C++中修改类的私有属性的方法

#include <iostream>

using std::cout;
using std::endl;

class A
{
private:
    int test1;
public:
    int test2;
public:
    A()
    {
        test1 = 10;
        test2 = 2;
    }
    void t()
    {
        cout << "This test1 is :" << test1 << endl;
        cout << "This test2 is :" << test2 << endl << endl;
    }
};

int
main(int argc, char **argv)
{
    A t;
    int *a;
    t.t();
    a = & t.test2;
    a --;
    *a = 30;
    t.t();
    cout << "I love this test..." << endl;
}