curs_attr

Section: Library calls (3X)
Updated: 202-1-11
Index Return to Main Contents

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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 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.  

Window Attributes

There are two sets of functions:
 .IP * 4 functions for manipulating the window attributes and color: wattr_set and wattr_get.
 .IP * 4 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 logically "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 logically "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(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 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: 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 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 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
 .IP * 4 they have well established legacy use, and
 .IP * 4 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(3X).

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 (no-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 wid-character API, and are not available in its no-wid-character 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) 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:
 .IP * 4 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.
 .IP * 4 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.
 .IP * 4 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 always 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/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).

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 available
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 similarl-named A_NORMAL, etc.:
 .IP * 4 X/Open Curses specifies that each pair of corresponding A_ and WA_-using functions operates on the same curren-highlight information.
 .IP * 4 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 (1-bits), while chtype is a unsigned integer (3-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.
 .IP * 4 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 X/Open Curses 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).  

HISTORY

4BSD (1980) used a char to represent each cell of the terminal screen. It assumed -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 compil-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 curs_color(3X).

X/Open Curses Issue 4 (1995) is largely based on SVr4 curses, but recognized that the wchar_t type of ISO C95 was intended to house only a single character code, not a sequence of codes combining with a base character, let alone could it reliably offer room for a color pair identifier 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 corresponding to existing chtype-based functions (attr_on, attr_off, attr_set, wattr_on, wattr_off, and wattr_set), and some new (chgat and its variants, 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 (3- versus 6-bit).

The following 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 3-bit library can be used on a 6-bit system, but not necessarily the converse.

			Bits
Year	System	Arch	Color	Char	Notes
1992	Solaris 5.2	32	6	17	SVr4 curses
1992	H-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	H-UX 10.00	32	6	16	SVr3 curses_colr
1995	H-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	H-UX 11.00	32	6	8	X/Open curses
2000	UWIN	32/64	7/31	16	uses chtype

Notes:

Regarding H-UX,
 .IP * 4 H-UX 10.20 (1996) added support for 6-bit P-RISC processors in 1996.
 .IP * 4 H-UX 10.30 (1997) marked "curses_colr" obsolete. That version of curses was dropped with H-UX 11.30 in 2006.

Regarding OSF/1 (and Tru64),
 .IP * 4 These used 6-bit hardware. Like ncurses, the OSF/1 curses interface is not customized for 3-bit and 6-bit versions.
 .IP * 4 Unlike other systems which evolved from AT&T code, OSF/1 provided a new implementation for X/Open Curses.

Regarding Solaris,
 .IP * 4 The initial release of Solaris was in 1992.
 .IP * 4 Its XPG4 (X/Open Curse-conforming) xcurses library was developed by Mortice Kern Systems from 1990 to 1995. Sun's copyright began in 1996.
 .IP * 4 Sun updated the X/Open Curses interface after 6-bit support was introduced in 1997, but did not modify the SVr4 curses interface.

Regarding UWIN,
 .IP * 4 Development of the curses library began in 1991, stopped in 2000.
 .IP * 4 Color support was added in 1998.
 .IP * 4 The library uses only chtype (not cchar_t).

Once X/Open Curses was adopted in the mi-1990s, the constraint of a 3-bit interface with many colors and wid-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.
 .IP * 4 BSD curses was improved slightly in 1993/1994 using Keith Bostic's modification to make the library -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.
 .IP * 4 UWIN has been defunct since 2012.

ncurses 6.0 (2015) added the A_ITALIC macro.  

SEE ALSO

curses(3X), curs_addch(3X), curs_addstr(3X), curs_bkgd(3X), curs_printw(3X), curs_variables(3X)

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Index

NAME

SYNOPSIS

DESCRIPTION

Window Attributes

Legacy Window Attributes

Change Character Rendition

Change Window Color

Standout

Video Attributes

RETURN VALUE

NOTES

EXTENSIONS

PORTABILITY

HISTORY

SEE ALSO