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Language: C++
Expertise: Beginner

Jan 18, 1999

When a derived class inherits from a private base, the is-a relation between a derived object and its private base does not exist. For example:

 
class Mem_Manager {/*..*/};
class List: private Mem_Manager {/*..*/};

void OS_Register( Mem_Manager& mm);

void main() 
{
  List li;
  OS_Register( li ); //compile time error; conversion from List & to Mem_Manager& is inaccessible 
}

Private inheritance is like containment. In the example, class List has a private base, Mem_Manager, which is responsible for its necessary memory bookkeeping. However, List is not a memory manager by itself. Therefore, private inheritance is used to block its misuse.