How do I separate interface from implementation in C++ (like Modula-2)?, C++ FAQ

C++ FAQ / Section 22 / FAQ 22.2

Section 22:

22.1	What's the big deal of separating interface from implementation?
22.2	How do I separate interface from implementation in C++ (like Modula-2)?
22.3	What is an ABC?
22.4	What is a "pure virtual" member function?
22.5	How do you define a copy constructor or assignment `operator` for a class that contains a pointer to a (abstract) base class?

[22.2] How do I separate interface from implementation in C++ (like Modula-2)?

Use an ABC.