Question

struct node
{
     int         info;
     struct node *llink;
     struct node *rlink;
};

typedef node *nodep;

What does it mean to have a structure’s pointer inside that structure itself?
Please explain the above structure in detail.

P.S.
I am NOT talking about the trees logic. I am talking about the C struct and the pointer’s behaviour.

EDIT 1:

struct node *llink How does the memory gets allocated to this? This is a type which hasn’t yet come into existence?

Answer 1

A pointer is just a reference to a location in memory (“address”). In the case of a node, a pointer to an instance of a node is a reference to the location in memory where that node instance is stored.

For your struct as defined, if you have an instance of a node that resides in one memory location, it can point to two other node instances that reside in their own memory locations (*llink, *rlink).

Using a real-world tree as a metaphor, the *llink and *rlink are pointers to left and right “branches” of a root node of a tree structure, respectively. Those pointers themselves may branch off into further and deeper left and right “subtrees”.

Have a read of this introduction to binary trees.