AcDbObject：要重写的基本函数

自定义类必须重写以下函数：

virtual Acad::ErrorStatus 
dwgInFields(AcDbDwgFiler* filer);
 
virtual Acad::ErrorStatus 
dwgOutFields(AcDbDwgFiler* filer) const;
 
virtual Acad::ErrorStatus 
dxfInFields(AcDbDxfFiler* filer);
 
virtual Acad::ErrorStatus 
dxfOutFields(AcDbDxfFiler* filer) const;
 
<Destructor> (~AcDbObject)