5.2.16 Getting characters from the keyboard

Procedure: getch win #:key y x

The getch routine reads a character from the terminal associated with the given window. In no-delay mode, if no input is waiting, the value #f is returned. In delay mode, the program waits until the system passes text through to the program. Depending on the setting of cbreak, this is after one character (cbreak mode), or after the first newline (nocbreak! mode). In halfdelay! mode, the program waits until a character is typed or the specified timeout has been reached.

Unless noecho! has been set, then the character will also be echoed into the designated window according to the following rules: If the character is the current erase character, left arrow, or backspace, the cursor is moved one space to the left and that screen position is erased as if delch had been called. If the character value is any other KEY_ define, the user is alerted with a beep call. Otherwise the character is simply output to the screen.

If keypad! is #t, and a function key is pressed, the integer keycode for that function key is returned instead of the raw characters. There is a list of possible function keys. See Table 5.3.

When a character that could be the beginning of a function key is received (which, on modern terminals, means an escape character), curses sets a timer. If the remainder of the sequence does not come in within the designated time, the character is passed through; otherwise, the function key value is returned. For this reason, many terminals experience a delay between the time a user presses the escape key and the escape is returned to the program.

If the window is not a pad, and it has been moved or modified since the last call to refresh, refresh will be called before another character is read.

Procedure: ungetch ch

The ungetch routine places ch back onto the input queue to be returned by the next call to getch. There is just one input queue for all windows.

It returns #f if there is no more space in the buffer, or #t otherwise.

Procedure: key-f n

This procedure returns the keycode for function key n.

The following function keys, might be returned by getch if keypad! has been enabled.

Note that almost all of these function keys do not exist on modern keyboards. The standard PC keyboard cannot be depended upon to have more than (key-f 1) through (key-f 12), KEY_PPAGE (Page Up), KEY_NPAGE (Page Down), KEY_HOME, KEY_END, KEY_IC (Insert), KEY_DC (Delete), KEY_BACKSPACE, KEY_DC (Delete), KEY_UP, KEY_DOWN, KEY_LEFT, and KEY_RIGHT.

Also, a common terminal is more likely to return C-M than KEY_ENTER when the RET key is pressed.

Procedure: has-key? ch

The has-key? routine takes a key value ch from the above list, and returns #t or #f according to whether the current terminal type recognizes a key with that value. Note that a few values do not correspond to a real key, e.g., KEY_RESIZE and KEY_MOUSE. See resizeterm for more details about KEY_RESIZE. For a discussion of KEY_MOUSE see Mouse handling.

Use of the ESC key by a programmer for a single character function is discouraged, as it will cause a delay of up to one second while the keypad code looks for a following function-key sequence.

Note that some keys may be the same as commonly used control keys, e.g., KEY_ENTER versus C-M, KEY_BACKSPACE versus C-H. Some curses implementations may differ according to whether they treat these control keys specially (and ignore the terminfo), or use the terminfo definitions. Ncurses uses the terminfo definition. If it says that KEY_ENTER is C-M, getch will return KEY_ENTER when you press C-M.

When using getch, wgetch, mvgetch, or mvwgetch, nocbreak mode (nocbreak!) and echo mode (echo!) should not be used at the same time. Depending on the state of the TTY driver when each character is typed, the program may produce undesirable results.

Historically, the set of keypad macros was largely defined by the extremely function-key-rich keyboard of the AT&T 7300, aka 3B1, aka Safari 4. Modern personal computers usually have only a small subset of these. IBM PC-style consoles typically support little more than KEY_UP, KEY_DOWN, KEY_LEFT, KEY_RIGHT, KEY_HOME, KEY_END, KEY_NPAGE, KEY_PPAGE, and function keys 1 through 12. The ins key is usually mapped to KEY_IC