返回指向排序列表的指针;C++中的链表

我希望这个函数sortPair接受2个节点指针，并返回一个指针，指向按字母顺序排序的2个元素的列表。下面的代码是我到目前为止拥有的代码。如果有人能让我知道我哪里出错了，那就太好了。

  struct Node{
        string val;
        Node* next;
    };
Node* sortPair (Node* p1, Node* p2){
    //Assert that neither pointer is null
    assert(p1!=NULL);
    assert(p2!=NULL);
    Node* head=NULL;
    Node* current=NULL;
    Node* last = NULL;
    current = new Node();
    if(p1-> val >p2-> val)   //If p1->val comes before p2->val in the alphabet
    {
        current->val = p1->val;
        head = current;
        last = current;
        current = new Node();
        current -> val = p2->val;
        last = current;
        last ->next = NULL;
    }
    else
    {
        current->val = p2->val;
        head = current;
        last = current;
        current = new Node();
        current -> val = p1->val;
        last = current;
        last ->next = NULL;
    }
        return head;
}