curs_attr(3x) Library calls curs_attr(3x)
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
#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);
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 screen.
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.
There are two sets of functions:
o functions for manipulating the window attributes and color:
wattr_set and wattr_get.
o 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.
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 it:
compatibility.
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)).
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)).
The routine color_set sets the current color of the given window to the
foreground/background combination described by the color pair
parameter.
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
o they have well established legacy use, and
o 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)).
Name Description
-----------------------------------------------------------------
A_NORMAL Normal display (no highlight)
A_STANDOUT Best highlighting mode of the terminal
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_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 attron, etc.):
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
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.
All routines return the integer OK on success, or ERR on failure.
X/Open Curses does not specify any error conditions.
This implementation
o returns an error if the window pointer is null.
o returns an error if the color pair parameter for wcolor_set is
outside the range 0..COLOR_PAIRS-1.
o does not return an error if either of the parameters of wattr_get
used for retrieving attribute or color pair values is NULL.
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.
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.
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 extended color pairs:
o 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.
o 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.
o For functions which turn attributes off, e.g., wattr_off, the opts
parameter is ignored except except to check that it is NULL.
These functions are described 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:
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
XSI 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.:
o The XSI curses standard specifies that each pair of corresponding
A_ and WA_-using functions operates on the same current-highlight
information.
o However, in some implementations, those symbols have unrelated
values.
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 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.
o 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
parameter 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 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 capability).
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 legacy applications.
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 chronology.
Goodheart's book UNIX Curses Explained (1991) describes SVr3 (1987),
commenting on several functions:
o the attron, attroff, attrset functions (and most of the functions
found in SVr4 but not in BSD curses) were introduced by System V,
o the alternate character set feature with A_ALTCHARSET was added in
SVr2 and improved in SVr3 (by adding acs_map[]),
o start_color and related color-functions were introduced by System
V.3.2,
o 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.
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 U/Win 32/64 7/31 16 uses chtype
Notes:
Regarding HP-UX,
o HP-UX 10.20 (1996) added support for 64-bit PA-RISC processors
in 1996.
o 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),
o These used 64-bit hardware. Like ncurses, the OSF/1 curses
interface is not customized for 32-bit and 64-bit versions.
o Unlike other systems which evolved from AT&T code, OSF/1
provided a new implementation for X/Open curses.
Regarding Solaris,
o The initial release of Solaris was in 1992.
o The xpg4 (X/Open) curses was developed by MKS from 1990 to 1995.
Sun's copyright began in 1996.
o Sun updated the X/Open curses interface after 64-bit support was
introduced in 1997, but did not modify the SVr4 curses
interface.
Regarding U/Win,
o Development of the curses library began in 1991, stopped in
2000.
o Color support was added in 1998.
o 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 as needed.
Other interfaces are rarely used now:
o 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
standout attribute to a structure member.
The resulting 4.4BSD curses was replaced by ncurses over the next
ten years.
o U/Win is rarely used now.
curses(3x), curs_addch(3x), curs_addstr(3x), curs_bkgd(3x),
curs_printw(3x), curs_variables(3x)
ncurses 6.4 2024-03-16 curs_attr(3x)