ncurses(3X) manual page
Table of Contents
ncurses - CRT screen handling and optimization
package
#include <curses.h>
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 5.9 (patch 20110404).
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 directory) 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 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:
setlocale(LC_ALL, "");
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 programs want this), the following sequence should be used:
initscr(); cbreak(); noecho();
Most programs would additionally use the sequence:
nonl();
intrflush(stdscr, FALSE);
keypad(stdscr, TRUE);
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() for further details.]
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 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 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 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 contents 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 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 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
/a/att4424.
(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
$HOME/myterms/a/att4424,
and if that fails, it then checks
/a/att4424.
This is useful for developing experimental definitions or when write permission
in 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.
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:
- ncurses
- 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 an integer.
- Each
cell (row and column) in a WINDOW is stored as a chtype.
- ncursesw
- 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 characters:
- cchar_t
- 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.
- wchar_t
- stores a "wide" character. Like
chtype, this may be an integer.
- wint_t
- 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 "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 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.
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 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.
- BAUDRATE
- 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.
- Because this
name is also used in development environments to represent
- the C compiler’s
name, ncurses ignores it if it does not happen to be a single character.
- COLUMNS
- Specify the width of the screen in characters. Applications running
in a windowing environment usually are able to obtain the width of the
window in which they are executing. If neither the COLUMNS value nor the
terminal’s screen size is available, ncurses uses the size which may be
specified in the terminfo database (i.e., the cols capability).
- It is important
that your application use a correct size for the screen.
- This is not always
possible because your application may be running on a host which does not
honor NAWS (Negotiations About Window Size), or because you are temporarily
running as another user. However, setting COLUMNS and/or LINES overrides
the library’s use of the screen size obtained from the operating system.
- Either COLUMNS or LINES symbols may be specified independently.
- This is
mainly useful to circumvent legacy misfeatures of terminal descriptions,
e.g., xterm which commonly specifies a 65 line screen. For best results, lines
and cols should not be specified in a terminal description for terminals
which are run as emulations.
- Use the use_env function to disable all use
of external environment
- (including system calls) to determine the screen
size.
- ESCDELAY
- Specifies the total time, in milliseconds, for which ncurses
will await a character sequence, e.g., a function key. The default value,
1000 milliseconds, is enough for most uses. However, it is made a variable
to accommodate unusual applications.
- The most common instance where you
may wish to change this value
- is to work with slow hosts, e.g., running on
a network. If the host cannot read characters rapidly enough, it will have
the same effect as if the terminal did not send characters rapidly enough.
The library will still see a timeout.
- Note that xterm mouse events are built
up from character sequences
- received from the xterm. If your application
makes heavy use of multiple-clicking, you may wish to lengthen this default
value because the timeout applies to the composed multi-click event as well
as the individual clicks.
- In addition to the environment variable,
- this
implementation provides a global variable with the same name. Portable applications
should not rely upon the presence of ESCDELAY in either form, but setting
the environment variable rather than the global variable does not create
problems when compiling an application.
- HOME
- Tells ncurses where your home
directory is. That is where it may read and write auxiliary terminal descriptions:
- $HOME/.termcap
$HOME/.terminfo - LINES
- Like COLUMNS, specify the height of the screen in
characters. See COLUMNS for a detailed description.
- MOUSE_BUTTONS_123
- This
applies only to the OS/2 EMX port. It specifies the order of buttons on
the mouse. OS/2 numbers a 3-button mouse inconsistently from other platforms:
1 = left
2 = right
3 = middle.
This 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.
- NCURSES_ASSUMED_COLORS
- Override the compiled-in assumption
that the terminal’s default colors are white-on-black (see default_colors(3X)
).
You may set the foreground and background color values with this environment
variable by proving a 2-element list: foreground,background. For example,
to tell ncurses to not assume anything about the colors, set this to "-1,-1".
To make it green-on-black, set it to "2,0". Any positive value from zero to
the terminfo max_colors value is allowed.
- NCURSES_GPM_TERMS
- This applies
only to ncurses configured to use the GPM interface.
- If present,
- the environment
variable is a list of one or more terminal names against which the TERM
environment variable is matched. Setting it to an empty value disables the
GPM interface; using the built-in support for xterm, etc.
- If the environment
variable is absent,
- ncurses will attempt to open GPM if TERM contains "linux".
- NCURSES_NO_HARD_TABS
- Ncurses may use tabs as part of the cursor movement
optimization. In some cases, your terminal driver may not handle these properly.
Set this environment variable to disable the feature. You can also adjust
your stty settings to avoid the problem.
- NCURSES_NO_MAGIC_COOKIES
- Some terminals
use a magic-cookie feature which requires special handling to make highlighting
and other video attributes display properly. You can suppress the highlighting
entirely for these terminals by setting this environment variable.
- NCURSES_NO_PADDING
- Most of the terminal descriptions in the terminfo database are written
for real "hardware" terminals. Many people use terminal emulators which
run in a windowing environment and use curses-based applications. Terminal
emulators can duplicate all of the important aspects of a hardware terminal,
but they do not have the same limitations. The chief limitation of a hardware
terminal from the standpoint of your application is the management of dataflow,
i.e., timing. Unless a hardware terminal is interfaced into a terminal concentrator
(which does flow control), it (or your application) must manage dataflow,
preventing overruns. The cheapest solution (no hardware cost) is for your
program to do this by pausing after operations that the terminal does slowly,
such as clearing the display.
- As a result, many terminal descriptions (including
the vt100)
- have delay times embedded. You may wish to use these descriptions,
but not want to pay the performance penalty.
- Set the NCURSES_NO_PADDING
symbol to disable all but mandatory
- padding. Mandatory padding is used as
a part of special control sequences such as flash.
- NCURSES_NO_SETBUF
- 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.
- NCURSES_NO_UTF8_ACS
- During initialization, the ncurses library checks for special cases where
VT100 line-drawing (and the corresponding alternate character set capabilities)
described in the terminfo are known to be missing. Specifically, when running
in a UTF-8 locale, the Linux console emulator and the GNU screen program
ignore these. Ncurses checks the TERM environment variable for these. For
other special cases, you should set this environment variable. Doing this
tells ncurses to use Unicode values which correspond to the VT100 line-drawing
glyphs. That works for the special cases cited, and is likely to work for
terminal emulators.
- When setting this variable, you should set it to a nonzero
value.
- Setting it to zero (or to a nonnumber) disables the special check
for "linux" and "screen".
- As an alternative to the environment variable,
- ncurses checks for an extended terminfo capability U8. This is a numeric
capability which can be compiled using tic -x. For example
# linux console, if patched to provide working
# VT100 shift-in/shift-out, with corresponding font.
linux-vt100|linux console with VT100 line-graphics,
U8#0, use=linux,
# uxterm with vt100Graphics resource set to false
xterm-utf8|xterm relying on UTF-8 line-graphics,
U8#1, use=xterm,
- The name "U8" is chosen to be two characters,
- to permit it to be used by
applications that use ncurses’ termcap interface.
- NCURSES_TRACE
- During initialization,
the ncurses debugging library checks the NCURSES_TRACE 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.
- TERMCAP
- If the ncurses library has been configured with termcap
support, ncurses will check for a terminal’s description in termcap form
if it is not available in the terminfo database.
- The TERMCAP 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., /etc/termcap.
- TERMINFO
- 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
- $HOME/.terminfo
-
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
- TERMINFO_DIRS
- 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.
- TERMPATH
- 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.
Several different configurations
are possible, depending on the configure script options used when building
ncurses. There are a few main options whose effects are visible to the applications
developer using ncurses:
- --disable-overwrite
- The standard include for ncurses
is as noted in SYNOPSIS:
#include <curses.h>
- This option is used to avoid
filename conflicts when ncurses
- is not the main implementation of curses
of the computer. If ncurses is installed disabling overwrite, it puts its
headers in a subdirectory, e.g.,
#include <ncurses/curses.h>
- It also omits a
symbolic link which would allow you to use -lcurses
- to build executables.
- --enable-widec
- The configure script renames the library and (if the --disable-overwrite
option is used) puts the header files in a different subdirectory. All of
the library names have a "w" appended to them, i.e., instead of
-lncurses
- you link with
-lncursesw
- You must also 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 applications require more
than a pointer to WINDOWs. If the headers are installed allowing overwrite,
the wide-character library’s headers should be installed last, to allow applications
to be built using either library from the same set of headers.
- --with-shared
- --with-normal
- --with-debug
- --with-profile
- The shared and normal (static) library
names differ by their suffixes, e.g., libncurses.so and libncurses.a. The debug
and profiling libraries add a "_g" and a "_p" to the root names respectively,
e.g., libncurses_g.a and libncurses_p.a.
- --with-trace
- The trace function normally
resides in the debug library, but it is sometimes useful to configure this
in the shared library. Configure scripts should check for the function’s
existence rather than assuming it is always in the debug library.
- /usr/share/tabset
- directory containing initialization files for the terminal capability database
/usr/share/terminfo terminal capability database
terminfo() and
related pages whose names begin "curs_" for detailed routine descriptions.
curs_variables(3X)
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 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 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_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
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 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.
- The WINDOW structure’s internal details can be
hidden from application programs. See curs_opaque(3X)
for the discussion
of is_scrollok, etc.
- This implementation can be configured to provide rudimentary
support for multi-threaded applications. See curs_threads(3X)
for details.
- 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 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 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 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.
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