Union

1. Union names form a separate namespace

   struct UNION {
     member1type member1;
     member2type member2;
   };
   

   usage in declarations and definitions requires keyword union in C (recommended to C++ too)

   union UNION u;
   

2. typedef can be used to shorten declarations and definitions

   typedef union UNION Union;
   Union u;
   

3. typedef and union declarations can be combined into one construct

   typedef union UNION {
     member1type member1;
     member2type member2;
   } Union;
   

4. Typically, inner union declaration needs no name

   typedef union {
     member1type member1;
     member2type member2;
   } Union;