#include<iostream>
using namespace std;
class Boat
{
public:
Boat(int w=0) {weight=w;}
void coutB() {cout<<"Boat weight="<<weight<<endl;}
friend void totalWeight(); //定义totalweight为boat的友元函数
private:
int weight;
};

class Car
{
Car(int w=0) {weight=w;}
void coutB() {cout<<"Car weight="<<weight<<endl;}
friend void totalWeight(); //定义totalweight为car的友元函数
private:
int weight;
};

void totalWeight()
{
int B,C;
B=boat.weight;
C=car.weight; //通过对象访问其weight
cout<<"total weight="<<B+C<<endl;
}

void main()
{
Boat boat(120);
Car car(110); //生成对象
totalWeight();
}

实现功能:totalweight计算两者的重量之和
编译报错:error C2065: 'boat' : undeclared identifier
error C2228: left of '.weight' must have class/struct/union type
error C2065: 'car' : undeclared identifier
error C2228: left of '.weight' must have class/struct/union type
error C2248: 'Car::Car' : cannot access private member declared in class 'Car'
see declaration of 'Car::Car'



请高手帮忙!!1
谢谢先~

小写的car和boat是对象啊~
我还是看不出来哪的问题!

一个友类是对这个类的
不是对这个对象的
void totalWeight()
{
int B,C;
B=boat.weight;
C=car.weight; //通过对象访问其weight
cout<<"total weight="<<B+C<<endl;
}

void main()
{
Boat boat(120);
Car car(110); //生成对象
totalWeight();
}

我改了,还是不行
我刚开始学,对这方面的语法还不太熟,能请你说的详细点吗?

#include<iostream>
using namespace std;
class Boat
{
public:
Boat(int w=0) {weight=w;}
void coutB() {cout<<"Boat weight="<<weight<<endl;}
friend void totalWeight(Boat &a,Car &b); //定义totalweight为boat的友元函数
private:
int weight;
};

class Car
{
Car(int w=0) {weight=w;}
void coutB() {cout<<"Car weight="<<weight<<endl;}
friend void totalWeight(Boat &a,Car &b); //定义totalweight为car的友元函数
private:
int weight;
};

void totalWeight(Boat &p1,Car &p2)
{
int x,y;
x=p1.weight;
y=p2.weight; //通过对象访问其weight
cout<<"total weight="<<x+y<<endl;
}

void main()
{
Boat boat(120);
Car car(110); //生成对象
totalWeight(boat,car);
}

还有一个问题,就是友元函数对类的访问只能通过参数传递吗?

#include<iostream>

using namespace std;

class Boat
{
private:

int weight;

public:

Boat(int w=0)
{
weight=w;
}
void coutB()
{
cout<<"Boat weight="<<weight<<endl;
}
friend int totalWeight(Boat &a);

};
int totalWeight(Boat &a)
{
int B;
return B=a.weight;
}

class Car
{
private:

int weight;

public:

Car(int w=0)
{
weight=w;
}
void coutB()
{
cout<<"Car weight="<<Car::weight<<endl;
}

friend int totalWeight1(Car &b);

};

int totalWeight1(Car &b)
{
int C;
return C=b.weight;
}

int main()
{
Boat boat(120);

Car car(110);

cout<<totalWeight(boat)+totalWeight1(car);

return 0;
}

这是我改了你程序的一些代码还有格式
用楼主你写的代码调不了``可能是我水平问题吧