- support. If the header is included, its symbols may be made
- visible. That depends on the value used for <STRONG>_XOPEN_SOURCE</STRONG> feature
- test macro.
-
- <STRONG>o</STRONG> X/Open Curses documents one required header, in a special case:
- <stdarg.h> before <curses.h> to prototype the <STRONG>vw_printw</STRONG> and
- <STRONG>vw_scanw</STRONG> functions (as well as the obsolete the <STRONG>vwprintw</STRONG> and
- <STRONG>vwscanw</STRONG> functions). Each of those uses a <STRONG>va_list</STRONG> parameter.
-
- The two obsolete functions were introduced in SVr3. The other
- functions were introduced in X/Open Curses. In between, SVr4
- curses provided for the possibility that an application might
- include either <varargs.h> or <stdarg.h>. Initially, that was done
- by using <STRONG>void*</STRONG> for the <STRONG>va_list</STRONG> parameter. Later, a special type
- (defined in <stdio.h>) was introduced, to allow for compiler type-
- checking. That special type is always available, because <stdio.h>
- is always included by <curses.h>.
-
- None of the X/Open Curses implementations require an application to
- include <stdarg.h> before <curses.h> because they either have
- allowed for a special type, or (like <EM>ncurses</EM>) include <stdarg.h>
- directly to provide a portable interface.
+ support. If <EM>wchar.h</EM> is included, its symbols <STRONG>may</STRONG> be made visible
+ depending on the value of the <STRONG>_XOPEN_SOURCE</STRONG> feature test macro.
+
+ <STRONG>o</STRONG> X/Open Curses mandates an application's inclusion of one standard C
+ library header in a special case: <EM>stdarg.h</EM> before <EM>curses.h</EM> to
+ prototype the functions <EM>vw</EM><STRONG>_</STRONG><EM>printw</EM> and <EM>vw</EM><STRONG>_</STRONG><EM>scanw</EM> (as well as the
+ obsolete <EM>vwprintw</EM> and <EM>vwscanw</EM>). Each of these takes a variadic
+ argument list, a <EM>va</EM><STRONG>_</STRONG><EM>list</EM> parameter, like that of <STRONG>printf(3)</STRONG>.
+
+ SVr3 <EM>curses</EM> introduced the two obsolete functions, and X/Open
+ Curses the others. In between, SVr4 <EM>curses</EM> provided for the
+ possibility that an application might include either <EM>varargs.h</EM> or
+ <EM>stdarg.h</EM>. These represented contrasting approaches to handling
+ variadic argument lists. The older interface, <EM>varargs.h</EM>, used a
+ pointer to <EM>char</EM> for variadic functions' <EM>va</EM><STRONG>_</STRONG><EM>list</EM> parameter. Later,
+ the list acquired its own standard data type, <EM>va</EM><STRONG>_</STRONG><EM>list</EM>, defined in
+ <EM>stdarg.h</EM>, empowering the compiler to check the types of a function
+ call's actual parameters against the formal ones declared in its
+ prototype.
+
+ No conforming implementations of X/Open Curses require an
+ application to include <EM>stdarg.h</EM> before <EM>curses.h</EM> because they either
+ have allowed for a special type, or, like <EM>ncurses</EM>, they include
+ <EM>stdarg.h</EM> themselves to provide a portable interface.