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

Provided by: ncurses-doc_6.4+20240113-1ubuntu2_all

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
       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 the standard C library's
       putchar(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(3NCURSES) is  enabled,  the  scrolling
           region is scrolled up one line.

       •   If  scrollok(3NCURSES)  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, using the same convention as
       unctrl(3NCURSES):

       •   Control characters are displayed in the ^X notation.

       •   Values above 128 are either  meta  characters  (if  the  screen  has  not  been  initialized,  or  if
           meta(3NCURSES)  has been called with a TRUE E parameter), shown in the M-X notation, or are displayed
           as themselves.  In the latter case, the  values  may  not  be  printable;  this  follows  the  X/Open
           specification.

       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(3NCURSES) 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(3NCURSES), 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(3NCURSES)  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

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.

• HP-UX 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(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 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).