/* Code for exercise 25.5. |  | "C++ Solutions--Companion to The C++ Programming Language, Third Edition" | by David Vandevoorde; Addison-Wesley 1998; ISBN 0-201-30965-3. | | Permission to use, copy, modify, distribute and sell this software | and its documentation for any purpose is hereby granted without fee. | The author makes no representations about the suitability of this | software for any purpose.  It is provided "as is" without express or | implied warranty. `----------------------------------------------------------------------*/#include <iostream>struct Filter {   struct Retry {      virtual char const* message() { return 0; }   };   virtual ~Filter() {}   virtual void start() {}   virtual int read() = 0;   virtual void write() {}   virtual void compute() {}   virtual int result() = 0;   virtual int retry(Retry &m) {      std::cerr << m.message() << '\n';      return 2;   }};int main_loop(Filter *p) {   for (;;) {      try {         p->start();         while (p->read()) {            p->compute();            p->write();         }         return p->result();      }      catch(Filter::Retry &m) {         if (int i = p->retry(m))            return i;      }      catch (...) {         std::cerr << "Fatal filter error.\n";         return 1;      }   }}struct UniqueWords: Filter {   UniqueWords(std::istream &in, std::ostream &out)      : in_(in), out_(out), n_eliminated_(0) {}   virtual int read()      { in_ >> next_word_; return in_.good(); }   virtual void compute() {      if (last_word_==next_word_) {         next_word_ = ""; // Kill next word         ++n_eliminated_;      } else         last_word_ = next_word_;   }   virtual void write() { out_ << next_word_ << '\n'; }   virtual int result() { return n_eliminated_; }private:   std::istream &in_;   std::ostream &out_;   std::string last_word_, next_word_;   int n_eliminated_;};int main() {   UniqueWords uniq(std::cin, std::cout);   main_loop(&uniq);   std::cerr << "Eliminated " << uniq.result() << " duplicates.\n";   return 0;}