Initialization

The library uses the locale which the calling program has initialized. That is normally done with setlocale(3):

setlocale(LC_ALL, "");

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(3NCURSES) 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 tput init command after the shell environment variable TERM has been exported. (The BSD-style tset(1) utility also performs this function.) See subsection “Tabs and Initialization” of terminfo(5).

Overview

A curses library abstracts the terminal screen by representing all or part of it as a WINDOW data structure. A window is a rectangular grid of character cells, addressed by row and column coordinates (y, x), with the upper left corner as (0, 0). A window called stdscr, the same size as the terminal screen, is always available. Create others with newwin(3NCURSES).

A curses library does not manage overlapping windows. (See panel(3NCURSES) if you desire this.) You can either use stdscr to manage one screen-filling window, or tile the screen into non-overlapping windows and not use stdscr at all. Mixing the two approaches will result in unpredictable, and undesired, effects.

Functions permit manipulation of a window and the cursor identifying the cell within it at which the next output operation will occur. Among those, the most basic are move(3NCURSES) and addch(3NCURSES): these place the cursor and write a character to stdscr, respectively. As a rule, window-addressing functions feature names prefixed (or infixed, see below) with “w”; these allow the user to specify a pointer to a WINDOW. Counterparts not thus prefixed (or infixed) affect stdscr. Because moving the cursor prior to another operation is so common, curses generally also provides functions with a “mv” prefix as a convenience. Thus, the library defines all of addch, waddch, mvaddch, and mvwaddch. When both prefixes are present, the order of arguments is a WINDOW pointer first, then a y and x coordinate pair.

Updating the terminal screen with every curses call can cause unpleasant flicker or inefficient use of the communications channel to the device. Therefore, after using curses functions to accumulate a set of desired updates that make sense to present together, call refresh(3NCURSES) to tell the library to make the user's screen look like stdscr. ncurses optimizes its output by computing a minimal number of operations to mutate the screen from its state at the previous refresh to the new one. Effective optimization demands accurate information about the terminal device: the management of such information is the province of the terminfo(3NCURSES) API, a feature of every standard curses implementation.

Special windows called pads may also be manipulated. These are windows that are not constrained to the size of the terminal screen and whose contents need not be completely displayed. See pad(3NCURSES).

In addition to drawing characters on the screen, rendering 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. See attr(3NCURSES).

curses predefines constants for a small set of line-drawing and other graphics corresponding to the DEC Alternate Character Set (ACS), a feature of VT100 and other terminals. See waddch(3NCURSES) and wadd_wch(3NCURSES).

curses is implemented using the operating system's terminal driver; keystroke events are received not as scan codes but as byte sequences. Graphical keycaps (alphanumeric and punctuation keys, and the space) appear as-is. Everything else, including the tab, enter/return, keypad, arrow, and function keys, appears as a control character or a multibyte escape sequence. curses translates these into unique key codes. See getch(3NCURSES).

Effects of GUIs and Environment Variables

The selection of an appropriate value of TERM in the process environment is essential to correct curses and terminfo library operation. A well-configured system selects a correct TERM value automatically; tset(1) may assist with troubleshooting exotic situations.

If the environment variables LINES and COLUMNS are set, or if the curses program is executing in a graphical windowing environment, the information obtained thence overrides that obtained by terminfo. An ncurses extension supports resizable terminals; see wresize(3NCURSES).

If the environment variable TERMINFO is defined, a curses program checks first for a terminal type description in the location it identifies. TERMINFO is useful for developing experimental type descriptions or when write permission to /etc/terminfo is not available.

See section “ENVIRONMENT” below.

Naming Conventions

Many curses functions have two or more versions. Those prefixed with “w” require a window argument. Four functions prefixed with “p” require a pad argument. Those without a prefix generally operate on stdscr.

In function synopses, ncurses man pages apply the following names to parameters.

Wide and Non-wide Character Configurations

This manual page describes functions that appear in any configuration of the library. There are two common configurations; see section “ALTERNATE CONFIGURATIONS” below.

ncurses

is the library in its “non-wide” configuration, handling only eight-bit characters. It stores a character combined with attributes in a chtype datum, which is often an alias of int.

Attributes alone (with no corresponding character) can be stored in variables of chtype or attr_t type. In either case, they are represented as an integral bit mask.

Each cell of a WINDOW is stored as a chtype.

ncursesw

is the library in its “wide” configuration, which handles character encodings requiring a larger data type than char (a byte-sized type) can represent. It adds about one third more calls using additional data types that can store such multibyte characters.

The wide library provides additional functions that complement those in the non-wide library where the size of the underlying character type is significant. A somewhat regular naming convention relates many of the wide variants to their non-wide counterparts; where a non-wide function name contains “ch” or “str”, prefix it with “_w” to obtain the wide counterpart. For example, waddch becomes wadd_wch.

This convention is inapplicable to some non-wide function names, so other transformations are used for the wide configuration: in the window background management functions, “bkgd” becomes “bkgrnd”; the window border-drawing and -clearing functions are suffixed with “_set”.

Function Name Index

The following table lists the curses functions provided in the non-wide and wide APIs and the corresponding man pages that describe them. Those flagged with “*” are ncurses-specific, neither described by X/Open Curses nor present in SVr4.

Depending on the configuration, additional sets of functions may be available:

CC (command character)

When set, change the command_character (cmdch) capability value of 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.

BAUDRATE

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.

COLUMNS

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.

ESCDELAY

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.

HOME

Tells ncurses where your home directory is. That is where it may read and write auxiliary terminal descriptions:

$HOME/.termcap
$HOME/.terminfo

LINES

Like COLUMNS, specify the height of the screen in characters. See COLUMNS for a detailed description.

MOUSE_BUTTONS_123

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.

NCURSES_ASSUMED_COLORS

Override the compiled-in assumption that the terminal's default colors are white-on-black (see default_colors(3NCURSES)). 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.

NCURSES_CONSOLE2

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.

NCURSES_GPM_TERMS

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_NO_HARD_TABS

ncurses may use tabs as part of cursor movement optimization. In some cases, your terminal driver may not handle these properly. Set this environment variable to any value to disable the feature. You can also adjust your stty(1) settings to avoid the problem.

NCURSES_NO_MAGIC_COOKIE

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 to any value.

NCURSES_NO_PADDING

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.

NCURSES_NO_SETBUF

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(3) 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.

NCURSES_NO_UTF8_ACS

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 tic -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,
        U8#1, use=xterm,

The name “U8” is chosen to be two characters, to permit it to be used by applications that use ncurses' termcap interface.

NCURSES_TRACE

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 trace(3NCURSES) for more information.

TERM

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.

TERMCAP

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.

TERMINFO

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:

•

Normally these are stored in a directory tree, using subdirectories named by the first letter of the terminal names therein.

This is the scheme used in System V, which legacy Unix systems use, and the TERMINFO variable is used by curses applications on those systems to override the default location of the terminal database.

•

If ncurses is built to use hashed databases, then each entry in this list may be the path of a hashed database file, e.g.,

/usr/share/terminfo.db

/usr/share/terminfo/

• If ncurses is built with a support for reading termcap files directly, then an entry in this list may be the path of a termcap file.
• If the TERMINFO variable begins with “hex:” or “b64:”, ncurses uses the remainder of that variable as a compiled terminal description. You might produce the base64 format using infocmp(1):

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:

TERMINFO_DIRS

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.

TERMPATH

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.

Error Checking

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.

Padding Differences

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.

Header Files

The header file curses.h itself includes the header files stdio.h and unctrl.h.

X/Open Curses has more to say, but does not finish the story:

Here is a more complete story:

•

Starting with BSD curses, all implementations have included <stdio.h>.

BSD curses included <curses.h> and <unctrl.h> from an internal header file curses.ext (“ext” abbreviated “externs”).

BSD curses used <stdio.h> internally (for printw and scanw), but nothing in <curses.h> itself relied upon <stdio.h>.

•

SVr2 curses added newterm(3NCURSES), which relies upon <stdio.h>. That is, the function prototype uses FILE.

SVr4 curses added putwin and getwin, which also use <stdio.h>.

X/Open Curses documents all three of these functions.

SVr4 curses and X/Open Curses do not require the developer to include <stdio.h> before including <curses.h>. Both document curses showing <curses.h> as the only required header.

As a result, standard <curses.h> will always include <stdio.h>.

•

X/Open Curses is inconsistent with respect to SVr4 regarding <unctrl.h>.

As noted in util(3NCURSES), ncurses includes <unctrl.h> from <curses.h> (like SVr4).

•

X/Open's comments about <term.h> and <termios.h> may refer to HP-UX and AIX:

HP-UX curses includes <term.h> from <curses.h> to declare setupterm in curses.h, but ncurses (and Solaris curses) do not.

AIX curses includes <term.h> and <termios.h>. Again, ncurses (and Solaris curses) do not.

•

X/Open says that <curses.h> may include <term.h>, but there is no requirement that it do that.

Some programs use functions declared in both <curses.h> and <term.h>, and must include both headers in the same module. Very old versions of AIX curses required including <curses.h> before including <term.h>.

Because ncurses header files include the headers needed to define datatypes used in the headers, ncurses header files can be included in any order. But for portability, you should include <curses.h> before <term.h>.

•

X/Open Curses says "may make visible" because including a header file does not necessarily make all symbols in it visible (there are ifdef's to consider).

For instance, in ncurses <wchar.h> may be included if the proper symbol is defined, and if ncurses is configured for wide-character support. If the header is included, its symbols may be made visible. That depends on the value used for _XOPEN_SOURCE feature test macro.

•

X/Open Curses documents one required header, in a special case: <stdarg.h> before <curses.h> to prototype the vw_printw and vw_scanw functions (as well as the obsolete the vwprintw and vwscanw functions). Each of those uses a va_list parameter.

The two obsolete functions were introduced in SVr3. The other functions were introduced in X/Open Curses. In between, SVr4 curses provided for the possibility that an application might include either <varargs.h> or <stdarg.h>. Initially, that was done by using void* for the va_list parameter. Later, a special type (defined in <stdio.h>) was introduced, to allow for compiler type-checking. That special type is always available, because <stdio.h> is always included by <curses.h>.

None of the X/Open Curses implementations require an application to include <stdarg.h> before <curses.h> because they either have allowed for a special type, or (like ncurses) include <stdarg.h> directly to provide a portable interface.