#define FGCLASS_LIST 0x00000001
#define FGCLASS_AIRPORTLIST 0x00000002
#define FGCLASS_PROPERTYLIST 0x00000004
-class GUI_ID { public: GUI_ID(int id) : id(id) {} int id; };
+class GUI_ID { public: GUI_ID(int id) : id(id) {} virtual ~GUI_ID() {} int id; };