queue.h

实现m阶B_树 （2）将线性表中的键值插入到B_树中（即建立索引）； （3）当删除和插入数据到线性表时

#ifndef QUEUE_H
#define QUEUE_H

#include<assert.h>
#include<iostream.h>

template <class Type> class Queue;

template <class Type> class QueueNode {	
friend class Queue<Type>;
private: 
    Type data;				 //队列结点数据
    QueueNode<Type> *link;  //结点链指针
    QueueNode ( Type d=0, QueueNode*l=NULL ) : data (d), link (l) { }
};  
  
template <class Type> class Queue {	
public: 
    Queue ( ) : rear ( NULL ), front ( NULL ) { }
    ~Queue ( );						
    void EnQueue ( const Type & item );
    Type DeQueue ( );					
    Type GetFront ( );					
    void MakeEmpty ( ) { front = rear = NULL; }
    int IsEmpty ( ) const{ return front == NULL; }	
private: 
    QueueNode<Type> *front, *rear; //队列指针
};

template <class Type> Queue<Type>::~Queue ( ) {
//队列的析构函数
   QueueNode<Type> *p;
    while ( front != NULL ) {	 //逐个结点释放
        p = front;  front = front->link;  delete p;
    }
}

template <class Type> void Queue<Type>:: EnQueue ( const Type & item ) {
//将新元素item插入到队列的队尾 
    if ( front == NULL )
	 front = rear = new QueueNode
			<Type> ( item, NULL );
    else rear = rear->link = new QueueNode
			<Type> ( item, NULL );
}

template <class Type> Type Queue<Type>::DeQueue ( ) {
//删去队头结点，并返回队头元素的值
    assert ( !IsEmpty ( ) );	//判队空的断言
    QueueNode<Type> *p = front;		
    Type retvalue = p->data;	//保存队头的值
    front = front->link;   delete p;	  //新队头
    return retvalue;				
}

template <class Type>Type Queue<Type>::GetFront ( ) {
//若队不空，则函数返回队头元素的值; 若//
//队空，则函数返回0。
    assert ( !IsEmpty ( ) );			
    return front->data;				
}

#endif