- 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. Win-
- dow-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 charac-
- ters 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 explic-
- itly. 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 pre-
- fer 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.]
+ curses offers configurable parameters permitting an application to
+ control the handling of input from the terminal. Some 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 inputcharacterreading
+ 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.
+
+
+
+ Normally, the terminal driver buffers typed characters, not delivering
+ them to an application until a line feed or carriage return is typed.
+ cbreak configures the terminal in cbreakmode, 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 returns the terminal to normal ("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 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.
- The halfdelay routine is used for half-delay mode, which is similar to
- cbreak mode in that characters typed by the user are immediately avail-
- able to the program. However, after blocking for tenths tenths of sec-
- onds, 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.
+ halfdelay configures half-delaymode, 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, 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.
- 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.
+ intrflush calls qiflush (see below) if bf is TRUE, and noqiflush if bf
+ is FALSE. It ignores its win argument.
- The keypad option enables the keypad of the user's terminal. If en-
- abled (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 se-
- quences 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.
+ 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(3x) 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.
- Initially, whether the terminal returns 7 or 8 significant bits on in-
- put 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 equiva-
- lent, 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 termi-
- nal when meta(win, TRUE) is called and rmm is sent when meta(win,
- FALSE) is called.
+ Initially, whether the terminal returns 7- or 8-bit character codes on
+ input depends on the configuration of the terminal driver; 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. The window argument, win, is always ignored. If the term-
+ info 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.
+
+
+
+ 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. In normal
+ (or "cooked") mode, the terminal driver always translates carriage
+ returns to line feeds.
- 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 imme-
- diately 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).
+ 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.
+
+
+
+ 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 and noqiflush configure the terminal driver's treatment of its
+ input and output queues when it handles the interrupt, suspend, or quit
+ characters in cbreak and "cooked" modes; 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
+ 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 you want output to continue after the handler exits
+ as though the interrupt had not occurred.
+
+
+
+ raw configures the terminal to read input in rawmode, 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 returns
+ the terminal to normal ("cooked") mode.
+
+
+
+ wtimeout configures whether a curses input character reading function
+ called on window win uses blocking or non-blocking reads. If delay is
+ negative, a blocking read is used, waiting indefinitely for input. If
+ delay is zero, a non-blocking read is used; 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.
- The curses library does "line-breakout optimization" by looking for ty-
- peahead periodically while updating the screen. If input is found, and
- it is coming from a tty, the current update is postponed until re-
- fresh(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.
+ 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(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.
- 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 descrip-
- tions.
+ timeout and wtimeout return no value.
- 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 initial-
- ized. Also,
+ cbreak, nocbreak, echo, noecho, halfdelay, intrflush, keypad, meta,
+ nodelay, notimeout, nl, nonl, raw, noraw, and typeahead return OK on
+ success and ERR on failure.
- halfdelay
- returns an error if its parameter is outside the range
- 1..255.
+ In ncurses, the functions in the previous paragraph return ERR if
+ o the terminal is not initialized or
-
- 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 pro-
- gram remains in cooked mode.
-
- When keypad is first enabled, ncurses loads the key-definitions for the
- current terminal description. If the terminal description includes ex-
- tended 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 previ-
- ous loads of terminal descriptions) may differ from one execution of a
- program to the next. The generated keycodes are recognized by the key-
- name function (which will then return a name beginning with "k" denot-
- ing the terminfo capability name rather than "K", used for curses key-
- names). On the other hand, an application can use define_key to estab-
- lish 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 ca-
- pability's value is the same as a previously-loaded key definition, the
- later definition is the one used.
+ owin is NULL (except for 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.
- Note that echo, noecho, halfdelay, intrflush, meta, nodelay, notimeout,
- noqiflush, qiflush, timeout, and wtimeout may be macros.
+ 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 calls with 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 corresponding to cbreak, echo,
+ nl, and raw, permitting their states to be queried by the application.
+
+ QuerySetReset
+ ------------------------------
+ is_cbreak cbreak nocbreak
+ is_echo echo noecho
+ is_nl nl nonl
+ is_raw raw noraw
+
+ In each case, the function returns
- 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.
+ 1 if the option is set,
+
+ 0 if the option is reset, or
+
+ -1 if the library is not initialized.
+
+
+
+ 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 curses 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 remains in normal
+ ("cooked") mode.
+
+ 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(3x), 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(3x) 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(3x), and reassign the 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. 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.
+
+
+
+ 4BSD curses (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.