C + + Callback interface declaration __c++

When writing callback functions in Java, it is convenient to declare and implement the callback interface with interface.

The C + + declaration callback interface can declare a pure virtual class.

What is a pure virtual class.

A: A pure virtual class is a class that has only declarations that are not implemented.

Such as

Class Ainterface

{

virtual void fun () = 0;

}

Note: virtual void fun () = 0; is a declaration fun is a pure virtual function. If there is no = 0, then fun is just a virtual function, i.e.

Class Ainterface

{

virtual void fun ();

This class cannot be called a pure virtual class.

So

Class Ainterface

{

virtual void fun ();

} (Error-declaring method when implementation is not written)

And

Class Ainterface

{

virtual void fun () = 0;

What's the difference? (at present, the niche only encounters the following problem, so it can only talk so much.) ）

Declare a virtual class instead of a pure virtual class in a. h file, and the virtual function needs to have an implementation, otherwise the error prompt for "unresolved external" "" is present at link.

To modify the method:

If the virtual class does not write the implementation, the following method declaration will not have this error

Class Ainterface

{

virtual void Fun () {};

(the method is declared correctly when the implementation is not written)