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);
/* (integer) constants */
/* ... */ WACS_BLOCK;
/* ... */ WACS_BOARD;
/* ... */ WACS_BTEE;
/* ... */ WACS_BULLET;
/* ... */ WACS_CKBOARD;
/* ... */ WACS_DARROW;
/* ... */ WACS_DEGREE;
/* ... */ WACS_DIAMOND;
/* ... */ WACS_HLINE;
/* ... */ WACS_LANTERN;
/* ... */ WACS_LARROW;
/* ... */ WACS_LLCORNER;
/* ... */ WACS_LRCORNER;
/* ... */ WACS_LTEE;
/* ... */ WACS_PLMINUS;
/* ... */ WACS_PLUS;
/* ... */ WACS_RARROW;
/* ... */ WACS_RTEE;
/* ... */ WACS_S1;
/* ... */ WACS_S9;
/* ... */ WACS_TTEE;
/* ... */ WACS_UARROW;
/* ... */ WACS_ULCORNER;
/* ... */ WACS_URCORNER;
/* ... */ WACS_VLINE;
/* extensions */
/* ... */ WACS_GEQUAL;
/* ... */ WACS_LEQUAL;
/* ... */ WACS_NEQUAL;
/* ... */ WACS_PI;
/* ... */ WACS_S3;
/* ... */ WACS_S7;
/* ... */ WACS_STERLING;
/* extensions for thick lines */
/* ... */ WACS_T_BTEE;
/* ... */ WACS_T_HLINE;
/* ... */ WACS_T_LLCORNER;
/* ... */ WACS_T_LRCORNER;
/* ... */ WACS_T_LTEE;
/* ... */ WACS_T_PLUS;
/* ... */ WACS_T_RTEE;
/* ... */ WACS_T_TTEE;
/* ... */ WACS_T_ULCORNER;
/* ... */ WACS_T_URCORNER;
/* ... */ WACS_T_VLINE;
/* extensions for double lines */
/* ... */ WACS_D_BTEE;
/* ... */ WACS_D_HLINE;
/* ... */ WACS_D_LLCORNER;
/* ... */ WACS_D_LRCORNER;
/* ... */ WACS_D_LTEE;
/* ... */ WACS_D_PLUS;
/* ... */ WACS_D_RTEE;
/* ... */ WACS_D_TTEE;
/* ... */ WACS_D_ULCORNER;
/* ... */ WACS_D_URCORNER;
/* ... */ WACS_D_VLINE;
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).
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
window's background character; see curs_bkgrnd(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 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.
Adding spacing characters with wadd_wch causes it to wrap at the right
margin of the window:
o If the cursor is not at the bottom of the scrolling region and
advancement occurs at the right margin, the cursor automatically
wraps to the beginning of the next line.
o If the cursor is at the bottom of the scrolling region when
advancement occurs at the right margin, and scrollok(3x) is enabled
for win, the scrolling region scrolls up one line and the cursor
wraps as above. Otherwise, advancement and scrolling do not occur,
and wadd_wch returns ERR.
A window's margins may coincide with the screen boundaries. This may
be a problem when ncurses updates the screen to match the curses
window. When their right and bottom margins coincide, ncurses uses
different strategies to handle the variations of scrolling and wrapping
at the lower-right corner by depending on the terminal capabilities:
o If the terminal does not automatically wrap as characters are added
at the right margin (i.e., auto right margins), ncurses writes the
character directly.
o If the terminal has auto right margins, but also has capabilities
for turning auto margins off and on, ncurses turns the auto margin
feature off temporarily when writing to the lower-right corner.
o If the terminal has an insertion mode which can be turned off and
on, ncurses writes the character just before the lower-right
corner, and then inserts a character to push the update into the
corner.
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. curses uses the ACS
default listed below if the terminal type lacks the acs_chars (acsc)
capability; that capability does not define a replacement for the
character; or if the terminal type and locale configuration require
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 U+25ae # 0 solid square block
WACS_BOARD U+2592 # h board of squares
WACS_BTEE U+2534 + v bottom tee
WACS_BULLET U+00b7 o ~ bullet
WACS_CKBOARD U+2592 : a checker board (stipple)
WACS_DARROW U+2193 v . arrow pointing down
WACS_DEGREE U+00b0 ' f degree symbol
WACS_DIAMOND U+25c6 + ` diamond
WACS_GEQUAL U+2265 > > greater-than-or-equal-to
WACS_HLINE U+2500 - q horizontal line
WACS_LANTERN U+2603 # i lantern symbol
WACS_LARROW U+2190 < , arrow pointing left
WACS_LEQUAL U+2264 < y less-than-or-equal-to
WACS_LLCORNER U+2514 + m lower left-hand corner
WACS_LRCORNER U+2518 + j lower right-hand corner
WACS_LTEE U+2524 + t left tee
WACS_NEQUAL U+2260 ! | not-equal
WACS_PI U+03c0 * { greek pi
WACS_PLMINUS U+00b1 # g plus/minus
WACS_PLUS U+253c + n plus
WACS_RARROW U+2192 > + arrow pointing right
WACS_RTEE U+251c + u right tee
WACS_S1 U+23ba - o scan line 1
WACS_S3 U+23bb - p scan line 3
WACS_S7 U+23bc - r scan line 7
WACS_S9 U+23bd _ s scan line 9
WACS_STERLING U+00a3 f } pound-sterling symbol
WACS_TTEE U+252c + w top tee
WACS_UARROW U+2191 ^ - arrow pointing up
WACS_ULCORNER U+250c + l upper left-hand corner
WACS_URCORNER U+2510 + k upper right-hand corner
WACS_VLINE U+2502 | x vertical line
The ncurses wide API also defines symbols for thick lines (acsc "J"
through "N", "T" through "X", and "Q"):
Unicode ASCII acsc
ACS Name Default Default Char Glyph Name
------------------------------------------------------------------------
WACS_T_BTEE U+253b + V thick tee pointing up
WACS_T_HLINE U+2501 - Q thick horizontal line
WACS_T_LLCORNER U+2517 + M thick lower left corner
WACS_T_LRCORNER U+251b + J thick lower right corner
WACS_T_LTEE U+252b + T thick tee pointing right
WACS_T_PLUS U+254b + N thick large plus
WACS_T_RTEE U+2523 + U thick tee pointing left
WACS_T_TTEE U+2533 + W thick tee pointing down
WACS_T_ULCORNER U+250f + L thick upper left corner
WACS_T_URCORNER U+2513 + K thick upper right corner
WACS_T_VLINE U+2503 | X thick vertical line
and for double lines (acsc "A" through "I", plus "R" and "Y"):
Unicode ASCII acsc
ACS Name Default Default Char Glyph Name
------------------------------------------------------------------------
WACS_D_BTEE U+2569 + H double tee pointing up
WACS_D_HLINE U+2550 - R double horizontal line
WACS_D_LLCORNER U+255a + D double lower left corner
WACS_D_LRCORNER U+255d + A double lower right corner
WACS_D_LTEE U+2560 + F double tee pointing right
WACS_D_PLUS U+256c + E double large plus
WACS_D_RTEE U+2563 + G double tee pointing left
WACS_D_TTEE U+2566 + I double tee pointing down
WACS_D_ULCORNER U+2554 + C double upper left corner
WACS_D_URCORNER U+2557 + B double upper right corner
WACS_D_VLINE U+2551 | 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, these functions fail if
o the curses screen has not been initialized,
o (for functions taking a WINDOW pointer argument) win is a null
pointer,
o wrapping to a new line is impossible because scrollok(3x) has not
been called on win (or stdscr, as applicable) 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 symbols WACS_S3, WACS_S7, WACS_LEQUAL, WACS_GEQUAL, WACS_PI,
WACS_NEQUAL, and WACS_STERLING are not standard. However, many
publicly available terminfo entries include acs_chars (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 WACS-prefixed names for them.
Applications employing ncurses extensions should condition their use on
the visibility of the NCURSES_VERSION preprocessor macro.
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. ncurses extends those symbols, providing new
definitions not found in SVr4 implementations.
Not all Unicode-capable terminals provide support for VT100-style
alternate character sets (i.e., the acsc_chars (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 System V curses (AIX, HP-UX, Solaris) use
only the acsc_chars (acsc) character-mapping to provide this feature.
As a result, those implementations can use only 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.
ncurses uses the Unicode values instead of the terminal type
description's acsc_chars (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.
X/Open Curses Issue 4 (1995) initially specified these functions. The
System V Interface Definition (SVID) Version 4 of the same year
specified functions named waddwch (and the usual variants), echowchar,
and wechowchar. 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. SVID defined no WACS_ symbols.
X/Open Curses Issue 4 also defined many of the WACS_ constants,
excepting WACS_GEQUAL, WACS_LEQUAL, WACS_NEQUAL, WACS_PI, WACS_S3,
WACS_S7, and WACS_STERLING; and those for drawing thick and double
lines.
ncurses 5.3 (2002) furnished the remaining WACS_ constants.
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 2025-04-19 curs_add_wch(3x)