C++利用友元可在外部函数中访问类的私有函数:
#include<iostream>
using namespace std;
class A{
void fun1(){cout<<"hello\n";}
friend int main();
friend class B;
};
class B{
void fun2();
friend int main();
};
void B::fun2(){
A a;
a.fun1();
}
int main(){
A a;
B b;
a.fun1();
b.fun2();
return 0;
}