Overloading operator<< for printing as a member
class TestClass {
public:
    ostream& operator<<(ostream& os) {
        return os << "I'm in the class, msg=" << msg << endl;
    }

private:
    string msg;
};


int main(int argc, char** argv) {
    TestClass obj = TestClass();
    cout << obj;

    return 0;
}

ostream& operator<<(ostream& os, TestClass& obj) {
    return os << "I'm outside of the class and can't access msg" << endl;
}

class TestClass {
public:
    friend ostream& operator<<(ostream& os, TestClass const & tc) {
        return os << "I'm a friend of the class, msg=" << tc.msg << endl;
    }

private:
    string msg;
};

class TestClass {
public:
    ostream& print(ostream& os) const {
        return os << "I'm in the class, msg=" << msg << endl;
    }

private:
    string msg;
};


ostream& operator<<(ostream& os, TestClass& obj) {
    return obj.print(os);
}

int main(int argc, char** argv) {
    TestClass obj;
    cout << obj;

    return 0;
}

class TestClass
{
public:
    // Have a nice friend.
    // This tightly binds this operator to the class.
    // But that is not a problem as in reality it is already tightly bound.
    friend ostream& operator<<(ostream& os, TestClass const& data)
    {
        return os << "I'm in the class, msg=" << data.msg << endl;
    }

private:
    string msg;
};