In big projects, sometimes you want to write almost similar classes, which is more or less similar. For instance, assume you have a request base class, and the derived classes should implement some common virtual functions.

Usually one easy method is to copy-paste one of the existing derived class so that by making minor change, we can start the next derived class. While doing so, just remember – you are making one of the dangerous, hard to detect bug. When you try to compile your source, the second derived class you created, will show the error