|ncurses(3X)||Miscellaneous Library Functions||ncurses(3X)|
ncurses - CRT screen handling and optimization package
The ncurses library routines give the user a terminal-independent method of updating character screens with reasonable optimization. This implementation is “new curses” (ncurses) and is the approved replacement for 4.4BSD classic curses, which has been discontinued. This describes ncurses version 6.4 (patch 20221231).
The ncurses library emulates the curses library of System V Release 4 UNIX, and XPG4 (X/Open Portability Guide) curses (also known as XSI curses). XSI stands for X/Open System Interfaces Extension. The ncurses library is freely redistributable in source form. Differences from the SVr4 curses are summarized under the EXTENSIONS and PORTABILITY sections below and described in detail in the respective EXTENSIONS, PORTABILITY and BUGS sections of individual man pages.
The ncurses library also provides many useful extensions, i.e., features which cannot be implemented by a simple add-on library but which require access to the internals of the library.
A program using these routines must be linked with the -lncurses option, or (if it has been generated) with the debugging library -lncurses_g. (Your system integrator may also have installed these libraries under the names -lcurses and -lcurses_g.) The ncurses_g library generates trace logs (in a file called “trace” in the current directory) that describe curses actions. See also the section on ALTERNATE CONFIGURATIONS.
The ncurses package supports: overall screen, window and pad manipulation; output to windows and pads; reading terminal input; control over terminal and curses input and output options; environment query routines; color manipulation; use of soft label keys; terminfo capabilities; and access to low-level terminal-manipulation routines.
The library uses the locale which the calling program has initialized. That is normally done with setlocale(3):
If the locale is not initialized, the library assumes that characters are printable as in ISO-8859-1, to work with certain legacy programs. You should initialize the locale and not rely on specific details of the library when the locale has not been setup.
The function initscr or newterm must be called to initialize the library before any of the other routines that deal with windows and screens are used. The routine endwin(3X) must be called before exiting.
To get character-at-a-time input without echoing (most interactive, screen oriented programs want this), the following sequence should be used:
initscr(); cbreak(); noecho();
Most programs would additionally use the sequence:
intrflush(stdscr, FALSE); keypad(stdscr, TRUE);
Before a curses program is run, the tab stops of the terminal should be set and its initialization strings, if defined, must be output. This can be done by executing the gtput init command after the shell environment variable TERM has been exported. gtset(1) is usually responsible for doing this. [See terminfo(5) for further details.]
The ncurses library permits manipulation of data structures, called windows, which can be thought of as two-dimensional arrays of characters representing all or part of a CRT screen. A default window called stdscr, which is the size of the terminal screen, is supplied. Others may be created with newwin.
Note that curses does not handle overlapping windows, that's done by the panel(3X) library. This means that you can either use stdscr or divide the screen into tiled windows and not using stdscr at all. Mixing the two will result in unpredictable, and undesired, effects.
Windows are referred to by variables declared as WINDOW *. These data structures are manipulated with routines described here and elsewhere in the ncurses manual pages. Among those, the most basic routines are move and addch. More general versions of these routines are included with names beginning with w, allowing the user to specify a window. The routines not beginning with w affect stdscr.
After using routines to manipulate a window, refresh(3X) is called, telling curses to make the user's CRT screen look like stdscr. The characters in a window are actually of type chtype, (character and attribute data) so that other information about the character may also be stored with each character.
Special windows called pads may also be manipulated. These are windows which are not constrained to the size of the screen and whose contents need not be completely displayed. See curs_pad(3X) for more information.
In addition to drawing characters on the screen, video attributes and colors may be supported, causing the characters to show up in such modes as underlined, in reverse video, or in color on terminals that support such display enhancements. Line drawing characters may be specified to be output. On input, curses is also able to translate arrow and function keys that transmit escape sequences into single values. The video attributes, line drawing characters, and input values use names, defined in <curses.h>, such as A_REVERSE, ACS_HLINE, and KEY_LEFT.
If the environment variables LINES and COLUMNS are set, or if the program is executing in a window environment, line and column information in the environment will override information read by terminfo. This would affect a program running in an AT&T 630 layer, for example, where the size of a screen is changeable (see ENVIRONMENT).
If the environment variable TERMINFO is defined, any program using curses checks for a local terminal definition before checking in the standard place. For example, if TERM is set to att4424, then the compiled terminal definition is found in
(The a is copied from the first letter of att4424 to avoid creation of huge directories.) However, if TERMINFO is set to $HOME/myterms, curses first checks
and if that fails, it then checks
This is useful for developing experimental definitions or when write permission in /usr/gnu/share/terminfo is not available.
The integer variables LINES and COLS are defined in <curses.h> and will be filled in by initscr with the size of the screen. The constants TRUE and FALSE have the values 1 and 0, respectively.
The curses routines also define the WINDOW * variable curscr which is used for certain low-level operations like clearing and redrawing a screen containing garbage. The curscr can be used in only a few routines.
Many curses routines have two or more versions. The routines prefixed with w require a window argument. The routines prefixed with p require a pad argument. Those without a prefix generally use stdscr.
The routines prefixed with mv require a y and x coordinate to move to before performing the appropriate action. The mv routines imply a call to move before the call to the other routine. The coordinate y always refers to the row (of the window), and x always refers to the column. The upper left-hand corner is always (0,0), not (1,1).
The routines prefixed with mvw take both a window argument and x and y coordinates. The window argument is always specified before the coordinates.
In each case, win is the window affected, and pad is the pad affected; win and pad are always pointers to type WINDOW.
Option setting routines require a Boolean flag bf with the value TRUE or FALSE; bf is always of type bool. Most of the data types used in the library routines, such as WINDOW, SCREEN, bool, and chtype are defined in <curses.h>. Types used for the terminfo routines such as TERMINAL are defined in <term.h>.
This manual page describes functions which may appear in any configuration of the library. There are two common configurations of the library:
The following table lists the curses routines provided in the “normal” and “wide” libraries and the names of the manual pages on which they are described. Routines flagged with “*” are ncurses-specific, not described by XPG4 or present in SVr4.
|curses Routine Name||Manual Page Name|
Depending on the configuration, additional sets of functions may be available:
Routines that return an integer return ERR upon failure and an integer value other than ERR upon successful completion, unless otherwise noted in the routine descriptions.
As a general rule, routines check for null pointers passed as parameters, and handle this as an error.
All macros return the value of the w version, except setscrreg, wsetscrreg, getyx, getbegyx, and getmaxyx. The return values of setscrreg, wsetscrreg, getyx, getbegyx, and getmaxyx are undefined (i.e., these should not be used as the right-hand side of assignment statements).
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. Most “mv”-prefixed functions (except variadic functions such as mvprintw) are provided both as macros and functions.
Routines that return pointers return NULL on error.
The following environment symbols are useful for customizing the runtime behavior of the ncurses library. The most important ones have been already discussed in detail.
When set, change occurrences of the command_character (i.e., the cmdch capability) of the loaded terminfo entries to the value of this variable. Very few terminfo entries provide this feature.
Because this name is also used in development environments to represent the C compiler's name, ncurses ignores it if it does not happen to be a single character.
The debugging library checks this environment variable when the application has redirected output to a file. The variable's numeric value is used for the baudrate. If no value is found, ncurses uses 9600. This allows testers to construct repeatable test-cases that take into account costs that depend on baudrate.
Specify the width of the screen in characters. Applications running in a windowing environment usually are able to obtain the width of the window in which they are executing. If neither the COLUMNS value nor the terminal's screen size is available, ncurses uses the size which may be specified in the terminfo database (i.e., the cols capability).
It is important that your application use a correct size for the screen. This is not always possible because your application may be running on a host which does not honor NAWS (Negotiations About Window Size), or because you are temporarily running as another user. However, setting COLUMNS and/or LINES overrides the library's use of the screen size obtained from the operating system.
Either COLUMNS or LINES symbols may be specified independently. This is mainly useful to circumvent legacy misfeatures of terminal descriptions, e.g., xterm which commonly specifies a 65 line screen. For best results, lines and cols should not be specified in a terminal description for terminals which are run as emulations.
Use the use_env function to disable all use of external environment (but not including system calls) to determine the screen size. Use the use_tioctl function to update COLUMNS or LINES to match the screen size obtained from system calls or the terminal database.
Specifies the total time, in milliseconds, for which ncurses will await a character sequence, e.g., a function key. The default value, 1000 milliseconds, is enough for most uses. However, it is made a variable to accommodate unusual applications.
The most common instance where you may wish to change this value is to work with slow hosts, e.g., running on a network. If the host cannot read characters rapidly enough, it will have the same effect as if the terminal did not send characters rapidly enough. The library will still see a timeout.
Note that xterm mouse events are built up from character sequences received from the xterm. If your application makes heavy use of multiple-clicking, you may wish to lengthen this default value because the timeout applies to the composed multi-click event as well as the individual clicks.
In addition to the environment variable, this implementation provides a global variable with the same name. Portable applications should not rely upon the presence of ESCDELAY in either form, but setting the environment variable rather than the global variable does not create problems when compiling an application.
Tells ncurses where your home directory is. That is where it may read and write auxiliary terminal descriptions:
Like COLUMNS, specify the height of the screen in characters. See COLUMNS for a detailed description.
This applies only to the OS/2 EMX port. It specifies the order of buttons on the mouse. OS/2 numbers a 3-button mouse inconsistently from other platforms:
1 = left
2 = right
3 = middle.
This variable lets you customize the mouse. The variable must be three numeric digits 1-3 in any order, e.g., 123 or 321. If it is not specified, ncurses uses 132.
Override the compiled-in assumption that the terminal's default colors are white-on-black (see default_colors(3X)). You may set the foreground and background color values with this environment variable by proving a 2-element list: foreground,background. For example, to tell ncurses to not assume anything about the colors, set this to "-1,-1". To make it green-on-black, set it to "2,0". Any positive value from zero to the terminfo max_colors value is allowed.
This applies only to the MinGW port of ncurses.
The Console2 program's handling of the Microsoft Console API call CreateConsoleScreenBuffer is defective. Applications which use this will hang. However, it is possible to simulate the action of this call by mapping coordinates, explicitly saving and restoring the original screen contents. Setting the environment variable NCGDB has the same effect.
This applies only to ncurses configured to use the GPM interface.
If present, the environment variable is a list of one or more terminal names against which the TERM environment variable is matched. Setting it to an empty value disables the GPM interface; using the built-in support for xterm, etc.
If the environment variable is absent, ncurses will attempt to open GPM if TERM contains “linux”.
Ncurses may use tabs as part of the cursor movement optimization. In some cases, your terminal driver may not handle these properly. Set this environment variable to disable the feature. You can also adjust your stty(1) settings to avoid the problem.
Some terminals use a magic-cookie feature which requires special handling to make highlighting and other video attributes display properly. You can suppress the highlighting entirely for these terminals by setting this environment variable.
Most of the terminal descriptions in the terminfo database are written for real “hardware” terminals. Many people use terminal emulators which run in a windowing environment and use curses-based applications. Terminal emulators can duplicate all of the important aspects of a hardware terminal, but they do not have the same limitations. The chief limitation of a hardware terminal from the standpoint of your application is the management of dataflow, i.e., timing. Unless a hardware terminal is interfaced into a terminal concentrator (which does flow control), it (or your application) must manage dataflow, preventing overruns. The cheapest solution (no hardware cost) is for your program to do this by pausing after operations that the terminal does slowly, such as clearing the display.
As a result, many terminal descriptions (including the vt100) have delay times embedded. You may wish to use these descriptions, but not want to pay the performance penalty.
Set the NCURSES_NO_PADDING environment variable to disable all but mandatory padding. Mandatory padding is used as a part of special control sequences such as flash.
This setting is obsolete. Before changes
ncurses enabled buffered output during terminal initialization. This was done (as in SVr4 curses) for performance reasons. For testing purposes, both of ncurses and certain applications, this feature was made optional. Setting the NCURSES_NO_SETBUF variable disabled output buffering, leaving the output in the original (usually line buffered) mode.
In the current implementation, ncurses performs its own buffering and does not require this workaround. It does not modify the buffering of the standard output.
The reason for the change was to make the behavior for interrupts and other signals more robust. One drawback is that certain nonconventional programs would mix ordinary stdio calls with ncurses calls and (usually) work. This is no longer possible since ncurses is not using the buffered standard output but its own output (to the same file descriptor). As a special case, the low-level calls such as putp still use the standard output. But high-level curses calls do not.
During initialization, the ncurses library checks for special cases where VT100 line-drawing (and the corresponding alternate character set capabilities) described in the terminfo are known to be missing. Specifically, when running in a UTF-8 locale, the Linux console emulator and the GNU screen program ignore these. Ncurses checks the TERM environment variable for these. For other special cases, you should set this environment variable. Doing this tells ncurses to use Unicode values which correspond to the VT100 line-drawing glyphs. That works for the special cases cited, and is likely to work for terminal emulators.
When setting this variable, you should set it to a nonzero value. Setting it to zero (or to a nonnumber) disables the special check for “linux” and “screen”.
As an alternative to the environment variable, ncurses checks for an extended terminfo capability U8. This is a numeric capability which can be compiled using gtic -x. For example
# linux console, if patched to provide working # VT100 shift-in/shift-out, with corresponding font. linux-vt100|linux console with VT100 line-graphics,
U8#0, use=linux, # uxterm with vt100Graphics resource set to false xterm-utf8|xterm relying on UTF-8 line-graphics,
The name “U8” is chosen to be two characters, to permit it to be used by applications that use ncurses' termcap interface.
During initialization, the ncurses debugging library checks the NCURSES_TRACE environment variable. If it is defined, to a numeric value, ncurses calls the trace function, using that value as the argument.
The argument values, which are defined in curses.h, provide several types of information. When running with traces enabled, your application will write the file trace to the current directory.
See curs_trace(3X) for more information.
Denotes your terminal type. Each terminal type is distinct, though many are similar.
TERM is commonly set by terminal emulators to help applications find a workable terminal description. Some of those choose a popular approximation, e.g., “ansi”, “vt100”, “xterm” rather than an exact fit. Not infrequently, your application will have problems with that approach, e.g., incorrect function-key definitions.
If you set TERM in your environment, it has no effect on the operation of the terminal emulator. It only affects the way applications work within the terminal. Likewise, as a general rule (xterm(1) being a rare exception), terminal emulators which allow you to specify TERM as a parameter or configuration value do not change their behavior to match that setting.
If the ncurses library has been configured with termcap support, ncurses will check for a terminal's description in termcap form if it is not available in the terminfo database.
The TERMCAP environment variable contains either a terminal description (with newlines stripped out), or a file name telling where the information denoted by the TERM environment variable exists. In either case, setting it directs ncurses to ignore the usual place for this information, e.g., /etc/termcap.
ncurses can be configured to read from multiple terminal databases. The TERMINFO variable overrides the location for the default terminal database. Terminal descriptions (in terminal format) are stored in terminal databases:
TERMINFO="$(infocmp -0 -Q2 -q)" export TERMINFO
Setting TERMINFO is the simplest, but not the only way to set location of the default terminal database. The complete list of database locations in order follows:
Specifies a list of locations to search for terminal descriptions. Each location in the list is a terminal database as described in the section on the TERMINFO variable. The list is separated by colons (i.e., ":") on Unix, semicolons on OS/2 EMX.
There is no corresponding feature in System V terminfo; it is an extension developed for ncurses.
If TERMCAP does not hold a file name then ncurses checks the TERMPATH environment variable. This is a list of filenames separated by spaces or colons (i.e., ":") on Unix, semicolons on OS/2 EMX.
If the TERMPATH environment variable is not set, ncurses looks in the files
/etc/termcap, /usr/share/misc/termcap and $HOME/.termcap,
in that order.
The library may be configured to disregard the following variables when the current user is the superuser (root), or if the application uses setuid or setgid permissions:
$TERMINFO, $TERMINFO_DIRS, $TERMPATH, as well as $HOME.
Several different configurations are possible, depending on the configure script options used when building ncurses. There are a few main options whose effects are visible to the applications developer using ncurses:
The ncurses library can be compiled with an option (-DUSE_GETCAP) that falls back to the old-style /etc/termcap file if the terminal setup code cannot find a terminfo entry corresponding to TERM. Use of this feature is not recommended, as it essentially includes an entire termcap compiler in the ncurses startup code, at significant cost in core and startup cycles.
The ncurses library includes facilities for capturing mouse events on certain terminals (including xterm). See the curs_mouse(3X) manual page for details.
The ncurses library includes facilities for responding to window resizing events, e.g., when running in an xterm. See the resizeterm(3X) and wresize(3X) manual pages for details. In addition, the library may be configured with a SIGWINCH handler.
The ncurses library extends the fixed set of function key capabilities of terminals by allowing the application designer to define additional key sequences at runtime. See the define_key(3X) key_defined(3X), and keyok(3X) manual pages for details.
The ncurses library can exploit the capabilities of terminals which implement the ISO-6429 SGR 39 and SGR 49 controls, which allow an application to reset the terminal to its original foreground and background colors. From the users' perspective, the application is able to draw colored text on a background whose color is set independently, providing better control over color contrasts. See the default_colors(3X) manual page for details.
The ncurses library includes a function for directing application output to a printer attached to the terminal device. See the curs_print(3X) manual page for details.
The ncurses library is intended to be BASE-level conformant with XSI Curses. The EXTENDED XSI Curses functionality (including color support) is supported.
A small number of local differences (that is, individual differences between the XSI Curses and ncurses calls) are described in PORTABILITY sections of the library man pages.
In many cases, X/Open Curses is vague about error conditions, omitting some of the SVr4 documentation.
Unlike other implementations, this one checks parameters such as pointers to WINDOW structures to ensure they are not null. The main reason for providing this behavior is to guard against programmer error. The standard interface does not provide a way for the library to tell an application which of several possible errors were detected. Relying on this (or some other) extension will adversely affect the portability of curses applications.
Most of the extensions provided by ncurses have not been standardized. Some have been incorporated into other implementations, such as PDCurses or NetBSD curses. Here are a few to consider:
In historic curses versions, delays embedded in the capabilities cr, ind, cub1, ff and tab activated corresponding delay bits in the UNIX tty driver. In this implementation, all padding is done by sending NUL bytes. This method is slightly more expensive, but narrows the interface to the UNIX kernel significantly and increases the package's portability correspondingly.
The header file <curses.h> automatically includes the header files <stdio.h> and <unctrl.h>.
X/Open Curses has more to say, but does not finish the story:
The inclusion of <curses.h> may make visible all symbols from the headers <stdio.h>, <term.h>, <termios.h>, and <wchar.h>.
Here is a more complete story:
If standard output from a ncurses program is re-directed to something which is not a tty, screen updates will be directed to standard error. This was an undocumented feature of AT&T System V Release 3 curses.
Zeyd M. Ben-Halim, Eric S. Raymond, Thomas E. Dickey. Based on pcurses by Pavel Curtis.