Why do we need virtual functions in c++?

Here is how I understood not just what virtual functions are, but why they're required:

Let's say you have these two classes:

class Animal { public: void eat() { std::cout << "I'm eating generic food."; } }; class Cat : public Animal { public: void eat() { std::cout << "I'm eating a rat."; } };

In your main function:

Animal *animal = new Animal; Cat *cat = new Cat; animal->eat(); // Outputs: "I'm eating generic food." cat->eat(); // Outputs: "I'm eating a rat."

So far so good, right? Animals eat generic food, cats eat rats, all without virtual.

Let's change it a little now so that eat() is called via an intermediate function (a trivial function just for this example):

// This can go at the top of the main.cpp file void func(Animal *xyz) { xyz->eat(); }

Now our main function is:

Animal *animal = new Animal; Cat *cat = new Cat; func(animal); // Outputs: "I'm eating generic food." func(cat); // Outputs: "I'm eating generic food."

Uh oh... we passed a Cat into func(), but it won't eat rats. Should you overload func() so it takes a Cat*? If you have to derive more animals from Animal they would all need their own func().

The solution is to make eat() from the Animal class a virtual function:

class Animal { public: virtual void eat() { std::cout << "I'm eating generic food."; } }; class Cat : public Animal { public: void eat() { std::cout << "I'm eating a rat."; } };

Main:

func(animal); // Outputs: "I'm eating generic food." func(cat); // Outputs: "I'm eating a rat."

Done.

https://stackoverflow.com/questions/2391679/why-do-we-need-virtual-functions-in-c

 

 

 

Why do we need virtual functions in C++?

binding 과 관련된 일이다..필요하면 early binding/late binding 찾아봐

https://www.geeksforgeeks.org/virtual-function-cpp/