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.
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 BUGS sections
below and described in detail in the EXTENSIONS 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.
The ncurses package supports: overall screen, window and pad manipulation; output to windows 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 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 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 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 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. 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 else-
where 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 charac-
ters 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 constrained to the size of the screen and whose con-
tents need not be completely displayed. See curs_pad(3X) for more information.
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 program 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 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 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.
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
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 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 completion, unless otherwise
noted in the routine descriptions.
All macros return the value of the w version, except setscrreg, wsetscrreg, getyx, getbegyx, 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 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 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 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. However, this is not always possible because your applica-
tion may be running on a host which does not honor NAWS (Negotiations About Window Size), or because you are temporarily running as
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 this feature.
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.
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 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.
Most of the terminal descriptions in the terminfo database are written for real "hardware" terminals. Many people use terminal emula-
tors 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 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 original (usually line buffered) mode.
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 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 information
denoted by the TERM symbol exists. In either case, setting it directs ncurses to ignore the usual place for this information, e.g.,
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 ter-
minal 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: $TERMINFO, $TERMINFO_DIRS, $TERMPATH, as well as $HOME.
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 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 addi-
tional key sequences at runtime. See the define_key(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 background 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 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 conformant with the XSI Curses standard. Certain portions of the EXTENDED XSI Curses
functionality (including color support) are supported. The following EXTENDED XSI Curses calls in support of wide (multibyte) characters
are not yet implemented: add_wchnstr, add_wchstr, addnwstr, addwstr, bkgrnd, bkgrndset, border_set, box_set, erasewchar, get_wch, get_wstr,
getbkgrnd, getn_wstr, getwchtype, hline_set, in_wch, in_wchnstr, in_wchstr, innwstr, ins_nwstr, ins_wch, ins_wstr, inwchnstr, inwchstr,
inwstr, key_name, killwchar, mvadd_wchnstr, mvadd_wchstr, mvaddnwstr, mvaddwstr, mvget_wch, mvget_wstr, mvgetn_wstr, mvhline_set, mvin_wch,
mvinnwstr, mvins_nwstr, mvins_wch, mvins_wstr, mvinwchnstr, mvinwchstr, mvinwchstr, mvinwstr, mvvline_set, mvwadd_wchnstr, mvwadd_wchstr,
mvwaddnwstr, mvwaddwstr, mvwget_ch, mvwget_wch, mvwget_wstr, mvwgetn_wstr, mvwhline_set, mvwin_wch, mvwin_wchnstr, mvwin_wchstr, mvwinnw-
str, mvwins_nwstr, mvwins_wch, mvwins_wstr, mvwinwchnstr. mvwinwstr, mvwvline_set, pecho_wchar, slk_wset, term_attrs, unget_wch,
vhline_set, vid_attr, vid_puts, vline_set, wadd_wchnstr, wadd_wchstr, waddnwstr, waddwstr, waddwstr, wbkgrnd, wbkgrndset, wbkgrndset, wbor-
der_set, wget_wch, wget_wstr, wgetbkgrnd, wgetn_wstr, whline_set, win_wch, win_wchnstr, win_wchstr, winnwstr, wins_nwstr, wins_wch,
wins_wstr, winwchnstr, winwchstr, winwstr, wunctrl, wvline_set,
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 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.
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 correspondingly.
In the XSI standard and SVr4 manual pages, many entry points have prototype arguments of the for char *const (or cchar_t *const, or wchar_t
*const, or void *const). Depending on one's interpretation of the ANSI C standard (see section 22.214.171.124), these declarations are either (a)
meaningless, or (b) meaningless and illegal. The declaration const char *x is a modifiable pointer to unmodifiable data, but char *const
x' is an unmodifiable pointer to modifiable data. Given that C passes arguments by value, <type> *const as a formal type is at best dubi-
ous. Some compilers choke on the prototypes. Therefore, in this implementation, they have been changed to const <type> * globally.
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.