stack链式C++

#include <iostream>
using namespace std;

typedef struct _node{
    int data;
    struct _node* next;
    _node(int e ,struct _node* p = nullptr){
        data = e;
        next = p;   
    }
}node;

class stack{
public:
    stack():m_start(new node(-1,nullptr)){}
    ~stack(){
        while(m_start->next != nullptr){
            node* pdel = m_start;
            m_start = m_start->next;
            delete pdel;
        }
        m_start = nullptr;
    }

    void push(int e);
    void pop();
    int  top();
    bool isEmpty(); 
private:
    node* m_start;
};
//头插法
void stack::push(int e){
    node* pnew = new node(e,nullptr);
    pnew->next = m_start->next;
    m_start->next = pnew;
}

void stack::pop(){
    if(m_start->next != nullptr){
        node* pdel = m_start->next;
        m_start->next = m_start->next->next;
        delete pdel;    
    }else{
        cout << "stack is empty.\n";
    }
}

int  stack::top(){
    if(m_start->next != nullptr){
        return m_start->next->data;
    }else{
        cout << "stack is empty.\n";
        exit(1);
    }
}

bool stack::isEmpty(){
    return m_start->next == nullptr;
}


int main(){
    stack s;
    s.push(1);
    s.push(2);
    s.push(3);
    while(!s.isEmpty()){
        cout << s.top() << ends;
        s.pop();    
    }
    cout << endl;
    s.pop();

    return 0;
}