Dynamic cast

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In the C++ programming language, the dynamic_cast operator is a part of the run-time type information (RTTI) system that performs a typecast. Unlike an ordinary C-style typecast, a type safety check is performed at runtime, and if the types are not compatible, an exception will be thrown (when dealing with references) or a null pointer will be returned (when dealing with pointers). In this regard, dynamic_cast behaves like a Java typecast.

Example code

Suppose some function takes an object of type A as its argument, and wishes to perform some additional operation if the object passed is an instance of B, a subclass of A. This can be accomplished using dynamic_cast as follows.

#include <typeinfo> // For std::bad_cast
#include <iostream> // For std::cerr, etc.
 
class A
{
public:
	// Since RTTI is included in the virtual method table there should be at least one virtual function.
	virtual ~A() { };
 
	// other members...
};
 
class B : public A
{
public:
	void methodSpecificToB() { };
 
	// other members.
};
 
void my_function(A& my_a)
{
	try
	{
		B& my_b = dynamic_cast<B&>(my_a);
		my_b.methodSpecificToB();
	}
	catch (const std::bad_cast& e)
	{
		std::cerr << e.what() << '\n';
		std::cerr << "This object is not of type B\n";
	}
}

A similar version of my_function can be written with pointers instead of references:

void my_function(A* my_a)
{
	B* my_b = dynamic_cast<B*>(my_a);
 
	if (my_b != nullptr)
		my_b->methodSpecificToB();
	else
		std::cerr << "This object is not of type B\n";
}

See also

External links

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