C++ Doubly linked list - deleting element from the tail using pop_back()

Question

My pop_back() function is supposed to remove the last element in a doubly linked list. However, my current code removes the last two elements rather than just one. I have set up my pop_front() function similar to this one, which works just fine. I am having trouble figuring out what I've done wrong.

Here is part of my linkedlist header with struct Node:

class linkedlist
{
private:
    struct Node{
        Node* next;
        Node* prev;
        element_type data;
    };
    Node* head;
    Node* tail;
    unsigned int numElements;

My pop_back() function from the public section of linkedlist:

void linkedlist::pop_back()
{
    if (empty())
        return;
    else {
        Node *delBack = tail;
        Node *nodeToDelete = delBack;
        delBack = delBack->prev;
        delBack->next = NULL;
        delete nodeToDelete;
        tail = delBack;
        numElements--;
    }
}

If the problem is not immediately obvious, then it's possible the error is buried somewhere else in the code. Still searching.

Answer 1

Though the function does not delete two nodes simultaneously nevertheless the function is wrong. It does not check whether tail->prev is equal to nullptr and it does not set head to nullptr when the list becomes empty. The function can look the following way.

void linkedlist::pop_back()
{
    if ( tail )
    {
        Node *nodeToDelete = tail;
        tail = tail->prev;

        if ( tail )
        {
            tail->next = nullptr;
        }
        else
        {
            head = nullptr;
        }

        delete nodeToDelete;
        numElements--;
    }
}