C++ is a statically typed language that encourages strong type safety. However, there may be scenarios where you need to identify the type of an object during runtime. For such cases, C++ provides two mechanisms: Type Traits and Run-Time Type Identification (RTTI). In this article, we will explore how C++ handles runtime type identification.

Type Traits

Type Traits are a set of template classes that allow compile-time introspection of types. They provide information about the characteristics, properties, and operations that can be performed on a type. Type Traits are part of the <type_traits> header in the C++ Standard Library.

Commonly used Type Traits include:

• std::is_same<T, U>: Determines if T and U are the same type.
• std::is_const<T>: Checks if T is a constant type.
• std::is_pointer<T>: Checks if T is a pointer type.

By utilizing Type Traits, you can make compile-time decisions based on type information, rather than relying on runtime introspection.

Run-Time Type Identification (RTTI)

In certain cases, compile-time type information is insufficient, and you need to determine the actual type of an object during runtime. C++ provides RTTI as a mechanism to achieve this.

RTTI allows you to:

• Determine the type of an object dynamically at runtime.
• Perform type-safe casts between base and derived classes.

To enable RTTI in a class, it must meet two requirements:

1. It must have at least one virtual function.
2. It must be polymorphic (have at least one virtual function).

The RTTI mechanism in C++ provides the following features:

• dynamic_cast<TargetType>(ptr): It allows you to perform a runtime-checked, type-safe downcasting between polymorphic types. If the conversion is not possible, dynamic_cast returns a null pointer or throws an exception (if casting pointers or references respectively).
• typeid(expression): It returns a reference to the type_info object representing the dynamic type of the expression. It’s mainly used for type comparison.

Here’s an example of using RTTI:

#include <iostream>
#include <typeinfo>

class Base {
public:
    virtual ~Base() {}
};

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

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

    if (Derived* derivedPtr = dynamic_cast<Derived*>(basePtr)) {
        derivedPtr->doSomething();
    }

    std::cout << typeid(*basePtr).name();  // Prints "Derived" since the dynamic type is Derived

    delete basePtr;
    return 0;
}

In the above example, we create a Base class and a Derived class that derives from Base. We then use dynamic_cast to safely downcast the Base pointer to a Derived pointer, enabling us to call the doSomething function. Additionally, we use typeid to determine the dynamic type of the object pointed to by basePtr.

By utilizing the power of Type Traits and RTTI, you can make your C++ code more flexible and dynamic when needed.

#Cplusplus #RTTI