C++ 用类封装实现队列

#include<stdlib.h> 
#include <iostream>
using std::cout;
using std::endl;

#define SUM 3 //此处设置队列的大小，因为队列节点是 malloc 的空间，一般不用设置队列上限。但是为了测试方便就加了上限

typedef struct QNode{
    int data;
    struct QNode *pNext;
}QNode,*pQNode;

class Queue{
    private:
        pQNode m_front;
        pQNode m_rear;
        int m_sum;//队列中节点数目
    public:
        Queue();
        ~Queue();
        void push(int x);
        void pop();
        int front();
        int back();
        bool empty();
        bool full();
};
Queue::Queue(){
    m_front = m_rear =(pQNode)malloc(sizeof(QNode));
    m_front->pNext = NULL;
    m_sum = 0;
}
Queue::~Queue(){//清空队列
    pQNode p,q;
    m_rear = m_front;
    p = m_front->pNext;
    m_front->pNext = NULL;
    while(p){
        q = p;
        p = p->pNext;
        free(q);
    }
    free(m_front);
}
void Queue::push(int x){
    if(!full()){
        pQNode p =(pQNode)malloc(sizeof(QNode));
        p->data = x;
        p->pNext = NULL;
        cout<< "进队列元素是"<< x <<endl;
        m_rear->pNext = p;
        m_rear = p;
        m_sum++;
    }else{
        cout << "队列已满" <<endl;
    }
}
void Queue::pop(){
  
    pQNode tmp;//指向被删除节点，方便释放空间&判断被删节点是否是对尾节点
    if(empty()){
        cout << "队列为空,出队失败" <<endl;
        return ;
    }
    cout <<"删除的队列头是:" << m_front->pNext->data <<endl;
    tmp = m_front->pNext;
    m_front->pNext = tmp->pNext;
    if(m_rear == tmp){
        m_rear = m_front;
    }
    free(tmp);
    m_sum--;
}
int Queue::front(){
    if(empty()){
        cout << "队列为空" <<endl;
        return -1;//队列为空
    }else{
        return m_front->pNext->data;
    }
}
int Queue::back(){
    if(empty()){
        cout <<"队列为空" <<endl;
        return -1;//队列为空
    }else{
        return m_rear->data;
    }
}
bool Queue::empty(){
    if(m_front == m_rear){
        return true;
    }else
        return false;
}
bool Queue::full(){
    if(m_sum < SUM){
        return false;
    }else
        return true;
}

int main(){
    Queue que;
    int ret;

    que.pop();
    que.push(1);
    que.push(2);

    que.pop();
    if((ret = que.front()) != -1){
        cout << "队列头元素是:"<< ret <<endl;
    }
    if((ret = que.back()) != -1){
        cout << "队列尾元素是:" << ret <<endl;
    }
    que.push(3);
    que.push(4);
    que.push(5);

    if((ret = que.front()) != -1){
        cout << "队列头元素是:"<< ret <<endl;
    }
    if((ret = que.back()) != -1){
        cout << "队列尾元素是:" << ret <<endl;
    }

    return 0;
    
}