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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | NOTES | EXTENSIONS | PORTABILITY | HISTORY | SEE ALSO | COLOPHON |
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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
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.
• 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(3X), 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
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:
• 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.
• 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:
• 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.
• 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.
• 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
These functions return OK on success and ERR on failure.
In ncurses, these functions fail 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(3X) 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
position.
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.
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:
• useful graphic symbols with a standard ACS_ symbol, (e.g., the
line-drawing symbols),
• possibly useful characters (these non-standard symbols),
• 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:
• ACS_BOARD corresponds to the VT100 symbol for newline
• 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.
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 compatibility.
• 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.
• 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-
character 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
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.
• If it can, call either waddch or wadd_wch.
• 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)
This page is part of the ncurses (new curses) project.
Information about the project can be found at
⟨https://invisible-island.net/ncurses/ncurses.html⟩. If you have a
bug report for this manual page, send it to bug-ncurses@gnu.org.
This page was obtained from the tarball ncurses-6.6.tar.gz fetched
from ⟨https://ftp.gnu.org/gnu/ncurses/⟩ on 2026-01-16. If you
discover any rendering problems in this HTML version of the page,
or you believe there is a better or more up-to-date source for the
page, or you have corrections or improvements to the information
in this COLOPHON (which is not part of the original manual page),
send a mail to man-pages@man7.org
ncurses @NCURSES_MAJOR@.@NCU... 2025-11-11 curs_addch(3X)
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HTML rendering created 2026-01-16 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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