attr(3NCURSES) Library calls attr(3NCURSES)
NAME
attr_get, wattr_get, attr_set, wattr_set, attr_off, wattr_off, attr_on,
wattr_on, attroff, wattroff, attron, wattron, attrset, wattrset, chgat,
wchgat, mvchgat, mvwchgat, color_set, wcolor_set, standend, wstandend,
standout, wstandout - manipulate attributes of character cells in curses
windows
SYNOPSIS
#include <curses.h>
int attr_get(attr_t *attrs, short *pair, void *opts);
int wattr_get(WINDOW *win, attr_t *attrs, short *pair, void *opts);
int attr_set(attr_t attrs, short pair, void *opts);
int wattr_set(WINDOW *win, attr_t attrs, short pair, void *opts);
int attr_off(attr_t attrs, void *opts);
int wattr_off(WINDOW *win, attr_t attrs, void *opts);
int attr_on(attr_t attrs, void *opts);
int wattr_on(WINDOW *win, attr_t attrs, void *opts);
int attroff(int attrs);
int wattroff(WINDOW *win, int attrs);
int attron(int attrs);
int wattron(WINDOW *win, int attrs);
int attrset(int attrs);
int wattrset(WINDOW *win, int attrs);
int chgat(int n, attr_t attr, short pair, const void *opts);
int wchgat(WINDOW *win,
int n, attr_t attr, short pair, const void *opts);
int mvchgat(int y, int x,
int n, attr_t attr, short pair, const void *opts);
int mvwchgat(WINDOW *win, int y, int x,
int n, attr_t attr, short pair, const void *opts);
int color_set(short pair, void* opts);
int wcolor_set(WINDOW *win, short pair, void* opts);
int standend(void);
int wstandend(WINDOW *win);
int standout(void);
int wstandout(WINDOW *win);
DESCRIPTION
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 charac-
ter, 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 screen.
These routines do not affect the attributes used when erasing portions
of the window. See bkgd(3NCURSES) for functions which modify the at-
tributes used for erasing and clearing.
Window Attributes
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 log-
ically “or”-ed together in attr, without affecting other attributes.
Use attr_off and wattr_off to turn off window attributes, again values
logically “or”-ed 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 logi-
cally “or”-ed 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(3NCURSES)). 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 logically “or”-ed 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 it: compati-
bility.
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, al-
though ncurses provides getattrs (see legacy(3NCURSES)).
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 act-
ing.
In these functions, the color pair argument is a color pair index (as in
the first argument of init_pair, see color(3NCURSES)).
Change Window Color
The routine color_set sets the current color of the given window to the
foreground/background combination described by the color pair parameter.
Standout
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 Curses 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.
Video Attributes
The following video attributes, defined in curses.h, can be passed to
attron, attroff, attrset, and logically “or”-ed with characters passed
to addch(3NCURSES).
Name Description
──────────────────────────────────────────────────────────────────
A_NORMAL Normal display (no highlight)
A_STANDOUT Best highlighting mode available
A_UNDERLINE Underlining
A_REVERSE Reverse video
A_BLINK Blinking
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_ATTRIBUTES Mask to extract character code
A_CHARTEXT Mask to extract attributes
A_COLOR Mask to extract color pair identifier
attr_on, attr_off, and attr_set support the foregoing as well as the
following additional attributes.
Name Description
──────────────────────────────────────────────────────────────────
WA_HORIZONTAL Horizontal highlight
WA_LEFT Left highlight
WA_LOW Low highlight
WA_RIGHT Right highlight
WA_TOP Top highlight
WA_VERTICAL Vertical highlight
RETURN VALUE
These functions return OK on success and ERR on failure.
In ncurses, they return ERR if win is NULL.
wcolor_set returns ERR if pair is outside the range 0..COLOR_PAIRS-1.
wattr_get does not fail if its attrs or pair parameter is NULL.
Functions prefixed with “mv” first perform cursor movement and fail if
the position (y, x) is outside the window boundaries.
NOTES
attr_on, attr_off, attr_set, wattr_set, chgat, mvchgat, mvwchgat,
wchgat, and color_set are part of ncurses's wide-character API, and are
not available in its non-wide configuration.
attron, wattron, attroff, wattroff, attrset, wattrset, standout, and
standend may be implemented as macros.
Color pair values may be logically “or”-ed 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
logically “or” this value within the alternate functions. You must use
ncurses ABI 6 to support more than 256 color pairs.
EXTENSIONS
This implementation provides the A_ITALIC attribute for terminals which
have the enter_italics_mode (sitm) and exit_italics_mode (ritm) capabil-
ities. Italics are not mentioned in X/Open Curses. Unlike the other
video attributes, A_ITALIC is unrelated to the set_attributes capabili-
ties. 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 para-
meter to support extended color pairs:
• For functions which modify the color, e.g., wattr_set and wattr_on,
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 to retrieving it via the
standard pointer to short parameter.
• For functions which turn attributes off, e.g., wattr_off, the opts
parameter is ignored except to check that it is NULL.
PORTABILITY
These functions are described in X/Open Curses Issue 4. It specifies no
error conditions for them.
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.
SVr4 describes the functions not taking attr_t or pair arguments as al-
ways returning 1.
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.
X/Open Curses states that whether the traditional functions attron/at-
troff/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).
X/Open 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:
Name Description
──────────────────────────────────────────────────────────────────
WA_NORMAL Normal display (no highlight)
WA_STANDOUT Best highlighting mode of the terminal
WA_UNDERLINE Underlining
WA_REVERSE Reverse video
WA_BLINK Blinking
WA_DIM Half bright
WA_BOLD Extra bright or bold
WA_ALTCHARSET Alternate character set
X/Open Curses does not assign values to these symbols, nor does it state
whether or not they are related to the similarly-named A_NORMAL, etc.:
• X/Open Curses specifies that each pair of corresponding A_ and
WA_-using functions operates on the same current-highlight informa-
tion.
• However, in some implementations, those symbols have unrelated val-
ues.
For example, the Solaris xpg4 (X/Open) curses declares attr_t to be
an unsigned short integer (16-bits), while chtype is a unsigned in-
teger (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 A_COLOR.
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.
• Because ncurses's attr_t can hold a color pair (in the A_COLOR
field), a call to wattr_on, wattr_off, or wattr_set may alter the
window's color. If the color pair information in the attribute pa-
rameter is zero, no change is made to the window's color.
This is consistent with SVr4 curses; X/Open Curses does not specify
this.
The X/Open Curses extended conformance level adds new highlights A_HORI-
ZONTAL, 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 capability).
HISTORY
4BSD (1980) used a char to represent each cell of the terminal screen.
It assumed 7-bit character codes, employing the eighth bit of a byte to
represent a standout attribute (often implemented as bold and/or reverse
video). It introduced standout, standend, wstandout, and wstandend
functions to manipulate this bit. Despite their inflexibility, they
carried over into System V curses and ultimately X/Open Curses due to
their pervasive use in legacy applications. While some 1980s terminals
supported a variety of video attributes, BSD curses could do nothing
with them.
SVr2 (1984) provided an improved curses library, introducing chtype to
create the abstract notion of a curses character; this was by default an
unsigned short, with a provision for compile-time redefinition to other
integral types (a freedom not necessarily available to users of shared
libraries, and in any event a source license was necessary to exercise
it). It added the functions attron, attroff, attrset, wattron,
wattroff, and wattrset, and defined the A_ macros listed above (except
for A_ITALIC and A_COLOR) for use by applications to manipulate other
attributes. The values of these macros were not necessarily the same in
different systems, even among those certified as System V.
SVr3.2 (1988) added the A_COLOR macro along with a color system; see
color(3NCURSES).
X/Open Curses Issue 4 (1995) is largely based on SVr4 curses, but recog-
nized that the wchar_t type of ISO C95 was intended to house only a sin-
gle character code, not a sequence of codes combining with a base char-
acter, let alone could it reliably offer room for a color pair identi-
fier and a set of attribute bits with a potential for further growth —
thus the standard invented the curses complex character type cchar_t and
a separate type attr_t for storage of attribute bits. The new types
brought along several new functions to manipulate them, some correspond-
ing to existing chtype-based functions (attr_on, attr_off, attr_set,
wattr_on, wattr_off, and wattr_set), and some new (chgat and its vari-
ants, color_set, and wcolor_set).
Different Unix systems used differently sized bit fields in chtype for
the character code and the color pair identifier, and took into account
platforms' different integer sizes (32- versus 64-bit).
The following table showing the number of bits for A_COLOR and
A_CHARTEXT was gleaned from the curses header files for various operat-
ing systems and architectures. The inferred architecture and notes re-
flect 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 converse.
Bits
Year System Arch Color Char Notes
─────────────────────────────────────────────────────────────────────────
1992 Solaris 5.2 32 6 17 SVr4 curses
1992 HP-UX 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 UWIN 32/64 7/31 16 uses chtype
Notes:
Regarding HP-UX,
• 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 in-
terface is not customized for 32-bit and 64-bit versions.
• Unlike other systems which evolved from AT&T code, OSF/1 provided
a new implementation for X/Open Curses.
Regarding Solaris,
• The initial release of Solaris was in 1992.
• Its XPG4 (X/Open Curses-conforming) xcurses library was developed
by Mortice Kern Systems 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.
Regarding UWIN,
• Development of the curses library began in 1991, stopped in 2000.
• Color support was added in 1998.
• The library uses only chtype (not 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 as needed.
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(1). He moved
the standout attribute to a structure member. The resulting 4.4BSD
curses was replaced by ncurses over the next ten years.
• UWIN has been defunct since 2012.
ncurses 6.0 (2015) added the A_ITALIC macro.
SEE ALSO
ncurses(3NCURSES), addch(3NCURSES), addstr(3NCURSES), bkgd(3NCURSES),
printw(3NCURSES), curses_variables(3NCURSES)
ncurses 6.5 2025-02-15 attr(3NCURSES)
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