Ubuntu Manpage: addch, waddch, mvaddch, mvwaddch, echochar, wechochar - add a curses character to a window and advance

name
synopsis
description
return value
notes
portability
see also

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 term‐
info 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)).