Thread: Fields of a struct after freeing it - C

Hey all.

Suppose we have the following struct definition of Stack data structure implementation:

Code:

typedef struct StrStackLink {
   char* str;
   struct StrStackLink *next;
} StrStackLink; 

struct StrStack {
   StrStackLink* top;
};

Where its Pop method implementation is shown below:

Code:

char* StrStackPop(StrStack* stack)
{
   char *s;
   StrStackLink *p;
   assert( stack != NULL );
   if (stack->top == NULL) {
      return NULL;
   }
   s = stack->top->str;
   p = stack->top; // This lives in the HEAP
   stack->top = p->next;
   free(p);
   return s;
}

My question is about the line:

Code:

   s = stack->top->str;

Why is it correct?
After we free p struct (which is the former top), its str field is not "disappeared"?

Thanks in advance!