cppreference.com > C/C++ Keywords > union
union
Syntax:
  union union-name {
  public-members-list;    
  private:
  private-members-list;
  } object-list;

A union is like a class, except that all members of a union share the same memory location and are by default public rather than private. For example:

   union Data {
     int i;
     char c;
   };