Run-time type information

In programming, RTTI (Run-Time Type Information, or Run-Time Type Identification) refers to a C++ system that keeps information about an object's data type in memory at runtime. Run-time type information can apply to simple data types, such as integers and characters, or to generic objects. It's the C++ implementation of a more generic concept called reflection.

In order for the dynamic_cast<> operation, the typeid operator or exceptions to work in C++, RTTI must be enabled.

C++ Example

/* A base class pointer can point to objects of any class which is derived * from it. RTTI is useful to identify which type (derived class) of object is * pointed by a base class pointer. */

#include

class abc // base class{public: virtual void hello() { std::cout << "in abc"; ;

class xyz : public abc{ public: void hello() { std::cout << "in xyz"; ;

int main(){ abc *abc_pointer = new xyz(); xyz *xyz_pointer;

// to find whether abc is pointing to xyz type of object xyz_pointer = dynamic_cast(abc_pointer);

if (xyz_pointer != NULL) std::cout << "abc pointer is pointing to a xyz class object"; // identified else std::cout << "abc pointer is NOT pointing to a xyz class object";

delete abc_pointer;

return 0;}

----

An instance where RTTI is used is illustrated below:

class base { virtual ~base(){;

class derived : public base { public: virtual ~derived(){} int compare (derived &ref);};

int my_comparison_method_for_generic_sort (base &ref1, base &ref2){ derived & d = dynamic_cast(ref1); // rtti used here // RTTI enables the process to throw a bad_cast exception // if the cast is not successful return d.compare (dynamic_cast(ref2));}

See also

* Reflection