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) mode.
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 nocbreak.]
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 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(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 curses.
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(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
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
returns an error if its parameter is outside the range
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.
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
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.
This page is part of the ncurses (new curses) project. Information
about the project can be found at
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