// B8.cpp - convert string to numeric type

#include <iostream>
#include <iomanip>
#include <sstream>
using namespace std;

////// start of required answer /////////////////////

template <class T> T convert(const string &s) {

  T temp;
  istringstream in(s.c_str());
  if(!in.good()) {
    string errorStr = "error creating istringstream";
    throw exception(errorStr.c_str());
  }
  in >> temp;
  if(!in.eof() && !in.good()) {
    string errorStr = "error converting string ";
    errorStr += s;
    errorStr += " to type ";
    errorStr += typeid(temp).name();
    throw exception(errorStr.c_str());
  }
  return temp;
}
////// end of required answer ///////////////////////

void main() {

  try {
    string test[] = { "-73", "3.1415927", "2.5xyz", "<>[]{}" };

    for(int i=0; i<4; i++) {
      cout << "\n  the string is \"" << setw(10) << test[i] 
           << "\" and the converted value is " << convert<double>(test[i]);
    }
  }
  catch(exception &e) {
    cout << "\n--- " << e.what() << " ---";
  }
  cout << "\n\n";
}