curs_attr(3x) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | VIDEO ATTRIBUTES | NOTES | HISTORY | EXTENSIONS | PORTABILITY | RETURN VALUE | SEE ALSO | COLOPHON

curs_attr(3X)                                              curs_attr(3X)

NAME         top

       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         top

       #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         top

       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.

       Routines which do not have a WINDOW* parameter apply to stdscr.
       For example, attr_set is the stdscr variant of wattr_set.

   Window attributes
       There are two sets of functions:

       •   functions for manipulating the window attributes and color:
           wattr_set and wattr_get.

       •   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

       •   they have well established legacy use, and

       •   there is no ambiguity about the way the attributes might be
           combined with a color pair.

VIDEO ATTRIBUTES         top

       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.

NOTES         top

       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.

HISTORY         top

       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.

              Year   System        Arch    Color   Char   Notes
              ────────────────────────────────────────────────────────────────
              1992   Solaris 5.2   32      6       17     SVr4 curses
              1992   HPUX 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,

          •   HP-UX 10.20 (1996) added support for 64-bit PA-RISC
              processors in 1996.

          •   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),

          •   These used 64-bit hardware.  Like ncurses, the OSF/1
              curses interface is not customized for 32-bit and 64-bit
              versions.

          •   Unlike other systems which evolved from AT&T code, OSF/1
              provided a new implementation for X/Open curses.

          Regarding Solaris,

          •   The initial release of Solaris was in 1992.

          •   The xpg4 (X/Open) curses was developed by MKS from 1990 to
              1995.  Sun's copyright began in 1996.

          •   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,

          •   Development of the curses library began in 1991, stopped
              in 2000.

          •   Color support was added in 1998.

          •   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:

       •   BSD curses was improved slightly in 1993/1994 using Keith
           Bostic's modification to make the library 8-bit clean for
           nvi.  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         top

       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, 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
           retrieving it via the standard pointer to short parameter.

       The remaining functions which have opts, but do not manipulate
       color, e.g., wattr_on and wattr_off are not used by this
       implementation except to check that they are NULL.

PORTABILITY         top

       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:

              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.:

       •   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.

       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         top

       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         top

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

COLOPHON         top

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       ⟨git://ncurses.scripts.mit.edu/ncurses.git⟩ on 2021-04-01.  (At
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                                                           curs_attr(3X)