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curs_inopts

Section: Library calls (3X)
Updated: 202-1-04
Index Return to Main Contents

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 no-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 whol-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 hal-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 tent-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 hal-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. (Wid-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.

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 no-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 no-blocking reads. If delay is negative, curses uses a blocking read, waiting indefinitely for input. If delay is zero, the read is no-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
.IP * 4 the library's TERMINAL structure for the device has not been initialized with initscr(3X), newterm(3X), or setupterm(3X), or
.IP * 4 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, -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.

Lo-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 buil-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.