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);
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. 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).)
If advancement occurs at the right margin,
o the cursor automatically wraps to the beginning of the next line,
then,
o if it was at the bottom of the scrolling region, and if
scrollok(3x) is enabled for win, the scrolling region scrolls up
one line.
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, it is drawn 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.
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.) See curs_attr(3x) for values of predefined
constants that can be usefully "or"ed with characters. A ch whose
character component is a space, and whose only attribute is A_NORMAL,
is a blank character, and therefore combines with the background
character; see curs_bkgd(3x).
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. The ACS default listed below is used
if the acs_chars (acsc) terminfo 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 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, waddch and wechochar return ERR if
o the curses screen has not been initialized,
o win is NULL,
o wrapping to a new line is impossible because scrollok(3x) has not
been called on win 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.
SVr4 and other versions of curses implement the TABSIZE variable, but
X/Open Curses does not specify it; see curs_variables(3x).
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.
This implementation uses an array, acs_map, as did SVr4 curses.
NetBSD 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.
Some ACS 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. However, many publicly available terminfo entries
include acsc capabilities in which their key characters (pryz{|}) are
embedded, and a second-hand list of their character descriptions has
come to light. The ncurses developers invented ACS-prefixed names for
them.
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
bit operations 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) curses introduced waddch.
SVr3 (1987) added wechochar.
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 2025-01-18 curs_addch(3x)