Creating a mirror of a Binary Tree(or Binary Search Tree)

void BinaryTree::mirror(tree_node* node) { 

  if (node==NULL) {
    return;
  }
  else {
    tree_node* temp;

    // do the subtrees
    mirror(node->left);
    mirror(node->right);

    // swap the pointers in this node
    temp = node->left;
    node->left = node->right;
    node->right = temp;
  }
}