'\" t
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.\" $Id: curs_addch.3x,v 1.81 2024/03/23 20:38:57 tom Exp $
.TH curs_addch 3X 2024-03-23 "ncurses @NCURSES_MAJOR@.@NCURSES_MINOR@" "Library calls"
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.SH NAME
\fB\%addch\fP,
\fB\%waddch\fP,
\fB\%mvaddch\fP,
\fB\%mvwaddch\fP,
\fB\%echochar\fP,
\fB\%wechochar\fP \-
add a \fIcurses\fR 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);
.fi
.SH DESCRIPTION
.SS "Adding Characters"
.B \%waddch
puts the character
.I ch
at the cursor position of 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
If advancement occurs at the right margin,
.bP
the cursor automatically wraps to the beginning of the next line;
and
.bP
at the bottom of the current scrolling region,
and if \fB\%scrollok\fP(3X) is enabled for
.IR win ,
the scrolling region scrolls up one line.
.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 current line
of the window.
.bP
Line feed does a \fB\%clrtoeol\fP(3X),
then moves the cursor to the left margin on the next line of the window,
scrolling the window if the cursor was already on the last line.
.bP
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
.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).
.bP
.B \%waddch
displays control characters in
.BI \*^ X
notation.
.bP
Character codes above 127 are either meta characters
(if the screen has not been initialized,
or if \fB\%meta\fP(3X) has been called with a
.B TRUE
.I bf
parameter)
that render in
.BI M\- X
notation,
or they display as themselves.
In the latter case,
the values may not be printable;
.\" XXX: The following claim could be clearer.
this follows the X/Open specification.
.PP
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
Video attributes can be combined with a character argument passed to
.B \%waddch
by logical-ORing them into the character.
(Thus,
text,
including attributes,
can be copied from one place to another using \fB\%winch\fP(3X) and
.BR \%waddch .)
See \fB\%curs_attr\fP(3X) for values of predefined video attribute
constants that can be usefully OR'ed with characters.
.SS "Echoing Characters"
.B \%echochar
and
.B \%wechochar
are equivalent to calling
.RB \%( w ) addch
followed by
.RB \%( w ) refresh .
.I curses
interprets these functions as a hint that only a single 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 \%ACS_
that can be used with
.B \%waddch
to write line-drawing and other special characters to the screen.
.I \%ncurses
terms these
.I "forms-drawing characters."
The ACS default listed below is used if the
.B \%acs_chars
.RB ( \%acsc )
.I \%term\%info
capability does not define a terminal-specific 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
.B \%acs_chars
string capability,
and the characters in it may appear on the screen if the terminal's
database entry incorrectly advertises ACS support.
The name \*(``ACS\*('' originates in the Alternate Character Set feature
of the DEC VT100 terminal.
.PP
.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 ,
.B \%waddch
returns
.B ERR
if it is not possible to add a complete character at the cursor
position,
as when conversion of a multibyte character to a byte sequence fails,
or at least one of the resulting bytes cannot be added to the window.
See section \*(``PORTABILITY\*('' below regarding the use of
.B \%waddch
with multibyte characters.
.PP
If \fB\%scrollok\fP(3X) is not enabled,
.B \%waddch
can successfully write a character at the bottom right location of the
window.
However,
.I \%ncurses
returns
.B ERR
because it is not possible to wrap to a new line.
.PP
Functions with a \*(``mv\*('' prefix first perform cursor movement using
\fB\%wmove\fP(3X) and fail if the position is outside the window,
or
(for \*(``mvw\*('' functions)
if the
.I \%WINDOW
pointer is null.
.SH NOTES
.BR \%addch ,
.BR \%mvaddch ,
.BR \%mvwaddch ,
and
.B \%echochar
may be implemented as macros.
.SH PORTABILITY
X/Open Curses,
Issue 4 describes these functions.
It specifies no error conditions for them.
The defaults specified for forms-drawing characters apply in the POSIX
locale.
.SS "ACS Symbols"
X/Open Curses states that the
.B \%ACS_
definitions are
.I char
constants.
.PP
Some implementations are problematic.
.bP
Solaris
.IR curses ,
for example,
define the ACS symbols as constants;
others define them as elements of an array.
.IP
This implementation uses an array,
.BR \%acs_map ,
as did SVr4
.IR curses .
NetBSD also uses an array,
actually named
.BR \%_acs_char ,
with a
.B \%#define
for compatibility.
.bP
HP-UX
.I curses
equates some of the
.B \%ACS_
symbols to the analogous
.B \%WACS_
symbols as if the
.B \%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
.B \%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
Some ACS symbols
.RB ( \%ACS_S3 ,
.BR \%ACS_S7 ,
.BR \%ACS_LEQUAL ,
.BR \%ACS_GEQUAL ,
.BR \%ACS_PI ,
.BR \%ACS_NEQUAL ,
and
.BR \%ACS_STERLING )
were not documented in any publicly released System\ V.
However,
many publicly available
.I \%term\%info
entries include
.B \%acsc
strings in which their key characters (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.
.PP
The
.I displayed
values of
.B \%ACS_
constants depend on
.bP
the
.I \%ncurses
ABI\(emfor 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
.B \%waddch
contains a single character.
As discussed in \fB\%curs_attr\fP(3X),
that character may have been more than eight bits wide in an SVr3 or
SVr4 implementation,
but in the X/Open Curses model,
the details are not given.
The important distinction between SVr4
.I curses
and X/Open Curses is that the latter separates non-character information
(attributes and color)
from the character code,
which SVr4 packs into a
.I \%chtype
for passage to
.BR \%waddch .
.PP
In
.IR \%ncurses ,
.I \%chtype
holds an eight-bit character.
But
.I \%ncurses
allows a multibyte character to be passed in a succession of calls to
.BR \%waddch .
Other implementations do not;
a
.B \%waddch
call transmits exactly one character,
which may be rendered in one or more screen locations depending on
whether it is printable.
.PP
Depending on the locale settings,
.I \%ncurses
inspects the byte passed in each
.B \%waddch
call,
and checks whether the latest call continues a multibyte sequence.
When a character is
.IR complete ,
.I \%ncurses
displays the character and advances the window's current location.
.PP
If the calling application interrupts the succession of bytes in
a multibyte character sequence by moving the current location
(for example,
with \fB\%wmove\fP(3X)),
.I \%ncurses
discards the incomplete character.
.PP
For portability to other implementations,
do not rely upon this behavior.
Check whether a character can be represented as a single byte in the
current locale.
.bP
If it can,
call either
.B \%waddch
or \fB\%wadd_wch\fP(3X).
.bP
If it cannot,
use only
\fB\%wadd_wch\fP(3X).
.SS TABSIZE
SVr4 and other versions of
.I curses
implement the
.B \%TABSIZE
variable,
but X/Open Curses does not specify it
(see \fB\%curs_variables\fP(3X)).
.SH SEE ALSO
\fB\%curses\fP(3X),
\fB\%curs_addchstr\fP(3X),
\fB\%curs_addstr\fP(3X),
\fB\%curs_attr\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)
.PP
\fB\%curs_add_wch\fP(3X) describes comparable functions of the
.I \%ncurses
library in its wide-character configuration
.RI ( \%ncursesw ).