Disadvantage of inheritance in c plus plus?

Answer 1

The only real disadvantage to inheritance is that additional memory must be set aside for the derived class virtual table. This is essentially a table of function pointers where each entry refers to the most-derived override for each virtual function. In order to use inheritance, the least-derived base class (or classes) must declare a virtual destructor. All derived class destructors are then implicitly virtual. Any class within the hierarchy can (optionally) declare one or more virtual functions which any derivative can override with its own implementation. If any class declares a pure-virtual method, that class is automatically an abstract base class and must be overridden by a more derived class. Only classes that provide or inherit a complete implementation can be instantiated. The base class that declares a pure-virtual method can (optionally) provide an implementation but that implementation cannot be inherited, it can only be called, explicitly, by a derived class override. When we instantiate objects of a derived class, there is only one virtual table regardless of the number of objects instantiated, thus the cost is minimal (dependant upon the actual number of most-derived overrides). When referring to base classes, the same table is used, but only the portion that is visible to the base class is actually accessible to it. That is, it cannot invoke overrides for virtual functions that were declared by any of its derivatives, it can only invoke those it declared itself or that were inherited from its base classes. However, the pointers for those it knows about will always point to the most-derived override, as determined by the most-derived class in the hierarchy.

Since virtual tables are only required to enable runtime polymorphic behaviour, it would be disadvantageous to use inheritance upon a class that was not intended to be used polymorphically. That is, where you wished to create a derived class but did not wish others to derive from your class. The simplest method of doing so would be to use composition rather than inheritance, by embedding the base class instead of inheriting from it. The virtual table for the base class would still exist, of course, but would not be associated with your derived class. The derived class could declare its own virtual methods (including a virtual destructor) but that would defeat the purpose of using composition, and, in turn, would generate a second virtual table specific to your composite. However, in some cases this may be desirable because embedded objects can greatly simplify the composite interface (through delegation rather than overrides) whilst allowing your composite class to be used polymorphically. Ultimately it all comes down to what it is you are trying to achieve and what implementation details you are trying to hide.

Answer 2

C is not an object-oriented language and therefore does not natively support the notion of inheritance. It is possible to model inheritance in C, but without the means of encapsulating objects it is just as error-prone as "traditional" C and simply not worth the additional effort and complexity. It's far easier to use a language that is specifically intended for the purpose. In this case, C++ would be a good choice because virtually everything you can do in C you can also do in C++ (and in many cases do it better), to the extent that you rarely need to use anything lower than C++. Plus you gain all the advantages C++ has to offer, including native support for object-oriented programming paradigms.