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Creating Truly Maintainable Class Factories

November 2000/Creating Truly Maintainable Class Factories/Listing 4

Listing 4: Partial listing of class dll_object_ref

< class object >
class dll_object_ref
      friend class dll_object_ptr< object >;

      // not shown: invariant()


         ( dll_sentinel&         dll
         , std::string const& function_name )
         : m_dll( dll ), m_count( 1 ), m_obj( NULL )
         #ifdef _WIN32
            typedef object* (WINAPI* p_instantiate)( );
         #elif defined( _DLSYM )
            typedef object* (* p_instantiate)( );
            #error Unsupported Platform.   Please port me

         void* pvfunc = m_dll.find_func( function_name );
         if ( !_pvfunc )
            throw dll_exception
               ( "Could not find instantiation routine." );

         p_instantiate pfunc = 
            *reinterpret_cast<p_instantiate*>( &_pvfunc );
         m_obj = pfunc( );

         assert( invariant() );

      virtual ~dll_object_ref( )
         assert( invariant() );
         m_obj = NULL;
         } // ~dll_object_ref( )

      // not shown: functions ref and unref

   private: // data

      dll_sentinel   m_dll;
      object*          m_obj;
      unsigned long m_count;

   }; // class dll_object_ref< >

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