You're right. Enqueue is wrong, it should be: if ( !m_pHead ) m_pHead = p ; else m_pTail->next = p; m_pTail = p; For some reason,

You're right. Enqueue is wrong, it should be: if ( !m_pHead ) m_pHead = p ; else m_pTail->next = p; m_pTail = p; For some reason, the author is inserting the node in front of the tail leading to the error.