derived class can not access base class protected member?

Hello everyone,


I met with a strange issue that derived class function can not access base class's protected member. Do you know why?

Here is the error message and code.

Code:

---

error C2248: 'base::~base' : cannot access protected member declared in class 'base'

---

Code:

---

class base
{
protected:
        ~base() {}
private:
        void foo()
        {
                base* b = new base;
                delete b;
        }
};

class derived : public base
{
public:
        ~derived() {}
private:
        void goo()
        {
                base* b = new derived;
                delete b; // error in this line
        }
};

---

thanks in advance,
George

It is not so clear when you invoke the destructor via delete, so perhaps try out this example instead:

Code:

---

class base
{
protected:
        void foo()
        {
        }
};

class derived : public base
{
public:
        void goo()
        {
                base* b = new derived;
        b->foo();
                delete b;
        }
};

---

If you want it even clearer, change derived to:

Code:

---

class derived : public base
{
public:
        void goo()
        {
                base b;
        b.foo();
        }
};

---

So the derived object is not trying to access foo() as a derived class, but as if it were not related to base or as if goo() was a free non-friend function calling b.foo().

First of all, your base class destructor should be virtual!

Next, your derived class can call protected members of the base class directly, but not through a pointer like that.

In LaserLight's example, calling b->foo() will still fail, but you can call foo() just by itself.