// In header: <boost/program_options/errors.hpp>

class validation_error :
  public boost::program_options::error_with_option_name
{
public:
  enum kind_t { multiple_values_not_allowed = = 30, 
                at_least_one_value_required, invalid_bool_value, 
                invalid_option_value, invalid_option };
  // construct/copy/destruct
  validation_error(kind_t, const std::string & = "", const std::string & = "", 
                   int = 0);
  ~validation_error();
  // protected member functions
  std::string get_template(kind_t);
};