定义两个类共同的友元函数

#include<iostream>
using namespace std;

class Car;//为了使class Boat中可以定义Car类，可以暂时先声明可以引用Car类
class Boat
{
public:
    Boat(int tBweight=0)
    {
        Bweight=tBweight;
    }
    friend class Car;
    friend void getTotalWeight(Car &C,Boat &B);//共同友元函数在每个引用的类都要定义
private:
    int Bweight;
};

class Car
{
public:
    Car(int tCweight=0)
    {
        Cweight=tCweight;
    }
    friend class Boat;
    friend void getTotalWeight(Car &C,Boat &B);//共同友元函数在每个引用的类都要定义
private:
    int Cweight;
};

void getTotalWeight(Car &C,Boat &B)
{
    int all;
    all=B.Bweight+C.Cweight;
    cout<<all<<endl;
}

void main()
{
    Boat boat(1);
    Car car(2);
    getTotalWeight(car,boat);
}