What are the benefits of unnamed structs / unions in C?

Question

I found one code implemented as the similar demo shown below ..

struct st
{
 int a;
 struct
 {
 int b;
 };
};

6.58 Unnamed struct/union fields within structs/unions

As permitted by ISO C11.

But What are benefits of it ?

Because anyway I can access the data members in a same manner like

int main()
{
 struct st s;
 s.a=11;
 s.b=22;
 return 0;
}

compiled on gcc 4.5.2 with ,

gcc -Wall demo.c -o demo 

and no errors ,

Answer 1

It does not have to be an anonymous struct inside a struct, which I do not find very useful: this will typically only change the layout slightly by introducing more padding, with no other visible effects (compared to inlining the members of the child struct into the parent struct).

I think that the advantage of anonymous struct/unions is elsewhere: they can be used to place an anonymous struct inside an union or an anonymous union inside a struct.

Example:

union u
{
  int i;
  struct { char b1; char b2; char b3; char b4; };
};