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 bkgd(3NCURSES) for functions which modify the attributes used for erasing and clearing.

attrset(A_BOLD | COLOR_PAIR(pair));
attr_set(A_BOLD, pair, NULL);

int value = A_BOLD | COLOR_PAIR(input);
int output = PAIR_NUMBER(value);

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) 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 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:

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:

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 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 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 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 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 (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 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 converse.

Notes:

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)