// modified from: http://onlamp.com/pub/a/onlamp/2006/04/06/boostregex.html?page=3

#include <iostream>
#include <string>
#include <regex>

int main( ) 
{
  while (true)
  {
    std::string expr, s;
    std::cout << "Expression: ";
    std::getline(std::cin, expr);
    if (!std::cin || expr == "quit") return 0; 
    std::cout << "String:     ";
    std::getline(std::cin, s);
    try
    {
      std::smatch matches;
      if (std::regex_match(s, matches, std::regex(expr)))
      {
        // matches[0] contains the original string.
        // matches[n] contains a sub_match object for each matching subexpression
        for (size_t i = 0; i < matches.size(); i++)
        {
          // sub_match is pair of iterators to the first
          // and one past the last chars of the matching subexpression
          // (matches[i].first, matches[i].second); 
          std::string match = matches[i];
          std::cout << "\tmatches[" << i << "] = " << match << '\n';
        }
      }
      else std::cout << "The regexp \"" << expr 
                     << "\" does not match \"" << s << "\"\n";
    }
    catch (std::regex_error& e)
    {
      std::cout << expr << " is not a valid regular expression: \""
                << e.what() << "\"\n";
    }
  }
  return 0;
}