Virtual Inheritance C
Multiple inheritance in C is a powerful, but tricky tool, that often leads to problems if not used carefully. This article will teach you how to use virtual inheritance to solve some of these common problems programmers run into. If you're not familiar with multiple inheritance, check out this article on multiple inheritance.
Virtual inheritance is a C technique that ensures that only one copy of a base class's member variables are inherited by second-level derivatives a.k.a. grandchild derived classes. Without virtual inheritance, if two classes B and C inherit from class A, and class D inherits from both B and C, then D will contain two copies of A's
In order to prevent this kind of problem, you should use the virtual inheritance, which will know to refer to the right Ambig function. So - define class C public virtual Base class D public virtual Base class Right public C, public D
C vtables - Part 3 - Virtual Inheritance 1763 words Tue, Mar 15, 2016 In Part 1 and Part 2 of this series we talked about how vtables work in the simplest cases, and then in multiple inheritance. Virtual inheritance complicates things even further. As you may remember, virtual inheritance means that there's only one instance of a base class in a concrete class.
Virtual inheritance is a C technique that ensures only one copy of a base class ' s member variables are inherited by grandchild derived classes. Without virtual inheritance, if two classes B and C inherit from a class A , and a class D inherits from both B and C , then D will contain two copies of A ' s member variables one via B , and one
Only one instance of A subclass is created in memory Even though A reached D via two routes, both references point to the same single instance This ensures No ambiguity - d.x clearly points to the only Ax instance Changes to A automatically reflect everywhere via the shared instance A's state is not duplicated between B and C Virtual inheritance thus elegantly solves the diamond
How to Use Virtual Inheritance. To inherit virtually we simply add a keyword virtual before our base class name in the derived class declaration like this class B virtual public A public int i 6 class C virtual public A public int i 7 The addition of the virtual keyword indicates that we want to inherit from A virtually.
The base specifications may contain the keyword virtual to indicate virtual inheritance. This keyword may appear before or after the access specifier, if any. If virtual inheritance is used, the base class is referred to as a virtual base class. Multiple base classes can be specified, separated by commas.
The C rules say that virtual base classes are constructed before all non-virtual base classes. The thing you as a programmer need to know is this constructors for virtual base classes anywhere in your class's inheritance hierarchy are called by the quotmost derivedquot class's constructor.
Virtual base classes are used in virtual inheritance in a way of preventing multiple quotinstancesquot of a given class appearing in an inheritance hierarchy when using multiple inheritances. Need for Virtual Base Classes Consider the situation where we have one class A. This class A is inherited by two other classes B and C.
