c++类的类型转换问题

Question

我想将Soldier类的对象John转换成Sergeant类（代表升官了），名字不变，但我发现我的代码实现不了，原因是重定义了。我想知道有没有什么办法可以不改我的对象名字（John）而转换它的类类型

#include<iostream>
using namespace std;

class Soldier {
	friend class Sergeant;
public:
	Soldier(long long a, string b, string c, int d) :id(a), name(b), sex(c), year(d) {}
private:
	long long id;
	string name;
	string sex;
	int year;
};

class Sergeant {
public:
	Sergeant() {}
	Sergeant(long long a, string b, string c) :id(a), name(b), sex(c) {}
	Sergeant(Soldier& sd) {
		id = sd.id;
		name = sd.name;
		sex = sd.sex;
	}
	void Display() {
		cout << "name: " << name << endl
			<< "id: " << id << endl
			<< "sex: " << sex << endl;
	}
private:
	long long id;
	string name;
	string sex;

};



int main() {
	Soldier John(20200001, "John", "male", 2);
	Sergeant John = John;    //这行和下一行都是错误的
	John.Display();
	return 0;
}

有大佬回答的话我会非常感激的    ||o(*°▽°*)o|Ю

Answer 1

这行代码变量名称与上一行重名了吧 Sergeant John = John;