自定义类模板 实现Queue

#include "stdafx.h"#include <iostream>using namespace std;// 错误的例子//template <class T> class ListItem;//template <class T> class List {//public://List<T> ();//List<T> ( const List<T>& );//List<T>& operator = (const List<T>&);////~List();////void insert(ListItem* ptr, T value_);//ListItem *find(T value_);////private://ListItem *front;//ListItem *end;//};template <class Type>class QueueItem {public:QueueItem(const Type &t) : item(t), next(0) {}Type item;QueueItem *next;};template <class Type>class Queue {public:Queue() : head(0),tail(0) {}Queue(const Queue &Q):head(0), tail(0) {copy_elems(Q);}template <class Type2> // 这里重新声明的目的是为了支持类型转换Queue<Type>& operator=(const Queue<Type2>&);~Queue() { destroy(); }Type& front() { return head->item; }const Type &front() const { return head->item; }void push( const Type& );void pop();bool empty() const {return head == 0;}private:QueueItem<Type> *head;QueueItem<Type> *tail;void destroy();void copy_elems(const Queue&);};template <class Type>void Queue<Type>::push( const Type& val){QueueItem<Type> *pt = new QueueItem<Type>(val);if(empty())head = tail = pt;else {tail->next = pt;tail = pt;}}template <class Type>void Queue<Type>::pop(){QueueItem<Type>* p = head;head = head->next;delete p;}template <class Type>void Queue<Type>::destroy(){while(!empty())pop();}template <class Type>void Queue<Type>::copy_elems(const Queue& orig){for(QueueItem<Type>* pt = orig.head;pt;pt = pt->next)push(pt->item);}template <class Type>template <class Type2> // 这里重新声明的目的是为了支持类型转换Queue<Type>& Queue<Type>::operator=( const Queue<Type2>& orig){if((void*)this == (void*)&orig) {*this;}Queue<Type2> tmp(orig);destroy(); // deletewhile(!tmp.empty()){push(tmp.front());tmp.pop();}return *this;}int main(){Queue<int> qi;short s = 43;int i = 23;qi.push(s);qi.push(i);Queue<float> ai;ai = qi;Queue<int> bi;return 0;}