Segmentation fault, binary search tree in c

Question

I want to insert data to the tree using this function:

struct treeNode{
    data* val;
    struct treeNode *left, *right, *parent;
};


void insert(data *d, struct treeNode **leaf, struct treeNode **leaf_par)
{
    if( *leaf == 0 )
    {
        *leaf = (struct treeNode*) malloc( sizeof( struct treeNode ) );
        (*leaf)->val = d;
        /* initialize the children to null */
        (*leaf)->left = 0;
        (*leaf)->right = 0;
        /* initialize the parent */
        (*leaf)->parent = *leaf_par;  //here I receive segmentation fault
    }
    else if(strcmp(d->name, (*leaf)->val->name) < 0)
    {
        insert( d, &(*leaf)->left, &(*leaf) );
    }
    else if(strcmp(d->name, (*leaf)->val->name) > 0)
    {
        insert( d, &(*leaf)->right, &(*leaf) );
    }
}

In main I have:

struct treeNode *root = NULL;
data d1 = {"Smith"};
insert(&d1, &root, NULL);

Segmentation fault is there:

(*leaf)->parent = *leaf_par;

At first time *leaf_par is NULL and I don't know why it's not running correctly. How should I fix my insert function? Without "parent" pointer it's easy, but I have to do that with "parent" and it's not working.

Answer 1

You are trying to dereference NULL; don't do that.

A simple fix for your first insert is:

insert(&d1, &root, &root);

Deeper inserts into the recursion will fix the pointer.