Character classification and character transformation macros are defined in /usr/include/ctype.h. The Solaris 8 environment provides a new set of ctype macros. The new macros support character classification and transformation semantics defined by XPG4. To access the new set of macros, one of the following conditions must be met:
_XPG4_CHAR_CLASS is defined.
_XOPEN_SOURCE and _XOPEN_VERSION=4 are defined.
_XOPEN_SOURCE and _XOPEN_SOURCE_EXTENDED=1 are defined.
This means that all XPG4 and XPG4.2 applications automatically have the new macros. Since _XOPEN_SOURCE, _XOPEN_VERSION, and _XOPEN_SOURCE_EXTENDED bring in extra XPG4 related features in addition to new ctype macros, non-XPG4 or XPG4.2 applications should use __XPG4_CHAR_CLASS__.
There are corresponding ctype functions. The Solaris 8 functions also support XPG4 semantics.
Refer to the ctype(3C) man page for details.