ncurses - CRT screen handling and optimization package
The ncurses library routines give the user a terminal-
independent method of updating character screens with rea-
sonable optimization. This implementation is "new curses"
(ncurses) and is the approved replacement for 4.4BSD clas-
sic curses, which has been discontinued. This describes
ncurses version 5.9 (patch 20150215).
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 direc-
tory) 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 ter-
minal input; control over terminal and curses input and
output options; environment query routines; color manipu-
lation; 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 initial-
ize 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 programs want this), the fol-
lowing 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 ter-
minal 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. tset(1) is usually responsible
for doing this. [See terminfo(5) for further details.]
The ncurses library permits manipulation of data struc-
tures, 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 win-
dows 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 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 dis-
played. See curs_pad(3x) for more information.
In addition to drawing characters on the screen, video
attributes and colors may be supported, causing the char-
acters 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 pro-
gram 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 defini-
tion 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 avail-
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 val-
ues 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 rou-
tines prefixed with w require a window argument. The rou-
tines prefixed with p require a pad argument. Those with-
out 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 WIN-
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 WIN-
DOW, 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
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 an integer.
Each cell (row and column) in a WINDOW is
stored as a chtype.
the so-called "wide" library, which handles
multibyte characters (see the section 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 charac-
corresponds to chtype. However it is a
structure, because more data is stored
than can fit into an integer. The char-
acters 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 sepa-
rate 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 size.
The "wide" library provides new functions
which are analogous to functions in the "nor-
mal" library. There is a naming convention
which relates many of the normal/wide vari-
ants: a "_w" is inserted into the name. For
example, waddch becomes wadd_wch.
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.
curses Routine Name Manual Page Name
Routines that return an integer return ERR upon failure
and an integer value other than ERR upon successful com-
pletion, unless otherwise noted in the routine descrip-
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).
Routines that return pointers return NULL on error.
The following environment symbols are useful for customiz-
ing the runtime behavior of the ncurses library. The most
important ones have been already discussed in detail.
CC 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 ter-
minfo entries provide this feature.
Because this name is also used in development envi-
ronments to represent the C compiler's name, ncurses
ignores it if it does not happen to be a single char-
The debugging library checks this environment vari-
able 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
Specify the width of the screen in characters.
Applications running in a windowing environment usu-
ally 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
Use the use_env function to disable all use of exter-
nal environment (but not including system calls) to
determine the screen size. Use the use_tioctl func-
tion to update COLUMNS or LINES to match the screen
size obtained from system calls or the terminal data-
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 vari-
able 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 char-
acter 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 imple-
mentation 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 applica-
HOME Tells ncurses where your home directory is. That is
where it may read and write auxiliary terminal
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 termi-
nal's default colors are white-on-black (see
default_colors(3x)). You may set the foreground and
background color values with this environment vari-
able 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 posi-
tive value from zero to the terminfo max_colors value
This applies only to the MinGW port of ncurses.
The Console2 program's handling of the Microsoft Con-
sole 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 environ-
ment variable NCGDB has the same effect.
This applies only to ncurses configured to use the
If present, the environment variable is a list of one
or more terminal names against which the TERM envi-
ronment 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 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 termi-
nals 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 applica-
tions. 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., tim-
ing. Unless a hardware terminal is interfaced into a
terminal concentrator (which does flow control), it
(or your application) must manage dataflow, prevent-
ing 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
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
This setting is obsolete. Before changes
o started with 5.9 patch 20120825 and
o continued though 5.9 patch 20130126
ncurses enabled buffered output during terminal ini-
tialization. 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 vari-
able 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 out-
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
During initialization, the ncurses library checks for
special cases where VT100 line-drawing (and the cor-
responding 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 termi-
When setting this variable, you should set it to a
nonzero value. Setting it to zero (or to a nonnum-
ber) disables the special check for "linux" and
As an alternative to the environment variable,
ncurses checks for an extended terminfo capability
U8. This is a numeric capability which can be com-
piled 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,
# 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 per-
mit it to be used by applications that use ncurses'
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.
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 def-
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 termi-
nal. 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.
If the ncurses library has been configured with term-
cap 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.
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:
o the last directory to which ncurses wrote, if
any, is searched first
o the directory specified by the TERMINFO environ-
o directories listed in the TERMINFO_DIRS environ-
o one or more directories whose names are config-
ured and compiled into the ncurses library, i.e.,
minfo:/usr/share/terminfo (corresponding to
the TERMINFO_DIRS variable)
o /usr/share/terminfo (corresponding to the
Specifies a list of directories to search for termi-
nal 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. Normally these are stored in a directory tree,
using subdirectories named by the first letter of the
terminal names therein.
If ncurses is built with a hashed database, then each
entry in this list can also be the path of the corre-
sponding database file.
If ncurses is built with a support for reading term-
cap files directly, then an entry in this list may be
the path of a termcap file.
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
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
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 SYN-
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,
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.,
you link with
You must also define _XOPEN_SOURCE_EXTENDED when com-
piling 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 struc-
ture 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 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.
The shared and normal (static) library names differ
by their suffixes, e.g., libncurses.so and libn-
curses.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 assum-
ing it is always in the debug library.
directory containing initialization files for the
terminal capability database /usr/share/terminfo ter-
minal 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/term-
cap 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) man-
ual pages for details.
The ncurses library can exploit the capabilities of termi-
nals which implement the ISO-6429 SGR 39 and SGR 49 con-
trols, 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 col-
ored text on a background whose color is set indepen-
dently, 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 confor-
mant with XSI Curses. The EXTENDED XSI Curses functional-
ity (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
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 applica-
tion which of several possible errors were detected.
Relying on this (or some other) extension will adversely
affect the portability of curses applications.
This implementation also contains several extensions:
o The routine has_key is not part of XPG4, nor is it
present in SVr4. See the curs_getch(3x) manual page
o The routine slk_attr is not part of XPG4, nor is it
present in SVr4. See the curs_slk(3x) manual page for
o The routines getmouse, mousemask, ungetmouse, mousein-
terval, and wenclose relating to mouse interfacing are
not part of XPG4, nor are they present in SVr4. See
the curs_mouse(3x) manual page for details.
o The routine mcprint was not present in any previous
curses implementation. See the curs_print(3x) manual
page for details.
o The routine wresize is not part of XPG4, nor is it
present in SVr4. See the wresize(3x) manual page for
o The WINDOW structure's internal details can be hidden
from application programs. See curs_opaque(3x) for
the discussion of is_scrollok, etc.
o This implementation can be configured to provide rudi-
mentary support for multi-threaded applications. See
curs_threads(3x) for details.
o This implementation can also be configured to provide
a set of functions which improve the ability to manage
multiple screens. See curs_sp_funcs(3x) for details.
In historic curses versions, delays embedded in the capa-
bilities cr, ind, cub1, ff and tab activated corresponding
delay bits in the UNIX tty driver. In this implementa-
tion, all padding is done by sending NUL bytes. This
method is slightly more expensive, but narrows the inter-
face 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>.
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 fea-
ture of AT&T System V Release 3 curses.
Zeyd M. Ben-Halim, Eric S. Raymond, Thomas E. Dickey.
Based on pcurses by Pavel Curtis.