Extending a struct in C

Question

I recently came across a colleague\'s code that looked like this:

typedef struct A {
  int x;
}A;

typedef struct B {
  A a;
  int d;
}B;

void fn(){
  B *b;         


        

Answer 1

That's a horrible idea. As soon as someone comes along and inserts another field at the front of struct B your program blows up. And what is so wrong with b.a.x?