How can I protect derived classes from breaking when I change the internal parts of the base class?, C++ FAQ

C++ FAQ

From Marshall Cline: Bjarne Stroustrup, Herb Sutter, Andrei Alexandrescu, Pearson / Addison-Wesley Publishers and I collaborated to create a new C++ Super-FAQ! It's a team effort, with huge contributions from each of us and with amazing support from dozens of brilliant editors. The result is "awesomer" than ever! I originally wrote/published the FAQ in 1991 and now look forward to this new phase - and to continue working with it for another 20 years!

On a personal note, I'm at Oculus VR and it is amazing - fabulous people doing fabulous work. We're hiring more fabulous people so write me if that's you!

FAQ: How can I protect derived classes from breaking when I change the internal parts of the base class? ←(in the new Super-FAQ)

It's in Section: Inheritance — basics:

FAQ: Is inheritance important to C++?
FAQ: When would I use inheritance?
FAQ: How do you express inheritance in C++?
FAQ: Is it OK to convert a pointer from a derived class to its base class?
FAQ: What's the difference between public, private, and protected?
FAQ: Why can't my derived class access private things from my base class?
FAQ: How can I protect derived classes from breaking when I change the internal parts of the base class? (this FAQ)
FAQ: Protected data vs. private data with protected access functions?
FAQ: Okay, so exactly how should I decide whether to build a "protected interface"?