以下是实现：

template <typename T>
class QueueNode
{
public:
	QueueNode(T data) :m_data(data), m_pNext(nullptr) {}
	QueueNode(T data, QueueNode* next) :m_data(data), m_pNext(next) {}


	T getData() { return m_data; }
	QueueNode* getNext() { return m_pNext; }

	void setData(T d) { m_data = d; }
	void setNext(QueueNode* n) { m_pNext = n; }
private:
	int m_data;           //数据
    QueueNode* m_pNext;  //下个数据
};

template <typename T>
class DoubleQueue
{
public:
	DoubleQueue():m_pFront(nullptr), m_pBack(nullptr){}

	void push_back(T data)
	{
		if (m_pBack)
		{
            QueueNode<T>* tmp = new QueueNode<T>(data, m_pBack);
            m_pBack->setNext(tmp);
            m_pBack = tmp;
		}
		else
		{//null
			m_pBack = new QueueNode<T>(data);
            m_pFront = m_pBack;
		}
	}

	void push_front(T data)
	{
		if (m_pFront)
		{
            QueueNode<T>* tmp = new QueueNode<T>(data, m_pFront);
            m_pFront->setNext(tmp);
            m_pFront = tmp;
		}
		else
		{//null
			m_pFront = new QueueNode<T>(data);
            m_pBack = m_pFront;
		}
	}

	T pop_back()
	{
        if (m_pBack)
        {
            T retValue = m_pBack->getData();
            QueueNode<T>* freeObj = m_pBack;
            m_pBack = m_pBack->getNext();

            if (m_pBack == nullptr)
                m_pFront = nullptr;

            delete freeObj;
            freeObj = nullptr;

            return retValue;
        }

        return T();
	}

    T pop_front()
    {
        if (m_pFront)
        {
            T retValue = m_pFront->getData();
            QueueNode<T>* freeObj = m_pFront;
            m_pFront = m_pFront->getNext();

            if (m_pFront == nullptr)
                m_pBack = nullptr;

            delete freeObj;
            freeObj = nullptr;

            return retValue;
        }
    }

    T back() {return m_pBack->getData();}
	T front() { return m_pFront->getData(); }

private:
	QueueNode<T>* m_pFront;
	QueueNode<T>* m_pBack;
};