+ <STRONG>o</STRONG> U+2500 BOX DRAWINGS LIGHT HORIZONTAL
+
+ <STRONG>o</STRONG> U+2501 BOX DRAWINGS HEAVY HORIZONTAL
+
+ <STRONG>o</STRONG> U+2550 BOX DRAWINGS DOUBLE HORIZONTAL
+
+
+</PRE><H2><a name="h2-RETURN-VALUE">RETURN VALUE</a></H2><PRE>
+ All routines return the integer <STRONG>ERR</STRONG> upon failure and <STRONG>OK</STRONG> on success.
+
+ X/Open does not define any error conditions. This implementation
+ returns an error
+
+ <STRONG>o</STRONG> if the window pointer is null or
+
+ <STRONG>o</STRONG> if it is not possible to add a complete character in the window.
+
+ The latter may be due to different causes:
+
+ <STRONG>o</STRONG> If <STRONG>scrollok</STRONG> 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
+
+ <STRONG>o</STRONG> 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
+ <STRONG>wmove</STRONG>, and return an error if the position is outside the window, or if
+ the window pointer is null.
+
+
+</PRE><H2><a name="h2-NOTES">NOTES</a></H2><PRE>
+ Note that <STRONG>add_wch</STRONG>, <STRONG>mvadd_wch</STRONG>, <STRONG>mvwadd_wch</STRONG>, and <STRONG>echo_wchar</STRONG> may be macros.
+
+
+</PRE><H2><a name="h2-PORTABILITY">PORTABILITY</a></H2><PRE>
+ 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 <STRONG>cchar_t</STRONG> data, e.g., in the discussion of <STRONG>border_set</STRONG>. A
+ few implementations are problematic:
+
+ <STRONG>o</STRONG> NetBSD curses defines the symbols as a <STRONG>wchar_t</STRONG> within a <STRONG>cchar_t</STRONG>.
+
+ <STRONG>o</STRONG> HPUX curses equates some of the <EM>ACS</EM><STRONG>_</STRONG> symbols to the analogous <EM>WACS</EM><STRONG>_</STRONG>
+ symbols as if the <EM>ACS</EM><STRONG>_</STRONG> 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 <STRONG>acsc</STRONG> 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 <STRONG>acsc</STRONG> 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 <STRONG>acsc</STRONG> mapping as discussed in <STRONG><A HREF="ncurses.3x.html">ncurses(3x)</A></STRONG> for the
+ environment variable <STRONG>NCURSES_NO_UTF8_ACS</STRONG>. In contrast, for the same
+ cases, the line-drawing characters described in <STRONG><A HREF="curs_addch.3x.html">curs_addch(3x)</A></STRONG> will use
+ only the ASCII default values.
+
+ Having Unicode available does not solve all of the problems with line-
+ drawing for curses:
+
+ <STRONG>o</STRONG> The closest Unicode equivalents to the VT100 graphics <EM>S1</EM>, <EM>S3</EM>, <EM>S7</EM>
+ and <EM>S9</EM> frequently are not displayed at the regular intervals which
+ the terminal used.
+
+ <STRONG>o</STRONG> The <EM>lantern</EM> 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 <EM>storm</EM> <EM>lantern</EM> 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 <EM>storm</EM> <EM>lanterns</EM> 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: <section> U+00A7 (section
+ mark), <Theta> U+0398 (theta), <Phi> U+03A6 (phi), <delta> U+03B4
+ (delta), U+2327 (x in a rectangle), U+256C (forms double vertical
+ and horizontal), and U+2612 (ballot box with x).
+
+
+</PRE><H2><a name="h2-SEE-ALSO">SEE ALSO</a></H2><PRE>