addch(3NCURSES) Library calls addch(3NCURSES)
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(3NCURSES) describes the variants of this function.
Construct a curses character from a char by assignment. Subsection
“Video Attributes” of attron(3NCURSES) describes how to manipulate its
attributes and color pair. (A color pair selection is not honored un-
less initialized; see start_color(3NCURSES).)
If advancement occurs at the right margin,
• the cursor automatically wraps to the beginning of the next line,
then,
• if it was at the bottom of the scrolling region, and if
scrollok(3NCURSES) 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.
• Backspace moves the cursor one character left; at the left margin of
a window, it does nothing.
• Carriage return moves the cursor to the left margin on the same line
of the window.
• Line feed does a clrtoeol(3NCURSES), then advances as if from the
right margin.
• 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
curses_variables(3NCURSES).
If ch is any other nonprintable character, it is drawn in printable form
using the same convention as unctrl(3NCURSES). Calling winch(3NCURSES)
on the location of a nonprintable character does not return the charac-
ter itself, but its unctrl(3NCURSES) 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(3NCURSES) and waddch.) See attr(3NCURSES) for values of prede-
fined 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 bkgd(3NCURSES).
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 char-
acters, 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. 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 Uni-
code. 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 in-
correctly advertises ACS support. The name “ACS” originates in the Al-
ternate 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, waddch and wechochar return ERR if
• the curses screen has not been initialized,
• (for functions taking a WINDOW pointer argument) win is a null
pointer,
• wrapping to a new line is impossible because scrollok(3NCURSES) has
not been called on win (or stdscr, as applicable) when a write to
its bottom right location is attempted, or
• it is not possible to add a complete character at the cursor posi-
tion.
The last may be due to different causes:
• conversion of a wide character to a multibyte character sequence can
fail, or
• 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 de-
scriptions has come to light. The ncurses developers invented ACS-pre-
fixed 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.
• 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 com-
patibility.
• HP-UX curses equates some of the ACS_ symbols to the analogous WACS_
symbols as if the ACS_ symbols were wide characters (see
add_wch(3NCURSES)). The misdefined symbols are the arrows and oth-
ers that are not used for line drawing.
• 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
• the ncurses ABI—for example, wide-character versus non-wide-charac-
ter configurations (the former is capable of displaying Unicode
while the latter is not), and
• whether the locale uses UTF-8 encoding.
In certain cases, the terminal is unable to display forms-drawing char-
acters except by using UTF-8; see the discussion of the
NCURSES_NO_UTF8_ACS environment variable in ncurses(3NCURSES).
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
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 attr(3NCURSES) 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 de-
pending on whether it is printable (see unctrl(3NCURSES)). 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(3NCURSES)—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.
• If it can, call either waddch or wadd_wch.
• 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
add_wch(3NCURSES) describes comparable functions of the ncurses library
in its wide-character configuration (ncursesw).
ncurses(3NCURSES), addchstr(3NCURSES), addstr(3NCURSES), attr(3NCURSES),
bkgd(3NCURSES), clear(3NCURSES), inch(3NCURSES), outopts(3NCURSES),
refresh(3NCURSES), curses_variables(3NCURSES), putchar(3)
ncurses 6.5 2025-02-01 addch(3NCURSES)
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