derived class can not access base class protected member?

**George2** · 10-21-2007

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

**laserlight** · 10-21-2007

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().

**cpjust** · 10-21-2007

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.

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