#include <iostream>
 
class Base
{
	public:
	Base() = default;
	virtual ~Base() = default;
 
	int x;
};
 
class DerivedA : public Base
{
	int y;
};
 
class DerivedB : public Base
{
	float y;
};
 
int main()
{
	Base *base = new DerivedA;
 
	DerivedA *derivedA = dynamic_cast<DerivedA*>(base);
	DerivedB *derivedB = dynamic_cast<DerivedB*>(base);
 
	std::cout << "derivedA is " << (derivedA?"valid" : "null") << std::endl;
	std::cout << "derivedB is " << (derivedB?"valid" : "null") << std::endl;
 
	delete base;
 
	return 0;
}

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