c++ recursive traversals duty pointers

template <class t>
void bt<t>::inorder(void (*inorderptr)(t&))
 {
     inorderptr(inorder(this->root));
 }
template <class t>
void bt<t>::inorder(node<t>* root) const
 {
    (root->left != null)
       inorder(root->left);
       //something here
    (root->right != null)
       inorder(root->right);
 }

ok i am perplexing emanate traversal around recursion. i indeed posted problem before nonetheless i going wrong due me carrying duty pointer. i don't know i'm suspect do. i've got open coupling calls private one... nonetheless open one duty being upheld i even it?? i feel dense even someone give me little idea i'm certain i'd it. i only don't know where here.

an instance formula calls this:

first.inorder(print_val)