Description

   The decc$validate_wchar function provides a convenient way to
   verify whether a specified argument of wchar_t type is a valid
   wide character in the current program's locale.

   One reason to call decc$validate_wchar is that the isw* wide-
   character classification functions and macros do not validate
   their argument before dereferencing the classmask array
   describing character properties. Passing an isw* function a value
   that exceeds the maximum wide-character value for the current
   program's locale can result in an attempt to access memory beyond
   the allocated classmask array.

   A standard way to validate a wide character is to call the wctomb
   function, but this way is less convenient because it requires
   declaring a multibyte character array of sufficient size and
   passing it to wctomb.