A pointer to base class cannot operate member object only exist in its derived class?

[northfly]

The following won't work

#include <iostream>
using namespace std;

class base {
public:
	int b;
};

class derived:public base {
public:
	int d;
};

int main() {
	derived D;
	base *  bp=& D;

	cout<<D.b<<endl;
	cout<<D.d<<endl;

	cout<<bp->b<<endl;
        cout<<bp->d<<endl;//error message: d cannot be resolved
	return 0;
}

then What can I do to let the more universal pointer to use that specific new object?

if this cannot be done, then I feel the usage of polymorphism is very limited!!! Hope I am wrong.

[TarikNeaj]

Its very limited becuase you're using it wrong :p Polymorphism is to be used with virtual functions. Here is an example.

class base {
public:
	virtual int func(int x) = 0;
};

class derived :public base {
public:
	int func(int x)
	{
		cout << "My age is ";
		return x;
		cout << endl;
	}
};

int main() {
	derived D;
	base *  bp = &D;

	cout << bp->func(19) << endl;

	system("pause");
	return 0;
}

output:

My age is 19

https://www.youtube.com/watch?v=tvC1WCdV1XU&list=PLAE85DE8440AA6B83&ab_channel=thenewboston

Watch video 55-57.

[northfly]

Thanks!