Dynamic cast

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 (when dealing with references) or return a null pointer (when dealing with pointers) 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.

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 // For std::bad_cast
#include // For std::cout, etc.

class A{public: // Since RTTI is included in the virtual method table 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(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(my_a);

if (my_b != NULL) my_b->methodSpecificToB(); else std::cout << "This object is not of type B" << std::endl;}

External links

* [http://publib.boulder.ibm.com/infocenter/macxhelp/v6v81/index.jsp?topic=/com.ibm.vacpp6m.doc/language/ref/clrc05keyword_dynamic_cast.htm dynamic_cast operator at IBM Mac OS X Compilers]
* [http://msdn2.microsoft.com/en-us/library/cby9kycs.aspx dynamic_cast operator at MSDN]