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 5.5 (patch 20060715).
The ncurses routines emulate the curses(3X) library of System V Release
4 UNIX, and the XPG4 curses standard (XSI curses) but the ncurses
library is freely redistributable in source form. Differences from the
SVr4 curses are summarized under the EXTENSIONS and PORTABILITY sec-
tions below and described in detail in the respective EXTENSIONS,
PORTABILITY and BUGS sections of individual man pages.
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
The ncurses package supports: overall screen, window and pad manipula-
tion; output to windows and pads; reading terminal input; control over
terminal and curses input and output options; environment query rou-
tines; color manipulation; use of soft label keys; terminfo capabili-
ties; and access to low-level terminal-manipulation routines.
To initialize the routines, the routine initscr or newterm must be
called 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 programs want this), the following sequence should be
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 initialization strings, if defined, must be output. This
can be done by executing the tput init command after the shell environ-
ment variable TERM has been exported. tset(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 charac-
ters 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. Mix-
ing 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 which 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 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
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 informa-
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 val-
ues. The video attributes, line drawing characters, and input values
use names, defined in <curses.h>, such as A_REVERSE, ACS_HLINE, and
If the environment variables LINES and COLUMNS are set, or if the pro-
gram is executing in a window environment, line and column information
in the environment will override information read by terminfo. This
would effect 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 com-
piled 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 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 rou-
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 coor-
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. The variables ch and attrs below
are always of type chtype. The types WINDOW, SCREEN, bool, and chtype
are defined in <curses.h>. The type TERMINAL is defined in <term.h>.
All other arguments are integers.
Routine Name Index
The following table lists each curses routine and the name of the man-
ual page on which it is described. Routines flagged with '*' are
ncurses-specific, not described by XPG4 or present in SVr4.
curses Routine Name Manual Page Name
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, 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
Routines that return pointers return NULL on error.
The following environment symbols are useful for customizing the run-
time 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 redirected 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.
Specify the width of the screen in characters. Applications run-
ning 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 sys-
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 emula-
Use the use_env function to disable all use of external environ-
ment (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 pro-
vides 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:
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 inconsis-
tently 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 assume_default_colors(3X)). You
may set the foreground and background color values with this envi-
ronment variable by proving a 2-element list: foreground,back-
ground. 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 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 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 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 initial-
ization. This is done (as in SVr4 curses) for performance rea-
sons. For testing purposes, both of ncurses and certain applica-
tions, this feature is made optional. Setting the NCURSES_NO_SET-
BUF variable disables output buffering, leaving the output in the
original (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 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.
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 argu-
The argument values, which are defined in curses.h, provide sev-
eral types of information. 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 database.
The TERMCAP symbol contains either a terminal description (with
newlines stripped out), or a file name telling where the informa-
tion denoted by the TERM symbol exists. In either case, setting
it directs ncurses to ignore the usual place for this information,
Overrides the directory in which ncurses searches for your termi-
nal 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
- 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 descrip-
tions. The list is separated by colons (i.e., ":") on Unix, semi-
colons on OS/2 EMX. All of the terminal descriptions are in ter-
minfo 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/term-
cap, /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 config-
ure script options used when building ncurses. There are a few main
options whose effects are visible to the applications developer using
The standard include for ncurses is as noted in SYNOPSIS:
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 subdi-
It also omits a symbolic link which would allow you to use
-lcurses to build executables.
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) func-
tions. The curses.h file which is installed for the wide-charac-
ter 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.
The shared and normal (static) library names differ by their suf-
fixes, 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.
The trace function normally resides in the debug library, but it
is sometimes useful to configure this in the shared library. Con-
figure 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 capa-
bility database /usr/share/terminfo terminal capability database
terminfo(5) and related pages whose names begin "curs_" for detailed
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 term-
cap 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
The ncurses library includes facilities for responding to window resiz-
ing 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 back-
ground 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_col-
ors(3X) manual page for details.
The ncurses library includes a function for directing application out-
put 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 the
XSI Curses standard. 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.
The routine has_key is not part of XPG4, nor is it present in SVr4.
See the curs_getch(3X) manual page for details.
The routine slk_attr is not part of XPG4, nor is it present in SVr4.
See the curs_slk(3X) manual page for details.
The routines getmouse, mousemask, ungetmouse, mouseinterval, and wen-
close relating to mouse interfacing are not part of XPG4, nor are they
present in SVr4. See the curs_mouse(3X) manual page for details.
The routine mcprint was not present in any previous curses
implementation. See the curs_print(3X) manual page for details.
The routine wresize is not part of XPG4, nor is it present in SVr4.
See the wresize(3X) manual page for details.
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 NUL sends.
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 <unctrl.h>.
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.