newline or carriage
return is typed. The cbreak routine disables line buffering and
erase/kill character-processing (interrupt and flow control characters are
unaffected), making characters typed by the user immediately available to the
program. The nocbreak routine returns the terminal to normal (cooked)
Initially the terminal may or may not be in cbreak mode, as the mode is
inherited; therefore, a program should call cbreak or nocbreak
explicitly. Most interactive programs using curses set the cbreak
mode. Note that cbreak overrides raw.
[See curs_getch(3X) for a
discussion of how these routines interact with echo and noecho.]
The echo and noecho routines control whether characters typed by
the user are echoed by getch as they are typed. Echoing by the tty
driver is always disabled, but initially getch is in echo mode, so
characters typed are echoed. Authors of most interactive programs prefer to do
their own echoing in a controlled area of the screen, or not to echo at all, so
they disable echoing by calling noecho.
[See curs_getch(3X) for a
discussion of how these routines interact with cbreak and
The halfdelay routine is used for half-delay mode, which is similar to
cbreak mode in that characters typed by the user are immediately
available to the program. However, after blocking for tenths tenths of
seconds, ERR is returned if nothing has been typed. The value of tenths
must be a number between 1 and 255. Use nocbreak to leave half-delay
If the intrflush option is enabled, (bf is TRUE), when an
interrupt key is pressed on the keyboard (interrupt, break, quit) all output in
the tty driver queue will be flushed, giving the effect of faster response to
the interrupt, but causing curses to have the wrong idea of what is on
the screen. Disabling (bf is FALSE), the option prevents the
flush. The default for the option is inherited from the tty driver settings.
The window argument is ignored.
The keypad option enables the keypad of the user’s terminal. If
enabled (bf is TRUE), the user can press a function key
(such as an arrow key) and wgetch returns a single value
representing the function key, as in KEY_LEFT. If disabled
(bf is FALSE), curses does not treat function keys
specially and the program has to interpret the escape sequences
itself. If the keypad in the terminal can be turned on (made to
transmit) and off (made to work locally), turning on this option
causes the terminal keypad to be turned on when wgetch is
called. The default value for keypad is false.
Initially, whether the terminal returns 7 or 8 significant bits on
input depends on the control mode of the tty driver [see termio(7)].
To force 8 bits to be returned, invoke meta(win,
TRUE); this is equivalent, under POSIX, to setting the CS8 flag
on the terminal. To force 7 bits to be returned, invoke
meta(win, FALSE); this is equivalent, under POSIX,
to setting the CS7 flag on the terminal. The window argument,
win, is always ignored. If the terminfo capabilities smm
(meta_on) and rmm (meta_off) are defined for the terminal,
smm is sent to the terminal when meta(win,
TRUE) is called and rmm is sent when meta(win,
FALSE) is called.
The nodelay option causes getch to be a non-blocking call.
If no input is ready, getch returns ERR. If disabled
(bf is FALSE), getch waits until a key is pressed.
While interpreting an input escape sequence, wgetch sets a timer
while waiting for the next character. If notimeout(win,
TRUE) is called, then wgetch does not set a timer. The
purpose of the timeout is to differentiate between sequences received
from a function key and those typed by a user.
The raw and noraw routines place the terminal into or out of raw
mode. Raw mode is similar to cbreak mode, in that characters typed are
immediately passed through to the user program. The differences are that in
raw mode, the interrupt, quit, suspend, and flow control characters are all
passed through uninterpreted, instead of generating a signal. The behavior of
the BREAK key depends on other bits in the tty driver that are not set by
When the noqiflush routine is used, normal flush of input and
output queues associated with the INTR, QUIT and
SUSP characters will not be done [see termio(7)]. When
qiflush is called, the queues will be flushed when these control
characters are read. You may want to call noqiflush() in a signal
handler if you want output to continue as though the interrupt
had not occurred, after the handler exits.
The timeout and wtimeout routines set blocking or
non-blocking read for a given window. If delay is negative,
blocking read is used (i.e., waits indefinitely for
input). If delay is zero, then non-blocking read is used
(i.e., read returns ERR if no input is waiting). If
delay is positive, then read blocks for delay
milliseconds, and returns ERR if there is still no input.
Hence, these routines provide the same functionality as nodelay,
plus the additional capability of being able to block for only
delay milliseconds (where delay is positive).
The curses library does “line-breakout optimization” by looking for
typeahead periodically while updating the screen. If input is found,
and it is coming from a tty, the current update is postponed until
refresh or doupdate is called again. This allows faster
response to commands typed in advance. Normally, the input FILE
pointer passed to newterm, or stdin in the case that
initscr was used, will be used to do this typeahead checking.
The typeahead routine specifies that the file descriptor
fd is to be used to check for typeahead instead. If fd is
-1, then no typeahead checking is done.
All routines that return an integer return ERR upon failure and OK (SVr4
specifies only "an integer value other than ERR") upon successful
completion, unless otherwise noted in the preceding routine descriptions.
X/Open does not define any error conditions.
In this implementation,
functions with a window parameter will return an error if it is null.
Any function will also return an error if the terminal was not initialized.
These functions are described in the XSI Curses standard, Issue 4.
The ncurses library obeys the XPG4 standard and the historical practice of the
AT&T curses implementations, in that the echo bit is cleared when curses
initializes the terminal state. BSD curses differed from this slightly; it
left the echo bit on at initialization, but the BSD raw call turned it
off as a side-effect. For best portability, set echo or noecho explicitly
just after initialization, even if your program remains in cooked mode.
Note that echo, noecho, halfdelay, intrflush,
meta, nodelay, notimeout, noqiflush,
qiflush, timeout, and wtimeout may be macros.
The noraw and nocbreak calls follow historical practice in that
they attempt to restore to normal (`cooked’) mode from raw and cbreak modes
respectively. Mixing raw/noraw and cbreak/nocbreak calls leads to tty driver
control states that are hard to predict or understand; it is not recommended.