|  | 
           
Determine if an io_service contains a specified
          service type.
        
template< typename Service> friend bool has_service( io_service & ios);
          This function is used to determine whether the io_service contains a service
          object corresponding to the given service type.
        
                The io_service
                object that owns the service.
              
          A boolean indicating whether the io_service contains the service.
        
          Header: asio/io_service.hpp
        
          Convenience header: asio.hpp