https://invisible-island.net/ncurses/man/
curs_addch(3x) Library calls curs_addch(3x)
addch, waddch, mvaddch, mvwaddch, echochar, wechochar - add a curses
character to a window and advance the cursor
#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;
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.
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.
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
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.
addch, mvaddch, mvwaddch, and echochar may be implemented as macros.
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.
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.
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).
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.
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.
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 6.5 2025-08-16 curs_addch(3x)