Access Violation with helper functions

I have class A trying to access helper functions in class B.

class A has a friend class B declaration and vice verse.

However when class B tries to use the helper function I get an access violation.

Code:

---

class A{
    friend B;
    private:
            string a;

    public:
            string returnString(){ return a; }
};

---

Can anyone tell me what's wrong with that?

Thanks,
Lang

more code please.

Bad design. If A needs B's privates, and B needs A's privates, then maybe you need an C class with those parts, and make A and B derived from it. However, that depends on what exactly one needs from the other. However, you should avoid using friends at all.

Try cleaning the solution. If you have MSVS 7 and up, click Build -> Clean Solution.

Also close it and remove the following files: *.aps, *.ncb, *.suo

Ok, thanks for the quick reply. GCDEF asked for more code so this is class Car.

Code:

---

//We fordward reference the parkingLot class because Class Car has yet to be defined
//but our parkingLot class requires it.
class parkingLot;

using namespace std;

class Car{
friend parkingLot;
private:
        string plateNumber;
       
public:
        Car (string argString){
                this->plateNumber = argString;
        }

        string getPlateNumber(){ return plateNumber; }
};

---

This is class parkingLot;

Code:

---

class parkingLot{
        friend Car;
private:
        int lot_number;                // the identification number of the parking lot
        int capacity;                        // the maximum number of car it can accommodate
        int car_count;                        // the number of cars currently in the lot
        double hourly_rate;                // the hourly rate
        double max_charge;                // the maximum charge for each car
        double revenue;                // the daily revenue of this rate
       
        Car ** parking_spots;                // a dynamic array of pointers to Car,
                                                                // representing parking spots in the lot
       
public:
        parkingLot(int argNumber, int argCapacity, double hourlyRate, double maxCharge){
                lot_number = argNumber;
                capacity = argCapacity;
                hourly_rate = hourlyRate;
                max_charge = maxCharge;
                revenue = 0;
                car_count = 0;

                parking_spots = new Car *[capacity];
        }

        int enter(Car * argCar, int hour, int min){
                if (car_count == capacity) return 1; //parking lot full

                for (int i = 0; i < capacity; ++i){
                        if (parking_spots[i] != NULL){ // we have to make sure its not null to compare license plates
                                if (argCar->getPlateNumber() == parking_spots[i]->getPlateNumber()){
                                        return 2; //2 = car already in parking lot
                                }
                        }
                }

                for (int i = 0; i < capacity; ++i){
                        if (parking_spots[i] == NULL){
                                parking_spots[i] = argCar; //found an empty spot, break, there's no use to keep looking
                                break;
                        }
                }

                argCar->park(this, hour, min);
                cout << argCar->toString() << " enters Lot " << lot_number << " at " << hour << ":" << min;

                ++car_count;
                return 0; // no error
        }

};

---

I just need class parkingLot to have the ability to call Car::getPlateNumber()

Thanks,
Lang

What I meant was code that calls the function. I see

if (argCar->getPlateNumber() == parking_spots[i]->getPlateNumber())

Are you sure argCar and parking_spots[i] are both valid pointers?

Quote:

---

I just need class parkingLot to have the ability to call Car::getPlateNumber()

---

And why do they have to be friends for that? :confusion: That is a public methods. As long as you have an object or valid pointer to object of type Car, you can call it. No need for friends. As I already said, don't use friends. Friends are like guns. For the simple fact that you have one, but you don't have to use it.

cilu makes a good point. As long as getPlateNumber is public, which it is, you don't need a friend class. That's not the cause of your crash however. Check your pointers when you try to call the function.

Thanks for the help guys!

parking_spots[i] was not NULL but it was an invalid pointer. Is there anyway to detect that? Or should I just set every value in my parking_spots array to NULL?

Thanks,
Lang

After this line
parking_spots = new Car *[capacity];
you'd need to initialize it to NULLs. You're declaring a bunch of pointers, but not initializing them.

Yes, I tried that and it worked.

Thanks for the help everone.