add_wch(3NCURSES) Library calls add_wch(3NCURSES)
NAME
add_wch, wadd_wch, mvadd_wch, mvwadd_wch, echo_wchar, wecho_wchar - add
a curses complex character to a window, possibly advancing the cursor
SYNOPSIS
#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;
DESCRIPTION
wadd_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(3NCURSES) describes the variants of this function.
Construct a curses complex character from a wchar_t with
setcchar(3NCURSES). Much behavior depends on whether the wide charac-
ters in wch are spacing or non-spacing; see subsection “Complex Charac-
ters” below.
• If wch contains a spacing character, then any character at the cur-
sor is first removed. The complex character wch, with its attrib-
utes and color pair identifier, becomes the base of the active com-
plex character.
• 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,
• the cursor automatically wraps to the beginning of the next line,
then,
• if it was at the bottom of the scrolling region, and if
scrollok(3NCURSES) 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.
• 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 same line
of the window.
• Line feed does a clrtoeol(3NCURSES), then advances as if from the
right margin.
• 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 wch is any other nonprintable character, it is drawn in printable
form using the same convention as wunctrl(3NCURSES). Calling
win_wch(3NCURSES) on the location of a nonprintable character does not
return the character itself, but its wunctrl(3NCURSES) representation.
A cchar_t can be copied from place to place using win_wch(3NCURSES) and
wadd_wch. See attr(3NCURSES) 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 back-
ground character; see bkgrnd(3NCURSES).
wecho_wchar
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 be-
ing output; for non-control characters, a considerable performance gain
may be enjoyed by employing them.
Forms-Drawing Characters
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-spe-
cific 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 charac-
ters in it may appear on the screen if the terminal type's database en-
try 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 de-
tails). Here are its descriptions for the normal, thick, and double
horizontal lines:
• U+2500 BOX DRAWINGS LIGHT HORIZONTAL
• U+2501 BOX DRAWINGS HEAVY HORIZONTAL
• U+2550 BOX DRAWINGS DOUBLE HORIZONTAL
RETURN VALUE
These functions return OK on success and ERR on failure.
In ncurses, wadd_wch and wecho_wchar return ERR if
• the curses screen has not been initialized,
• (for functions taking a WINDOW pointer argument) win is a null
pointer,
• wrapping to a new line is impossible because scrollok(3NCURSES) has
not been called on win (or stdscr, as applicable) when writing to
its bottom right location is attempted, or
• it is not possible to add a complete character at the cursor posi-
tion.
Functions prefixed with “mv” first perform cursor movement and fail if
the position (y, x) is outside the window boundaries.
NOTES
add_wch, mvadd_wch, mvwadd_wch, and echo_wchar may be implemented as
macros.
EXTENSIONS
The symbols (WACS_S3, WACS_S7, WACS_LEQUAL, WACS_GEQUAL, WACS_PI,
WACS_NEQUAL, and WACS_STERLING) are not standard. However, many pub-
licly 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 de-
velopers invented WACS-prefixed names for them.
PORTABILITY
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:
• NetBSD curses defines the symbols as a wchar_t within a cchar_t.
• 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 def-
initions not found in SVr4 implementations.
Not all Unicode-capable terminals provide support for VT100-style alter-
nate 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. Exist-
ing 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 descrip-
tion's acsc_chars (acsc) mapping as discussed in ncurses(3NCURSES) for
the environment variable NCURSES_NO_UTF8_ACS. In contrast, for the same
cases, the line-drawing characters described in addch(3NCURSES) will use
only the ASCII default values.
Having Unicode available does not solve all of the problems with line-
drawing for curses:
• 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.
• 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: § U+00A7 (section mark), Θ
U+0398 (theta), Φ U+03A6 (phi), δ U+03B4 (delta), ⌧ U+2327 (x in a
rectangle), ╬ U+256C (forms double vertical and horizontal), and ☒
U+2612 (ballot box with x).
Complex Characters
The complex character type cchar_t can store more than one wide charac-
ter (wchar_t). X/Open Curses does not mention this possibility, speci-
fying behavior only where wch is a single character, either spacing or
non-spacing.
ncurses assumes that wch is constructed using setcchar(3NCURSES), and in
turn that the result
• contains at most one spacing character at the beginning of its list
of wide characters, and zero or more non-spacing characters, or
• holds one non-spacing character.
In the latter case, ncurses adds the non-spacing character to the active
complex character.
HISTORY
X/Open Curses Issue 4 (1995) initially specified these functions. The
System V Interface Definition (SVID) Version 4 of the same year speci-
fied 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, except-
ing 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.
SEE ALSO
addch(3NCURSES) describes comparable functions of the ncurses library in
its non-wide-character configuration.
ncurses(3NCURSES), addwstr(3NCURSES), add_wchstr(3NCURSES),
attr(3NCURSES), bkgrnd(3NCURSES), clear(3NCURSES), getcchar(3NCURSES),
outopts(3NCURSES), refresh(3NCURSES), curses_variables(3NCURSES),
putwc(3)
ncurses 6.5 2025-02-01 add_wch(3NCURSES)
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