Ubuntu Manpage: attr_get, wattr_get, attr_set, wattr_set, attr_off, wattr_off, attr_on, wattr

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 - curses character and window
       attribute control routines

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 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
bkgd(3NCURSES) 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.

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 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 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)).

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 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 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 the routines
       attron,  attroff,  and  attrset,  or  OR'd  with  the  characters  passed  to  addch  (see
       addch(3NCURSES)).

              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.

NOTES

       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.

HISTORY

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:

• 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 System V.3.2,

• 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.

Year System Arch Color Char Notes
────────────────────────────────────────────────────────────────
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

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 interface 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.

• 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.

Regarding U/Win,

• Development of the curses library began in 1991, stopped in 2000.

• 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 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 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.

EXTENSIONS

       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:

       •   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 except to check that it is NULL.

PORTABILITY

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:

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.:

• The XSI curses standard specifies that each pair of corresponding A_ and WA_-using
functions operates on the same current-highlight information.

• 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.

• 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).

RETURN VALUE

       All routines return the integer OK on success, or ERR on failure.

       X/Open does not define any error conditions.

       This implementation

       •   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 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.