#include <iostream>
#include <string>
#include <boost/regex.hpp>  // Boost.Regex lib

using namespace std;

int main( ) {

  std::string s,sre;

  //regular expression with [:xdigit:]
  sre="a[[[:xdigit:]]x]z";
  
  s="afzaxz";
  
  boost::regex re;
  //re.assign(sre, boost::regex_constants::icase);
  re.assign(sre, boost::regex_constants::perl | boost::regex_constants::icase);
  std::string::const_iterator start, end;
  start = s.begin();
  end = s.end();
  boost::match_results<std::string::const_iterator> what; 
  boost::match_flag_type flags = boost::match_default;
  

  while(regex_search(start, end, what, re, flags) && (start != end)) 
   { 

     cout << "Searching in string" << std::string(start,end) << endl;
     cout << "Found Pattern:start:" << std::string(what[0].first, what[0].second) << ":end:\nPattern starts at :" << what[0].first - s.begin()  << "\nPattern ends at: " << (what[0].second - 1) - s.begin() << "\nPattern length:" << what[0].length() << endl;
     
      flags |= boost::match_prev_avail; 
      flags |= boost::match_not_bob; 
      start++;
   } 

}