ncurses - CRT screen handling and optimization package
The ncurses library routines give the user a terminal-independent method of updating char-
acter screens with reasonable optimization. This implementation is ``new curses''
(ncurses) and is the approved replacement for 4.4BSD classic curses, which has been dis-
continued. This describes ncurses version 5.7 (patch 20100109).
The ncurses library emulates the ncurses(3NCURSES) 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 PORTABIL-
ITY 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
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 win-
dows 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:
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 must be
called before exiting.
To get character-at-a-time input without echoing (most interactive, screen oriented pro-
grams want this), the following sequence should be used:
initscr(); cbreak(); noecho();
Most programs would additionally use the sequence:
Before a curses program is run, the tab stops of the terminal should be set and its ini-
tialization 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. tset(1) is usu-
ally responsible for doing this. [See terminfo(5) for further details.]
Beware: the terminal your program is running may or may not have the features you expect.
Ncurses makes no attempt to check available features in advance. This is upto the program-
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 sup-
plied. Others may be created with newwin.
Note that curses does not handle overlapping windows, that's done by the panel(3CURSES)
library. This means that you can either use stdscr or divide the screen into tiled win-
dows and not using stdscr at all. Mixing the two will result in unpredictable, and unde-
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 rou-
tines 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 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 con-
strained to the size of the screen and whose contents need not be completely displayed.
See pad(3NCURSES) for more information.
In addition to drawing characters on the screen, video attributes and colors may be sup-
ported, 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 func-
tion 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 infor-
mation 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/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
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.
Routine and Argument Names
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 "normal" library, which handles 8-bit characters. The normal (8-bit)
library stores characters combined with attributes in chtype data.
Attributes alone (no corresponding character) may be stored in chtype or the
equivalent attr_t data. In either case, the data is stored in something like
Each cell (row and column) in a WINDOW is stored as a chtype.
the so-called "wide" library, which handles multibyte characters (See the sec-
tion on ALTERNATE CONFIGURATIONS). The "wide" library includes all of the
calls from the "normal" library. It adds about one third more calls using
data types which store multibyte characters:
corresponds to chtype. However it is a structure, because more data is
stored than can fit into an integer. The characters are large enough to
require a full integer value - and there may be more than one character
per cell. The video attributes and color are stored in separate fields
of the structure.
Each cell (row and column) in a WINDOW is stored as a cchar_t.
stores a "wide" character. Like chtype, this may be an integer.
stores a wchar_t or WEOF - not the same, though both may have the same
The "wide" library provides new functions which are analogous to functions in
the "normal" library. There is a naming convention which relates many of the
normal/wide variants: a "_w" is inserted into the name. For example, waddch
Routine Name Index
The following table lists each curses routine and the name of the manual page on which it
is described. Routines flagged with `*' are ncurses-specific, not described by XPG4 or
present in SVr4.
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.
All macros return the value of the w version, except setscrreg, wsetscrreg, getyx, getbe-
gyx, and getmaxyx. The return values of setscrreg, wsetscrreg, getyx, getbegyx, and get-
maxyx are undefined (i.e., these should not be used as the right-hand side of assignment
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.
The debugging library checks this environment symbol when the application has redi-
rected output to a file. The symbol'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.
CC When set, change occurrences of the command_character (i.e., the cmdch capability) of
the loaded terminfo entries to the value of this symbol. Very few terminfo entries
provide this feature.
Because this name is also used in development environments to represent the C com-
piler's name, ncurses ignores it if it does not happen to be a single character.
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 exe-
cuting. 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
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 use-
ful to circumvent legacy misfeatures of terminal descriptions, e.g., xterm which com-
monly 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 (including system
calls) to determine the screen size.
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 vari-
able 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 aux-
iliary terminal descriptions:
Like COLUMNS, specify the height of the screen in characters. See COLUMNS for a
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 symbol lets you customize the mouse. The symbol 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(3NCURSES)). You may set the foreground and background
color values with this environment variable by proving a 2-element list: fore-
ground,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 posi-
tive value from zero to the terminfo max_colors value is allowed.
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 dis-
ables 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 con-
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.
Some terminals use a magic-cookie feature which requires special handling to make
highlighting and other video attributes display properly. You can suppress the high-
lighting 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 limi-
tations. 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 embed-
ded. You may wish to use these descriptions, but not want to pay the performance
Set the NCURSES_NO_PADDING symbol to disable all but mandatory padding. Mandatory
padding is used as a part of special control sequences such as flash.
Normally ncurses enables buffered output during terminal initialization. This is
done (as in SVr4 curses) for performance reasons. For testing purposes, both of
ncurses and certain applications, this feature is made optional. Setting the
NCURSES_NO_SETBUF variable disables output buffering, leaving the output in the orig-
inal (usually line buffered) mode.
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 corre-
spond 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".
During initialization, the ncurses debugging library checks the NCURSES_TRACE symbol.
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 informa-
tion. When running with traces enabled, your application will write the file trace
to the current directory.
TERM Denotes your terminal type. Each terminal type is distinct, though many are similar.
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
The TERMCAP symbol contains either a terminal description (with newlines stripped
out), or a file name telling where the information denoted by the TERM symbol exists.
In either case, setting it directs ncurses to ignore the usual place for this infor-
mation, e.g., /etc/termcap.
Overrides the directory in which ncurses searches for your terminal description.
This is the simplest, but not the only way to change the list of directories. The
complete list of directories in order follows:
- the last directory to which ncurses wrote, if any, is searched first
- the directory specified by the TERMINFO symbol
- directories listed in the TERMINFO_DIRS symbol
- one or more directories whose names are configured and compiled into the ncurses
library, e.g., /usr/share/terminfo
Specifies a list of directories to search for terminal descriptions. The list is
separated by colons (i.e., ":") on Unix, semicolons on OS/2 EMX. All of the terminal
descriptions are in terminfo form, which makes a subdirectory named for the first
letter of the terminal names therein.
If TERMCAP does not hold a file name then ncurses checks the TERMPATH symbol. This
is a list of filenames separated by spaces or colons (i.e., ":") on Unix, semicolons
on OS/2 EMX. If the TERMPATH symbol 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: $TER-
MINFO, $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 standard include for ncurses is as noted in SYNOPSIS:
This option is used to avoid filename conflicts when ncurses is not the main imple-
mentation of curses of the computer. If ncurses is installed disabling overwrite, it
puts its headers in a subdirectory, e.g.,
It also omits a symbolic link which would allow you to use -lcurses to build executa-
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
you link with
You must also define _XOPEN_SOURCE_EXTENDED when compiling for the wide-character
library to use the extended (wide-character) functions. 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 appli-
cations require more than a pointer to WINDOWs. If the headers are installed allow-
ing 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.
The shared and normal (static) library names differ by their suffixes, e.g., libn-
curses.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.
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.
directory containing initialization files for the terminal capability database
/usr/share/terminfo terminal capability database
terminfo(5) and related pages whose names begin "curs_" for detailed routine descriptions.
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 corre-
sponding 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
The ncurses library includes facilities for capturing mouse events on certain terminals
(including xterm). See the mouse(3NCURSES) 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(3NCURSES) and wresize(3NCURSES) 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(3NCURSES) key_defined(3NCURSES), and keyok(3NCURSES) 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 origi-
nal 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 bet-
ter control over color contrasts. See the default_colors(3NCURSES) manual page for
The ncurses library includes a function for directing application output to a printer
attached to the terminal device. See the print(3NCURSES) 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.
This implementation also contains several extensions:
The routine has_key is not part of XPG4, nor is it present in SVr4. See the
getch(3NCURSES) manual page for details.
The routine slk_attr is not part of XPG4, nor is it present in SVr4. See the
slk(3NCURSES) manual page for details.
The routines getmouse, mousemask, ungetmouse, mouseinterval, and wenclose relating to
mouse interfacing are not part of XPG4, nor are they present in SVr4. See the
mouse(3NCURSES) manual page for details.
The routine mcprint was not present in any previous curses implementation. See the
print(3NCURSES) manual page for details.
The routine wresize is not part of XPG4, nor is it present in SVr4. See the wre-
size(3NCURSES) manual page for details.
The WINDOW structure's internal details can be hidden from application programs. See
opaque(3NCURSES) for the discussion of is_scrollok, etc.
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
The header file <curses.h> automatically includes the header files <stdio.h> and <unc-
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.