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.

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

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

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)).

These video attributes are supported by attr_on and related functions (which also support the attributes recognized by attron, etc.):

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:

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.

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 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:

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:

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.

SEE ALSO¶

ncurses(3NCURSES), addch(3NCURSES), addstr(3NCURSES), bkgd(3NCURSES), printw(3NCURSES), curses_variables(3NCURSES)