队列的实现

//队列的实现#ifndef MINIQUEUE_H#define MINIQUEUE_H#include <iostream>#include <string>#include <exception>#include <new>using std::string;//自定义异常类class underflowException :  public std::exception {public: underflowException(const string& msg = ""):msgString(msg)    {}  virtual const char* what() const throw()  {    return msgString.c_str();  }  ~underflowException() throw()  {}protected:    string msgString;};class memoryAllocationError : public std::exception{public: memoryAllocationError(const string& msg = ""):msgString(msg)    {}  virtual const char* what() const throw()  {    return msgString.c_str();  }  ~ memoryAllocationError() throw()  {}protected:    string msgString;};template <class T>struct Node{    T data;    Node<T> *next;    Node():next(NULL)    {}    Node(const T& n = T(), Node<T> *ptr = NULL): data(n), next(ptr)    {}};template <class T>class MiniQueue{public:    //默认构造函数    MiniQueue():first(NULL),last(NULL),length(0)    {}    //析构函数    ~MiniQueue()    {        clear();    }    //拷贝构造函数    MiniQueue(const MiniQueue<T>& rhs);    //重载复制操作符operator=    MiniQueue<T> & operator=( const MiniQueue<T>& rhs);    bool empty() const    {        return length == 0;    }    size_t size() const    {        return length;    }    void push(const T& val);    void pop();    T & front();    const T& front() const;    T& back();    const T& back() const;private:    Node<T> *first;  //指向队首第一个元素    Node<T> *last ;  //指向对尾最后一个元素    int length;    void copy(const MiniQueue<T>& rhs);    void clear();    Node<T>* getNode( const T& val);};template <class T>Node<T>* MiniQueue<T>::getNode(const T& val){    Node<T> *newNode = new Node<T>(val, NULL );    if (newNode == NULL )        throw memoryAllocationError("MiniQueue: getNode()  memory allocation failure");    return newNode;}template <class T>void MiniQueue<T>::copy(const MiniQueue<T>& rhs){    Node<T> *p = rhs.first; //p用于遍历被拷贝的队列    Node<T> *newNode;    first = last = NULL;    if( p != NULL )    {        first = last = new Node<T>( p->data );        p = p->next;        while ( p != NULL)        {            newNode = getNode( p->data );            last->next = newNode;            last = newNode;            p = p->next;        }    }    // the size of the new list is the size of rhs    length = rhs.length;}template <class T>MiniQueue<T> & MiniQueue<T>::operator=( const MiniQueue<T>& rhs){    if ( *this != rhs )    {        clear();        copy(rhs);    }    return *this;}template <class T>void MiniQueue<T>::clear(){    Node<T> *curr = first;    Node<T> * p;    while(curr != NULL )    {        p = curr;        curr = curr->next;        delete p;    }    first = last = NULL;    length = 0;}template <class T>void MiniQueue<T>::push(const T& val){    Node<T> *newNode = getNode(val);    if (first == NULL )        first = last = newNode;    else    {        last->next = newNode;        last = newNode;    }    length++;}template <class T>void MiniQueue<T>::pop(){    Node<T> *p = first;    //如果队列为空，产生异常    if (empty())        throw underflowException("MiniQuee pop():empty queue.");    first = first->next;    if ( first == NULL)        last = NULL;    delete p;    length--;}template <class T>T& MiniQueue<T>::front(){    if(length == 0)        throw underflowException("MiniQuee pop():empty queue.");    return first->data;}template <class T>const T& MiniQueue<T>::front() const{    if(length == 0)        throw underflowException("MiniQuee pop():empty queue.");    return first->data;}template <class T>T& MiniQueue<T>::back(){    if(length == 0)        throw underflowException("MiniQuee pop():empty queue.");    return last->data;}template <class T>const T& MiniQueue<T>::back() const{    if(length == 0)        throw underflowException("MiniQuee pop():empty queue.");    return first->data;}#endif //MINIQUEUE_H