curs_addch(3) Library calls curs_addch(3)
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);
DESCRIPTION
Adding Characters
waddch puts the character ch at the cursor position of window win, then
advances the cursor position, analogously to the standard C library's
putchar(3). ncurses(3X) describes the variants of this function.
If advancement occurs at the right margin,
o the cursor automatically wraps to the beginning of the next line;
and
o at the bottom of the current 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 current
line of the window.
o Line feed does a clrtoeol(3X), then moves the cursor to the left
margin on the next line of the window, and if scrollok(3X) is
enabled for win, scrolls the window if the cursor was already on
the last line.
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.
ch may contain rendering and/or color attributes, and others can be
combined with the parameter by logically "or"ing with it. (A character
with its attributes can be copied from place to place using winch(3X)
and waddch.) See curs_attr(3X) for values of predefined video attribute
constants that can be usefully "or"ed with characters.
Echoing Characters
echochar and wechochar are equivalent to calling (w)addch followed by
(w)refresh. curses interprets these functions as a hint that only a
single character is being output; 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 special characters 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 string
capability, and the characters in it may appear on the screen if the
terminal'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, waddch returns ERR if it is not possible to add a complete
character at the cursor position, as when conversion of a multibyte
character to a byte sequence fails, or at least one of the resulting
bytes cannot be added to the window. See section "PORTABILITY" below
regarding the use of waddch with multibyte characters.
waddch can successfully write a character at the bottom right location
of the window. However, ncurses returns ERR if scrollok(3X) is not
enabled in that event, because it is not possible to wrap to a new
line.
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.
PORTABILITY
X/Open Curses, Issue 4 describes these functions. It specifies no
error conditions for them.
SVr4 curses 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, define 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 strings 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)).
Character Set
X/Open Curses assumes that the parameter passed to waddch contains a
single character. As discussed in curs_attr(3X), that character may
have been more than eight bits wide in an SVr3 or SVr4 implementation,
but in the X/Open Curses model, the details are not given. The
important distinction between SVr4 curses and X/Open Curses is that the
latter separates non-character information (attributes and color) from
the character code, which SVr4 packs into a chtype for passage to
waddch.
In ncurses, chtype holds an eight-bit character. But the library
allows a multibyte character to be passed in 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.
Depending on the locale settings, ncurses inspects the byte passed in
each waddch call, and checks whether the latest call continues a
multibyte sequence. 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 this
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(3X).
o If it cannot, use only wadd_wch(3X).
TABSIZE
SVr4 and other versions of curses implement the TABSIZE variable, but
X/Open Curses does not specify it (see curs_variables(3X)).
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_clear(3X), curs_inch(3X), curs_outopts(3X), curs_refresh(3X),
curs_variables(3X), putchar(3)
ncurses 6.5 2024-04-20 curs_addch(3)
ncurses 6.5 - Generated Thu May 2 09:34:25 CDT 2024