Manpages - curs_add_wch.3x

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

#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/ );**

All routines return the integer ERR upon failure and OK on success.

X/Open does not define any error conditions. This implementation returns 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 resulting 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.

Note that add_wch, mvadd_wch, mvwadd_wch, and echo_wchar may be macros.

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 misdefined 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, providing new definitions which are not in the SVr4 implementations.

Not all Unicode-capable terminals provide support for VT100-style alternate character sets (i.e., the acsc capability), with their corresponding 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 implementations 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 terminal 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 *curs_addch*(3X) 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).

*curses*(3X), *curs_addch*(3X), *curs_attr*(3X), *curs_clear*(3X), *curs_outopts*(3X), *curs_refresh*(3X), *putwc*(3)