GCC Issue with unnammed nested struct in c

Question

struct xx
{
 int x;
 struct yy *p;
 struct
 {
 int s;
 };
 struct
 {
 int s;
 };    
};

int main()
{    
 struct xx xyz;
 printf("%d",sizeof(xyz));
 return 0;
}

the above code compile well without any warning. Here my question is
1. How can I distinguish two 's' variable.
2. What is use case.

Answer 1

You must be using an old version of GCC, it is an error with GCC 4.6 and later.