need opening category vigilant around duty pointer - binary hunt tree category origination related

creating traversals binary hunt tree recursion.

void inorder(void (*inorderptr)(t&)) 
{ 
    if(this->left != null) 
        inorder((*inorderptr)(this->left)); 
    inorderptr(this->data); 
    if(this->right != null) 
        inorder((*inorderptr)(this->right)); 
} 

here function. apparently wrong. duty called this:

first.inorder(print_vals);

first object, imitation vals simply duty prints information object. there 3 values any object, data, left, right. i indeed opening those equipment function?