Pure virtual functions in C ++

If a pure virtual function is defined in a class, we can simply understand that this class is an interface. (The so-called interface is actually a standard. This is why the standard defined by the company is interfaces .)

Interface classes cannot be instantiated. That is to say, the standard is not a specific thing (there are various ways for everyone to implement the standard. Only when you implement it will you have something specific. For such a specific thing, there will be an instance)

After understanding this, I defined an interface,

I also want to define an interface, but I want to expand the original interface. Of course, you only need to inherit it. After inheriting the original interface, you can have the original interface and then define the Extended Interface.

Of course, if an interface class is inherited but the interface is not implemented, the subclass is still an interface.

Still cannot be instantiated.