plucky (3) qiflush.3ncurses.gz
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(3NCURSES)
in the non-wide character curses API and wget_wch(3NCURSES) in the wide character API. In addition to
the variant forms of these described in ncurses(3NCURSES), the curses functions wgetstr(3NCURSES) and
wget_wstr(3NCURSES) 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), the input character
reading function returns a value representing the function key, such as KEY_LEFT. (Wide-character API
users: wget_wch(3NCURSES) returns KEY_CODE_YES to indicate the availability of a function key code in its
wch parameter.) If disabled (bf is FALSE), curses does not treat function keys specially and the program
has to interpret escape sequences itself. If the terminal's keypad can be turned on (made to transmit)
and off (made to work locally), keypad configures it consistently with the bf parameter. 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 to the terminal and
disabling it sends 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 the input character reading function reads an ESC character, it sets a timer while waiting for the
next character. 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. To configure the timeout rather than
disabling it, see wtimeout below.
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 interrupt 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 for input while updating the screen. If any is found, the
update is postponed until the next wrefresh(3NCURSES) or doupdate(3NCURSES) call, allowing faster
response to user key strokes. The library tests the file descriptor corresponding to the FILE stream
pointer passed to newterm(3NCURSES) (or stdin if initscr(3NCURSES) 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
• the library's TERMINAL structure for the device has not been initialized with initscr(3NCURSES),
newterm(3NCURSES), or setupterm(3NCURSES), or
• 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.
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 did turn 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, ncurses loads the key definitions for the current terminal description. If
the terminal description includes extended string capabilities, for example, by using the -x option of
tic(1), then ncurses also defines keys for the capabilities whose names begin with “k”. Corresponding
key codes are generated and (depending on previous loads of terminal descriptions) may differ from one
execution of a program to the next. The generated key codes are recognized by keyname(3NCURSES), which
then returns 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(3NCURSES) to bind a specific key
to a string of the programmer's choice. This feature enables an application to check for its presence
with tigetstr(3NCURSES), and reassign the key code to match its own needs.
Low-level applications can use tigetstr(3NCURSES) 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 terminfo_variables(3NCURSES). 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. These are loaded after the predefined keys, and if a capability's value
is the same as a previously loaded key definition, 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 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
ncurses(3NCURSES), getch(3NCURSES), initscr(3NCURSES), util(3NCURSES), define_key(3NCURSES), termios(3), terminfo_variables(3NCURSES)