Using anonymous union , we can get address without such warning:

 #pragma pack(push, 4)
 typedef struct {
    union {
      int a;
      char a_addr[sizeof(int)];
    };
    union {
      double b;
      char b_addr[sizeof(double)];
    };
 } my_t;
 #pragma pack(pop)

use it as this: &my.b_addr.