gistfile1

struct {
     int a;
     union {
       int b;
       float c;
     };
     int d;
   } foo;

A possible use as "class interface":

struct state_machine_t {
        int some_state;
        // etc.
};

struct stateful_object_t {
        struct state_machine_t;
};

void transition( struct stateful_object_t* o) {
        o.some_state = 77;
        // etc.
}

// same interface as stateful_object_t !
//
struct automat_t {
        struct state_machine_t;
        char* name;
        // etc.
};

main() {
        struct automat_t automat;
        transition((struct stateful_object_t*)&automat);
}