关于#c++#的问题，如何解决？

c++题目：定义一个类Counter,包含私有成员int n，重载运算符+，实现对象相加。求解答。

class Counter
{

    friend Counter operator+(Counter& c1, Counter& c2);
public:
    int  getm_n(int n)
    {
        int m_n = n;
        return m_n;
    }
    void setm_n(int n)
    {
        int m_n = n;
    }
private:
    int n;
    
};
 Counter operator+(Counter& c1, Counter& c2)
{
    Counter temp;
    temp.n = c1.n + c2.n;
    return temp;
}
int main()
{
    Counter c1;
    c1.setm_n(1);
    Counter c2;
    c1.setm_n(2);
    Counter c3;
    Counter c3 = c1 + c2;
    cout << c3.getm_n;
    
}

我的最后一行错了，编译器给的原因是：
指向绑定函数的指针只能用于调用函数

试试这样

class Counter
{
    friend Counter operator+(const Counter& c1, const Counter& c2);
public:
    int getm_n()
    {
        return n;
    }
    void setm_n(int n)
    {
        this->n = n;
    }
private:
    int n;
    
};

Counter operator+(const Counter& c1, const Counter& c2)
{
    Counter temp;
    temp.n = c1.n + c2.n;
    return temp;
}

int main()
{
    Counter c1;
    c1.setm_n(1);
    Counter c2;
    c2.setm_n(2);
    Counter c3 = c1 + c2;
    cout << c3.getm_n();
    
    return 0;
}

getm_n 是一个函数，要加括号并传参数