getch(3ncurses)

NAME

getch, wgetch, mvgetch, mvwgetch, ungetch, has_key - get (or push back) characters from curses terminal keyboard

SYNOPSIS

#include <curses.h>

int getch(void);
int wgetch(WINDOW *win);
int mvgetch(int y, int x);
int mvwgetch(WINDOW *win, int y, int x);
int ungetch(int ch);
int has_key(int ch);

DESCRIPTION

The getch, wgetch, mvgetch and mvwgetch, routines read a character from the window. In no-delay mode, if no input is waiting, the value ERR 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 half-delay 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 the window is not a pad, and it has been moved or modified since the last call to wrefresh, wrefresh will be called before another character is read.

If keypad is TRUE, and a function key is pressed, the token for that function key is returned instead of the raw characters. Possible function keys are defined in <curses.h> as macros with values outside the range of 8-bit characters whose names begin with KEY_. Thus, a variable intended to hold the return value of a function key must be of short size or larger.

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.

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

Function Keys

The following function keys, defined in <curses.h>, might be returned by getch if keypad has been enabled. Note that not all of these are necessarily supported on any particular terminal.

Name Key name

KEY_BREAK Break key

KEY_DOWN The four arrow keys ...

KEY_UP

KEY_LEFT

KEY_RIGHT

KEY_HOME Home key (upward+left arrow)

KEY_BACKSPACE Backspace

KEY_F0 Function keys; space for 64 keys

is reserved.

KEY_F(n) For 0 <= n <= 63

KEY_DL Delete line

KEY_IL Insert line

KEY_DC Delete character

KEY_IC Insert char or enter insert mode

KEY_EIC Exit insert char mode

KEY_CLEAR Clear screen

KEY_EOS Clear to end of screen

KEY_EOL Clear to end of line

KEY_SF Scroll 1 line forward

KEY_SR Scroll 1 line backward (reverse)

KEY_NPAGE Next page

KEY_PPAGE Previous page

KEY_STAB Set tab

KEY_CTAB Clear tab

KEY_CATAB Clear all tabs

KEY_ENTER Enter or send

KEY_SRESET Soft (partial) reset

KEY_RESET Reset or hard reset

KEY_PRINT Print or copy

KEY_LL Home down or bottom (lower left)

KEY_A1 Upper left of keypad

KEY_A3 Upper right of keypad

KEY_B2 Center of keypad

KEY_C1 Lower left of keypad

KEY_C3 Lower right of keypad

KEY_BTAB Back tab key

KEY_BEG Beg(inning) key

KEY_CANCEL Cancel key

KEY_CLOSE Close key

KEY_COMMAND Cmd (command) key

KEY_COPY Copy key

KEY_CREATE Create key

KEY_END End key

KEY_EXIT Exit key

KEY_FIND Find key

KEY_HELP Help key

KEY_MARK Mark key

KEY_MESSAGE Message key

KEY_MOUSE Mouse event read

KEY_MOVE Move key

KEY_NEXT Next object key

KEY_OPEN Open key

KEY_OPTIONS Options key

KEY_PREVIOUS Previous object key

KEY_REDO Redo key

KEY_REFERENCE Ref(erence) key

KEY_REFRESH Refresh key

KEY_REPLACE Replace key

KEY_RESIZE Screen resized

KEY_RESTART Restart key

KEY_RESUME Resume key

KEY_SAVE Save key

KEY_SBEG Shifted beginning key

KEY_SCANCEL Shifted cancel key

KEY_SCOMMAND Shifted command key

KEY_SCOPY Shifted copy key

KEY_SCREATE Shifted create key

KEY_SDC Shifted delete char key

KEY_SDL Shifted delete line key

KEY_SELECT Select key

KEY_SEND Shifted end key

KEY_SEOL Shifted clear line key

KEY_SEXIT Shifted exit key

KEY_SFIND Shifted find key

KEY_SHELP Shifted help key

KEY_SHOME Shifted home key

KEY_SIC Shifted input key

KEY_SLEFT Shifted left arrow key

KEY_SMESSAGE Shifted message key

KEY_SMOVE Shifted move key

KEY_SNEXT Shifted next key

KEY_SOPTIONS Shifted options key

KEY_SPREVIOUS Shifted prev key

KEY_SPRINT Shifted print key

KEY_SREDO Shifted redo key

KEY_SREPLACE Shifted replace key

KEY_SRIGHT Shifted right arrow

KEY_SRSUME Shifted resume key

KEY_SSAVE Shifted save key

KEY_SSUSPEND Shifted suspend key

KEY_SUNDO Shifted undo key

KEY_SUSPEND Suspend key

KEY_UNDO Undo key

Keypad is arranged like this:

+-----+------+-------+

| A1 | up | A3 |

+-----+------+-------+

|left | B2 | right |

+-----+------+-------+

| C1 | down | C3 |

+-----+------+-------+

The has_key routine takes a key value from the above list, and returns TRUE or FALSE 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(3NCURSES) for more details about KEY_RESIZE, and mouse(3NCURSES) for a discussion of KEY_MOUSE.

RETURN VALUE

All routines return the integer ERR upon failure and an integer value other than ERR (OK in the case of ungetch()) upon successful completion.

ungetch

returns an error if there is no more room in the FIFO.

wgetch

returns an error if the window pointer is null, or if its timeout expires without having any data.

NOTES

Use of the escape 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 control/M, KEY_BACKSPACE versus control/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 control/M, getch will return KEY_ENTER when you press control/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.

Note that getch, mvgetch, and mvwgetch may be macros.

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.

PORTABILITY

The *get* functions are described in the XSI Curses standard, Issue 4. They read single-byte characters only. The standard specifies that they return ERR on failure, but specifies no error conditions.

The echo behavior of these functions on input of KEY_ or backspace characters was not specified in the SVr4 documentation. This description is adopted from the XSI Curses standard.

The behavior of getch and friends in the presence of handled signals is unspecified in the SVr4 and XSI Curses documentation. Under historical curses implementations, it varied depending on whether the operating system's implementation of handled signal receipt interrupts a read(2) call in progress or not, and also (in some implementations) depending on whether an input timeout or non-blocking mode has been set.

Programmers concerned about portability should be prepared for either of two cases: (a) signal receipt does not interrupt getch; (b) signal receipt interrupts getch and causes it to return ERR with errno set to EINTR. Under the ncurses implementation, handled signals never interrupt getch.

The has_key function is unique to ncurses. We recommend that any code using it be conditionalized on the NCURSES_VERSION feature macro.

SEE ALSO

ncurses(3NCURSES), inopts(3NCURSES), mouse(3NCURSES), move(3NCURSES), refresh(3NCURSES), resizeterm(3NCURSES).

Comparable functions in the wide-character (ncursesw) library are described in get_wch(3NCURSES).

getch(3NCURSES)