Cannot cast "derived" to its private base class "base" [duplicate]

Question

I'm encountering an error when trying to create an object which inherits from a class which inherits from a class which defines pure virtual functions. I'm not sure what is wrong. I know I need to override the pure virtual functions in my derived class but it's not working. I only want to override the function in my ProduceItem class and not my Celery class because I want the Celery class to inherit the overridden methods from ProduceItem.

In Main:

    GroceryItem *cel = new Celery(1.5); //Cannot cast 'Celery' to its private base class GroceryItem


    class GroceryItem
    {
    public:
        virtual double GetPrice() = 0;
        virtual double GetWeight() = 0;
        virtual std::string GetDescription() = 0;

    protected:
        double price;
        double weight;
        std::string description;

    };

ProduceItem header file:

#include "GroceryItem.h"

class ProduceItem : public GroceryItem
{
public:
    ProduceItem(double costPerPound);
    double GetCost();
    double GetWeight();
    double GetPrice();
    std::string GetDescription();
protected:
    double costPerPound;
};

ProduceItem.cpp file:

#include <stdio.h>
#include "ProduceItem.h"
ProduceItem::ProduceItem(double costPerPound)
{
    price = costPerPound * weight;
}

double ProduceItem::GetCost()
{
    return costPerPound * weight;
}

double ProduceItem::GetWeight()
{
    return weight;
}

double ProduceItem::GetPrice()
{
    return price;
}

std::string ProduceItem::GetDescription()
{
    return description;
}

Celery header file:

#ifndef Lab16_Celery_h
#define Lab16_Celery_h
#include "ProduceItem.h"

class Celery : ProduceItem
{
public:
    Celery(double weight);
    double GetWeight();
    double GetPrice();
    std::string GetDescription();

};

#endif

Celery.cpp file:

#include <stdio.h>
#include "Celery.h"

Celery::Celery(double weight) : ProduceItem(0.79)
{
    ProduceItem::weight = weight;
    description = std::string("Celery");
}

Answer 1

You are using private inheritance here: class Celery : ProduceItem. The default inheritance level for classes is private.

Change it to class Celery : public ProduceItem

Note that when you delete that pointer, you will leak memory because you don't have virtual destructors. Just add definitions like this to your classes:

virtual ~GroceryItem() {}

Answer 2

Inheritance of classes is private by default. Usually, and in your case, you want public inheritance. So:

class Celery : public ProduceItem

And similar on class ProduceItem.

Note that for structs, inheritance is public by default (you can say struct Foo : private Bar if you want).