/* Code for exercise 17.3. |  | "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>#include <fstream>#include <set>#include <string>// using std::string;bool load_nospace_word(istream &input, string &word) {   return input >> word;}bool load_letter_word(istream &input, string &word) {   bool result;   char c;   while (input.get(c))      if (isalpha(c)) {         word = c;         break;      }   while (result = input.get(c)) {      if (!isalpha(c)) {         input.putback(c);         break;      }      word += c;   }   return result;}typedef bool (*Loader)(istream&, string&);main(int argc, char *argv[]) {   istream *input;   Loader loader;   int name_pos;   if (argc>1 && strcmp(argv[1], "-letters")==0) {      name_pos = 2;      loader = &load_letter_word;   } else {      name_pos = 1;      loader = &load_nospace_word;   }   if (argc==name_pos)      input = &cin;   else   if (argc==name_pos+1)      input = new ifstream(argv[name_pos]);   else {      cerr << "Unexpected arguments.\n";      exit(-1);   }   string word;   std::set<string, std::less<string> > listing;   while (loader(*input, word))      listing.insert(word);   std::copy(listing.begin(), listing.end(),             std::ostream_iterator<string>(cout, "\n"));   if (argc==name_pos+1)      delete input;   return 0;}