curs_inopts(3X) Library calls curs_inopts(3X)

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

#include <curses.h>
int cbreak(void);
int nocbreak(void);
int echo(void);
int noecho(void);
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);
int nl(void);
int nonl(void);
int raw(void);
int noraw(void);
void qiflush(void);
void noqiflush(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);

ncurses provides several functions that 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 desired.

Normally, the terminal 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 terminal 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 half-delay mode.

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 terminal driver queue is 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 terminal driver settings. The win 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 terminal 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 called.

The nl and nonl routines control whether the underlying display device translates the return key into newline on input.

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.

When interpreting an 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 distinguish sequences produced by a function key from 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 terminal 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 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, a blocking read is used (i.e., waits indefinitely for input). If delay is zero, then a 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).

curses does “line-breakout optimization” by looking for typeahead periodically while updating the screen. If input is found, and it is coming from a terminal, 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 descriptions.

X/Open Curses does not specify 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. Also,

returns an error if its parameter is outside the range 1..255.

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 normal (“cooked”) mode from raw and cbreak modes respectively. Mixing raw/noraw and cbreak/nocbreak calls leads to terminal driver control states that are hard to predict or understand; doing so is not recommended.

ncurses provides four “is_” functions that may be used to detect if the corresponding flags were set or reset.

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

if the flag is set,
if the flag is reset, or
if the library is not initialized.

They were designed for ncurses(3X), and are not found in SVr4 curses, 4.4BSD curses, or any other previous curses implementation.

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, Version 2 describes these functions.

ncurses follows X/Open Curses and the historical practice of 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.

X/Open Curses is ambiguous regarding whether raw should disable the CR/LF translations controlled by nl and nonl. BSD curses did turn off these translations; AT&T curses (at least as late as SVr1) 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, 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(3X) 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(3X) 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.

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.

curses(3X), curs_getch(3X), curs_initscr(3X), curs_util(3X), define_key(3X), termios(3)

2024-04-13 ncurses 6.5