为什么main函数里b.print()会出错？

为什么main函数里b.print()会出错？

#include <iostream>
#include <string>
using namespace std;
class netuser {
private:
    string id, email, code;
    
public:
    netuser() {
        this->id = "无名氏";
        this->code = "出错啦";
        this->email = id + "@gpnu.edu.cn";
        ntotalnumber++;
    }
    netuser(string id, int code) {
        this->id = id;
        this->code = code;
        this->email = email;
        
        ntotalnumber++;
    }
    static int ntotalnumber;
    static void printotal();
    void print();
};
 int netuser::ntotalnumber = 0;
 void netuser::printotal() {
     cout << "用户数：" << ntotalnumber << endl;
 }
 void netuser::print() {
     cout << " " << id << " " << code << " " << email << endl;
 }
 int main()
 {
     netuser a( "JJ.Lin", 123);
     a.printotal();
     a.print();
     netuser b();
     b.printtotal();
     b.print();
     return 0;
 }

netuser b;

int main()
{
    netuser a("JJ.Lin", 123);
    a.printotal();
    a.print();
    netuser b;
    netuser::printotal();
    b.print();
    return 0;
}