构造函数作为友元函数的参数

#include<iostream>
using namespace std;
class A
{
public:
    friend void test(A a);
    int a1;
    A()
    {
        cout<<"A"<<"\n";
    }

};
    void test(A a)
    {
        a.a1=1;
        cout<<a.a1<<"\n";
    }

int main()
{
test(A());
return 0;
}