These routines manipulate the current attributes of the named
window, which then apply to all characters that are written into
the window with waddch, waddstr and wprintw. Attributes are a
property of the character, and move with the character through
any scrolling and insert/delete line/character operations. To
the extent possible, they are displayed as appropriate
modifications to the graphic rendition of characters put on the
These routines do not affect the attributes used when erasing
portions of the window. See curs_bkgd(3X) for functions which
modify the attributes used for erasing and clearing.
Routines which do not have a WINDOW* parameter apply to stdscr.
For example, attr_set is the stdscr variant of wattr_set.
There are two sets of functions:
• functions for manipulating the window attributes and color:
wattr_set and wattr_get.
• functions for manipulating only the window attributes (not
color): wattr_on and wattr_off.
The wattr_set function sets the current attributes of the given
window to attrs, with color specified by pair.
Use wattr_get to retrieve attributes for the given window.
Use attr_on and wattr_on to turn on window attributes, i.e.,
values OR'd together in attr, without affecting other attributes.
Use attr_off and wattr_off to turn off window attributes, again
values OR'd together in attr, without affecting other attributes.
Legacy window attributes
The X/Open window attribute routines which set or get, turn on or
off are extensions of older routines which assume that color
pairs are OR'd into the attribute parameter. These newer
routines use similar names, because X/Open simply added an
underscore (_) for the newer names.
The int datatype used in the legacy routines is treated as if it
is the same size as chtype (used by addch(3X)). It holds the
common video attributes (such as bold, reverse), as well as a few
bits for color. Those bits correspond to the A_COLOR symbol.
The COLOR_PAIR macro provides a value which can be OR'd into the
attribute parameter. For example, as long as that value fits
into the A_COLOR mask, then these calls produce similar results:
attrset(A_BOLD | COLOR_PAIR(pair));
attr_set(A_BOLD, pair, NULL);
However, if the value does not fit, then the COLOR_PAIR macro
uses only the bits that fit. For example, because in ncurses
A_COLOR has eight (8) bits, then COLOR_PAIR(259) is 4 (i.e., 259
is 4 more than the limit 255).
The PAIR_NUMBER macro extracts a pair number from an int (or
chtype). For example, the input and output values in these
statements would be the same:
int value = A_BOLD | COLOR_PAIR(input);
int output = PAIR_NUMBER(value);
The attrset routine is a legacy feature predating SVr4 curses but
kept in X/Open Curses for the same reason that SVr4 curses kept
The remaining attr* functions operate exactly like the
corresponding attr_* functions, except that they take arguments
of type int rather than attr_t.
There is no corresponding attrget function as such in X/Open
Curses, although ncurses provides getattrs (see curs_legacy(3X)).
Change character rendition
The routine chgat changes the attributes of a given number of
characters starting at the current cursor location of stdscr. It
does not update the cursor and does not perform wrapping. A
character count of -1 or greater than the remaining window width
means to change attributes all the way to the end of the current
line. The wchgat function generalizes this to any window; the
mvwchgat function does a cursor move before acting.
In these functions, the color pair argument is a color-pair index
(as in the first argument of init_pair, see curs_color(3X)).
Change window color
The routine color_set sets the current color of the given window
to the foreground/background combination described by the color
The routine standout is the same as attron(A_STANDOUT). The
routine standend is the same as attrset(A_NORMAL) or attrset(0),
that is, it turns off all attributes.
X/Open does not mark these “restricted”, because
• they have well established legacy use, and
• there is no ambiguity about the way the attributes might be
combined with a color pair.
The following video attributes, defined in <curses.h>, can be
passed to the routines attron, attroff, and attrset, or OR'd with
the characters passed to addch (see curs_addch(3X)).
A_NORMAL Normal display (no highlight)
A_STANDOUT Best highlighting mode of the terminal.
A_REVERSE Reverse video
A_DIM Half bright
A_BOLD Extra bright or bold
A_PROTECT Protected mode
A_INVIS Invisible or blank mode
A_ALTCHARSET Alternate character set
A_ITALIC Italics (non-X/Open extension)
A_CHARTEXT Bit-mask to extract a character
A_COLOR Bit-mask to extract a color (legacy routines)
These video attributes are supported by attr_on and related
functions (which also support the attributes recognized by
WA_HORIZONTAL Horizontal highlight
WA_LEFT Left highlight
WA_LOW Low highlight
WA_RIGHT Right highlight
WA_TOP Top highlight
WA_VERTICAL Vertical highlight
The return values of many of these routines are not meaningful
(they are implemented as macro-expanded assignments and simply
return their argument). The SVr4 manual page claims (falsely)
that these routines always return 1.
These functions may be macros:
attroff, wattroff, attron, wattron, attrset, wattrset,
standend and standout.
Color pair values can only be OR'd with attributes if the pair
number is less than 256. The alternate functions such as
color_set can pass a color pair value directly. However, ncurses
ABI 4 and 5 simply OR this value within the alternate functions.
You must use ncurses ABI 6 to support more than 256 color pairs.
X/Open Curses is largely based on SVr4 curses, adding support for
“wide-characters” (not specific to Unicode). Some of the X/Open
differences from SVr4 curses address the way video attributes can
be applied to wide-characters. But aside from that, attrset and
attr_set are similar. SVr4 curses provided the basic features
for manipulating video attributes. However, earlier versions of
curses provided a part of these features.
As seen in 2.8BSD, curses assumed 7-bit characters, using the
eighth bit of a byte to represent the standout feature (often
implemented as bold and/or reverse video). The BSD curses
library provided functions standout and standend which were
carried along into X/Open Curses due to their pervasive use in
Some terminals in the 1980s could support a variety of video
attributes, although the BSD curses library could do nothing with
those. System V (1983) provided an improved curses library. It
defined the A_ symbols for use by applications to manipulate the
other attributes. There are few useful references for the
Goodheart's book UNIX Curses Explained (1991) describes SVr3
(1987), commenting on several functions:
• the attron, attroff, attrset functions (and most of the
functions found in SVr4 but not in BSD curses) were
introduced by System V,
• the alternate character set feature with A_ALTCHARSET was
added in SVr2 and improved in SVr3 (by adding acs_map),
• start_color and related color-functions were introduced by
• pads, soft-keys were added in SVr3, and
Goodheart did not mention the background character or the cchar_t
type. Those are respectively SVr4 and X/Open features. He did
mention the A_ constants, but did not indicate their values.
Those were not the same in different systems, even for those
marked as System V.
Different Unix systems used different sizes for the bit-fields in
chtype for characters and colors, and took into account the
different integer sizes (32-bit versus 64-bit).
This table showing the number of bits for A_COLOR and A_CHARTEXT
was gleaned from the curses header files for various operating
systems and architectures. The inferred architecture and notes
reflect the format and size of the defined constants as well as
clues such as the alternate character set implementation. A
32-bit library can be used on a 64-bit system, but not
necessarily the reverse.
1992 Solaris 5.2 32 6 17 SVr4 curses
1992 HPUX 9 32 no 8 SVr2 curses
1992 AIX 3.2 32 no 23 SVr2 curses
1994 OSF/1 r3 32 no 23 SVr2 curses
1995 HP-UX 10.00 32 6 16 SVr3 “curses_colr”
1995 HP-UX 10.00 32 6 8 SVr4, X/Open curses
1995 Solaris 5.4 32/64 7 16 X/Open curses
1996 AIX 4.2 32 7 16 X/Open curses
1996 OSF/1 r4 32 6 16 X/Open curses
1997 HP-UX 11.00 32 6 8 X/Open curses
2000 U/Win 32/64 7/31 16 uses chtype
• HP-UX 10.20 (1996) added support for 64-bit PA-RISC
processors in 1996.
• HP-UX 10.30 (1997) marked “curses_colr” obsolete. That
version of curses was dropped with HP-UX 11.30 in 2006.
Regarding OSF/1 (and Tru64),
• These used 64-bit hardware. Like ncurses, the OSF/1
curses interface is not customized for 32-bit and 64-bit
• Unlike other systems which evolved from AT&T code, OSF/1
provided a new implementation for X/Open curses.
• The initial release of Solaris was in 1992.
• The xpg4 (X/Open) curses was developed by MKS from 1990 to
1995. Sun's copyright began in 1996.
• Sun updated the X/Open curses interface after 64-bit
support was introduced in 1997, but did not modify the
SVr4 curses interface.
• Development of the curses library began in 1991, stopped
• Color support was added in 1998.
• The library uses only chtype (no cchar_t).
Once X/Open curses was adopted in the mid-1990s, the constraint
of a 32-bit interface with many colors and wide-characters for
chtype became a moot point. The cchar_t structure (whose size
and members are not specified in X/Open Curses) could be extended
Other interfaces are rarely used now:
• BSD curses was improved slightly in 1993/1994 using Keith
Bostic's modification to make the library 8-bit clean for
nvi. He moved standout attribute to a structure member.
The resulting 4.4BSD curses was replaced by ncurses over the
next ten years.
• U/Win is rarely used now.
This implementation provides the A_ITALIC attribute for terminals
which have the enter_italics_mode (sitm) and exit_italics_mode
(ritm) capabilities. Italics are not mentioned in X/Open Curses.
Unlike the other video attributes, A_ITALIC is unrelated to the
set_attributes capabilities. This implementation makes the
assumption that exit_attribute_mode may also reset italics.
Each of the functions added by XSI Curses has a parameter opts,
which X/Open Curses still (after more than twenty years)
documents as reserved for future use, saying that it should be
NULL. This implementation uses that parameter in ABI 6 for the
functions which have a color-pair parameter to support extendedcolor pairs:
• For functions which modify the color, e.g., wattr_set, if
opts is set it is treated as a pointer to int, and used to
set the color pair instead of the short pair parameter.
• For functions which retrieve the color, e.g., wattr_get, if
opts is set it is treated as a pointer to int, and used to
retrieve the color pair as an int value, in addition
retrieving it via the standard pointer to short parameter.
The remaining functions which have opts, but do not manipulate
color, e.g., wattr_on and wattr_off are not used by this
implementation except to check that they are NULL.
These functions are supported in the XSI Curses standard, Issue
4. The standard defined the dedicated type for highlights,
attr_t, which was not defined in SVr4 curses. The functions
taking attr_t arguments were not supported under SVr4.
Very old versions of this library did not force an update of the
screen when changing the attributes. Use touchwin to force the
screen to match the updated attributes.
The XSI Curses standard states that whether the traditional
functions attron/attroff/attrset can manipulate attributes other
than A_BLINK, A_BOLD, A_DIM, A_REVERSE, A_STANDOUT, or
A_UNDERLINE is “unspecified”. Under this implementation as well
as SVr4 curses, these functions correctly manipulate all other
highlights (specifically, A_ALTCHARSET, A_PROTECT, and A_INVIS).
XSI Curses added these entry points:
attr_get, attr_on, attr_off, attr_set, wattr_on,
wattr_off, wattr_get, wattr_set
The new functions are intended to work with a new series of
highlight macros prefixed with WA_. The older macros have direct
counterparts in the newer set of names:
WA_NORMAL Normal display (no highlight)
WA_STANDOUT Best highlighting mode of the terminal.
WA_REVERSE Reverse video
WA_DIM Half bright
WA_BOLD Extra bright or bold
WA_ALTCHARSET Alternate character set
XSI curses does not assign values to these symbols, nor does it
state whether or not they are related to the similarly-named
• The XSI curses standard specifies that each pair of
corresponding A_ and WA_-using functions operates on the same
• However, in some implementations, those symbols have
For example, the Solaris xpg4 (X/Open) curses declares attr_t
to be an unsigned short integer (16-bits), while chtype is a
unsigned integer (32-bits). The WA_ symbols in this case are
different from the A_ symbols because they are used for a
smaller datatype which does not represent A_CHARTEXT or
In this implementation (as in many others), the values happen
to be the same because it simplifies copying information
between chtype and cchar_t variables.
The XSI standard extended conformance level adds new highlights
A_HORIZONTAL, A_LEFT, A_LOW, A_RIGHT, A_TOP, A_VERTICAL (and
corresponding WA_ macros for each). As of August 2013, no known
terminal provides these highlights (i.e., via the sgr1
All routines return the integer OK on success, or ERR on failure.
X/Open does not define any error conditions.
• returns an error if the window pointer is null.
• returns an error if the color pair parameter for wcolor_set
is outside the range 0..COLOR_PAIRS-1.
• does not return an error if either of the parameters of
wattr_get used for retrieving attribute or color-pair values
Functions with a “mv” prefix first perform a cursor movement
using wmove, and return an error if the position is outside the
window, or if the window pointer is null.
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