Story About Union

（Union）is a space saving special class.A union can have multiple data members.However, only one data member can have a value at any time. When a member is assigned a value, other members become undefined.

• The default access control character is public
• It can contain constructors and destructors
• Cannot contain a member of a reference type
• Cannot inherit from other classes, cannot be a base class
• Cannot contain virtual functions
• Anonymous union can directly access union members in the scope of definition
• Anonymous union cannot contain protected or private members
• Global anonymous union must be static