LinkQueue class

  1 #include <cstddef>
  2 
  3 struct Node{
  4     Node * next;
  5 
  6     Node() { next = NULL;}
  7     Node(const Node & node) {
  8         next = node.next;
  9     }
 10 };
 11 
 12 enum Error_code {
 13     succeed,
 14     overflow,
 15     underflow
 16 };
 17 
 18 class LinkQueue {
 19 public:
 20     LinkQueue();
 21     LinkQueue(const LinkQueue & rhs);
 22     ~LinkQueue();
 23 
 24     LinkQueue & operator=(const LinkQueue & rhs);
 25 
 26     bool empty() const;
 27     Error_code append(const Node & item);
 28     Error_code serve();
 29     Error_code retrieve(Node & item) const;
 30     int size() const;
 31 
 32 protected:
 33     Node * front, * rear;
 34 };
 35 
 36 LinkQueue::LinkQueue() {
 37     front = rear = NULL;
 38 }
 39 
 40 LinkQueue::~LinkQueue() {
 41     while (!empty())
 42         serve();
 43 }
 44 
 45 LinkQueue::LinkQueue(const LinkQueue & rhs) {
 46     Node * new_front=NULL, * new_rear=NULL;
 47     Node * new_copy, * old_node=rhs.front;
 48     if (old_node != NULL) {
 49         new_front=new_copy=new Node(*old_node);
 50         while (old_node->next != NULL) {
 51             old_node = old_node->next;
 52             new_copy->next = new Node(*old_node);
 53             new_copy = new_copy->next;
 54         }
 55         new_rear = new_copy;
 56     }
 57 
 58     front = new_front;
 59     rear = new_rear;
 60 }
 61 
 62 int LinkQueue::size() const {
 63     Node * window = front;
 64     int count = 0;
 65 
 66     while(window != NULL) {
 67         window = window->next;
 68         count++;
 69     }
 70 
 71     return count;
 72 }
 73 
 74 Error_code LinkQueue::serve() {
 75     if (front == NULL)
 76         return underflow;
 77 
 78     Node * old_front = front;
 79     front = front->next;
 80     if (front == NULL)
 81         rear = NULL;
 82 
 83     delete old_front;
 84 
 85     return succeed;
 86 }
 87 
 88 bool LinkQueue::empty() const{
 89     if (front == NULL)
 90         return true;
 91     return false;
 92 }
 93 
 94 Error_code LinkQueue::append(const Node & item) {
 95     Node * new_rear = new Node(item);
 96     if (new_rear == NULL)
 97         return overflow;
 98     if (rear == NULL)
 99         front = rear = new_rear;
100     else {
101         rear->next = new_rear;
102         rear = new_rear;
103     }
104     return succeed;
105 }
106 
107 Error_code LinkQueue::retrieve(Node & item) const{
108     if (front == NULL)
109         return underflow;
110     item = *front;
111     return succeed;
112 }