class A{public:A (){a = 1;}void print(){cout <<a<<endl;}//friend class B; 友元类也可放在此处 private:int a;friend class B;//这里不能为friend B; };class B{public:void f(A& _a){_a.a = 2;//由于用到A的成员变量 //则必须先声明类A }};int main(){A a;a.print();B b;b.f(a);a.print();return 0;}```cpp在这里插入代码片
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