AcRxObject AcGiDrawable AcHeapOperators AcDbObject AcDbEntity AcDbViewport
class AcDbViewport : public AcDbEntity;
dbents.h
The AcDbViewport class represents the VIEWPORT entity within AutoCAD.
Do not derive from this class. Attempting to do so will cause your application to halt AutoCAD.
Most AcDbViewport properties are reset to default values when the viewport is appended to a database. Therefore, you should always wait until you have added a new AcDbViewport object to the database before you change its property values.