dynamic_cast.md

Dynamic casting in C++ is performed using the dynamic_cast operator. It is primarily used for safely downcasting pointers or references within a hierarchy of classes involving polymorphism. Unlike other casting operators, dynamic_cast checks the validity of the cast at runtime.

When to Use

1. Downcasting: You can use dynamic_cast to convert a pointer (or reference) from a base class to a derived class.
2. Polymorphism: It works only with pointers or references to polymorphic types (i.e., classes with at least one virtual function).

Syntax

Pointers:

Derived* d = dynamic_cast<Derived*>(base_ptr);

References:

Derived& d = dynamic_cast<Derived&>(base_ref);

Example

Consider the following example involving a base class Animal and a derived class Dog.

class Animal {
public:
    virtual void makeSound() {} // Making it polymorphic
};

class Dog : public Animal {
public:
    void makeSound() { std::cout << "Woof" << std::endl; }
    void fetchStick() { std::cout << "Fetching stick" << std::endl; }
};

int main() {
    Animal* animalPtr = new Animal();
    Animal* dogPtr = new Dog();

    Dog* d;

    // Successful dynamic cast
    d = dynamic_cast<Dog*>(dogPtr);
    if(d) {
        d->fetchStick(); // Output: "Fetching stick"
    }

    // Unsuccessful dynamic cast
    d = dynamic_cast<Dog*>(animalPtr);
    if(d == nullptr) {
        std::cout << "Failed to cast Animal to Dog." << std::endl; // Output: "Failed to cast Animal to Dog."
    }

    return 0;
}