- The XSI Curses standard, Issue 4 describes these func-
- tions. It states that <STRONG>unctrl</STRONG> and <STRONG>wunctrl</STRONG> will return a
- null pointer if unsuccessful, but does not define any er-
- ror conditions.
+ The XSI Curses standard, Issue 4 describes these func-
+ tions. It states that <STRONG>unctrl</STRONG> and <STRONG>wunctrl</STRONG> will return a
+ null pointer if unsuccessful, but does not define any er-
+ ror conditions. This implementation checks for three cas-
+ es:
+
+ <STRONG>o</STRONG> the parameter is a 7-bit US-ASCII code. This is
+ the case that X/Open Curses documented.
+
+ <STRONG>o</STRONG> the parameter is in the range 128-159, i.e., a C1
+ control code. If <STRONG>use_legacy_coding</STRONG> has been called
+ with a <STRONG>2</STRONG> parameter, <STRONG>unctrl</STRONG> returns the parameter,
+ i.e., a one-character string with the parameter as
+ the first character. Otherwise, it returns ``~@'',
+ ``~A'', etc., analogous to ``^@'', ``^A'', C0 con-
+ trols.
+
+ X/Open Curses does not document whether <STRONG>unctrl</STRONG> can
+ be called before initializing curses. This imple-
+ mentation permits that, and returns the ``~@'',
+ etc., values in that case.
+
+ <STRONG>o</STRONG> parameter values outside the 0 to 255 range. <STRONG>unc-</STRONG>
+ <STRONG>trl</STRONG> returns a null pointer.