text: #ifndef STAN_IO_VALIDATE_ZERO_BUF_HPP
  #define STAN_IO_VALIDATE_ZERO_BUF_HPP
  
  #include <boost/lexical_cast/bad_lexical_cast.hpp>
  #include <string>
  
  namespace stan {
    namespace io {
  
      /**
       * Throw an bad-cast exception if the specified buffer contains
       * a digit other than 0 before an e or E.  The buffer argument
       * must implement <code>size_t size()</code> method and <code>char
       * operator[](size_t)</code>.
       *
       * @tparam B Character buffer type 
       * @throw <code>boost::bad_lexical_cast</code> if the buffer
       * contains non-zero characters before an exponentiation symbol.
       */ 
      template <typename B>
      void validate_zero_buf(const B& buf) {
        for (size_t i = 0; i < buf.size(); ++i) {
          if (buf[i] == 'e' || buf[i] == 'E')
            return;
          if (buf[i] >= '1' && buf[i] <= '9')
            boost::conversion::detail::throw_bad_cast<std::string, double>();
        }
      }
  
    }
  }
  #endif
  