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RETURN VALUE

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.

ENVIRONMENT

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.

CC command-character
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.

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 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 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.

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 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 curs_trace(3X) 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 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:

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.

/usr/share/terminfo.db

rather than

/usr/share/terminfo/

The hashed database uses less disk-space and is a little faster than the directory tree. However, some applications assume the existence of the directory tree, reading it directly rather than using the terminfo library calls.

TERMINFO="$(infocmp -0 -Q2 -q)"
export TERMINFO

The compiled description is used if it corresponds to the terminal identified by the TERM variable.

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.

ALTERNATE CONFIGURATIONS

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:
--disable-overwrite

The standard include for ncurses is as noted in SYNOPSIS:

#include <curses.h>

This option is used to avoid filename conflicts when ncurses is not the main implementation of curses of the computer. If ncurses is installed disabling overwrite, it puts its headers in a subdirectory, e.g.,

#include <ncurses/curses.h>

It also omits a symbolic link which would allow you to use -lcurses to build executables.

--enable-widec

The configure script renames the library and (if the --disable-overwrite option is used) puts the header files in a different subdirectory. All of the library names have a “w” appended to them, i.e., instead of

-lncurses

you link with

-lncursesw

You must also enable the wide-character features in the header file when compiling for the wide-character library to use the extended (wide-character) functions. The symbol which enables these features has changed since XSI Curses, Issue 4:

The curses.h file which is installed for the wide-character library is designed to be compatible with the normal library’s header. Only the size of the WINDOW structure differs, and very few applications require more than a pointer to WINDOWs.

If the headers are installed allowing overwrite, the wide-character library’s headers should be installed last, to allow applications to be built using either library from the same set of headers.

--with-pthread

The configure script renames the library. All of the library names have a “t” appended to them (before any “w” added by --enable-widec).

The global variables such as LINES are replaced by macros to allow read-only access. At the same time, setter-functions are provided to set these values. Some applications (very few) may require changes to work with this convention.

--with-shared
--with-normal
--with-debug
--with-profile

The shared and normal (static) library names differ by their suffixes, e.g., libncurses.so and libncurses.a. The debug and profiling libraries add a “_g” and a “_p” to the root names respectively, e.g., libncurses_g.a and libncurses_p.a.

--with-trace

The trace function normally resides in the debug library, but it is sometimes useful to configure this in the shared library. Configure scripts should check for the function’s existence rather than assuming it is always in the debug library.

FILES

/usr/share/tabset

directory containing initialization files for the terminal capability database /etc/terminfo terminal capability database

SEE ALSO

terminfo(5) and related pages whose names begin “curs_” for detailed routine descriptions.
curses_variables(3NCURSES)
user_caps(5) for user-defined capabilities