RTTI (RunTime Type Information) in C++ (original) (raw)

Last Updated : 13 Dec, 2025

RTTI (Run-Time Type Information) allows a C++ program to identify the actual type of an object while the program is running. It plays an important role when working with inheritance and polymorphism.

It is mainly used when you work with classes that have virtual functions (polymorphic classes).
**Upcasting means converting a derived class object to a base class type. This is safe because the derived class has all attributes of base class.
**Downcasting means converting a base class pointer or reference back to a derived class type. This requires a runtime check to ensure the conversion is valid.

Runtime Cast

A runtime cast is a type conversion that checks its validity during program execution, typically used to safely downcast a base class pointer or reference to a derived class in an inheritance hierarchy.

Ensures type safety at runtime.
Implemented using dynamic_cast.
Returns a valid pointer if the cast is correct, or nullptr (for pointers) if it fails.

Upcasting

It Enables polymorphism, allowing derived objects to be accessed through base class interfaces.
It is safe because every derived class object is also a base class object.
It happens implicitly; no explicit cast is needed in most cases. C++ `

#include using namespace std;

class Base { public: void show() { cout << "Base class\n"; } };

class Derived : public Base { public: void show() { cout << "Derived class\n"; } };

int main() { Derived d;

// Upcasting: Derived object treated as Base
Base *b = &d;

b->show(); 
return 0;

}

Downcasting

Allows access to derived class-specific members when working through a base class pointer or reference.
It is commonly used in polymorphic class hierarchies where the actual object type is determined at runtime.
It is not inherently safe — the base pointer may not actually point to a derived class object. CPP `

#include using namespace std;

class Base { public: virtual void dummy() { } // Make Base polymorphic };

class Derived : public Base { public: void show() { cout << "Derived class\n"; } };

int main() { Base *b = new Derived;

// Downcasting: Convert Base pointer back to Derived pointer
Derived *d = dynamic_cast<Derived *>(b);

if (d != nullptr)
    d->show();
else
    cout << "Cannot cast";

delete b;
return 0;

}