curs_getch.3x - Man Page

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);

/* extension */
int has_key(int ch);

Description

Reading Characters

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.

If echo is enabled, and the window is not a pad, 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.
  • If the character is a carriage-return, and if nl is enabled, it is translated to a line-feed after echoing.
  • 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.

Keypad Mode

If keypad is TRUE, and a function key is pressed, the token for that function key is returned instead of the raw characters:

  • The predefined function keys are listed in <curses.h> as macros with values outside the range of 8-bit characters. Their names begin with KEY_.
  • Other (user-defined) function keys which may be defined using define_key(3X) have no names, but also are expected to have values outside the range of 8-bit characters.

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.

In ncurses, the timer normally expires after the value in ESCDELAY (see curs_variables(3X)). If notimeout is TRUE, the timer does not expire; it is an infinite (or very large) value. Because function keys usually begin with an escape character, the terminal may appear to hang in notimeout mode after pressing the escape key until another key is pressed.

Ungetting Characters

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.

Predefined Key Codes

The following special keys are defined in <curses.h>.

  • Except for the special case KEY_RESIZE, it is necessary to enable keypad for getch to return these codes.
  • Not all of these are necessarily supported on any particular terminal.
  • The naming convention may seem obscure, with some apparent misspellings (such as “RSUME” for “resume”). The names correspond to the long terminfo capability names for the keys, and were defined long ago, in the 1980s.

    NameKey name
    KEY_BREAKBreak key
    KEY_DOWNThe four arrow keys ...
    KEY_UP
    KEY_LEFT
    KEY_RIGHT
    KEY_HOMEHome key (upward+left arrow)
    KEY_BACKSPACEBackspace
    KEY_F0Function keys; space for 64 keys is reserved.
    KEY_F(n)For 0 ≤ n ≤ 63
    KEY_DLDelete line
    KEY_ILInsert line
    KEY_DCDelete character
    KEY_ICInsert char or enter insert mode
    KEY_EICExit insert char mode
    KEY_CLEARClear screen
    KEY_EOSClear to end of screen
    KEY_EOLClear to end of line
    KEY_SFScroll 1 line forward
    KEY_SRScroll 1 line backward (reverse)
    KEY_NPAGENext page
    KEY_PPAGEPrevious page
    KEY_STABSet tab
    KEY_CTABClear tab
    KEY_CATABClear all tabs
    KEY_ENTEREnter or send
    KEY_SRESETSoft (partial) reset
    KEY_RESETReset or hard reset
    KEY_PRINTPrint or copy
    KEY_LLHome down or bottom (lower left)
    KEY_A1Upper left of keypad
    KEY_A3Upper right of keypad
    KEY_B2Center of keypad
    KEY_C1Lower left of keypad
    KEY_C3Lower right of keypad
    KEY_BTABBack tab key
    KEY_BEGBeg(inning) key
    KEY_CANCELCancel key
    KEY_CLOSEClose key
    KEY_COMMANDCmd (command) key
    KEY_COPYCopy key
    KEY_CREATECreate key
    KEY_ENDEnd key
    KEY_EXITExit key
    KEY_FINDFind key
    KEY_HELPHelp key
    KEY_MARKMark key
    KEY_MESSAGEMessage key
    KEY_MOUSEMouse event occurred
    KEY_MOVEMove key
    KEY_NEXTNext object key
    KEY_OPENOpen key
    KEY_OPTIONSOptions key
    KEY_PREVIOUSPrevious object key
    KEY_REDORedo key
    KEY_REFERENCERef(erence) key
    KEY_REFRESHRefresh key
    KEY_REPLACEReplace key
    KEY_RESIZEScreen resized
    KEY_RESTARTRestart key
    KEY_RESUMEResume key
    KEY_SAVESave key
    KEY_SBEGShifted beginning key
    KEY_SCANCELShifted cancel key
    KEY_SCOMMANDShifted command key
    KEY_SCOPYShifted copy key
    KEY_SCREATEShifted create key
    KEY_SDCShifted delete char key
    KEY_SDLShifted delete line key
    KEY_SELECTSelect key
    KEY_SENDShifted end key
    KEY_SEOLShifted clear line key
    KEY_SEXITShifted exit key
    KEY_SFINDShifted find key
    KEY_SHELPShifted help key
    KEY_SHOMEShifted home key
    KEY_SICShifted insert key
    KEY_SLEFTShifted left arrow key
    KEY_SMESSAGEShifted message key
    KEY_SMOVEShifted move key
    KEY_SNEXTShifted next key
    KEY_SOPTIONSShifted options key
    KEY_SPREVIOUSShifted prev key
    KEY_SPRINTShifted print key
    KEY_SREDOShifted redo key
    KEY_SREPLACEShifted replace key
    KEY_SRIGHTShifted right arrow key
    KEY_SRSUMEShifted resume key
    KEY_SSAVEShifted save key
    KEY_SSUSPENDShifted suspend key
    KEY_SUNDOShifted undo key
    KEY_SUSPENDSuspend key
    KEY_UNDOUndo key

Keypad is arranged like this:

A1upA3
leftB2right
C1downC3

A few of these predefined values do not correspond to a real key:

  • KEY_RESIZE is returned when the SIGWINCH signal has been detected (see initscr(3X) and resizeterm(3X)). This code is returned whether or not keypad has been enabled.
  • KEY_MOUSE is returned for mouse-events (see curs_mouse(3X)). This code relies upon whether or not keypad(3X) has been enabled, because (e.g., with xterm(1) mouse prototocol) ncurses must read escape sequences, just like a function key.

Testing Key Codes

The has_key routine takes a key-code value from the above list, and returns TRUE or FALSE according to whether the current terminal type recognizes a key with that value.

The library also supports these extensions:

define_key

defines a key-code for a given string (see define_key(3X)).

key_defined

checks if there is a key-code defined for a given string (see key_defined(3X)).

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 ERR if there is no more room in the FIFO.

wgetch

returns ERR if the window pointer is null, or if its timeout expires without having any data, or if the execution was interrupted by a signal (errno will be set to EINTR).

Functions with a “mv” prefix first perform a cursor movement using wmove, and return an error if the position is outside the window, or if the window pointer is null.

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.

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.

Generally, KEY_ENTER denotes the character(s) sent by the Enter key on the numeric keypad:

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.

Extensions

has_key was designed for ncurses(3X), and is not found in SVr4 curses, 4.4BSD curses, or any other previous curses implementation.

Portability

Applications employing ncurses extensions should condition their use on the visibility of the NCURSES_VERSION preprocessor macro.

X/Open Curses, Issue 4, Version 2, describes getch, wgetch, mvgetch, mvwgetch, and ungetch. They read single-byte characters only. The standard specifies that they return ERR on failure, but describes no failure conditions.

The echo behavior of these functions on input of KEY_ or backspace characters was not specified in the SVr4 documentation. This description is adapted from X/Open Curses.

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

KEY_MOUSE is mentioned in X/Open Curses, along with a few related terminfo capabilities, but no higher-level functions use the feature. The implementation in ncurses is an extension.

KEY_RESIZE is an extension first implemented for ncurses. NetBSD curses later added this extension.

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.

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

curses(3X), curs_inopts(3X), curs_mouse(3X), curs_move(3X), curs_outopts(3X), curs_refresh(3X), curs_variables(3X), resizeterm(3X)

Comparable functions in the wide-character (ncursesw) library are described in curs_get_wch(3X).

Referenced By

The man pages getch.3x(3), has_key.3x(3), mvgetch.3x(3), mvwgetch.3x(3), ungetch.3x(3) and wgetch.3x(3) are aliases of curs_getch.3x(3).

2023-12-23 ncurses 6.4 Library calls