Dynamic cast
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- The title of this article should be dynamic_cast. The initial letter is capitalized and an underscore is substituted or omitted because of technical restrictions.
In the C++ programming language, the dynamic_cast operator is a part of the run-time type information (RTTI) system that performs a typecast. However, unlike an ordinary C-style typecast, a type safety check is incurred at runtime, and it will either throw an exception or return a null pointer if the types are not compatible. Thus, dynamic_cast behaves more like a typecast in a programming language such as Java, rather than the C-style casting which performs no runtime check.
[edit] 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 actually 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::cout, etc.
class A
{
public:
// Since RTTI is included in the vtable
// there should be at least one virtual function.
virtual void foo();
// 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 (std::bad_cast e)
{
std::cout << "This object is not of type B" << std::endl;
}
}
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)
my_b->methodSpecificToB();
else
std::cout << "This object is not of type B" << std::endl;
}
