C++ Brain Teasers: Exercise Your Mind/

...

/

Discussion: A Destructive Relationship

Discussion: A Destructive Relationship

Execute the code to understand the output and gain insights into destructors and virtual functions.

We'll cover the following...

Run the output

Now, it’s time to execute the code and observe the output.

C++ 17
#include <iostream>
#include <memory>
struct Widget
{
    virtual void draw() { std::cout << "Widget draw\n"; }
    virtual ~Widget() { std::cout << "Widget destructor\n"; }
};
struct Button : public Widget
{
    void draw() override { std::cout << "Button draw\n"; }
    ~Button() override { std::cout << "Button destructor\n"; }
};
int main()
{
    std::unique_ptr<Widget> widget = std::make_unique<Button>();
    widget->draw();
}

Understanding the output

When we call draw(), the program only prints Button draw. But when unique_ptr goes out of scope, and the destructor is called, the program prints both Button destructor and Widget destructor. Why is that?

Virtual functions

A common technique for dynamic polymorphism is using virtual functions. We ...