Why can't this friend function access the private variables?

Question

class Student{
public:
Student(int test)
:key(705)
{
    if(test == key)
    {cout << "A student is being verified with a correct key: "<< test << endl;
    allow=1;
    }
    else
    {
        cout << "Wrong key" ;
    }
}

friend void printResult();


private:
const int key;
int allow;


};

void printResult()
{
 if(allow==1)
 {
   cout<< " Maths: 75 \n Science:80 \n English: 75" << endl;
  }
}

int main()
{
int testkey;
cout << "Enter key for Bob: ";
cin >> testkey;

Student bob(testkey);

printResult();

}

The function printResult can't seem to access the variable allow, which is private, from the Student class. Did I prototype the printResult in the wrong place or was the syntax wrong? AFAIK, we can prototype friends anywhere in the class.

Answer 1

printResult is not a member function, so you need to give it a Student instance to act on. For example

void printResult(const Student& s)
{
 if(s.allow==1)
 {
   cout<< " Maths: 75 \n Science:80 \n English: 75" << endl;
  }
}

then

Student student(1);
printResult(student);

Answer 2

That's because allow belongs to an instance of the class, but no instance is being referred to.

You should probably make printResult a member function of the class instead of making it an external function or make the function take a reference to a Student instance so you can access the allow member via the instance.allow where instance is a parameter of type const Student&.