Diamond Inheritance of C + +

What do we talk about when we talk about C + +?

Encapsulation, inheritance, polymorphism. This is the three main features of the C + + language, and each time we talk about inheritance we inevitably have to talk about a very important question-diamond inheritance.

A. What is Diamond inheritance?

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For example, diamond inheritance is where multiple classes inherit the same common base class, and these derived classes are inherited by a class at the same time. What's wrong with this, let's take a look at a piece of code!

#include <iostream>using namespace Std;class base{protected:int _base;public:void fun () {cout << Base::fun "<< Endl;}}; Class A:public base{protected:int _a;}; Class B:public base{protected:int _b;}; Class D:p ublic A, public b{private:int _d;}; int main () {D d;d.fun ();//Compiler Error: Call ambiguous GetChar ();}

We can see that the object model of D holds two copies of base, and when we want to invoke the fun that we inherited from base, we get the problem of calling ambiguity , and it can result in data redundancy, so it's OK to just one copy, and we save two copies.

So how can we solve it?

The first workaround, use the domain to qualify the function we need to access

int main () {D d;d.a::fun ();d. B::fun (); GetChar ();}

This is not a problem, but it is very inconvenient, and when the program is very large, it can cause confusion in our minds.

So, C + + gave us a different solution-- virtual inheritance

B. Virtual inheritance

What is virtual inheritance?

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For example, virtual inheritance allows A and B to add the Virtural keyword when inheriting base, it is important to remember that not D uses virtual inheritance

So, how does virtual inheritance solve these annoying problems?

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We can see that the contents of the base are no longer saved in A and B, a copy of the offset address is saved, and then the data of base is saved in a common location so that the data redundancy is reduced, and we can use D.fun () directly to invoke the fun function in base.

#include <iostream>using namespace Std;class base{protected:int _base;public:void fun () {cout << Base::fun "<< Endl;}}; Class A:virtual public base{protected:int _a;}; Class B:virtual public base{protected:int _b;}; Class D:p ublic A, public b{private:int _d;}; int main () {D d;d.fun (); GetChar ();}

* virtual inheritance and virtual functions are completely different two concepts , I hope you do not mix, want to know the virtual function of the students can see the blogger's another blog post "C + + inheritance & polymorphism" http://zimomo.blog.51cto.com/ 10799874/1752936

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Diamond Inheritance of C + +