curs_addch(3X) Library calls curs_addch(3X)
NAME
addch, waddch, mvaddch, mvwaddch, echochar, wechochar - add a curses
character to a window and advance the cursor
SYNOPSIS
#include <curses.h>
int addch(const chtype ch);
int waddch(WINDOW * win, const chtype ch);
int mvaddch(int y, int x, const chtype ch);
int mvwaddch(WINDOW * win, int y, int x, const chtype ch);
int echochar(const chtype ch);
int wechochar(WINDOW * win, const chtype ch);
/* (integer) constants */
/* ... */ ACS_BLOCK;
/* ... */ ACS_BOARD;
/* ... */ ACS_BTEE;
/* ... */ ACS_BULLET;
/* ... */ ACS_CKBOARD;
/* ... */ ACS_DARROW;
/* ... */ ACS_DEGREE;
/* ... */ ACS_DIAMOND;
/* ... */ ACS_HLINE;
/* ... */ ACS_LANTERN;
/* ... */ ACS_LARROW;
/* ... */ ACS_LLCORNER;
/* ... */ ACS_LRCORNER;
/* ... */ ACS_LTEE;
/* ... */ ACS_PLMINUS;
/* ... */ ACS_PLUS;
/* ... */ ACS_RARROW;
/* ... */ ACS_RTEE;
/* ... */ ACS_S1;
/* ... */ ACS_S9;
/* ... */ ACS_TTEE;
/* ... */ ACS_UARROW;
/* ... */ ACS_ULCORNER;
/* ... */ ACS_URCORNER;
/* ... */ ACS_VLINE;
/* extensions */
/* ... */ ACS_GEQUAL;
/* ... */ ACS_LEQUAL;
/* ... */ ACS_NEQUAL;
/* ... */ ACS_PI;
/* ... */ ACS_S3;
/* ... */ ACS_S7;
/* ... */ ACS_STERLING;
DESCRIPTION
waddch
waddch writes the curses character ch to the window win, then advances
the cursor position, analogously to the standard C library's putchar(3).
ncurses(3X) describes the variants of this function.
Construct a curses character from a char by assignment or typecast.
Subsection "Video Attributes" of attron(3X) describes how to manipulate
its attributes and color pair. (A color pair selection is not honored
unless initialized; see start_color(3X).)
The object or expression ch may contain attributes and/or a color pair
identifier. (A chtype can be copied from place to place using winch(3X)
and waddch.) curses defines constants to aid the manipulation of
character attributes; see curs_attr(3X). A ch whose character component
is a space, and whose only attribute is A_NORMAL, is a blank character,
and therefore combines with the window's background character; see
curs_bkgd(3X).
If ch is a backspace, carriage return, line feed, or tab, the cursor
moves appropriately within the window.
o Backspace moves the cursor one character left; at the left margin of
a window, it does nothing.
o Carriage return moves the cursor to the left margin on the same line
of the window.
o Line feed does a clrtoeol(3X), then advances as if from the right
margin.
o 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 ch is any other nonprintable character, curses draws it in printable
form using the same convention as unctrl(3X). Calling winch(3X) on the
location of a nonprintable character does not return the character
itself, but its unctrl(3X) representation.
Adding printable characters with waddch causes it to wrap at the right
margin of the window:
o 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.
o 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 waddch 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:
o 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.
o 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.
o 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.
wechochar
echochar and wechochar are equivalent to calling (w)addch followed by
(w)refresh on stdscr or the specified window. 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.
Forms-Drawing Characters
curses defines macros starting with ACS_ that can be used with waddch 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.
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 + ` 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
RETURN VALUE
These functions return OK on success and ERR on failure.
In ncurses, these functions fail if
o the curses screen has not been initialized,
o (for functions taking a WINDOW pointer argument) win is a null
pointer,
o wrapping to a new line is impossible because scrollok(3X) has not
been called on win (or stdscr, as applicable) when a write to its
bottom right location is attempted, or
o it is not possible to add a complete character at the cursor
position.
The last may be due to different causes:
o conversion of a wide character to a multibyte character sequence can
fail, or
o 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 waddch with wide
characters.
Functions prefixed with "mv" first perform cursor movement and fail if
the position (y, x) is outside the window boundaries.
NOTES
addch, mvaddch, mvwaddch, and echochar may be implemented as macros.
EXTENSIONS
The symbols ACS_S3, ACS_S7, ACS_LEQUAL, ACS_GEQUAL, ACS_PI, ACS_NEQUAL,
and ACS_STERLING were not documented in any publicly released System V
and 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, which identifies them as VT100 special
characters.
The DEC Special Character and Line Drawing Set (VT100) is indexed by an
ASCII character in the range 96 (`) to 126 (~). That index character is
part of the definition for the curses ACS_ symbols. The VT100 special
characters can be categorized in three groups:
o useful graphic symbols with a standard ACS_ symbol, (e.g., the line-
drawing symbols),
o possibly useful characters (these non-standard symbols),
o representations of control characters (e.g., newline and vertical
tabulation).
A few ACS_ symbols do not fit into DEC's VT100 scheme. The AT&T Teletype
5410v1 arrow symbols and ACS_BLOCK use indices outside the range 96 to
126. Two of the Teletype symbols use indices in that range, with
different meaning versus the VT100:
o ACS_BOARD corresponds to the VT100 symbol for newline
o ACS_LANTERN corresponds to the VT100 symbol for vertical tabulation
AT&T defined ACS_ names for the most useful graphic symbols, as well as
for its own. Its header file commented:
/*
* Standard alternate character set. The current ACS world is
* evolving, so we support only a widely available subset: the
* line drawing characters from the VT100, plus a few from the
* Teletype 5410v1. Eventually there may be support of more
* sophisticated ACS line drawing, such as that in the Teletype
* 5410, the HP line drawing set, and the like. There may be
* support for some non line oriented characters as well.
*
* Line drawing ACS names are of the form ACS_trbl, where t is
* the top, r is the right, b is the bottom, and l is the left.
* t, r, b, and l might be B (blank), S (single), D (double), or
* T (thick). The subset defined here only uses B and S.
*/
Although these less-useful graphic symbols were not given names, they
were used in terminfo entries. The ncurses developers invented ACS-
prefixed names for them.
PORTABILITY
Applications employing ncurses extensions should condition their use on
the visibility of the NCURSES_VERSION preprocessor macro.
X/Open Curses Issue 4 describes these functions. It specifies no error
conditions for them.
SVr4 describes a successful return value only as "an integer value other
than ERR".
The defaults specified for forms-drawing characters apply in the POSIX
locale.
ACS Symbols
X/Open Curses states that the ACS_ definitions are char constants. Some
implementations are problematic.
o Solaris curses, for example, defines the ACS symbols as constants;
others define them as elements of an array.
SVr4 used an array, acs_map, as does ncurses. NetBSD curses also
uses an array, actually named _acs_char, with a "#define" for
compatibility.
o HP-UX curses equates some of the ACS_ symbols to the analogous WACS_
symbols as if the ACS_ symbols were wide characters (see
curs_add_wch(3X)). The misdefined symbols are the arrows and others
that are not used for line drawing.
o X/Open Curses (Issues 2 through 7) has a typographical error for the
ACS_LANTERN symbol, equating its "VT100+ Character" to "I" (capital
I), while the header files for SVr4 curses and other implementations
use "i" (small i).
None of the terminal descriptions on Unix platforms use uppercase I,
except for Solaris (in its terminfo entry for screen(1), apparently
based on the X/Open documentation around 1995). On the other hand,
its gs6300 (AT&T PC6300 with EMOTS Terminal Emulator) description
uses lowercase i.
The displayed values of ACS_ constants depend on
o the ncurses ABI -- for example, wide-character versus non-wide-
character configurations (the former is capable of displaying Unicode
while the latter is not), and
o whether the locale uses UTF-8 encoding.
In certain cases, the terminal is unable to display forms-drawing
characters except by using UTF-8; see the discussion of the
NCURSES_NO_UTF8_ACS environment variable in ncurses(3X).
Character Set
X/Open Curses assumes that the parameter passed to 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 chtype, though the use of bitwise
operators to combine the character code with attributes and a color pair
identifier into a chtype for passage to waddch is common. A portable
application uses only the macros discussed in curs_attr(3X) to manipulate
a chtype.
In ncurses, chtype holds an eight-bit character, but the library allows a
multibyte character sequence to be passed via a succession of calls to
waddch. Other implementations do not; a waddch call transmits exactly
one character, which may be rendered in one or more screen locations
depending on whether it is printable (see unctrl(3X)). Depending on the
locale, ncurses inspects the byte passed in each waddch call and checks
whether the latest call continues a multibyte character. When a
character is complete, 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 -- for
example, with wmove(3X) -- ncurses discards the incomplete character.
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.
o If it can, call either waddch or wadd_wch.
o If it cannot, use only wadd_wch.
HISTORY
4BSD (1980) introduced waddch and its variants.
SVr3 (1987) added the echochar and wechochar functions and most of the
ACS_ constants, except for ACS_GEQUAL, ACS_LEQUAL, ACS_NEQUAL, ACS_PI,
ACS_S3, ACS_S7, and ACS_STERLING.
ncurses 1.9.6 (1995) furnished the remaining ACS_ constants.
SEE ALSO
curs_add_wch(3X) describes comparable functions of the ncurses library in
its wide-character configuration (ncursesw).
curses(3X), curs_addchstr(3X), curs_addstr(3X), curs_attr(3X),
curs_bkgd(3X), curs_clear(3X), curs_inch(3X), curs_outopts(3X),
curs_refresh(3X), curs_variables(3X), putchar(3)
ncurses 6.6 2025-11-11 curs_addch(3X)