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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | NOTES | EXTENSIONS | PORTABILITY | HISTORY | SEE ALSO | COLOPHON |
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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
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. curses defines constants to aid the
manipulation of character attributes; see curs_attr(3X). 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.
• 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.
• 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.
• 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(3X), 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
curs_variables(3X).
If wch is any other nonprintable character, curses draws it in
printable form using the same convention as wunctrl(3X). Calling
win_wch(3X) on the location of a nonprintable character does not
retrieve 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:
• 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.
• 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:
• 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.
• 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.
• 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.
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 being 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. 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:
• U+2500 BOX DRAWINGS LIGHT HORIZONTAL
• U+2501 BOX DRAWINGS HEAVY HORIZONTAL
• U+2550 BOX DRAWINGS DOUBLE HORIZONTAL
These functions return OK on success and ERR on failure.
In ncurses, these functions fail 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(3X) 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
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:
• 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 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:
• 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
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
• 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.
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)
This page is part of the ncurses (new curses) project.
Information about the project can be found at
⟨https://invisible-island.net/ncurses/ncurses.html⟩. If you have a
bug report for this manual page, send it to bug-ncurses@gnu.org.
This page was obtained from the tarball ncurses-6.6.tar.gz fetched
from ⟨https://ftp.gnu.org/gnu/ncurses/⟩ on 2026-01-16. If you
discover any rendering problems in this HTML version of the page,
or you believe there is a better or more up-to-date source for the
page, or you have corrections or improvements to the information
in this COLOPHON (which is not part of the original manual page),
send a mail to man-pages@man7.org
ncurses @NCURSES_MAJOR@.@NCU... 2025-11-11 curs_add_wch(3X)
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HTML rendering created 2026-01-16 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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