add_wch(3NCURSES) add_wch(3NCURSES)
NAME
add_wch, wadd_wch, mvadd_wch, mvwadd_wch, echo_wchar, wecho_wchar - add
a complex character and rendition to a curses window, then advance the
cursor
SYNOPSIS
#include <curses.h>
int add_wch( const cchar_t *wch );
int wadd_wch( WINDOW *win, const cchar_t *wch );
int mvadd_wch( int y, int x, const cchar_t *wch );
int mvwadd_wch( WINDOW *win, int y, int x, const cchar_t *wch );
int echo_wchar( const cchar_t *wch );
int wecho_wchar( WINDOW *win, const cchar_t *wch );
DESCRIPTION
add_wch
The add_wch, wadd_wch, mvadd_wch, and mvwadd_wch functions put the com-
plex character wch into the given window at its current position, which
is then advanced. These functions perform wrapping and special-charac-
ter processing as follows:
• If wch refers to a spacing character, then any previous character
at that location is removed. A new character specified by wch is
placed at that location with rendition specified by wch. The cur-
sor then advances to the next spacing character on the screen.
• If wch refers to a non-spacing character, all previous characters
at that location are preserved. The non-spacing characters of wch
are added to the spacing complex character, and the rendition spec-
ified by wch is ignored.
• If the character part of wch is a tab, newline, backspace or other
control character, the window is updated and the cursor moves as if
addch were called.
echo_wchar
The echo_wchar function is functionally equivalent to a call to add_wch
followed by a call to refresh(3X). Similarly, the wecho_wchar is func-
tionally equivalent to a call to wadd_wch followed by a call to wre-
fresh. The knowledge that only a single character is being output is
taken into consideration and, for non-control characters, a consider-
able performance gain might be seen by using the *echo* functions in-
stead of their equivalents.
Line Graphics
Like addch(3X), addch_wch accepts symbols which make it simple to draw
lines and other frequently used special characters. These symbols cor-
respond to the same VT100 line-drawing set as addch(3X).
ACS Unicode ASCII acsc Glyph
Name Default Default char Name
────────────────────────────────────────────────────────────────────────
WACS_BLOCK 0x25ae # 0 solid square block
WACS_BOARD 0x2592 # h board of squares
WACS_BTEE 0x2534 + v bottom tee
WACS_BULLET 0x00b7 o ~ bullet
WACS_CKBOARD 0x2592 : a checker board (stipple)
WACS_DARROW 0x2193 v . arrow pointing down
WACS_DEGREE 0x00b0 ' f degree symbol
WACS_DIAMOND 0x25c6 + ` diamond
WACS_GEQUAL 0x2265 > > greater-than-or-equal-to
WACS_HLINE 0x2500 - q horizontal line
WACS_LANTERN 0x2603 # i lantern symbol
WACS_LARROW 0x2190 < , arrow pointing left
WACS_LEQUAL 0x2264 < y less-than-or-equal-to
WACS_LLCORNER 0x2514 + m lower left-hand corner
WACS_LRCORNER 0x2518 + j lower right-hand corner
WACS_LTEE 0x2524 + t left tee
WACS_NEQUAL 0x2260 ! | not-equal
WACS_PI 0x03c0 * { greek pi
WACS_PLMINUS 0x00b1 # g plus/minus
WACS_PLUS 0x253c + n plus
WACS_RARROW 0x2192 > + arrow pointing right
WACS_RTEE 0x251c + u right tee
WACS_S1 0x23ba - o scan line 1
WACS_S3 0x23bb - p scan line 3
WACS_S7 0x23bc - r scan line 7
WACS_S9 0x23bd _ s scan line 9
WACS_STERLING 0x00a3 f } pound-sterling symbol
WACS_TTEE 0x252c + w top tee
WACS_UARROW 0x2191 ^ - arrow pointing up
WACS_ULCORNER 0x250c + l upper left-hand corner
WACS_URCORNER 0x2510 + k upper right-hand corner
WACS_VLINE 0x2502 | x vertical line
The wide-character configuration of ncurses also defines symbols for
thick lines (acsc “J” to “V”):
ACS Unicode ASCII acsc Glyph
Name Default Default char Name
───────────────────────────────────────────────────────────────────────
WACS_T_BTEE 0x253b + V thick tee pointing up
WACS_T_HLINE 0x2501 - Q thick horizontal line
WACS_T_LLCORNER 0x2517 + M thick lower left corner
WACS_T_LRCORNER 0x251b + J thick lower right corner
WACS_T_LTEE 0x252b + T thick tee pointing right
WACS_T_PLUS 0x254b + N thick large plus
WACS_T_RTEE 0x2523 + U thick tee pointing left
WACS_T_TTEE 0x2533 + W thick tee pointing down
WACS_T_ULCORNER 0x250f + L thick upper left corner
WACS_T_URCORNER 0x2513 + K thick upper right corner
WACS_T_VLINE 0x2503 | X thick vertical line
and for double-lines (acsc “A” to “I”):
ACS Unicode ASCII acsc Glyph
Name Default Default char Name
────────────────────────────────────────────────────────────────────────
WACS_D_BTEE 0x2569 + H double tee pointing up
WACS_D_HLINE 0x2550 - R double horizontal line
WACS_D_LLCORNER 0x255a + D double lower left corner
WACS_D_LRCORNER 0x255d + A double lower right corner
WACS_D_LTEE 0x2560 + F double tee pointing right
WACS_D_PLUS 0x256c + E double large plus
WACS_D_RTEE 0x2563 + G double tee pointing left
WACS_D_TTEE 0x2566 + I double tee pointing down
WACS_D_ULCORNER 0x2554 + C double upper left corner
WACS_D_URCORNER 0x2557 + B double upper right corner
WACS_D_VLINE 0x2551 | Y double vertical line
Unicode's descriptions for these characters differs slightly from
ncurses, by introducing the term “light” (along with less important de-
tails). Here are its descriptions for the normal, thick, and double
horizontal lines:
• U+2500 BOX DRAWINGS LIGHT HORIZONTAL
• U+2501 BOX DRAWINGS HEAVY HORIZONTAL
• U+2550 BOX DRAWINGS DOUBLE HORIZONTAL
RETURN VALUE
All routines return the integer ERR upon failure and OK on success.
X/Open does not define any error conditions. This implementation re-
turns an error
• if the window pointer is null or
• if it is not possible to add a complete character in the window.
The latter may be due to different causes:
• If scrollok is not enabled, writing a character at the lower right
margin succeeds. However, an error is returned because it is not
possible to wrap to a new line
• If an error is detected when converting a multibyte character to a
sequence of bytes, or if it is not possible to add all of the re-
sulting bytes in the window, an error is returned.
Functions with a “mv” prefix first perform a cursor movement using
wmove, and return an error if the position is outside the window, or if
the window pointer is null.
NOTES
Note that add_wch, mvadd_wch, mvwadd_wch, and echo_wchar may be macros.
PORTABILITY
All of these functions are described in the XSI Curses standard, Issue
4. The defaults specified for line-drawing characters apply in the
POSIX locale.
X/Open Curses makes it clear that the WACS_ symbols should be defined
as a pointer to cchar_t data, e.g., in the discussion of border_set. A
few implementations are problematic:
• NetBSD curses defines the symbols as a wchar_t within a cchar_t.
• HPUX curses equates some of the ACS_ symbols to the analogous WACS_
symbols as if the ACS_ symbols were wide characters. The misde-
fined symbols are the arrows and other symbols which are not used
for line-drawing.
X/Open Curses does not define symbols for thick- or double-lines. SVr4
curses implementations defined their line-drawing symbols in terms of
intermediate symbols. This implementation extends those symbols, pro-
viding new definitions which are not in the SVr4 implementations.
Not all Unicode-capable terminals provide support for VT100-style al-
ternate character sets (i.e., the acsc capability), with their corre-
sponding line-drawing characters. X/Open Curses did not address the
aspect of integrating Unicode with line-drawing characters. Existing
implementations of Unix curses (AIX, HPUX, Solaris) use only the acsc
character-mapping to provide this feature. As a result, those imple-
mentations can only use single-byte line-drawing characters. Ncurses
5.3 (2002) provided a table of Unicode values to solve these problems.
NetBSD curses incorporated that table in 2010.
In this implementation, the Unicode values are used instead of the ter-
minal description's acsc mapping as discussed in ncurses(3X) for the
environment variable NCURSES_NO_UTF8_ACS. In contrast, for the same
cases, the line-drawing characters described in addch(3NCURSES) will
use only the ASCII default values.
Having Unicode available does not solve all of the problems with line-
drawing for curses:
• The closest Unicode equivalents to the VT100 graphics S1, S3, S7
and S9 frequently are not displayed at the regular intervals which
the terminal used.
• The lantern is a special case. It originated with the AT&T 4410
terminal in the early 1980s. There is no accessible documentation
depicting the lantern symbol on the AT&T terminal.
Lacking documentation, most readers assume that a storm lantern was
intended. But there are several possibilities, all with problems.
Unicode 6.0 (2010) does provide two lantern symbols: U+1F383 and
U+1F3EE. Those were not available in 2002, and are irrelevant
since they lie outside the BMP and as a result are not generally
available in terminals. They are not storm lanterns, in any case.
Most storm lanterns have a tapering glass chimney (to guard against
tipping); some have a wire grid protecting the chimney.
For the tapering appearance, ☃ U+2603 was adequate. In use on a
terminal, no one can tell what the image represents. Unicode calls
it a snowman.
Others have suggested these alternatives: § U+00A7 (section mark),
Θ U+0398 (theta), Φ U+03A6 (phi), δ U+03B4 (delta), ⌧ U+2327 (x in
a rectangle), ╬ U+256C (forms double vertical and horizontal), and
☒ U+2612 (ballot box with x).
SEE ALSO
ncurses(3NCURSES), addch(3NCURSES), attr(3NCURSES), clear(3NCURSES),
outopts(3NCURSES), refresh(3NCURSES), putwc(3)
add_wch(3NCURSES)
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