Specializing istream or ostream

When the iostream library is specialized for a new source or sink of characters the natural pattern is this: First derive a class from streambuf, such as fctbuf in the previous subtopic. Then derive classes from whichever of istream, ostream, or iostream is appropriate. For example, suppose we want to do this with the fctbuf class defined in the previous subtopic. The streams might get the definitions:

   class fctbase : virtual public ios {
   public:
   		fctbase(action a, open_mode m)
   			: buf(a,m) { init(&buf) ; }
   private:
   	fctbuf	buf ;
   } ;
   

   class ifctstream : public fctbase, public istream {
   public:
   		ifctbase(action a)
   			: fctbase(a, ios::in) { }
   } ;
   

   class ofctstream : public fctbase, public ostream {
   public:
   		ofctbase(action a)
   			: fctbase(a, ios::out) { }
   } ;
   

   class iofctstream : public fctbase, public iostream {
   public:
   		iofctstream(action a open_mode m)
   			: fctbase(a, m) { }
   } ;