cbreak, nocbreak, echo, noecho, halfdelay,
intrflush, keypad, meta, nodelay,
notimeout, raw, noraw, noqiflush, qiflush,
timeout, wtimeout, typeahead - curses input
The ncurses library provides several functions which let an application
change the way input from the terminal is handled. Some are global, applying
to all windows. Others apply only to a specific window. Window-specific
settings are not automatically applied to new or derived windows. An
application must apply these to each window, if the same behavior is needed.
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)
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);
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(3X) 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
If the intrflush option is enabled (bf is TRUE), and 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 the option (bf is FALSE) 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(3X) 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(3X) 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 termios(3)]. 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
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(3X)
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 termios(3)]. 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(3X) 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
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
These functions are described in the XSI Curses standard, Issue 4.
- returns an error if its parameter is outside the range 1..255.
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.
When keypad is first enabled, ncurses loads the
key-definitions for the current terminal description. If the terminal
description includes extended string capabilities, e.g., from using the
-x option of tic, then ncurses also defines keys for the
capabilities whose names begin with “k”. The corresponding
keycodes are generated and (depending on previous loads of terminal
descriptions) may differ from one execution of a program to the next. The
generated keycodes are recognized by the keyname function (which will
then return a name beginning with “k” denoting the terminfo
capability name rather than “K”, used for curses key-names).
On the other hand, an application can use define_key to establish a
specific keycode for a given string. This makes it possible for an
application to check for an extended capability's presence with
tigetstr, and reassign the keycode to match its own needs.
Low-level applications can use tigetstr to obtain the
definition of any particular string capability. Higher-level applications
which use the curses wgetch and similar functions to return keycodes
rely upon the order in which the strings are loaded. If more than one key
definition has the same string value, then wgetch can return only one
keycode. Most curses implementations (including ncurses) load key
definitions in the order defined by the array of string capability names.
The last key to be loaded determines the keycode which will be returned. In
ncurses, you may also have extended capabilities interpreted as key
definitions. These are loaded after the predefined keys, and if a
capability's value is the same as a previously-loaded key definition, the
later definition is the one used.
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.
curses(3X), curs_getch(3X), curs_initscr(3X),
curs_util(3X), define_key(3X), termios(3)