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curs_attr(3)                    Library calls                   curs_attr(3)


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:

       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.

   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 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

       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.

   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 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.


RETURN VALUE

       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 prefixed with "mv" first perform cursor movement and fail if
       the position (y, x) is outside the window boundaries.


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.


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:

       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.


PORTABILITY

       These functions are described in X/Open Curses, 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.

       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 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

       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.:

       o   X/Open Curses 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 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

       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.


SEE ALSO

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

ncurses 6.5                       2024-04-27                     curs_attr(3)

ncurses 6.5 - Generated Wed May 1 18:36:48 CDT 2024
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