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curs_addch 3x 2024-06-08 ncurses 6.5 Library calls

curs_addch(3x)                   Library calls                  curs_addch(3x)




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


waddch

       waddch writes the curses character ch to the window win, then  advances
       the   cursor   position,   analogously  to  the  standard  C  library's
       putchar(3).  ncurses(3x) describes the variants of this function.

       If advancement occurs at the right margin,

       o   the cursor automatically wraps to the beginning of the  next  line,
           then,

       o   if   it  was  at  the  bottom  of  the  scrolling  region,  and  if
           scrollok(3x) 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.

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

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

       o   Line feed does a clrtoeol(3x), then advances as if from  the  right
           margin.

       o   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
           curs_variables(3x).

       If ch is any other nonprintable character, it  is  drawn  in  printable
       form using the same convention as unctrl(3x).  Calling winch(3x) on the
       location of a nonprintable character  does  not  return  the  character
       itself, but its unctrl(3x) representation.

       The  object or expression ch may contain attributes and/or a color pair
       identifier.  (A  chtype  can  be  copied  from  place  to  place  using
       winch(3x)  and  waddch.)   See  curs_attr(3x)  for values of predefined
       constants that can be usefully "or"ed with characters.


wechochar

       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 (acsc)
       string capability, and the characters in it may appear on the screen if
       the terminal type'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

       o   win is NULL,

       o   wrapping to a new line is impossible because scrollok(3x)  has  not
           been  called  on  win  when a write to its bottom right location is
           attempted, or

       o   it is not possible to  add  a  complete  character  at  the  cursor
           position.

       The last may be due to different causes:

       o   conversion  of  a  wide character to a multibyte character sequence
           can fail, or

       o   at least one of the bytes resulting from wide character  conversion
           to  a  multibyte  character sequence cannot be added to the window.
           See section "PORTABILITY" below regarding the use  of  waddch  with
           wide characters.

       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.


EXTENSIONS


TABSIZE

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


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.

       o   Solaris  curses, for example, defines 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.

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

       o   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  capabilities 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

       o   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

       o   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(3x).


Character Set

       X/Open Curses assumes that the parameter passed to  waddch  contains  a
       single  character.   That  character may have been more than eight bits
       wide in an SVr3 or SVr4 implementation, but X/Open  Curses  leaves  the
       width  of  a non-wide character code unspecified.  The standard further
       does not specify the internal structure of a chtype, though the use  of
       bit  operations  to  combine  the  character code with attributes and a
       color pair identifier into a chtype for passage to waddch is common.  A
       portable application uses only the macros discussed in curs_attr(3x) to
       manipulate a chtype.

       In ncurses, chtype holds an eight-bit character, but the library allows
       a  multibyte  character sequence to be passed via 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  (see  unctrl(3x)).
       Depending  on  the  locale,  ncurses  inspects  the byte passed in each
       waddch call and checks whether the latest call  continues  a  multibyte
       character.    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(3x)--ncurses
       discards the incomplete character.

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

       o   If it can, call either waddch or wadd_wch(3x).

       o   If it cannot, use only wadd_wch(3x).


HISTORY

       The original curses in 4BSD (1980) introduced waddch.

       SVr3 (1987) added wechochar.


SEE ALSO

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

       curses(3x),    curs_addchstr(3x),    curs_addstr(3x),    curs_attr(3x),
       curs_clear(3x),   curs_inch(3x),   curs_outopts(3x),  curs_refresh(3x),
       curs_variables(3x), putchar(3)



ncurses 6.5                       2024-06-08                    curs_addch(3x)