目的是使用友元函数的方法求船和车重量的和

#include "iostream.h"
class Boat;
class Car{
friend int totalWeight(Boat &a,Car &b);
public:

    int GetNumber()
    {
        cin >> Number;
        return Number;
    }
    int GetWeight()
    {
        cin >> Weight;
        return Weight;
    }
     
private:
    int Number,Weight;
};
class Boat{
friend int totalWeight(Boat &a,Car &b);
public:
    int GetNumber()
    {
        cin >> Number;
        return Number;
    }
    int GetWeight()
    {
        cin >> Weight;
        return Weight;
    }
 
     
private:
    int Number,Weight;
};
int totalweight(Boat& a,Car& b)
{
 
    return a.Weight+b.Weight;
}
int main()
{
    Boat a;
    Car b;
    int x,y,z;
    x = a.GetWeight();
    y = b.GetWeight();
    z = totalweight(a,b);
    cout << z << endl;
    return 0;
}

结果显示错误如下：

--------------------Configuration: 1 - Win32 Debug--------------------
Compiling...
1.cpp
F:\New Folder (3)\5141\1.cpp(41) : error C2248: 'Weight' : cannot access private member declared in class 'Boat'
        F:\New Folder (3)\5141\1.cpp(36) : see declaration of 'Weight'
F:\New Folder (3)\5141\1.cpp(41) : error C2248: 'Weight' : cannot access private member declared in class 'Car'
        F:\New Folder (3)\5141\1.cpp(19) : see declaration of 'Weight'
Error executing cl.exe.

1.exe - 2 error(s), 0 warning(s)
 

试试去掉 class Boat

--------------------Configuration: 1 - Win32 Debug--------------------
Compiling...
1.cpp
F:\New Folder (3)\5141\1.cpp(3) : error C2061: syntax error : identifier 'Boat'
F:\New Folder (3)\5141\1.cpp(40) : error C2248: 'Weight' : cannot access private member declared in class 'Boat'
        F:\New Folder (3)\5141\1.cpp(35) : see declaration of 'Weight'
F:\New Folder (3)\5141\1.cpp(40) : error C2248: 'Weight' : cannot access private member declared in class 'Car'
        F:\New Folder (3)\5141\1.cpp(18) : see declaration of 'Weight'
Error executing cl.exe.

1.obj - 3 error(s), 0 warning(s)


缺少声明了

我修改了下，如下可以正常运行。你的友元函数定义和声明的不一致。在类内的声明是totalWeight(Boat &a,Car &b)，而后边的定义和使用都是totalweight(Boat& a,Car& b) ，当然是不行的。声明为友元的函数未被调用，而调用的函数没有被声明为友元函数。所以报了错误提示不能访问类的私有成员。

#include <iostream>
using namespace std;
 
class Boat;
class Car{
friend int totalWeight(Boat &a,Car &b);
public:
    int GetNumber()
    {
        cin >> Number;
        return Number;
    }
    int GetWeight()
    {
        cout<<"enter the weight of car:";
        cin >> Weight;
        return Weight;
    }
      
private:
    int Number;
    int Weight;
};
class Boat{
friend int totalWeight(Boat &a,Car &b);
public:
    int GetNumber()
    {
        cin >> Number;
        return Number;
    }
    int GetWeight()
    {
        cout<<"enter the weight of boat:";
        cin >> Weight;
        return Weight;
    }
 
      
private:
    int Number,Weight;
};
 
int totalWeight(Boat &a,Car &b){
    return a.Weight+b.Weight;
}
int main()
{
    Boat a;
    Car b;
    int x,y,z;
    x = a.GetWeight();
    y = b.GetWeight();
    z = totalWeight(a,b);
    cout << z << endl;
    return 0;
}

万分感谢~

确实如此~

大小写出了问题~

难怪看了半天没找出来问题~

问下  你用的是什么样的编程辅助工具  a2696026@  与好的给我个