https://invisible-island.net/ncurses/man/
curs_add_wch(3x) Library calls curs_add_wch(3x)
add_wch, wadd_wch, mvadd_wch, mvwadd_wch, echo_wchar, wecho_wchar - add
a curses complex character to a window, possibly advancing the cursor
#include <curses.h>
int add_wch(const cchar_t *wch);
int wadd_wch(WINDOW *win, const cchar_t *wch);
int mvadd_wch(int y, int x, const cchar_t *wch);
int mvwadd_wch(WINDOW *win, int y, int x, const cchar_t *wch);
int echo_wchar(const cchar_t *wch);
int wecho_wchar(WINDOW *win, const cchar_t *wch);
wadd_wch writes the curses complex character wch to the window win,
then may advance the cursor position, analogously to the standard C
library's putwchar(3). ncurses(3x) describes the variants of this
function.
Construct a curses complex character from a wchar_t with setcchar(3x).
Much behavior depends on whether the wide characters in wch are spacing
or non-spacing; see subsection "Complex Characters" below.
o If wch contains a spacing character, then any character at the
cursor is first removed. The complex character wch, with its
attributes and color pair identifier, becomes the base of the
active complex character.
o If wch contains only non-spacing characters, they are combined with
the active complex character. curses ignores its attributes and
color pair identifier, and does not advance the cursor.
Further non-spacing characters added with wadd_wch are not written at
the new cursor position but combine with the active complex character
until another spacing character is written to the window or the cursor
is moved.
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 wch 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 same
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 wch is any other nonprintable character, it is drawn in printable
form using the same convention as wunctrl(3x). Calling win_wch(3x) on
the location of a nonprintable character does not return the character
itself, but its wunctrl(3x) representation.
A cchar_t can be copied from place to place using win_wch(3x) and
wadd_wch. See curs_attr(3x) for values of predefined constants that
can be usefully "or"ed with characters. A complex character whose only
character component is a wide space, and whose only attribute is
WA_NORMAL, is a blank character, and therefore combines with the
background character; see curs_bkgrnd(3x).
echo_wchar and wecho_wchar are equivalent to calling (w)add_wch
followed by (w)refresh on stdscr or the specified window. curses
interprets these functions as a hint that only a single (complex)
character is being output; for non-control characters, a considerable
performance gain may be enjoyed by employing them.
curses defines macros starting with WACS_ that can be used with
wadd_wch to write line-drawing and other symbols 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.
Unicode ACS acsc
Symbol Default Default char Glyph Name
------------------------------------------------------------------------
WACS_BLOCK 0x25ae # 0 solid square block
WACS_BOARD 0x2592 # h board of squares
WACS_BTEE 0x2534 + v bottom tee
WACS_BULLET 0x00b7 o ~ bullet
WACS_CKBOARD 0x2592 : a checker board (stipple)
WACS_DARROW 0x2193 v . arrow pointing down
WACS_DEGREE 0x00b0 ' f degree symbol
WACS_DIAMOND 0x25c6 + ` diamond
WACS_GEQUAL 0x2265 > > greater-than-or-equal-to
WACS_HLINE 0x2500 - q horizontal line
WACS_LANTERN 0x2603 # i lantern symbol
WACS_LARROW 0x2190 < , arrow pointing left
WACS_LEQUAL 0x2264 < y less-than-or-equal-to
WACS_LLCORNER 0x2514 + m lower left-hand corner
WACS_LRCORNER 0x2518 + j lower right-hand corner
WACS_LTEE 0x2524 + t left tee
WACS_NEQUAL 0x2260 ! | not-equal
WACS_PI 0x03c0 * { greek pi
WACS_PLMINUS 0x00b1 # g plus/minus
WACS_PLUS 0x253c + n plus
WACS_RARROW 0x2192 > + arrow pointing right
WACS_RTEE 0x251c + u right tee
WACS_S1 0x23ba - o scan line 1
WACS_S3 0x23bb - p scan line 3
WACS_S7 0x23bc - r scan line 7
WACS_S9 0x23bd _ s scan line 9
WACS_STERLING 0x00a3 f } pound-sterling symbol
WACS_TTEE 0x252c + w top tee
WACS_UARROW 0x2191 ^ - arrow pointing up
WACS_ULCORNER 0x250c + l upper left-hand corner
WACS_URCORNER 0x2510 + k upper right-hand corner
WACS_VLINE 0x2502 | x vertical line
The wide-character configuration of ncurses also defines symbols for
thick lines (acsc "J" to "V"):
Unicode ASCII acsc
ACS Name Default Default Char Glyph Name
------------------------------------------------------------------------
WACS_T_BTEE 0x253b + V thick tee pointing up
WACS_T_HLINE 0x2501 - Q thick horizontal line
WACS_T_LLCORNER 0x2517 + M thick lower left corner
WACS_T_LRCORNER 0x251b + J thick lower right corner
WACS_T_LTEE 0x252b + T thick tee pointing right
WACS_T_PLUS 0x254b + N thick large plus
WACS_T_RTEE 0x2523 + U thick tee pointing left
WACS_T_TTEE 0x2533 + W thick tee pointing down
WACS_T_ULCORNER 0x250f + L thick upper left corner
WACS_T_URCORNER 0x2513 + K thick upper right corner
WACS_T_VLINE 0x2503 | X thick vertical line
and for double-lines (acsc "A" to "I"):
Unicode ASCII acsc
ACS Name Default Default Char Glyph Name
------------------------------------------------------------------------
WACS_D_BTEE 0x2569 + H double tee pointing up
WACS_D_HLINE 0x2550 - R double horizontal line
WACS_D_LLCORNER 0x255a + D double lower left corner
WACS_D_LRCORNER 0x255d + A double lower right corner
WACS_D_LTEE 0x2560 + F double tee pointing right
WACS_D_PLUS 0x256c + E double large plus
WACS_D_RTEE 0x2563 + G double tee pointing left
WACS_D_TTEE 0x2566 + I double tee pointing down
WACS_D_ULCORNER 0x2554 + C double upper left corner
WACS_D_URCORNER 0x2557 + B double upper right corner
WACS_D_VLINE 0x2551 | Y double vertical line
Unicode's descriptions for these characters differs slightly from
ncurses, by introducing the term "light" (along with less important
details). Here are its descriptions for the normal, thick, and double
horizontal lines:
o U+2500 BOX DRAWINGS LIGHT HORIZONTAL
o U+2501 BOX DRAWINGS HEAVY HORIZONTAL
o U+2550 BOX DRAWINGS DOUBLE HORIZONTAL
These functions return OK on success and ERR on failure.
In ncurses, wadd_wch and wecho_wchar return ERR if
o the curses screen has not been initialized,
o win is NULL,
o wrapping to a new line is impossible because scrollok(3x) has not
been called on win when writing to its bottom right location is
attempted, or
o it is not possible to add a complete character at the cursor
position.
Functions prefixed with "mv" first perform cursor movement and fail if
the position (y, x) is outside the window boundaries.
add_wch, mvadd_wch, mvwadd_wch, and echo_wchar may be implemented as
macros.
The TABSIZE variable is implemented in SVr4 and other versions of
curses, but is not specified by X/Open Curses (see curs_variables(3x)).
These functions are described in X/Open Curses Issue 4. It specifies
no error conditions for them.
The defaults specified for forms-drawing characters apply in the POSIX
locale. X/Open Curses makes it clear that the WACS_ symbols should be
defined as a pointer to cchar_t data, e.g., in the discussion of
border_set. A few implementations are problematic:
o NetBSD curses defines the symbols as a wchar_t within a cchar_t.
o 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 does not specify symbols for thick- or double-lines.
SVr4 curses implementations defined their line-drawing symbols in terms
of intermediate symbols. This implementation extends those symbols,
providing new definitions which are not in the SVr4 implementations.
Not all Unicode-capable terminals provide support for VT100-style
alternate character sets (i.e., the acsc capability), with their
corresponding line-drawing characters. X/Open Curses did not address
the aspect of integrating Unicode with line-drawing characters.
Existing implementations of Unix curses (AIX, HP-UX, Solaris) use only
the acsc character-mapping to provide this feature. As a result, those
implementations can only use single-byte line-drawing characters.
ncurses 5.3 (2002) provided a table of Unicode values to solve these
problems. NetBSD curses incorporated that table in 2010.
In this implementation, the Unicode values are used instead of the
terminal description's acsc mapping as discussed in ncurses(3x) for the
environment variable NCURSES_NO_UTF8_ACS. In contrast, for the same
cases, the line-drawing characters described in addch(3x) will use only
the ASCII default values.
Having Unicode available does not solve all of the problems with line-
drawing for curses:
o The closest Unicode equivalents to the VT100 graphics S1, S3, S7
and S9 frequently are not displayed at the regular intervals which
the terminal used.
o The lantern is a special case. It originated with the AT&T 4410
terminal in the early 1980s. There is no accessible documentation
depicting the lantern symbol on the AT&T terminal.
Lacking documentation, most readers assume that a storm lantern was
intended. But there are several possibilities, all with problems.
Unicode 6.0 (2010) does provide two lantern symbols: U+1F383 and
U+1F3EE. Those were not available in 2002, and are irrelevant
since they lie outside the Basic Multilingual Plane and as a result
are unavailable on many terminals. They are not storm lanterns, in
any case.
Most storm lanterns have a tapering glass chimney (to guard against
tipping); some have a wire grid protecting the chimney.
For the tapering appearance, U+2603 was adequate. In use on a
terminal, no one can tell what the image represents. Unicode calls
it a snowman.
Others have suggested these alternatives: <section> U+00A7 (section
mark), <Theta> U+0398 (theta), <Phi> U+03A6 (phi), <delta> U+03B4
(delta), U+2327 (x in a rectangle), U+256C (forms double vertical
and horizontal), and U+2612 (ballot box with x).
The complex character type cchar_t can store more than one wide
character (wchar_t). X/Open Curses does not mention this possibility,
specifying behavior only where wch is a single character, either
spacing or non-spacing.
ncurses assumes that wch is constructed using setcchar(3x), and in turn
that the result
o contains at most one spacing character at the beginning of its list
of wide characters, and zero or more non-spacing characters, or
o holds one non-spacing character.
In the latter case, ncurses adds the non-spacing character to the
active complex character.
These functions were initially specified by X/Open Curses Issue 4
(1995). The System V Interface Definition Version 4 of the same year
specified functions named waddwch and wechowchar (and the usual
variants). These were later additions to SVr4.x, not appearing in the
first SVr4 (1989). They differed from X/Open's later wadd_wch and
wecho_wchar in that they each took an argument of type wchar_t instead
of cchar_t.
curs_addch(3x) describes comparable functions of the ncurses library in
its non-wide-character configuration.
curses(3x), curs_addwstr(3x), curs_add_wchstr(3x), curs_attr(3x),
curs_bkgrnd(3x), curs_clear(3x), curs_getcchar(3x), curs_outopts(3x),
curs_refresh(3x), curs_variables(3x), putwc(3)
ncurses 6.5 2025-01-18 curs_add_wch(3x)