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The defaults specified for forms-drawing characters apply in the POSIX
locale.
+
+</PRE><H3><a name="h3-ACS-Symbols">ACS Symbols</a></H3><PRE>
X/Open Curses states that the <EM>ACS</EM><STRONG>_</STRONG> definitions are <STRONG>char</STRONG> constants. For
the wide-character implementation (see <STRONG>curs_add_wch</STRONG>), there are analo-
- gous <EM>WACS</EM><STRONG>_</STRONG> definitions which are <STRONG>cchar_t</STRONG> constants.
+ gous <EM>WACS</EM><STRONG>_</STRONG> definitions which are <STRONG>cchar_t</STRONG> constants. Some implementa-
+ tions are problematic:
+
+ <STRONG>o</STRONG> Some implementations define the ACS symbols to a constant (such as
+ Solaris), while others define those to entries in an array.
+
+ This implementation uses an array <STRONG>acs_map</STRONG>, as done in SVr4 curses.
+ NetBSD also uses an array, actually named <STRONG>_acs_char</STRONG>, with a <STRONG>#define</STRONG>
+ for compatibility.
+
+ <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 misde-
+ fined symbols are the arrows and other symbols which are not used
+ for line-drawing.
+
+ <STRONG>o</STRONG> X/Open Curses (issues 2 through 7) has a typographical error for
+ the ACS_LANTERN symbol, equating its "VT100+ Character" to <STRONG>I</STRONG> (capi-
+ tal I), while the header files for SVr4 curses and the various
+ implementations use <STRONG>i</STRONG> (lowercase).
+
+ None of the terminal descriptions on Unix platforms use uppercase-
+ I, except for Solaris (i.e., <EM>screen</EM>'s terminal description, appar-
+ ently based on the X/Open documentation around 1995). On the other
+ hand, the terminal description <EM>gs6300</EM> (AT&T PC6300 with EMOTS Ter-
+ minal Emulator) uses lowercase-i.
Some ACS symbols (ACS_S3, ACS_S7, ACS_LEQUAL, ACS_GEQUAL, ACS_PI,
ACS_NEQUAL, ACS_STERLING) were not documented in any publicly released
acters except by using UTF-8 (see the discussion of <STRONG>NCURSES_NO_UTF8_ACS</STRONG>
in <STRONG><A HREF="ncurses.3x.html">ncurses(3x)</A></STRONG>).
- The <STRONG>TABSIZE</STRONG> variable is implemented in some versions of curses, but is
- not part of X/Open curses.
+
+</PRE><H3><a name="h3-Character-Set">Character Set</a></H3><PRE>
+ X/Open Curses assumes that the parameter passed to <STRONG>waddch</STRONG> contains a
+ single character. As discussed in <STRONG><A HREF="curs_attr.3x.html">curs_attr(3x)</A></STRONG>, that character may
+ have been more than eight bits 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 non-char-
+ acter information (attributes and color) was separated from the charac-
+ ter information which is packed in a <STRONG>chtype</STRONG> to pass to <STRONG>waddch</STRONG>.
+
+ In this implementation, <STRONG>chtype</STRONG> holds an eight-bit character. But
+ ncurses allows multibyte characters to be passed in a succession of
+ calls to <STRONG>waddch</STRONG>. The other implementations do not do this; a call to
+ <STRONG>waddch</STRONG> passes exactly one character which may be rendered as one or
+ more cells on the screen depending on whether it is printable.
+
+ Depending on the locale settings, ncurses will inspect the byte passed
+ in each call to <STRONG>waddch</STRONG>, and check if the latest call will continue a
+ multibyte sequence. When a character is <EM>complete</EM>, ncurses displays the
+ character and moves to the next position in the screen.
+
+ If the calling application interrupts the succession of bytes in a
+ multibyte character by moving the current location (e.g., using <STRONG>wmove</STRONG>),
+ ncurses discards the partially built character, starting over again.
+
+ For portability to other implementations, do not rely upon this behav-
+ ior:
+
+ <STRONG>o</STRONG> check if a character can be represented as a single byte in the
+ current locale before attempting call <STRONG>waddch</STRONG>, and
+
+ <STRONG>o</STRONG> call <STRONG>wadd_wch</STRONG> for characters which cannot be handled by <STRONG>waddch</STRONG>.
+
+
+</PRE><H3><a name="h3-TABSIZE">TABSIZE</a></H3><PRE>
+ The <STRONG>TABSIZE</STRONG> variable is implemented in SVr4 and other versions of
+ curses, but is not part of X/Open curses (see <STRONG><A HREF="curs_variables.3x.html">curs_variables(3x)</A></STRONG> for
+ more details).
If <EM>ch</EM> is a carriage return, the cursor is moved to the beginning of the
current row of the window. This is true of other implementations, but
</li>
<li><a href="#h2-RETURN-VALUE">RETURN VALUE</a></li>
<li><a href="#h2-NOTES">NOTES</a></li>
-<li><a href="#h2-PORTABILITY">PORTABILITY</a></li>
+<li><a href="#h2-PORTABILITY">PORTABILITY</a>
+<ul>
+<li><a href="#h3-ACS-Symbols">ACS Symbols</a></li>
+<li><a href="#h3-Character-Set">Character Set</a></li>
+<li><a href="#h3-TABSIZE">TABSIZE</a></li>
+</ul>
+</li>
<li><a href="#h2-SEE-ALSO">SEE ALSO</a></li>
</ul>
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