In C++, when dealing with dynamic memory allocation, we often use smart pointers to manage the lifetime of objects. Two commonly used smart pointer types in the C++ standard library are std::unique_ptr and std::shared_ptr. These pointers provide a safer and more convenient way to handle resources compared to raw pointers.

std::unique_ptr

std::unique_ptr is a unique ownership smart pointer. It ensures single ownership of the resource it manages and provides automatic deallocation when the pointer goes out of scope. This type of pointer cannot be copied, only moved.

Using std::unique_ptr with polymorphic types requires some additional considerations. Polymorphism in C++ involves having a base class with virtual functions that can be overridden by derived classes. To support polymorphic behavior, the base class’s destructor must be declared as virtual. This allows objects to be correctly deallocated when referencing them through a base class pointer.

Here’s an example of using std::unique_ptr with a polymorphic type:

class Base {
public:
    virtual ~Base() {}
    virtual void foo() = 0;
};

class Derived : public Base {
public:
    void foo() override {
        // implementation
    }
};

std::unique_ptr<Base> ptr = std::make_unique<Derived>();
ptr->foo();

In this example, we declare a base class, Base, with a virtual destructor and a pure virtual function, foo(). We then create a derived class, Derived, that overrides the foo() function. We create a std::unique_ptr of type Base and assign it a std::unique_ptr created using std::make_unique<Derived>(). We can then call the overridden foo() function through the std::unique_ptr.

std::shared_ptr

std::shared_ptr is a shared ownership smart pointer. Unlike std::unique_ptr, std::shared_ptr allows multiple pointers to refer to the same object. It uses reference counting to track the number of references and automatically deallocates the object when the reference count becomes zero.

std::shared_ptr can also be used with polymorphic types in a similar manner:

std::shared_ptr<Base> ptr = std::make_shared<Derived>();
ptr->foo();

Here, we create a std::shared_ptr of type Base and assign it a std::shared_ptr created with std::make_shared<Derived>(). We can call the foo() function through the std::shared_ptr as well.

Conclusion

Using std::unique_ptr and std::shared_ptr with polymorphic types in C++ allows for better memory management and safer handling of resources. By following the guidelines for polymorphism with smart pointers, we can leverage the benefits of these smart pointers while still supporting polymorphic behavior. Remember to use the appropriate smart pointer type based on the ownership requirements of your code.

#cpp #smartpointers #polymorphism