//
// This is example code from Chapter 23.9 "Matching with regular expression" of
// "Programming -- Principles and Practice Using C++" by Bjarne Stroustrup
//

#include <boost/regex.hpp>
#include <fstream>
#include <iostream>
#include <stdexcept>
#include <string>

using namespace std;
using namespace boost;

/*
 * Can't include std_lib_facilities.h because of name clash
 * But we need error() functions from same, so here they are.
 */ 

// error() simply disguises throws:
inline void error(const string& s)
{
   throw runtime_error(s);
}

inline void error(const string& s, const string& s2)
{
   error(s+s2);
}

inline void error(const string& s, int i)
{
   ostringstream os;
   os << s <<": " << i;
   error(os.str());
}

//------------------------------------------------------------------------------

struct bad_from_string : std::bad_cast
// class for reporting string cast errors
{
   const char* what() const throw() // override bad_cast's what()
      {
         return "bad cast from string";
      }
};

//------------------------------------------------------------------------------

template<class T> T from_string(const string& s)
{
   istringstream is(s);
   T t;
   if (!(is >> t)) throw bad_from_string();
   return t;
}

//------------------------------------------------------------------------------

int main()
   try
      {
         ifstream in("table.txt");    // input file
         if (!in) error("no input file");

         string line;            // input buffer
         int lineno = 0;

         regex header( "^[\\w ]+(	[\\w ]+)*$");
         regex row( "^[\\w ]+(	\\d+)(	\\d+)(	\\d+)$");

         if (getline(in,line)) {        // check header line
            boost::smatch matches;
            if (!boost::regex_search(line, matches, header)) {
               error("no header");
            }
         }

         // column totals:
         int boys = 0;
         int girls = 0;

         // current line values:
         int curr_boy = 0;
         int curr_girl = 0;

         while (getline(in,line)) {    // extract and check data
            ++lineno;
            smatch matches;
            if (!regex_search(line, matches, row)) 
               error("bad line", lineno);

            // check row:
            curr_boy = from_string<int>(matches[1]);
            curr_girl = from_string<int>(matches[2]);
            int curr_total = from_string<int>(matches[3]);
            if (curr_boy+curr_girl != curr_total) error("bad row sum");

            boys += curr_boy;
            girls += curr_girl;
         }

         // check columns:
         if (2*curr_boy  != boys)  error("boys don't add up");
         if (2*curr_girl != girls) error("girls don't add up");
      }
   catch (std::exception& e) {
      cerr << "error: " << e.what() << '\n'; 
      return 1;
   }
   catch (...) {
      cerr << "Oops: unknown exception!\n"; 
      return 2;
   }

//------------------------------------------------------------------------------