I have a very simple binary tree structure, something like:

struct nmbintree_s {
    unsigned int size;
    int (*cmp)(const void *e1, const void *e2);
    void (*destructor)(void *data);
    nmbintree_node *root;
};

struct nmbintree_node_s {
    void *data;
    struct nmbintree_node_s *right;
    struct nmbintree_node_s *left;
};

Sometimes i need to extract a 'tree' from another and i need to get the size to the 'extracted tree' in order to update the size of the initial 'tree' .

I was thinking on two approaches:

1) Using a recursive function, something like:

unsigned int nmbintree_size(struct nmbintree_node* node) {
  if (node==NULL) {
    return(0);
  } 
  return( nmbintree_size(node->left) + nmbintree_size(node->right) + 1 );
} 

2) A preorder / inorder / postorder traversal done in an iterative way (using stack / queue) + counting the nodes.

What approach do you think is more 'memory failure proof' / performant ?

Any other suggestions / tips ?

NOTE: I am probably going to use this implementation in the future for small projects of mine. So I don't want to unexpectedly fail :).