Throw exception

Boost.Asio functions may throw boost::system::system_error exception. Take resolve as an example:

results_type resolve(BOOST_ASIO_STRING_VIEW_PARAM host,
    BOOST_ASIO_STRING_VIEW_PARAM service, resolver_base::flags resolve_flags)
{
  boost::system::error_code ec;
  ......
  boost::asio::detail::throw_error(ec, "resolve");
  return r;
}

There are two overloads of boost::asio::detail::throw_error functions:

inline void throw_error(const boost::system::error_code& err)
{
  if (err)
    do_throw_error(err);
}

inline void throw_error(const boost::system::error_code& err,
    const char* location)
{
  if (err)
    do_throw_error(err, location);
}

The differences of these two functions is just including "location" ("resolve" string in our example) or not. Accordingly, do_throw_error also have two overloads, I just take one as an example:

void do_throw_error(const boost::system::error_code& err, const char* location)
{
  boost::system::system_error e(err, location);
  boost::asio::detail::throw_exception(e);
}

boost::system::system_error derives from std::runtime_error:

class BOOST_SYMBOL_VISIBLE system_error : public std::runtime_error
{
......
public:
      system_error( error_code ec )
          : std::runtime_error(""), m_error_code(ec) {}

      system_error( error_code ec, const std::string & what_arg )
          : std::runtime_error(what_arg), m_error_code(ec) {}
......
      const error_code &  code() const BOOST_NOEXCEPT_OR_NOTHROW { return m_error_code; }
      const char *        what() const BOOST_NOEXCEPT_OR_NOTHROW;
......
}

what() member function returns the detailed information of exception.