Dynamically Allocating a Struct within a Struct

Question

I am dynamically allocating a struct which has a different struct as a member:

struct a {
   // other members
   struct b;
}

struct b

Answer 1

If you dynamically allocate (malloc) struct a as in

struct a *temp = (struct a *)malloc(sizeof(struct a));

you malloc space for a pointer to struct b (assuming that's what is in struct a) but you don't malloc space for struct b. That means later you'll have to do

temp->b = (struct b *)malloc(sizeof(struct b));

before you try and use struct b.

If you don't store a pointer to struct b but rather struct b directly then you'll get the automatic allocation when you define struct a.