# curs_attr 3x 2024-01-13 ncurses 6.4 Library calls

    curs_attr(3x)                    Library calls                   curs_attr(3x)

## 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 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 does not define 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 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.

## 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 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.:

           o   The XSI curses standard 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  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).

## 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 6.4                       2024-01-13                     curs_attr(3x)