Ubuntu Manpage: addch, waddch, mvaddch, mvwaddch, echochar, wechochar

NAME

       addch,  waddch, mvaddch, mvwaddch, echochar, wechochar - add a character (with attributes)
       to a curses window, then 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
       The addch, waddch, mvaddch and mvwaddch routines put  the  character  ch  into  the  given
       window  at  its  current  window  position, which is then advanced.  They are analogous to
       putchar(3) in stdio(3).  If the advance is at the right margin:

       •   The cursor automatically wraps to the beginning of the next line.

       •   At the bottom of the current  scrolling  region,  and  if  scrollok  is  enabled,  the
           scrolling region is scrolled up one line.

       •   If  scrollok  is  not enabled, writing a character at the lower right margin succeeds.
           However, an error is returned because it is not possible to wrap to a new line

       If ch is a tab, newline, carriage return or backspace, the cursor is  moved  appropriately
       within the window:

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

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

       •   Newline does a clrtoeol, then moves the cursor to the window left margin on  the  next
           line, scrolling the window if on the last line.

       •   Tabs  are considered to be at every eighth column.  The tab interval may be altered by
           setting the TABSIZE variable.

       If ch is any other nonprintable character, it is drawn in printable  form,  i.e.,  the  ^X
       notation used by unctrl(3X).  Calling winch after adding a nonprintable character does not
       return the character itself, but instead  returns  the  printable  representation  of  the
       character.

       Video  attributes  can  be  combined  with a character argument passed to addch or related
       functions by logical-ORing them into the character.  (Thus,  text,  including  attributes,
       can be copied from one place to another using inch(3X) and addch.)  See the attr(3NCURSES)
       page for values of predefined video attribute constants that can be  usefully  OR'ed  into
       characters.

   Echoing characters
       The  echochar  and wechochar routines are equivalent to a call to addch followed by a call
       to refresh(3X), or a call to waddch followed by a call to wrefresh.   The  knowledge  that
       only  a  single  character  is  being  output  is  used and, for non-control characters, a
       considerable performance gain may be  seen  by  using  these  routines  instead  of  their
       equivalents.

   Line Graphics
       The  following  variables  may  be  used to add line drawing characters to the screen with
       routines of the addch family.  The default character listed below  is  used  if  the  acsc
       capability  does not define a terminal-specific replacement for it, or if the terminal and
       locale configuration requires Unicode but the library is unable to use Unicode.

       The names are taken from VT100 nomenclature.

       ACS            ACS       acsc   Glyph
       Name           Default   char   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

       All routines return the integer ERR upon failure and  OK  on  success  (the  SVr4  manuals
       specify  only  “an  integer  value  other  than  ERR”)  upon successful completion, unless
       otherwise noted in the preceding routine descriptions.

       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.

       If it is not possible to add a complete character, an error is returned:

       •   If  scrollok  is  not enabled, writing a character at the lower right margin succeeds.
           However, an error is returned because it is not possible to wrap to a new line

       •   If an error is detected when converting a multibyte character to a sequence of  bytes,
           or  if it is not possible to add all of the resulting bytes in the window, an error is
           returned.

NOTES

       Note that addch, mvaddch, mvwaddch, and echochar may be macros.

PORTABILITY

All these functions are described in the XSI Curses standard, Issue 4. 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. For the wide-character
implementation (see curs_add_wch), there are analogous WACS_ definitions which are cchar_t
constants. Some implementations are problematic:

• Some implementations define the ACS symbols to a constant (such as Solaris), while
others define those to entries in an array.

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

• HPUX curses equates some of the ACS_ symbols to the analogous WACS_ symbols as if the
ACS_ symbols were wide characters. The misdefined symbols are the arrows and other
symbols which 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 the various implementations use i (lowercase).

None of the terminal descriptions on Unix platforms use uppercase-I, except for
Solaris (i.e., screen's terminal description, apparently based on the X/Open
documentation around 1995). On the other hand, the terminal description gs6300 (AT&T
PC6300 with EMOTS Terminal Emulator) uses lowercase-i.

Some ACS symbols (ACS_S3, ACS_S7, ACS_LEQUAL, ACS_GEQUAL, ACS_PI, ACS_NEQUAL,
ACS_STERLING) were not documented in any publicly released System V. However, many
publicly available terminfos 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 ACS-prefixed names for them were invented for ncurses(3NCURSES).

The displayed values for the ACS_ and WACS_ constants depend on

• the library configuration, i.e., ncurses versus ncursesw, where the latter is capable
of displaying Unicode while the former is not, and

• whether the locale uses UTF-8 encoding.

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

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 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 non-character
information (attributes and color) was separated from the character information which is
packed in a chtype to pass to waddch.

In this implementation, chtype holds an eight-bit character. But ncurses allows multibyte
characters to be passed in a succession of calls to waddch. The other implementations do
not do this; a call to waddch passes exactly one character which may be rendered as one or
more cells on the screen depending on whether it is printable.

Depending on the locale settings, ncurses will inspect the byte passed in each call to
waddch, and check if the latest call will continue a multibyte sequence. When a character
is complete, ncurses displays the character and moves to the next position in the screen.

If the calling application interrupts the succession of bytes in a multibyte character by
moving the current location (e.g., using wmove), ncurses discards the partially built
character, starting over again.

For portability to other implementations, do not rely upon this behavior:

• check if a character can be represented as a single byte in the current locale before
attempting call waddch, and

• call wadd_wch for characters which cannot be handled by waddch.

TABSIZE
The TABSIZE variable is implemented in SVr4 and other versions of curses, but is not part
of X/Open curses (see curses_variables(3NCURSES) for more details).