oracular (3) addch.3ncurses.gz

Provided by: ncurses-doc_6.5-2_all bug

NAME

       addch, waddch, mvaddch, mvwaddch, echochar, wechochar - add a curses character to a window
       and advance the cursor

SYNOPSIS

       #include <curses.h>

       int addch(const chtype ch);
       int waddch(WINDOW *win, const chtype ch);
       int mvaddch(int y, int x, const chtype ch);
       int mvwaddch(WINDOW *win, int y, int x, const chtype ch);

       int echochar(const chtype ch);
       int wechochar(WINDOW *win, const chtype ch);

DESCRIPTION

   Adding Characters
       waddch puts the character ch at the cursor position  of  window  win,  then  advances  the
       cursor  position,  analogously  to the standard C library's putchar(3).  ncurses(3NCURSES)
       describes the variants of this function.

       If advancement occurs at the right margin,

       •   the cursor automatically wraps to the beginning of the next line; and

       •   at the bottom of the current scrolling region, and if  scrollok(3NCURSES)  is  enabled
           for win, the scrolling region scrolls up one line.

       If  ch  is a backspace, carriage return, line feed, or tab, the cursor moves appropriately
       within the window.

       •   Backspace moves the cursor one character left; at the left margin of a window, it does
           nothing.

       •   Carriage return moves the cursor to the left margin on the current line of the window.

       •   Line  feed  does a clrtoeol(3NCURSES), then moves the cursor to the left margin on the
           next line of the window, and if scrollok(3NCURSES) is enabled  for  win,  scrolls  the
           window if the cursor was already on the last line.

       •   Tab  advances  the  cursor to the next tab stop (possibly on the next line); these are
           placed at every eighth column by default.  Alter the tab  interval  with  the  TABSIZE
           extension; see curses_variables(3NCURSES).

       If  ch  is any other nonprintable character, it is drawn in printable form, using the same
       convention as unctrl(3NCURSES).

       Calling winch(3NCURSES) on the location of a nonprintable character does  not  return  the
       character itself, but its unctrl(3NCURSES) representation.

       ch  may  contain  rendering  and/or  color attributes, and others can be combined with the
       parameter by logically “or”ing with it.  (A character with its attributes  can  be  copied
       from  place  to place using winch(3NCURSES) and waddch.)  See attr(3NCURSES) for values of
       predefined video attribute constants that can be usefully “or”ed with characters.

   Echoing Characters
       echochar and wechochar are equivalent to calling (w)addch followed by (w)refresh.   curses
       interprets  these  functions  as  a hint that only a single character is being output; for
       non-control characters, a considerable performance gain may be enjoyed by employing them.

   Forms-Drawing Characters
       curses defines macros starting with ACS_ that can be  used  with  waddch  to  write  line-
       drawing  and  other  special  characters to the screen.  ncurses terms these forms-drawing
       characters.  The ACS default listed  below  is  used  if  the  acs_chars  (acsc)  terminfo
       capability  does not define a terminal-specific replacement for it, or if the terminal and
       locale configuration requires Unicode to access these characters but the library is unable
       to use Unicode.  The “acsc char” column corresponds to how the characters are specified in
       the acs_chars string capability, and the characters in it may appear on the screen if  the
       terminal's  database  entry incorrectly advertises ACS support.  The name “ACS” originates
       in the Alternate Character Set feature of the DEC VT100 terminal.

                      ACS       acsc
       Symbol         Default   char   Glyph Name
       ───────────────────────────────────────────────────────────────────────────────────────────
       ACS_BLOCK      #         0      solid square block
       ACS_BOARD      #         h      board of squares
       ACS_BTEE       +         v      bottom tee
       ACS_BULLET     o         ~      bullet
       ACS_CKBOARD    :         a      checker board (stipple)
       ACS_DARROW     v         .      arrow pointing down
       ACS_DEGREE     '         f      degree symbol
       ACS_DIAMOND    +         `      diamond
       ACS_GEQUAL     >         >      greater-than-or-equal-to
       ACS_HLINE      -         q      horizontal line
       ACS_LANTERN    #         i      lantern symbol
       ACS_LARROW     <         ,      arrow pointing left
       ACS_LEQUAL     <         y      less-than-or-equal-to
       ACS_LLCORNER   +         m      lower left-hand corner
       ACS_LRCORNER   +         j      lower right-hand corner
       ACS_LTEE       +         t      left tee
       ACS_NEQUAL     !         |      not-equal
       ACS_PI         *         {      greek pi
       ACS_PLMINUS    #         g      plus/minus
       ACS_PLUS       +         n      plus
       ACS_RARROW     >         +      arrow pointing right
       ACS_RTEE       +         u      right tee
       ACS_S1         -         o      scan line 1
       ACS_S3         -         p      scan line 3
       ACS_S7         -         r      scan line 7
       ACS_S9         _         s      scan line 9
       ACS_STERLING   f         }      pound-sterling symbol
       ACS_TTEE       +         w      top tee
       ACS_UARROW     ^         -      arrow pointing up
       ACS_ULCORNER   +         l      upper left-hand corner
       ACS_URCORNER   +         k      upper right-hand corner
       ACS_VLINE      |         x      vertical line

RETURN VALUE

       These functions return OK on success and ERR on failure.

       In ncurses, waddch returns ERR if it is not possible to add a complete  character  at  the
       cursor  position, as when conversion of a multibyte character to a byte sequence fails, or
       at least one of  the  resulting  bytes  cannot  be  added  to  the  window.   See  section
       “PORTABILITY” below regarding the use of waddch with multibyte characters.

       waddch  can  successfully  write  a  character at the bottom right location of the window.
       However, ncurses returns ERR if scrollok(3NCURSES) is not enabled in that  event,  because
       it is not possible to wrap to a new line.

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

NOTES

       addch, mvaddch, mvwaddch, and echochar may be implemented as macros.

PORTABILITY

       X/Open Curses, Issue 4 describes these functions.  It specifies no  error  conditions  for
       them.

       SVr4 curses describes a successful return value only as “an integer value other than ERR”.

       The defaults specified for forms-drawing characters apply in the POSIX locale.

   ACS Symbols
       X/Open Curses states that the ACS_ definitions are char constants.

       Some implementations are problematic.

       •   Solaris  curses,  for example, define the ACS symbols as constants; others define them
           as elements of an array.

           This implementation uses an array, acs_map, as did SVr4 curses.  NetBSD also  uses  an
           array, actually named _acs_char, with a #define for compatibility.

       •   HP-UX curses equates some of the ACS_ symbols to the analogous WACS_ symbols as if the
           ACS_ symbols were wide characters (see add_wch(3NCURSES)).  The misdefined symbols are
           the arrows and others that are not used for line drawing.

       •   X/Open  Curses  (Issues  2  through  7)  has a typographical error for the ACS_LANTERN
           symbol, equating its “VT100+ Character” to “I” (capital I), while the header files for
           SVr4 curses and other implementations use “i” (small i).

           None  of  the  terminal  descriptions  on  Unix  platforms use uppercase I, except for
           Solaris (in  its  terminfo  entry  for  screen(1),  apparently  based  on  the  X/Open
           documentation  around  1995).   On  the other hand, its gs6300 (AT&T PC6300 with EMOTS
           Terminal Emulator) description uses lowercase i.

       Some  ACS  symbols  (ACS_S3,  ACS_S7,  ACS_LEQUAL,  ACS_GEQUAL,  ACS_PI,  ACS_NEQUAL,  and
       ACS_STERLING)  were  not  documented  in  any  publicly  released System V.  However, many
       publicly available terminfo entries include acsc strings in  which  their  key  characters
       (pryz{|}) are embedded, and a second-hand list of their character descriptions has come to
       light.  The ncurses developers invented ACS-prefixed names for them.

       The displayed values of ACS_ constants depend on

       •   the ncurses ABI—for example, wide-character versus  non-wide-character  configurations
           (the former is capable of displaying Unicode while the latter is not), and

       •   whether the locale uses UTF-8 encoding.

       In  certain  cases,  the  terminal is unable to display forms-drawing characters except by
       using UTF-8; see  the  discussion  of  the  NCURSES_NO_UTF8_ACS  environment  variable  in
       ncurses(3NCURSES)).

   Character Set
       X/Open Curses assumes that the parameter passed to waddch contains a single character.  As
       discussed in attr(3NCURSES), that character may have been more than eight bits wide in  an
       SVr3  or  SVr4  implementation, but in the X/Open Curses model, the details are not given.
       The important distinction between SVr4  curses  and  X/Open  Curses  is  that  the  latter
       separates  non-character information (attributes and color) from the character code, which
       SVr4 packs into a chtype for passage to waddch.

       In ncurses, chtype holds an eight-bit character.   But  the  library  allows  a  multibyte
       character  to be passed in a succession of calls to waddch.  Other implementations do not;
       a waddch call transmits exactly one character, which may be rendered in one or more screen
       locations depending on whether it is printable.

       Depending  on  the  locale settings, ncurses inspects the byte passed in each waddch call,
       and checks whether the latest call continues a multibyte sequence.  When  a  character  is
       complete, ncurses displays the character and advances the cursor.

       If  the  calling  application  interrupts the succession of bytes in a multibyte character
       sequence by  changing  the  current  location—for  example,  with  wmove(3NCURSES)—ncurses
       discards the incomplete character.

       For portability to other implementations, do not rely upon this behavior.  Check whether a
       character can be represented as a single byte in the current locale.

       •   If it can, call either waddch or wadd_wch(3NCURSES).

       •   If it cannot, use only wadd_wch(3NCURSES).

   TABSIZE
       SVr4 and other versions of curses implement the TABSIZE variable, but X/Open  Curses  does
       not specify it (see curses_variables(3NCURSES)).

SEE ALSO

       add_wch(3NCURSES)  describes  comparable  functions  of  the  ncurses library in its wide-
       character configuration (ncursesw).

       ncurses(3NCURSES), addchstr(3NCURSES), addstr(3NCURSES), attr(3NCURSES),  clear(3NCURSES),
       inch(3NCURSES),    outopts(3NCURSES),    refresh(3NCURSES),    curses_variables(3NCURSES),
       putchar(3)