ncurses/man/curs_addch.3x

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.\" $Id: curs_addch.3x,v 1.136 2025/04/19 22:53:46 tom Exp $
.TH curs_addch 3X 2025-04-19 "ncurses @NCURSES_MAJOR@.@NCURSES_MINOR@" "Library calls"
.ie \n(.g \{\
.ds `` \(lq
.ds '' \(rq
.ds '  \(aq
.ds ^  \(ha
.ds ~  \(ti
.\}
.el \{\
.ie t .ds `` ``
.el   .ds `` ""
.ie t .ds '' ''
.el   .ds '' ""
.ds       '  '
.ds       ^  ^
.ds       ~  ~
.\}
.
.de bP
.ie n  .IP \(bu 4
.el    .IP \(bu 2
..
.SH NAME
\fB\%addch\fP,
\fB\%waddch\fP,
\fB\%mvaddch\fP,
\fB\%mvwaddch\fP,
\fB\%echochar\fP,
\fB\%wechochar\fP \-
add a \fIcurses\fP character to a window and advance the cursor
.SH SYNOPSIS
.nf
\fB#include <curses.h>
.PP
\fBint addch(const chtype \fIch\fP);
\fBint waddch(WINDOW * \fIwin\fP, const chtype \fIch\fP);
\fBint mvaddch(int \fIy\fP, int \fIx\fP, const chtype \fIch\fP);
\fBint mvwaddch(WINDOW * \fIwin\fP, int \fIy\fP, int \fIx\fP, const chtype \fIch\fP);
.PP
\fBint echochar(const chtype \fIch\fP);
\fBint wechochar(WINDOW * \fIwin\fP, const chtype \fIch\fP);
.PP
\fI/* (integer) constants */\fP
/*\fI .\|.\|. */ \fBACS_BLOCK;\fR
/*\fI .\|.\|. */ \fBACS_BOARD;\fR
/*\fI .\|.\|. */ \fBACS_BTEE;\fR
/*\fI .\|.\|. */ \fBACS_BULLET;\fR
/*\fI .\|.\|. */ \fBACS_CKBOARD;\fR
/*\fI .\|.\|. */ \fBACS_DARROW;\fR
/*\fI .\|.\|. */ \fBACS_DEGREE;\fR
/*\fI .\|.\|. */ \fBACS_DIAMOND;\fR
/*\fI .\|.\|. */ \fBACS_HLINE;\fR
/*\fI .\|.\|. */ \fBACS_LANTERN;\fR
/*\fI .\|.\|. */ \fBACS_LARROW;\fR
/*\fI .\|.\|. */ \fBACS_LLCORNER;\fR
/*\fI .\|.\|. */ \fBACS_LRCORNER;\fR
/*\fI .\|.\|. */ \fBACS_LTEE;\fR
/*\fI .\|.\|. */ \fBACS_PLMINUS;\fR
/*\fI .\|.\|. */ \fBACS_PLUS;\fR
/*\fI .\|.\|. */ \fBACS_RARROW;\fR
/*\fI .\|.\|. */ \fBACS_RTEE;\fR
/*\fI .\|.\|. */ \fBACS_S1;\fR
/*\fI .\|.\|. */ \fBACS_S9;\fR
/*\fI .\|.\|. */ \fBACS_TTEE;\fR
/*\fI .\|.\|. */ \fBACS_UARROW;\fR
/*\fI .\|.\|. */ \fBACS_ULCORNER;\fR
/*\fI .\|.\|. */ \fBACS_URCORNER;\fR
/*\fI .\|.\|. */ \fBACS_VLINE;\fR
\fI/* extensions */\fP
/*\fI .\|.\|. */ \fBACS_GEQUAL;\fR
/*\fI .\|.\|. */ \fBACS_LEQUAL;\fR
/*\fI .\|.\|. */ \fBACS_NEQUAL;\fR
/*\fI .\|.\|. */ \fBACS_PI;\fR
/*\fI .\|.\|. */ \fBACS_S3;\fR
/*\fI .\|.\|. */ \fBACS_S7;\fR
/*\fI .\|.\|. */ \fBACS_STERLING;\fR
.fi
.SH DESCRIPTION
.SS waddch
.B \%waddch
writes the
.I curses
character
.I ch
to the window
.IR win ","
then advances the cursor position,
analogously to the standard C library's \fI\%putchar\fP(3).
\fB\%ncurses\fP(3X) describes the variants of this function.
.PP
Construct a
.I curses
character
from a
.I char
by assignment or typecast.
Subsection \*(``Video Attributes\*('' of \fB\%attron\fP(3X) describes
how to manipulate its attributes and color pair.
(A color pair selection is not honored unless initialized;
see \fB\%start_color\fP(3X).)
.PP
The object or expression
.I ch
may contain attributes and/or a color pair identifier.
(A
.I \%chtype
can be copied from place to place using \fB\%winch\fP(3X) and
.BR \%waddch .)
See \fB\%curs_attr\fP(3X) for values of predefined constants that can be
usefully \*(``or\*(''ed with characters.
A
.I ch
whose character component is a space,
and whose only attribute is
.BR \%A_NORMAL ,
is a
.IR "blank character" ","
and therefore combines with the window's background character;
see \fB\%curs_bkgd\fP(3X).
.PP
If
.I ch
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 ch
is any other nonprintable character,
it is drawn in printable form using the same convention as
\fB\%unctrl\fP(3X).
Calling \fB\%winch\fP(3X) on the location of a nonprintable character
does not return the character itself,
but its \fB\%unctrl\fP(3X) representation.
.PP
Adding printable characters with \fB\%waddch\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 \%waddch
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 wechochar
.B \%echochar
and
.B \%wechochar
are equivalent to calling
.RB \%( w ) addch
followed by
.RB \%( w ) refresh
on
.B \%stdscr
or the specified window.
.I curses
interprets these functions as a hint to its optimizer
that only a single character cell in the window
is being altered between refreshes;
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 \%ACS_
that can be used with
.B \%waddch
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 L  L  Lx.
\&	ACS	acsc	\&
Symbol	Default	char	Glyph Name
_
ACS_BLOCK	#	0	solid square block
ACS_BOARD	#	h	board of squares
ACS_BTEE	+	v	bottom tee
ACS_BULLET	o	\*~	bullet
ACS_CKBOARD	:	a	checker board (stipple)
ACS_DARROW	v	.	arrow pointing down
ACS_DEGREE	\*'	f	degree symbol
ACS_DIAMOND	+	\(ga	diamond
ACS_GEQUAL	>	>	greater-than-or-equal-to
ACS_HLINE	\-	q	horizontal line
ACS_LANTERN	#	i	lantern symbol
ACS_LARROW	<	,	arrow pointing left
ACS_LEQUAL	<	y	less-than-or-equal-to
ACS_LLCORNER	+	m	lower left-hand corner
ACS_LRCORNER	+	j	lower right-hand corner
ACS_LTEE	+	t	left tee
ACS_NEQUAL	!	|	not-equal
ACS_PI	*	{	greek pi
ACS_PLMINUS	#	g	plus/minus
ACS_PLUS	+	n	plus
ACS_RARROW	>	+	arrow pointing right
ACS_RTEE	+	u	right tee
ACS_S1	\-	o	scan line 1
ACS_S3	\-	p	scan line 3
ACS_S7	\-	r	scan line 7
ACS_S9	\&_	s	scan line 9
ACS_STERLING	f	}	pound-sterling symbol
ACS_TTEE	+	w	top tee
ACS_UARROW	\*^	\-	arrow pointing up
ACS_ULCORNER	+	l	upper left-hand corner
ACS_URCORNER	+	k	upper right-hand corner
ACS_VLINE	|	x	vertical line
.TE
.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 a write to its bottom right location is attempted,
or
.bP
it is not possible to add a complete character at the cursor position.
.PP
The last may be due to different causes:
.bP
conversion of a wide character to a multibyte character sequence can
fail,
or
.bP
at least one of the bytes resulting from wide character conversion to a
multibyte character sequence cannot be added to the window.
See section \*(``PORTABILITY\*('' below regarding the use of
.B \%waddch
with wide characters.
.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 \%addch ","
.BR \%mvaddch ","
.BR \%mvwaddch ","
and
.B \%echochar
may be implemented as macros.
.SH EXTENSIONS
The symbols
.IR \%ACS_S3 ","
.IR \%ACS_S7 ","
.IR \%ACS_LEQUAL ","
.IR \%ACS_GEQUAL ","
.IR \%ACS_PI ","
.IR \%ACS_NEQUAL ","
and
.I \%ACS_STERLING
were not documented in any publicly released System\ V
.\" And did not exist yet as late as SVr4.
.\" https://github.com/ryanwoodsmall/oldsysv/blob/master/\
.\"   sysvr4/svr4/lib/xlibcurses/screen/curses.ed
and 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 ACS-prefixed names for them.
.\" in v1_9_5_950928_e227
.SH PORTABILITY
Applications employing
.I \%ncurses
extensions should condition their use on the visibility of the
.B \%NCURSES_VERSION
preprocessor macro.
.PP
X/Open Curses Issue\ 4 describes these functions.
It specifies no error conditions for them.
.PP
SVr4 describes a successful return value only as
\*(``an integer value other than
.IR ERR \*(''. \" Courier roman in source; SVID 4, vol. 3, p. 472
.PP
The defaults specified for forms-drawing characters apply in the POSIX
locale.
.SS "ACS Symbols"
X/Open Curses states that the
.I \%ACS_
definitions are
.I char
constants.
Some implementations are problematic.
.bP
Solaris
.IR curses ,
for example,
defines the ACS symbols as constants;
others define them as elements of an array.
.IP
SVr4 used an array,
.IR \%acs_map ,
as does
.IR \%ncurses "."
NetBSD
.I curses
also uses an array,
actually named
.IR \%_acs_char ,
with a \%\*(``#define\*('' for compatibility.
.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
(see \fB\%curs_add_wch\fP(3X)).
The misdefined symbols are the arrows and others that are not used for
line drawing.
.bP
X/Open Curses
(Issues\ 2 through 7)
has a typographical error
for the
.I \%ACS_LANTERN
symbol, equating its \*(``VT100+ Character\*('' to \*(``I\*(''
(capital I),
while the header files for SVr4
.I curses
and other implementations use \*(``i\*(''
(small i).
.IP
None of the terminal descriptions on Unix platforms use uppercase I,
except for Solaris
(in its
.I \%term\%info
entry for \fI\%screen\fP(1),
apparently based on the X/Open documentation around 1995).
On the other hand,
its
.B \%gs6300
(AT&T PC6300 with EMOTS Terminal Emulator)
description uses lowercase i.
.PP
The
.I displayed
values of
.I \%ACS_
constants depend on
.bP
the
.I \%ncurses
ABI \(em
for example,
wide-character versus non-wide-character configurations
(the former is capable of displaying Unicode while the latter is not),
and
.bP
whether the locale uses UTF-8 encoding.
.PP
In certain cases,
the terminal is unable to display forms-drawing characters
.I except
by using UTF-8;
see the discussion of the
.I \%NCURSES_NO_UTF8_ACS
environment variable in \fB\%ncurses\fP(3X).
.SS "Character Set"
X/Open Curses assumes that the parameter passed to
.I \%waddch
contains a single character.
That character may have been more than eight bits wide in an SVr3 or
SVr4 implementation,
but X/Open Curses leaves the width of a non-wide character code
unspecified.
The standard further does not specify the internal structure of a
.IR chtype ","
though the use of bit operations to combine the character code with
attributes and a color pair identifier into a
.I \%chtype
for passage to
.I \%waddch
is common.
A portable application uses only the macros discussed in
\fB\%curs_attr\fP(3X) to manipulate a
.IR \%chtype "."
.PP
In
.IR \%ncurses ,
.I \%chtype
holds an eight-bit character,
but the library allows a multibyte character sequence to be passed via a
succession of calls to
.IR \%waddch "."
Other implementations do not;
a
.I \%waddch
call transmits exactly one character,
which may be rendered in one or more screen locations depending on
whether it is printable
(see \fB\%unctrl\fP(3X)).
Depending on the locale,
.I \%ncurses
inspects the byte passed in each
.I \%waddch
call and checks whether the latest call continues a multibyte character.
When a character is
.IR complete ","
.I \%ncurses
displays the character and advances the cursor.
If the calling application interrupts the succession of bytes in
a multibyte character sequence by changing the current location \(em
for example,
with \fB\%wmove\fP(3X) \(em
.I \%ncurses
discards the incomplete character.
.PP
For portability to other implementations,
do not rely upon the foregoing behavior.
Check whether a character can be represented as a single byte in the
current locale.
.bP
If it can,
call either
.I \%waddch
or
.IR \%wadd_wch "."
.bP
If it cannot,
use only
.IR \%wadd_wch "."
.SH HISTORY
4BSD (1980)
introduced
.I \%waddch
and its variants.
.PP
SVr3 (1987)
added the
.I \%echochar
and
.I \%wechochar
functions and most of the
.I ACS_
constants,
except for
.IR \%ACS_GEQUAL ","
.IR \%ACS_LEQUAL ","
.IR \%ACS_NEQUAL ","
.IR \%ACS_PI ","
.IR \%ACS_S3 ","
.IR \%ACS_S7 ","
and
.IR \%ACS_STERLING "."
.PP
.I \%ncurses
1.9.6 (1995)
furnished the remaining
.I ACS_
constants.
.SH SEE ALSO
\fB\%curs_add_wch\fP(3X) describes comparable functions of the
.I \%ncurses
library in its wide-character configuration
.RI \%( ncursesw ).
.PP
\fB\%curses\fP(3X),
\fB\%curs_addchstr\fP(3X),
\fB\%curs_addstr\fP(3X),
\fB\%curs_attr\fP(3X),
\fB\%curs_bkgd\fP(3X),
\fB\%curs_clear\fP(3X),
\fB\%curs_inch\fP(3X),
\fB\%curs_outopts\fP(3X),
\fB\%curs_refresh\fP(3X),
\fB\%curs_variables\fP(3X),
\fB\%putchar\fP(3)