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;
       };
Related topics: class struct