老师上课教的，但是忘记到底要怎么解决： 错误C2597 对非静态成员“Parent::_id”的非法引用

[猫凉]

#pragma once
#ifndef PARENT_H_
#define PARENT_H_
#include<iostream>
using namespace std;
class Parent {
private:
int _id;
protected:
int _age;
public:
Parent(int id=1000, int age=8) {
_id = id;
_age = age;
}
friend ostream & operator<<(ostream & out, const Parent & p) {
out << "id= " << _id << endl;
out << "age= " << _age << endl;
return out;
}
private:
void display() {
cout << "id= " << _id << endl;
cout << "age= " << _age << endl;
}
protected:
void setId(int id) {
_id = id;
}
};
class Child:public Parent {
public:
Child(int id = 2000, int age = 0) :Parent(id, age) {

}
void testParentMemberAccess(){
_age = 9;
setId(2000);
}
};

#endif // !PARENT_H_

#include"parent.h"
#include<iostream>
using namespace std;
int main() {
Parent p;
cout << p;
return 0;
}

[jiht594]

out << "id= " << p._id << endl;

[yshuise]

friend ostream & operator<<(ostream & out, const Parent & p) {
out << "id= " << p._id << endl;
out << "age= " <<p. _age << endl;
return out;
}

[yshuise]

friend ostream & operator<<(ostream & out, const Parent & p) {
out << "id= " << p._id << endl;
out << "age= " <<p. _age << endl;
return out;
}