path: root/man/curs_add_wch.3x

'\" t
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.\" $Id: curs_add_wch.3x,v 1.125 2025/11/12 01:06:36 tom Exp $
.TH curs_add_wch 3X 2025-11-11 "ncurses @NCURSES_MAJOR@.@NCURSES_MINOR@" "Library calls"
.ie \n(.g \{\
.ds `` \(lq
.ds '' \(rq
.\}
.el \{\
.ie t .ds `` ``
.el   .ds `` ""
.ie t .ds '' ''
.el   .ds '' ""
.\}
.
.de bP
.ie n  .IP \(bu 4
.el    .IP \(bu 2
..
.SH NAME
\fB\%add_wch\fP,
\fB\%wadd_wch\fP,
\fB\%mvadd_wch\fP,
\fB\%mvwadd_wch\fP,
\fB\%echo_wchar\fP,
\fB\%wecho_wchar\fP \-
add a \fIcurses\fR complex character to a window, possibly advancing the cursor
.SH SYNOPSIS
.nf
\fB#include <curses.h>
.PP
\fBint add_wch(const cchar_t * \fIwch\fP);
\fBint wadd_wch(WINDOW * \fIwin\fP, const cchar_t * \fIwch\fP);
\fBint mvadd_wch(int \fIy\fP, int \fIx\fP, const cchar_t * \fIwch\fP);
\fBint mvwadd_wch(WINDOW * \fIwin\fP, int \fIy\fP, int \fIx\fP, const cchar_t * \fIwch\fP);
.PP
\fBint echo_wchar(const cchar_t * \fIwch\fP);
\fBint wecho_wchar(WINDOW * \fIwin\fP, const cchar_t *\fIwch\fP);
.PP
\fI/* (integer) constants */\fP
/*\fI .\|.\|. */ \fBWACS_BLOCK;\fR
/*\fI .\|.\|. */ \fBWACS_BOARD;\fR
/*\fI .\|.\|. */ \fBWACS_BTEE;\fR
/*\fI .\|.\|. */ \fBWACS_BULLET;\fR
/*\fI .\|.\|. */ \fBWACS_CKBOARD;\fR
/*\fI .\|.\|. */ \fBWACS_DARROW;\fR
/*\fI .\|.\|. */ \fBWACS_DEGREE;\fR
/*\fI .\|.\|. */ \fBWACS_DIAMOND;\fR
/*\fI .\|.\|. */ \fBWACS_HLINE;\fR
/*\fI .\|.\|. */ \fBWACS_LANTERN;\fR
/*\fI .\|.\|. */ \fBWACS_LARROW;\fR
/*\fI .\|.\|. */ \fBWACS_LLCORNER;\fR
/*\fI .\|.\|. */ \fBWACS_LRCORNER;\fR
/*\fI .\|.\|. */ \fBWACS_LTEE;\fR
/*\fI .\|.\|. */ \fBWACS_PLMINUS;\fR
/*\fI .\|.\|. */ \fBWACS_PLUS;\fR
/*\fI .\|.\|. */ \fBWACS_RARROW;\fR
/*\fI .\|.\|. */ \fBWACS_RTEE;\fR
/*\fI .\|.\|. */ \fBWACS_S1;\fR
/*\fI .\|.\|. */ \fBWACS_S9;\fR
/*\fI .\|.\|. */ \fBWACS_TTEE;\fR
/*\fI .\|.\|. */ \fBWACS_UARROW;\fR
/*\fI .\|.\|. */ \fBWACS_ULCORNER;\fR
/*\fI .\|.\|. */ \fBWACS_URCORNER;\fR
/*\fI .\|.\|. */ \fBWACS_VLINE;\fR
\fI/* extensions */\fP
/*\fI .\|.\|. */ \fBWACS_GEQUAL;\fR
/*\fI .\|.\|. */ \fBWACS_LEQUAL;\fR
/*\fI .\|.\|. */ \fBWACS_NEQUAL;\fR
/*\fI .\|.\|. */ \fBWACS_PI;\fR
/*\fI .\|.\|. */ \fBWACS_S3;\fR
/*\fI .\|.\|. */ \fBWACS_S7;\fR
/*\fI .\|.\|. */ \fBWACS_STERLING;\fR
\fI/* extensions for thick lines */\fP
/*\fI .\|.\|. */ \fBWACS_T_BTEE;\fR
/*\fI .\|.\|. */ \fBWACS_T_HLINE;\fR
/*\fI .\|.\|. */ \fBWACS_T_LLCORNER;\fR
/*\fI .\|.\|. */ \fBWACS_T_LRCORNER;\fR
/*\fI .\|.\|. */ \fBWACS_T_LTEE;\fR
/*\fI .\|.\|. */ \fBWACS_T_PLUS;\fR
/*\fI .\|.\|. */ \fBWACS_T_RTEE;\fR
/*\fI .\|.\|. */ \fBWACS_T_TTEE;\fR
/*\fI .\|.\|. */ \fBWACS_T_ULCORNER;\fR
/*\fI .\|.\|. */ \fBWACS_T_URCORNER;\fR
/*\fI .\|.\|. */ \fBWACS_T_VLINE;\fR
\fI/* extensions for double lines */\fP
/*\fI .\|.\|. */ \fBWACS_D_BTEE;\fR
/*\fI .\|.\|. */ \fBWACS_D_HLINE;\fR
/*\fI .\|.\|. */ \fBWACS_D_LLCORNER;\fR
/*\fI .\|.\|. */ \fBWACS_D_LRCORNER;\fR
/*\fI .\|.\|. */ \fBWACS_D_LTEE;\fR
/*\fI .\|.\|. */ \fBWACS_D_PLUS;\fR
/*\fI .\|.\|. */ \fBWACS_D_RTEE;\fR
/*\fI .\|.\|. */ \fBWACS_D_TTEE;\fR
/*\fI .\|.\|. */ \fBWACS_D_ULCORNER;\fR
/*\fI .\|.\|. */ \fBWACS_D_URCORNER;\fR
/*\fI .\|.\|. */ \fBWACS_D_VLINE;\fR
.fi
.SH DESCRIPTION
.SS wadd_wch
.B \%wadd_wch
writes the
.I curses
complex character
.I wch
to the window
.IR win ","
then may advance the cursor position,
analogously to the standard C library's \fI\%putwchar\fP(3).
\fB\%ncurses\fP(3X) describes the variants of this function.
.PP
Construct a
.I curses
complex character
from a
.I wchar_t
with \fB\%setcchar\fP(3X).
A
.I \%cchar_t
can be copied from place to place using \fB\%win_wch\fP(3X) and
.BR \%wadd_wch "."
.I curses
defines constants to aid the manipulation of character attributes;
see \fB\%curs_attr\fP(3X).
A complex character whose only character component is a wide space,
and whose only attribute is
.BR \%WA_NORMAL ,
is a
.IR "blank character" ","
and therefore combines with the window's background character;
see \fB\%curs_bkgrnd\fP(3X).
.PP
Much behavior depends on whether the wide characters in
.I wch
are spacing or non-spacing;
see subsection \*(``Complex Characters\*('' below.
.bP
If
.I wch
contains a spacing character,
then any character at the cursor is first removed.
The complex character
.IR wch ","
with its attributes and color pair identifier,
becomes the
.I base
of the
.IR "active complex character" "."
.bP
If
.I wch
contains only non-spacing characters,
.\" XXX: see wadd_wch_literal (the beginning of the array may be
.\" nonspacing)
they are combined with the active complex character.
.I curses
ignores its attributes and color pair identifier,
and does not advance the cursor.
.PP
Further non-spacing characters added with
.B \%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.
.PP
If
.I wch
is a
backspace,
carriage return,
line feed,
or
tab,
the cursor moves appropriately within the window.
.bP
Backspace moves the cursor one character left;
at the left margin of a window,
it does nothing.
.bP
Carriage return moves the cursor to the left margin on the same line of
the window.
.bP
Line feed does a \fB\%clrtoeol\fP(3X),
then advances as if from the right margin.
.bP
Tab advances the cursor to the next tab stop
(possibly on the next line);
these are placed at every eighth column by default.
.IP
Alter the tab interval with the
.B \%TABSIZE
extension;
see \fB\%curs_variables\fP(3X).
.PP
If
.I wch
is any other nonprintable character,
.I curses
draws it in printable form using the same convention as
\fB\%wunctrl\fP(3X).
Calling \fB\%win_wch\fP(3X) on the location of a nonprintable character
does not retrieve the character itself,
but its \fB\%wunctrl\fP(3X) representation.
.PP
Adding spacing characters with \fB\%wadd_wch\fP
causes it to wrap at the right margin of the window:
.bP
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.
.bP
If the cursor is at the bottom of the scrolling region
when advancement occurs at the right margin,
and \fB\%scrollok\fP(3X) is enabled for
.IR win ,
the scrolling region scrolls up one line
and the cursor wraps as above.
Otherwise,
advancement and scrolling do not occur,
and
.B \%wadd_wch
returns
.BR ERR "."
.PP
A window's margins may coincide with the screen boundaries.
This may be a problem when
.I \%ncurses
updates the screen to match the curses window.
When their right and bottom margins coincide,
.I \%ncurses
uses different strategies to handle the variations of scrolling and wrapping
at the lower-right corner
by depending on the terminal capabilities:
.bP
If the terminal does not automatically wrap as characters
are added at the right margin
(i.e., auto right margins),
.I \%ncurses
writes the character directly.
.bP
If the terminal has auto right margins,
but also has capabilities for turning auto margins off and on,
.I \%ncurses
turns the auto margin feature off temporarily
when writing to the lower-right corner.
.bP
If the terminal has an insertion mode which can be turned off and on,
.I \%ncurses
writes the character just before the lower-right corner,
and then inserts a character to push the update into the corner.
.SS wecho_wchar
.B \%echo_wchar
and
.B \%wecho_wchar
are equivalent to calling
.RB \%( w ) add_wch
followed by
.RB \%( w ) refresh
on
.B \%stdscr
or the specified window.
.I 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.
.\" TODO: Combine the following with the "Line Drawing" subsection of
.\" terminfo(5) and replace this with a cross reference there.
.SS "Forms-Drawing Characters"
.I curses
defines macros starting with
.B \%WACS_
that can be used with
.B \%wadd_wch
to write line-drawing and other symbols to the screen.
.I \%ncurses
terms these
.I "forms-drawing characters."
.I curses
uses the ACS default listed below if the terminal type lacks the
.B \%acs_chars
.RB \%( 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
.B \%acs_chars
.RB \%( 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.
.PP
.ie t .ne 4v
.el   .ne 5v
.TS
Lb Lb Lb Lb Lb
Lb Lb Lb Lb Lb
Lb L  L  L  Lw(15n)x.
\&	Unicode	ACS	acsc	\&
Symbol	Default	Default	char	Glyph Name
_
WACS_BLOCK	U+25ae	#	0	T{
solid square block
T}
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	T{
checker board (stipple)
T}
WACS_DARROW	U+2193	v	.	T{
arrow pointing down
T}
WACS_DEGREE	U+00b0	'	f	degree symbol
WACS_DIAMOND	U+25c6	+	\(ga	diamond
WACS_GEQUAL	U+2265	>	>	T{
.if n .na \" avoid adjustment warning from groff
greater-than-or-equal-to
T}
WACS_HLINE	U+2500	\-	q	horizontal line
WACS_LANTERN	U+2603	#	i	lantern symbol
WACS_LARROW	U+2190	<	,	T{
arrow pointing left
T}
WACS_LEQUAL	U+2264	<	y	T{
.if n .na \" avoid adjustment warning from groff
less-than-or-equal-to
T}
WACS_LLCORNER	U+2514	+	m	T{
lower left-hand corner
T}
WACS_LRCORNER	U+2518	+	j	T{
lower right-hand corner
T}
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	>	+	T{
arrow pointing right
T}
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	}	T{
.if n .na \" avoid adjustment warning from groff
pound-sterling symbol
T}
WACS_TTEE	U+252c	+	w	top tee
WACS_UARROW	U+2191 	^	\-	T{
arrow pointing up
T}
WACS_ULCORNER	U+250c	+	l	T{
upper left-hand corner
T}
WACS_URCORNER	U+2510	+	k	T{
upper right-hand corner
T}
WACS_VLINE	U+2502	|	x	vertical line
.TE
.PP
The
.I \%ncurses
wide API also defines symbols for thick lines
.RB \%( acsc
\*(``J\*('' through \*(``N\*('',
\*(``T\*('' through \*(``X\*('',
and \*(``Q\*(''):
.PP
.TS
Lb Lb Lb Lb Lb
Lb Lb Lb Lb Lb
Lb L  L  L  Lw(14n)x.
\&	Unicode	ASCII	acsc	\&
ACS Name	Default	Default	Char	Glyph Name
_
WACS_T_BTEE	U+253b	+	V	T{
thick tee pointing up
T}
WACS_T_HLINE	U+2501	-	Q	T{
thick horizontal line
T}
WACS_T_LLCORNER	U+2517	+	M	T{
thick lower left corner
T}
WACS_T_LRCORNER	U+251b	+	J	T{
thick lower right corner
T}
WACS_T_LTEE	U+252b	+	T	T{
thick tee pointing right
T}
WACS_T_PLUS	U+254b	+	N	T{
thick large plus
T}
WACS_T_RTEE	U+2523	+	U	T{
thick tee pointing left
T}
WACS_T_TTEE	U+2533	+	W	T{
thick tee pointing down
T}
WACS_T_ULCORNER	U+250f	+	L	T{
thick upper left corner
T}
WACS_T_URCORNER	U+2513	+	K	T{
thick upper right corner
T}
WACS_T_VLINE	U+2503	|	X	T{
thick vertical line
T}
.TE
.PP
and for double lines
.RB \%( acsc
\*(``A\*('' through \*(``I\*('',
plus \*(``R\*('' and \*(``Y\*(''):
.PP
.TS
Lb Lb Lb Lb Lb
Lb Lb Lb Lb Lb
Lb L  L  L  Lw(14n)x.
\&	Unicode	ASCII	acsc	\&
ACS Name	Default	Default	Char	Glyph Name
_
WACS_D_BTEE	U+2569	+	H	T{
double tee pointing up
T}
WACS_D_HLINE	U+2550	-	R	T{
double horizontal line
T}
WACS_D_LLCORNER	U+255a	+	D	T{
double lower left corner
T}
WACS_D_LRCORNER	U+255d	+	A	T{
double lower right corner
T}
WACS_D_LTEE	U+2560	+	F	T{
double tee pointing right
T}
WACS_D_PLUS	U+256c	+	E	T{
double large plus
T}
WACS_D_RTEE	U+2563	+	G	T{
double tee pointing left
T}
WACS_D_TTEE	U+2566	+	I	T{
double tee pointing down
T}
WACS_D_ULCORNER	U+2554	+	C	T{
double upper left corner
T}
WACS_D_URCORNER	U+2557	+	B	T{
double upper right corner
T}
WACS_D_VLINE	U+2551	|	Y	T{
double vertical line
T}
.TE
.PP
Unicode's descriptions for these characters differs slightly from
\fI\%ncurses\fP,
by introducing the term \*(``light\*('' (along with less important details).
Here are its descriptions for the normal, thick, and double horizontal lines:
.bP
U+2500 BOX DRAWINGS LIGHT HORIZONTAL
.bP
U+2501 BOX DRAWINGS HEAVY HORIZONTAL
.bP
U+2550 BOX DRAWINGS DOUBLE HORIZONTAL
.SH RETURN VALUE
These functions return
.B OK
on success and
.B ERR
on failure.
.PP
In
.IR \%ncurses ,
these functions fail if
.bP
the
.I curses
screen has not been initialized,
.bP
(for functions taking a
.I \%WINDOW
pointer argument)
.I win
is a null pointer,
.bP
wrapping to a new line is impossible because \fB\%scrollok\fP(3X) has
not been called on
.I win
(or
.BR \%stdscr ","
as applicable)
when writing to its bottom right location is attempted,
or
.bP
it is not possible to add a complete character at the cursor position.
.PP
Functions prefixed with \*(``mv\*('' first perform cursor movement and
fail if the position
.RI ( y ,
.IR x )
is outside the window boundaries.
.SH NOTES
.BR add_wch ","
.BR mvadd_wch ","
.BR mvwadd_wch ","
and
.B echo_wchar
may be implemented as macros.
.SH EXTENSIONS
The symbols
.IR \%WACS_S3 ","
.IR \%WACS_S7 ","
.IR \%WACS_LEQUAL ","
.IR \%WACS_GEQUAL ","
.IR \%WACS_PI ","
.IR \%WACS_NEQUAL ","
and
.I \%WACS_STERLING
are not standard.
However,
many publicly available
.I \%term\%info
entries include
.B \%acs_chars
.RB \%( acsc )
capabilities in which their key characters
.RB ( pryz{|} )
are embedded,
and a second-hand list of their character descriptions has come to
light.
The
.I \%ncurses
developers invented WACS-prefixed names for them.
.\" in v5_2_20020209
.SH PORTABILITY
Applications employing
.I \%ncurses
extensions should condition their use on the visibility of the
.B \%NCURSES_VERSION
preprocessor macro.
.PP
These functions are described in X/Open Curses Issue\ 4.
It specifies no error conditions for them.
.PP
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
.I \%cchar_t
data, e.g., in the discussion of
.IR \%border_set "."
A few implementations are problematic:
.bP
NetBSD
.I curses
defines the symbols as a
.I \%wchar_t
within a
.IR \%cchar_t "."
.bP
HP-UX
.I curses
equates some of the
.I \%ACS_
symbols to the analogous
.I \%WACS_
symbols as if the
.I \%ACS_
symbols were
wide characters.
The misdefined symbols are the arrows
and other symbols which are not used for line-drawing.
.PP
X/Open Curses does not specify symbols for thick- or double-lines.
SVr4
.I curses
implementations defined their line-drawing symbols
in terms of intermediate symbols.
.I \%ncurses
extends those symbols,
providing new definitions not found in SVr4 implementations.
.PP
Not all Unicode-capable terminals provide support for VT100-style
alternate character sets (i.e., the
.I \%acsc_chars
.RB ( 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
.I curses
(AIX, HP-UX, Solaris)
use only the
.I \%acsc_chars
.RB ( acsc )
character-mapping to provide this feature.
As a result,
those implementations can use only single-byte line-drawing characters.
.I \%ncurses
5.3 (2002) provided a table of Unicode values to solve
these problems.
NetBSD
.I curses
incorporated that table in 2010.
.PP
.I \%ncurses
uses the Unicode values instead of the terminal type description's
.I \%acsc_chars
.RB ( acsc )
mapping as discussed in
\fB\%ncurses\fP(3X) for the environment variable
.IR \%NCURSES_NO_UTF8_ACS "."
In contrast, for the same cases, the line-drawing characters
described in \fB\%addch\fP(3X) will use only the ASCII default values.
.PP
Having Unicode available does not solve all of the problems with
line-drawing for
.IR curses ":"
.bP
The closest Unicode equivalents to the
VT100 graphics
.IR S1 ","
.IR S3 ","
.IR S7 ","
and
.I S9
frequently are not displayed at
the regular intervals which the terminal used.
.bP
The
.I 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.
.IP
Lacking documentation, most readers assume that a
.I "storm lantern"
was intended.
But there are several possibilities, all with problems.
.IP
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.
.IP
Most
.I "storm lanterns"
have a tapering glass chimney
(to guard against tipping);
some have a wire grid protecting the chimney.
.IP
For the tapering appearance, \[u2603] U+2603 was adequate.
In use on a terminal, no one can tell what the image represents.
Unicode calls it a snowman.
.IP
Others have suggested these alternatives:
\[sc] U+00A7 (section mark),
\[u0398] U+0398 (theta),
\[u03A6] U+03A6 (phi),
\[u03B4] U+03B4 (delta),
\[u2327] U+2327 (x in a rectangle),
\[u256C] U+256C (forms double vertical and horizontal), and
\[u2612] U+2612 (ballot box with x).
.SS "Complex Characters"
The complex character type
.I \%cchar_t
can store more than one wide character
.RI \%( wchar_t ).
X/Open Curses does not mention this possibility,
specifying behavior only where
.I wch
is a single character,
either spacing or non-spacing.
.PP
.I \%ncurses
assumes that
.I wch
is constructed using \fB\%setcchar\fP(3X),
and in turn that the result
.bP
contains at most one spacing character at the beginning of its list of
wide characters,
and zero or more non-spacing characters,
or
.bP
holds one non-spacing character.
.PP
In the latter case,
.I \%ncurses
adds the non-spacing character to the active complex character.
.SH HISTORY
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
.I \%waddwch
(and the usual variants),
.IR \%echowchar ","
and
.IR \%wechowchar "."
.\" SVID 4, vol 3., p. 475
These were later additions to
.RI SVr4. x ,
not appearing in the first SVr4 (1989).
They differed from X/Open's later
.I \%wadd_wch
and
.I \%wecho_wchar
in that they each took an argument of type
.I \%wchar_t
instead of
.IR \%cchar_t "."
SVID defined no
.I \% WACS_
symbols.
.PP
X/Open Curses Issue\ 4 also defined many of the
.I WACS_
constants,
excepting
.IR \%WACS_GEQUAL ","
.IR \%WACS_LEQUAL ","
.IR \%WACS_NEQUAL ","
.IR \%WACS_PI ","
.IR \%WACS_S3 ","
.IR \%WACS_S7 ","
and
.IR \%WACS_STERLING ";"
and those for drawing thick and double lines.
.PP
.I \%ncurses
5.3 (2002)
furnished the remaining
.I WACS_
constants.
.SH SEE ALSO
\fB\%curs_addch\fP(3X) describes comparable functions of the
.I \%ncurses
library in its non-wide-character configuration.
.PP
\fB\%curses\fP(3X),
\fB\%curs_addwstr\fP(3X),
\fB\%curs_add_wchstr\fP(3X),
\fB\%curs_attr\fP(3X),
\fB\%curs_bkgrnd\fP(3X),
\fB\%curs_clear\fP(3X),
\fB\%curs_getcchar\fP(3X),
\fB\%curs_outopts\fP(3X),
\fB\%curs_refresh\fP(3X),
\fB\%curs_variables\fP(3X),
\fB\%putwc\fP(3)