curs_inopts(3X) Library calls curs_inopts(3X)
NAME
cbreak, echo, halfdelay, intrflush, is_cbreak, is_echo, is_nl, is_raw,
keypad, meta, nl, nocbreak, nodelay, noecho, nonl, noqiflush, noraw,
notimeout, qiflush, raw, timeout, wtimeout, typeahead - get and set
curses terminal input options
SYNOPSIS
#include <curses.h>
int cbreak(void);
int nocbreak(void);
int echo(void);
int noecho(void);
int intrflush(WINDOW * win /* ignored */, bool bf);
int keypad(WINDOW * win, bool bf);
int meta(WINDOW * win /* ignored */, bool bf);
int nodelay(WINDOW * win, bool bf);
int notimeout(WINDOW * win, bool bf);
int nl(void);
int nonl(void);
void qiflush(void);
void noqiflush(void);
int raw(void);
int noraw(void);
int halfdelay(int tenths);
void timeout(int delay);
void wtimeout(WINDOW * win, int delay);
int typeahead(int fd);
/* extensions */
int is_cbreak(void);
int is_echo(void);
int is_nl(void);
int is_raw(void);
DESCRIPTION
curses offers configurable parameters permitting an application to
control the handling of input from the terminal. Some, such as those
affecting the terminal's mode or line discipline, are global, applying to
all windows; others apply only to a specific window. The library does
not automatically apply such parameters to new or derived windows; an
application must configure each window for the desired behavior.
Some descriptions below make reference to an input character reading
function: this is wgetch(3X) in the non-wide character curses API and
wget_wch(3X) in the wide character API. In addition to the variant forms
of these described in ncurses(3X), the curses functions wgetstr(3X) and
wget_wstr(3X) and their own variants call the appropriate input character
reading function.
cbreak, nocbreak
Normally, the terminal driver buffers typed characters, not delivering
them to an application until a line feed or carriage return is typed.
This canonical ("cooked") line discipline also supports software flow
control, simple line editing functions (character and word erase, and
whole-line erasure or "kill"), and job control. cbreak configures the
terminal in cbreak mode, which disables line buffering and erase and kill
character processing -- the interrupt, quit, suspend, and flow control
characters are unaffected -- and makes characters typed by the user
immediately available to the program. nocbreak restores canonical
("cooked") mode.
The state of the terminal is unknown to a curses application when it
starts; therefore, a program should call cbreak or nocbreak explicitly.
Most interactive programs using curses set cbreak mode. Calling cbreak
overrides raw. The man page for the input character reading function
discusses how cbreak and nocbreak interact with echo and noecho.
echo, noecho
echo and noecho determine whether characters typed by the user are
written to the curses window by the input character reading function as
they are typed. curses always disables the terminal driver's own
echoing. By default, a curses screen's echo option is set. 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 call noecho. The man
page for the input character reading function discusses how echo and
noecho interact with cbreak and nocbreak.
halfdelay
halfdelay configures 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 tenth-seconds, an input
character reading function returns ERR if no input is pending. The value
of tenths must be between 1 and 255. Use nocbreak to leave half-delay
mode.
intrflush
intrflush calls qiflush (see below) if bf is TRUE, and noqiflush if bf is
FALSE. It ignores its win argument.
keypad
keypad enables recognition of a terminal's function keys. If enabled (bf
is TRUE) then when an input character reading function reads ESC, it
waits for further input corresponding to an escape sequence defined by
the terminal type description. If a valid sequence populates the input
stream, the input character reading function returns a value representing
the function key, such as KEY_LEFT. (Wide-character API users:
wget_wch(3X) returns KEY_CODE_YES to indicate the availability of a
function key code in its wch parameter.) If the sequence is invalid, the
input character reading function returns only its last character. If
disabled (bf is FALSE), curses does not treat function keys specially and
the program has to interpret escape sequences itself. If the terminal
type description defines the keypad_local (rmkx) and keypad_xmit (smkx)
capabilities, enabling a window's keypad mode sets the terminal's keypad
to transmit, and disabling keypad mode sets the terminal's keypad to work
locally. By default, a window's keypad mode is off.
meta
Initially, whether the terminal returns 7- or 8-bit character codes on
input depends on the configuration of the terminal driver; on POSIX
systems, see termios(3). To force 8 bits to be returned, call meta(...,
TRUE); this is equivalent, on POSIX systems, to setting the CS8 flag on
the terminal. To force 7 bits to be returned, call meta(..., FALSE);
this is equivalent, on POSIX systems, to setting the CS7 flag on the
terminal. curses ignores the window argument win. If the terminfo
string capabilities meta_on (smm) and meta_off (rmm) are defined for the
terminal type, enabling meta mode sends smm's value to the terminal and
disabling it sends that of rmm to the terminal.
nl, nonl
Initially, whether the terminal reports a carriage return using the
character code for a line feed in cbreak or raw modes depends on the
configuration of the terminal driver; see termios(3). nl configures the
terminal to perform this translation. nonl disables it. Under its
canonical ("cooked") line discipline, the terminal driver always
translates carriage returns to line feeds.
nodelay
nodelay configures the input character reading function to be non-
blocking for window win. If no input is ready, the reading function
returns ERR. If disabled (bf is FALSE), the reading function does not
return until it has input.
notimeout
When keypad has been called on a window and the input character reading
function reads an ESC character from it, curses sets a timer while
waiting for the next character. If the timer elapses, curses interprets
the ESC as an explicit press of the terminal's Escape key (or
equivalent). notimeout(win, TRUE) disables this timer. The purpose of
the timeout is to distinguish sequences produced by a function key from
those typed by a user. If this timer is disabled, curses waits forever
for subsequent keystrokes until it determines the escape sequence to be
valid or invalid.
qiflush, noqiflush
qiflush and noqiflush configure the terminal driver's treatment of its
input and output queues when it handles the interrupt, suspend, or quit
characters under the canonical ("cooked") or cbreak line disciplines on
POSIX systems; see termios(3). The default behavior is inherited from
the terminal driver settings. Calling qiflush configures the terminal to
flush the queues (discarding their contents) when any of these events
occurs, giving the impression of faster response to user input, but
making the library's model of the screen contents incorrect. Calling
noqiflush prevents such flushing, but might frustrate impatient users on
slow connections if a curses update of the screen is in progress when the
event occurs; see typeahead below for a mitigation of this problem. You
may want to call noqiflush in a signal handler if, after the handler
exits, you want output to continue as though the signal had not occurred.
raw, noraw
raw configures the terminal to read input in raw mode, which is similar
to cbreak mode (see cbreak above) except that it furthermore passes
through the terminal's configured interrupt, quit, suspend, and flow
control characters uninterpreted to the application, instead of
generating a signal or acting on I/O flow. The behavior of the
terminal's "Break" key (if any) depends on terminal driver configuration
parameters that curses does not handle. noraw restores the terminal's
canonical ("cooked") line discipline.
timeout, wtimeout
wtimeout configures whether a curses input character reading function
called on window win uses blocking or non-blocking reads. If delay is
negative, curses uses a blocking read, waiting indefinitely for input.
If delay is zero, the read is non-blocking; an input character reading
function returns ERR if no input is pending. If delay is positive, an
input character reading function blocks for delay milliseconds, and
returns ERR if the delay elapses and there is still no input pending.
timeout calls wtimeout on stdscr.
typeahead
Normally, a curses library checks the terminal's input file descriptor
for activity with poll(2) or select(2) while updating the screen; if it
finds any, it postpones output until the next wrefresh(3X) or
doupdate(3X) call, allowing faster response to user key strokes. The
library tests the file descriptor corresponding to the FILE stream
pointer passed to newterm(3X) (or stdin if initscr(3X) was called), for
pending input. typeahead instructs curses to test file descriptor fd
instead. An fd of -1 disables the check.
RETURN VALUE
timeout and wtimeout return no value.
cbreak, nocbreak, echo, noecho, halfdelay, intrflush, keypad, meta,
nodelay, notimeout, nl, nonl, raw, noraw, and typeahead return OK on
success and ERR on failure.
In ncurses, the functions in the previous paragraph return ERR if
o the library's TERMINAL structure for the device has not been
initialized with initscr(3X), newterm(3X), or setupterm(3X), or
o win is a null pointer (except with intrflush and meta, which ignore
its value).
Further, halfdelay returns ERR if delay is outside the range 1..255.
See section "EXTENSIONS" below for the return values of is_cbreak,
is_echo, is_nl, and is_raw.
NOTES
echo, noecho, halfdelay, intrflush, meta, nl, nonl, nodelay, notimeout,
noqiflush, qiflush, timeout, and wtimeout may be implemented as macros.
noraw and nocbreak follow historical practice in that they attempt to
restore the terminal's canonical ("cooked") line discipline from raw and
cbreak, respectively. Mixing raw/noraw calls with cbreak/nocbreak calls
leads to terminal driver control states that are hard to predict or
understand; doing so is not recommended.
curses documentation uses the terms "delay" and "timeout" freely to
describe two related but distinct aspects of input handling, at the risk
of confusing the user. The functions halfdelay, nodelay, timeout, and
wtimeout configure whether the input character reading function
(wgetch(3X) or wget_wch(3X)) waits for keyboard input to begin, and for
how long. keypad configures whether that function waits for further
input if the first character it reads is ESC. Calling notimeout, which
has nothing to do with timeout or wtimeout, makes this delay in
expectation of further characters effectively infinite. X/Open Curses
affords no means of otherwise configuring the length of this second
delay, but an AIX and ncurses extension, ESCDELAY, is available both as
an environment variable and a global symbol permitting the user and
application, respectively, to do so; see ncurses(3X) and
curs_variables(3X).
EXTENSIONS
ncurses provides four "is_" functions corresponding to cbreak, echo, nl,
and raw, permitting their states to be queried by the application.
Query Set Reset
------------------------------
is_cbreak cbreak nocbreak
is_echo echo noecho
is_nl nl nonl
is_raw raw noraw
In each case, the function returns
1 if the option is set,
0 if the option is unset, or
-1 if the library's TERMINAL structure for the device has not been
initialized.
PORTABILITY
Applications employing ncurses extensions should condition their use on
the visibility of the NCURSES_VERSION preprocessor macro.
Except as noted in section "EXTENSIONS" above, X/Open Curses Issue 4
describes these functions. It specifies no error conditions for them.
SVr4 describes a successful return value only as "an integer value other
than ERR".
ncurses follows X/Open Curses and the historical practice of System V
curses, clearing the terminal driver's "echo" flag when initializing the
screen. BSD curses did not, but its raw function turned it off as a side
effect. For best portability, call echo or noecho explicitly just after
initialization, even if your program retains the terminal's canonical
("cooked") line discipline.
X/Open Curses is ambiguous regarding whether raw should disable the
carriage return and line feed translation feature controlled by nl and
nonl. BSD curses turned off these translations; System V curses did not.
ncurses does so, on the assumption that a programmer requesting raw input
wants a clean (ideally, 8-bit clean) connection that the operating system
will not alter.
When keypad is first enabled for a window, ncurses loads the standard
function key string capabilities for the terminal type description of its
screen; see the entries beginning with "key_" in terminfo(5). If that
description includes extended string capabilities, produced by the -x
option of tic(1), for example, then ncurses also defines keys for the
capabilities whose codes begin with "k". ncurses generates a numeric key
code for each such extended capability; depending on previous loads of
terminal type descriptions, these may differ from one execution of a
program to the next. keyname(3X) recognizes the generated key codes and
returns a name beginning with "k" denoting the terminfo capability name
rather than "KEY_", used for curses key names. On the other hand, an
application can use define_key(3X) to bind a selected key to a string of
the programmer's choice. This feature enables an application to check
for its presence with tigetstr(3X), and reassign the numeric key code to
match its own needs.
Low-level applications can use tigetstr(3X) to obtain the definition of
any string capability. curses applications use the input character
reading function to obtain key codes from input and rely upon the order
in which the string capabilities are loaded. Multiple key capability
strings can have the same value, but the input character reading function
can report only one key code. Most curses implementations (including
ncurses) load key definitions in the order they appear in the strfnames
array of string capability names; see term_variables(3X). The last
capability read using a particular definition determines the key code to
be reported. In ncurses, extended capabilities can be interpreted as key
definitions. The library loads these after its built-in definitions, and
if an extended capability's value is the same as one previously loaded,
the library uses the later definition.
HISTORY
4BSD (1980) introduced echo, noecho, nl, nonl, raw, and noraw.
SVr2 (1984) featured a new terminal driver, extending the curses API to
support it with cbreak, nocbreak, intrflush, keypad, meta, nodelay, and
typeahead.
SVr3 (1987) added halfdelay, notimeout, and wtimeout. qiflush and
noqiflush appeared in SVr3.1 (1987), at which point intrflush became a
wrapper for either of these functions, depending on the value of its
Boolean argument. SVr3.1 also added timeout.
ncurses 6.5 (2024) introduced is_cbreak, is_echo, is_nl, and is_raw.
Formerly, ncurses used nl and nonl to control the conversion of newlines
to carriage return/line feed on output as well as input. X/Open Curses
documents the use of these functions only for input. This difference
arose from converting the pcurses source (1986), which used ioctl(2)
calls and the sgttyb structure, to termios (the POSIX terminal API). In
the former, both input and output conversions were controlled via a
single option "CRMOD", while the latter separates these features.
Because that conversion interferes with output optimization, ncurses 6.2
(2020) amended nl and nonl to eliminate their effect on output.
SEE ALSO
curses(3X), curs_getch(3X), curs_initscr(3X), curs_util(3X),
define_key(3X), termios(3), term_variables(3X)
ncurses 6.6 2025-10-04 curs_inopts(3X)