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

I can see how this works but I would not call this good practice. This is depending on how the bytes of each data structure is placed in memory. Any time you are casting one complicated data structure to another (ie. structs), it's not a very good idea, especially when the two structures are not the same size.