CURSES(3XCURSES) X/Open Curses Library Functions CURSES(3XCURSES)


curses - introduction and overview of X/Open Curses


The Curses screen management package conforms fully with Issue 4, Version
2 of the X/Open Curses specification. It provides a set of
internationalized functions and macros for creating and modifying input
and output to a terminal screen. This includes functions for creating
windows, highlighting text, writing to the screen, reading from user
input, and moving the cursor.

X/Open Curses is a terminal-independent package, providing a common user
interface to a variety of terminal types. Its portability is
facilitated by the Terminfo database which contains a compiled
definition of each terminal type. By referring to the database
information X/Open Curses gains access to low-level details about
individual terminals.

X/Open Curses tailors its activities to the terminal type specified by
the TERM environment variable. The TERM environment variable may be
set in the Korn Shell (see ksh(1)) by typing:

export TERM=terminal_name

To set environment variables using other command line interfaces or
shells, see the environ(7) manual page.

Three additional environment variables are useful, and can be set in the
Korn Shell:

1. If you have an alternate Terminfo database containing terminal
types that are not available in the system default database
/usr/share/lib/terminfo, you can specify the TERMINFO
environment variable to point to this alternate database:

export TERMINFO=path

This path specifies the location of the alternate compiled
Terminfo database whose structure consists of directory names
0 to 9 and a to z (which represent the first letter of the
compiled terminal definition file name).

The alternate database specified by TERMINFO is examined
before the system default database. If the terminal type
specified by TERM cannot be found in either database, the
default terminal type dumb is assumed.

2. To specify a window width smaller than your screen width (for
example, in situations where your communications line is
slow), set the COLUMNS environment variable to the number of
vertical columns you want between the left and right margins:

export COLUMNS=number

The number of columns may be set to a number smaller than the
screen size; however, if set larger than the screen or window
width, the results are undefined.

The value set using this environment variable takes precedence
over the value normally used for the terminal.

3. To specify a window height smaller than your current screen
height (for example, in situations where your communications
line is slow), override the LINES environment variable by
setting it to a smaller number of horizontal lines:

export LINES=number

The number of lines may be set to a number smaller than the
screen height; however, if set larger than the screen or
window height, the results are undefined.

The value set using this environment variable takes precedence
over the value normally used for the terminal.

Data Types

X/Open Curses defines the following data types:

An integral type that holds an OR-ed set of attributes. The
attributes acceptable are those which begin with the WA_
prefix .

Boolean data type.

A type that refers to a string consisting of a spacing wide
character, up to 5 non-spacing wide characters, and zero or
more attributes of any type. See Attributes, Color Pairs, and
Renditions. A null cchar_t object terminates arrays of
cchar_t objects.

An integral type whose values are formed by OR-ing an
"unsigned char" with a color pair. and with zero or more
attributes. The attributes acceptable are those which begin
with the A_ prefix and COLOR_PAIR(3XCURSES)

An opaque data type associated with a terminal's display

An opaque data type associated with a terminal. It contains
information about the terminal's capabilities (as defined by
terminfo), the terminal modes, and current state of
input/output operations.

An integral data type whose values represent wide characters.

An opaque data type associated with a window.

Screens, Windows, and Terminals
The X/Open Curses manual pages refer at various points to screens,
windows (also subwindows, derived windows, and pads), and terminals. The
following list defines each of these terms.

A screen is a terminal's physical output device. The SCREEN
data type is associated with a terminal.

Window objects are two-dimensional arrays of characters and
their renditions. X/Open Curses provides stdscr, a default
window which is the size of of the terminal screen. You can use
the newwin(3XCURSES) function to create others.

To refer to a window, use a variable declared as WINDOW *. X/Open Curses
includes both functions that modify stdscr, and more general versions
that let you specify a window.

There are three sub-types of windows:

A window which has been created within another window
(the parent window) and whose position has been
specified with absolute screen coordinates. The
derwin(3XCURSES) and subwin(3XCURSES) functions can be
used to create subwindows.

Derived Window
A subwindow whose position is defined relative to the
parent window's coordinates rather than in absolute

A special type of window that can be larger than the
screen. For more information, see the newpad(3XCURSES)
man page.

A terminal is the input and output device which
character-based applications use to interact with the
user. The TERMINAL data type is associated with such a

Attributes, Color Pairs, and Renditions
A character's rendition consists of its attributes (such as underlining
or reverse video) and its color pair (the foreground and background
colors). When using waddstr(3XCURSES), waddchstr(3XCURSES),
wprintw(3XCURSES), winsch(3XCURSES), and so on, the window's rendition is
combined with that character's renditions. The window rendition is the
attributes and color set using the attroff(3XCURSES) and
attr_off(3XCURSES) sets of functions. The window's background character
and rendition are set with the bkgdset(3XCURSES) and bkgrndset(3XCURSES)
sets of functions.

When spaces are written to the screen, the background character and
window rendition replace the space. For example, if the background
rendition and character is A_UNDERLINE|'*', text written to the window
appears underlined and the spaces appear as underlined asterisks.

Each character written retains the rendition that it has obtained. This
allows the character to be copied "as is" to or from a window with the
addchstr(3XCURSES) or inch(3XCURSES) functions.

A_ Constant Values for Attributes
You can specify Attributes, Color Pairs, and Renditions attributes using
the constants listed in the tables below. The following constants modify
objects of type chtype:

| Constant Description |
|A_ALTCHARSET Alternate character set |
|A_ATTRIBUTES Bit-mask to extract attributes |
|A_BLINK Blinking |
|A_BOLD Bold |
|A_CHARTEXT Bit-mask to extract a character |
|A_COLOR Bit-mask to extract color-pair |
| information |
|A_DIM Half-bright |
|A_INVIS Invisible |
|A_PROTECT Protected |
|A_REVERSE Reverse video |
|A_STANDOUT Highlights specific to terminal |
|A_UNDERLINE Underline |

WA_ Constant Values for Attributes
The following constants modify objects of type attr_t:

| Constant Description |
|WA_ALTCHARSET Alternate character set |
|WA_ATTRIBUTES Attribute mask |
|WA_BLINK Blinking |
|WA_BOLD Bold |
|WA_DIM Half-bright |
|WA_HORIZONTAL Horizontal highlight |
|WA_INVIS Invisible |
|WA_LEFT Left highlist |
|WA_LOW Low highlist |
|WA_PROTECT Protected |
|WA_REVERSE Reverse video |
|WA_RIGHT Right highlight |
|WA_STANDOUT Highlights specific to terminal |
|WA_TOP Top highlight |
|WA_UNDERLINE Underline |
|WA_VERTICAL Vertical highlight |

Color Macros

Colors always appear in pairs; the foreground color of the character
itself and the background color of the field on which it is displayed.
The following color macros are defined:

| Macro Description |

Together, a character's attributes and its color pair form the
character's rendition. A character's rendition moves with the character
during any scrolling or insert/delete operations. If your terminal lacks
support for the specified rendition, X/Open Curses may substitute a
different rendition.

The COLOR_PAIR(3XCURSES) function modifies a chtype object. The
PAIR_NUMBER(3XCURSES) function extracts the color pair from a chtype

Functions for Modifying a Window's Color
The following functions modify a window's color:

| Function Description |
|attr_set(), wattr_set() Change the window's rendition. |
|color_set(), wcolor_set() Set the window's color |

Non-Spacing Characters
When the wcwidth(3C) function returns a width of zero for a character,
that character is called a non-spacing character. Non-spacing characters
can be written to a window. Each non-spacing character is associated with
a spacing character (that is, one which does not have a width of zero)
and modifies that character. You cannot address a non-spacing character
directly. Whenever you perform an X/Open Curses operation on the
associated character, you are implicitly addressing the non-spacing

Non-spacing characters do not have a rendition. For functions that use
wide characters and a rendition, X/Open Curses ignores any rendition
specified for non-spacing characters. Multi-column characters have one
rendition that applies to all columns spanned.

Complex Characters

The cchar_t date type represents a complex character. A complex character
may contain a spacing character, its associated non-spacing characters,
and its rendition. This implementation of complex characters supports up
to 5 non-spacing characters for each spacing character.

When a cchar_t object representing a non-spacing complex character is
written to the screen, its rendition is not used, but rather it becomes
associated with the rendition of the existing character at that location.
The setcchar(3XCURSES) function initializes an object of type cchar_t.
The getcchar(3XCURSES) function extracts the contents of a cchar_t

Display Operations

In adding internationalization support to X/Open Curses, every attempt
was made to minimize the number of changes to the historical CURSES
package. This enables programs written to use the historical
implementation of CURSES to use the internationalized version with little
or no modification. The following rules apply to the internationalized
X/Open Curses package:

o The cursor can be placed anywhere in the window. Window and
screen origins are (0,0).

o A multi-column character cannot be displayed in the last
column, because the character would appear truncated. Instead,
the background character is displayed in the last column and
the multi-column character appears at the beginning of the
next line. This is called wrapping.

If the original line is the last line in the scroll region and
scrolling is enabled, X/Open Curses moves the contents of each
line in the region to the previous line. The first line of
the region is lost. The last line of the scrolling region
contains any wrapped characters. The remainder of that line
is filled with the background character. If scrolling is
disabled, X/Open Curses truncates any character that would
extend past the last column of the screen.

o Overwrites operate on screen columns. If displaying a single-
column or multi-column character results in overwriting only
a portion of a multi-column character or characters,
background characters are displayed in place of the non-
overwritten portions.

o Insertions and deletions operate on whole characters. The
cursor is moved to the first column of the character prior to
performing the operation.

Overlapping Windows

When windows overlap, it may be necessary to overwrite only part of a
multi-column character. As mentioned earlier, the non-overwritten
portions are replaced with the background character. This results in
issues concerning the overwrite(3XCURSES), overlay(3XCURSES),
copywin(3XCURSES), wnoutrefresh(3XCURSES), and wrefresh(3XCURSES)

Special Characters

Some functions assign special meanings to certain special characters:

Moves the cursor one column towards the beginning
of the line. If the cursor was already at the
beginning of the line, it remains there. All
subsequent characters are added or inserted at this

Carriage Return
Moves the cursor to the beginning of the current
line. If the cursor was already at the beginning of
the line, it remains there. All subsequent
characters are added or inserted at this point.

When adding characters, X/Open Curses fills the
remainder of the line with the background character
(effectively truncating the newline) and scrolls
the window as described earlier. All subsequent
characters are inserted at the start of the new

When inserting characters, X/Open Curses fills the
remainder of the line with the background character
(effectively truncating the line), moves the cursor
to the beginning of a new line, and scrolls the
window as described earlier. All subsequent
characters are placed at the start of the new line.

moves subsequent characters to next horizontal tab
strop. Default tab stops are set at 0, 8, 16, and
so on.

When adding or inserting characters, X/Open Curses
inserts or adds the background character into each
column until the next tab stop is reached. If there
are no remaining tab stops on the current line,
wrapping and scrolling occur as described earlier.

Control Characters
When X/Open Curses functions perform special
character processing, they convert control
characters to the ^X notation, where X is a single-
column character (uppercase, if it is a letter) and
writes that notation to the window. Functions that
retrieve text from the window will retrieve the
converted notation not the original.

X/Open Curses displays non-printable bytes, that have their high bit set,
using the M-X meta notation where X is the non-printable byte with its
high bit turned off.

Input Processing

There are four input modes possible with X/Open Curses that affect the
behavior of input functions like getch(3XCURSES) and getnstr(3XCURSES).

Line Canonical (Cooked)
In line input mode, the terminal driver
handles the input of line units as well as
SIGERASE and SIGKILL character processing.
See termio(4I) for more information.

In this mode, the getch() and getnstr()
functions will not return until a complete
line has been read by the terminal driver, at
which point only the requested number of
bytes/characters are returned. The rest of
the line unit remains unread until subsequent
call to the getch() or getnstr() functions.

The functions nocbreak(3XCURSES) and
noraw(3XCURSES) are used to enter this mode.
These functions are described on the
cbreak(3XCURSES) man page which also details
which termios flags are enabled.

Of the modes available, this one gives
applications the least amount of control over
input. However, it is the only input mode
possible on a block mode terminal.

cbreak Mode
Byte/character input provides a finer degree
of control. The terminal driver passes each
byte read to the application without
interpreting erase and kill characters. It
is the application's responsibility to handle
line editing. It is unknown whether the signal
characters (SIGINTR, SIGQUIT, SIGSUSP) and
flow control characters (SIGSTART, SIGSTOP)
are enabled. To ensure that they are, call
the noraw() function first, then call the
cbreak() function.

halfdelay Mode
This is the same as the cbreak() mode with a
timeout. The terminal driver waits for a
byte to be received or for a timer to expire,
in which case the getch() function either
returns a byte or ERR respectively. This
mode overrides timeouts set for an individual
window with the wtimeout() function.

raw Mode
This mode provides byte/character input with
the most control for an application. It is
similar to cbreak() mode, but also disables
signal character processing (SIGINTR, SIGSUSP,
SIGQUIT) and flow control processing
(SIGSTART, SIGSTOP) so that the application
can process them as it wants.

These modes affect all X/Open Curses input. The default input mode is
inherited from the parent process when the application starts up.

A timeout similar to halfdelay(3XCURSES) can be applied to individual
windows (see timeout(3XCURSES)). The nodelay(3XCURSES) function is
equivalent to setting wtimeout(3XCURSES) for a window with a zero timeout
(non-blocking) or infinite delay (blocking).

To handle function keys, keypad(3XCURSES) must be enabled. When it is
enabled, the getch() function returns a KEY_ constant for a uniquely
encoded key defined for that terminal. When keypad() is disabled, the
getch() function returns the individual bytes composing the function key
(see getch(3XCURSES) and wget_wch(3XCURSES)). By default, keypad() is

When processing function keys, once the first byte is recognized, a timer
is set for each subsequent byte in the sequence. If any byte in the
function key sequence is not received before the timer expires, the
bytes already received are pushed into a buffer and the original first
byte is returned. Subsequent X/Open Curses input would take bytes from
the buffer until exhausted, after which new input from the terminal will
be requested. Enabling and disabling of the function key interbyte
timer is handled by the notimeout(3XCURSES) function. By default,
notimeout() is disabled (that is, the timer is used).

X/Open Curses always disables the terminal driver's echo processing.
The echo(3XCURSES) and noecho(3XCURSES) functions control X/Open Curses
software echoing. When software echoing is enabled, X/Open Curses
input functions echo printable characters, control keys, and meta keys
in the input window at the last cursor position. Functions keys are
never echoed. When software echoing is disabled, it is the
application's responsibility to handle echoing.


Example 1: Copying Single-Column Characters Over Single-Column Characters

In the upcoming examples, some characters have special meanings:

o {, [, and ( represent the left halves of multi-column
characters. }, ], and ) represent the corresponding right
halves of the same multi-column characters.

o Alphanumeric characters and periods (.) represent single-
column characters.

o The number sign (#) represents the background character.

copywin(s, t, 0, 1, 0, 1, 1, 3, 0)

s t -> t
abcdef ...... .bcd..
ghijkl ...... .hij..

There are no special problems with this situation.

Example 2: Copying Multi-column Characters Over Single-Column Characters

copywin(s, t, 0, 1, 0, 1, 1, 3, 0)

s t -> t
a[]def ...... .[]d..
gh()kl ...... .h()..

There are no special problems with this situation.

Example 3: Copying Single-Column Characters From Source Overlaps Multi-

column Characters In Target

copywin(s, t, 0, 1, 0, 1, 1, 3, 0)

s t -> t
abcdef [].... #bcd..
ghijk tol ...(). .hij#.

Overwriting multi-column characters in t has resulted in the # background
characters being required to erase the remaining halves of the target's
multi-column characters.

Example 4: Copy Incomplete Multi-column Characters From Source To Target.

copywin(s, t, 0, 1, 0, 1, 1, 3, 0)

s t -> t
[]cdef 123456 []cd56
ghi()l 789012 7hi()2

The ] and ( halves of the multi-column characters have been copied from
the source and expanded in the target outside of the specified target

Consider a pop-up dialog box that contains single-column characters and a
base window that contains multi-column characters and you do the

save=dupwin(dialog); /* create backing store */
overwrite(cursor, save); /* save region to be overlayed */
wrefresh(dialog); /* display dialog */
wrefresh(save); /* restore screen image */
delwin(save); /* release backing store */

You can use code similar to this to implement generic popup() and
popdown() routines in a variety of CURSES implementations (including BSD
UNIX, and UNIX System V). In the simple case where the base window
contains single-column characters only, it would correctly restore the
image that appeared on the screen before the dialog box was displayed.

However, with multi-column characters, the overwrite() function might
save a region with incomplete multi-column characters. The
wrefresh(dialog) statement results in the behavior described in example 3
above. The behavior described in this example (that is, example 4) allows
the wrefresh(save) statement to restore the window correctly.

Example 5: Copying An Incomplete Multi-column Character To Region Next To

Screen Margin (Not A Window Edge)

Two cases of copying an incomplete multi-column character to a region
next to a screen margin follow:

copywin(s, t, 0, 1, 0, 0, 1, 2, 0)

s t -> t
[]cdef 123456 #cd456
ghijkl 789012 hij012

The background character (#) replaces the ] character that would have
been copied from the source, because it is not possible to expand the
multi-column character to its complete form.

copywin(s, t, 0, 1, 0, 3, 1, 5, 0)

s t -> t
abcdef 123456 123bcd
ghi()l 789012 789hi#

This second example is the same as the first, but with the right margin.


See attributes(7) for descriptions of the following attributes:

|Interface Stability | Standard |
|MT-Level | Unsafe |


addchstr(3XCURSES), attr_off(3XCURSES), attroff(3XCURSES),
bkgdset(3XCURSES), bkgrndset(3XCURSES), cbreak(3XCURSES),
copywin(3XCURSES), derwin(3XCURSES), echo(3XCURSES), getcchar(3XCURSES),
getch(3XCURSES), getnstr(3XCURSES), halfdelay(3XCURSES), inch(3XCURSES),
keypad(3XCURSES), libcurses(3XCURSES), newpad(3XCURSES),
newwin(3XCURSES), nocbreak(3XCURSES), nodelay(3XCURSES),
noecho(3XCURSES), noraw(3XCURSES), notimeout(3XCURSES),
overlay(3XCURSES), overwrite(3XCURSES), setcchar(3XCURSES),
subwin(3XCURSES), timeout(3XCURSES), waddchstr(3XCURSES),
waddstr(3XCURSES), wget_wch(3XCURSES), winsch(3XCURSES),
wnoutrefresh(3XCURSES), wprintw(3XCURSES), wrefresh(3XCURSES),
wtimeout(3XCURSES), termio(4I), attributes(7), environ(7), standards(7)

June 5, 2002 CURSES(3XCURSES)