Материал из C\C++ эксперт
Class prototype
#include <iostream.h>
#include <math.h>
class A;
class B
{
int sum;
public:
B(){ sum=1;}
B(int a,int b){sum=a*a+b*b;}
int Larger(B b,A a);
};
class A //B must be before A, for A references the B::Larger()
{
friend int B::Larger(B b,A a);//use B::Larger()!
private:int num;
public:
A(){num=1;}
A(int a,int b){num=4*a+b;}
void Display(void){cout<<num<< endl;}
};
int B::Larger(B b,A a)
{
return (b.sum > a.num);
}
int main(void)
{
B objB(1,2);
A objA(3,3);
if(objB.Larger(objB,objA)) {
cout << "B obj is Larger , the small num is ";
objA.Display();
}else{
cout << "B obj is not Larger\n";
}
return 0;
}B obj is not Larger
