友员

#include <iostream>using namespace std;class A{int data;public:A(int d):data(d){}void show(){cout << "data=" << data << endl;}friend class B;     //友员类 };class B{public:void twice(A& a){a.data *= 2;}};int main(){A oa(50);B ob;ob.twice(oa);oa.show();return 0;}//===================================================================== #include <iostream>using namespace std;class A{int data;public:A(int d):data(d){}void show(){cout << "data=" << data << endl;}friend A add(const A& a1, const A& a2);   //授权 给这个函数，允许访问A类成员，友员不是成员 };A add(const A& a1,const A& a2){int sum = a1.data + a2.data;return A(sum);}int main(){A a1(40);A a2(50);add(a1, a2).show();return 0;}