Question

In Java, you can define an interface as a class with no actual code implementation, but only to define the methods that a class must implement. Those types can be passed as parameters to methods and returned from methods. In C++, a pure virtual class can’t be used as a parameter or return type, from what I can tell. Any way to mimic Java’s interface classes?

I have a string class in C++, and several subclasses for different encodings (like UTFxxx, ISOxxx, etc) that derive from the base string class. However, since there are so many different encodings, the base class has no meaningful implementation. But it would serve well as an interface if I could handle it as its own object and calls to that object would call on the correct subclass it was inherited to.

Answer 1

You cannot use a pure virtual class by value, but you can pass it around by pointer or by reference. This includes the ability to pass it around wrapped within a smart pointer type such as unique_ptr or shared_ptr.

You should also make sure that you mark the destructor on the interface with the virtual keyword to prevent potential memory leaks.