Keypad processing

The application can enable or disable keypad translation by calling keypad(). When translation is enabled, Curses attempts to translate a sequence of terminal input that represents the pressing of a function into a single key code. When translation is disabled, Curses passes terminal input to the application without such translation, and any interpretation of the input as representing the pressing of a keypad key must be done by the application.

The complete set of key codes for keypad keys that Curses can process is specified by the constants defined in <curses.h> whose names begin with "KEY_". Each terminal type described in the terminfo database may support some or all of these key codes. The terminfo database specifies the sequence of input characters from the terminal type that correspond to each key code.

The Curses inplementation cannot translate keypad keys on terminals where pressing the keys does not transmit a unique sequence.

When translation is enabled and a character that could be the beginning of a function key (such as escape) is received, Curses notes the time and begins accumulating characters. If Curses receives additional characters that represent the processing of a keypad key within an unspecified interval from the time the character was received, then Curses converts this input to a key code for presentation to the application. If such characters are not received during this interval, translation of this input does not occur and the individual characters are presented to the application separately. (Because Curses waits for this interval to accumulate a key code, many terminals experience a delay between the time a user presses the escape key and the time the escape key is returned to the application.)

In addition, No Timeout Mode provides that in any case where Curses has received part of a function key sequence, it waits indefinitely for the complete key sequence. The "unspecified interval" in the previous paragraph becomes infinite in No Timeout Mode. No Timeout Mode allows the use of function keys over slow communication lines. No Timeout Mode lets the user type the individual characters of a function key sequence, but also delays application response when the user types a character (not a function key) that begins a function key sequence. For this reason, in No Timeout Mode many terminals will appear to hang between the time a user presses the escape key and the time another key is pressed. No Timeout Mode is switchable by calling notimeout(3XCURSES).

If any special characters (<backspace>, <carriage return>, <newline>, <tab>) are defined or redefined to be characters that are members of a function key sequence, then Curses will be unable to recognize and translate those function keys.

Several of the modes discussed below are described in terms of availability of input. If keypad translation is enabled, then input is not available once Curses has begun receiving a keypad sequence until the sequence is completely received or the interval has elapsed.

Input Mode

The following four mutually-specific Curses modes let the application control the effect of flow-control characters, the interrupt character, the erase character, and the kill character:

The terminal interface settings are reported when the process calls initscr(3XCURSES) or newterm(3XCURSES) to initialize Curses and restores these settings when endwin(3XCURSES) is called. The initial input mode for Curses operations is especially unless Enhanced Curses compliance, in which the initial mode is cbreak mode, is supported.

The behavior of the BREAK key depends on other bits in the display driver that are not set by Curses.

Delay Mode

Two mutually-exclusive delay modes specify how quickly certain Curses functions return to the application when there is no terminal input waiting when the function is called:

No Delay

Delay

The effect of No Delay Mode on function key processing is unspecified.

Echo processing

Echo mode determines whether Curses echoes typed characters to the screen. The effect of Echo mode is analogous to the effect of the ECHO flag in the local mode field of the termios structure associated with the terminal device connected to the window. However, Curses always clears the ECHO flag when invoked, to inhibit the operating system from performing echoing. The method of echoing characters is not identical to the operating system's method of echoing characters, because Curses performs additional processing of terminal input.

If in Echo mode, Curses performs 's's own echoing. Any visible input character is stored in the current or specified window by the input function that the application called, at that window's cursor position, as though addch(3XCURSES) were called, with all consequent effects such as cursor movement and wrapping.

If not in Echo mode, any echoing of input must be performed by the application. Applications often perform their own echoing in a controlled area of the screen, or do not echo at all, so they disable Echo mode.

It may not be possible to turn off echo processing for synchronous and networked asynchronous terminals because echo processing is done directly by the terminals. Applications running on such terminals should be aware that any characters typed will appear on the screen at wherever the cursor is positioned.