Detailed explanation of C++ member functions: virtual inheritance and diamond problem of object methods

Virtual inheritance solves the "diamond problem" in multiple inheritance, when a class inherits from two or more subclasses with the same base class. By using the virtual keyword in the inheritance specification of a derived class, the derived class does not get a copy of the base class, but instead accesses the base class's methods indirectly through pointers. This way, the derived class only gets one method from the class that ultimately derives from the base class, thus avoiding ambiguity.

C Detailed explanation of member functions: Virtual inheritance of object methods and the diamond problem

Virtual inheritance is a An inheritance mechanism that solves the "diamond problem" in multiple inheritance. The diamond problem occurs when a class simultaneously inherits from two or more subclasses that have the same base class.

Practical case:

Consider the following code snippet:

class Animal {
public:
    virtual void makeSound() {
        cout << "Animal makes a sound" << endl;
    }
};

class Cat : public Animal {
public:
    virtual void makeSound() {
        cout << "Cat meows" << endl;
    }
};

class Dog : public Animal {
public:
    virtual void makeSound() {
        cout << "Dog barks" << endl;
    }
};

class Siamese : public Cat, public Dog { // 钻石问题
};

According to normal inheritance rules, the Siamese class will be from # The ##Cat and Dog classes inherit a makeSound() method respectively. However, this leads to ambiguity when calling the makeSound() method, since there are two methods with the same name in the Siamese class.

Solve the diamond problem:

In order to solve the diamond problem, we can use virtual inheritance. In virtual inheritance, the derived class does not obtain an actual copy of the base class, but indirectly accesses the base class's methods through a pointer.

To use virtual inheritance, use the

virtual keyword in the derived class inheritance specification:

class Siamese : public virtual Cat, public virtual Dog {
};

In this way, the

Siamese class will only get one The makeSound() method from a class ultimately derived from the Animal class (one of Cat or Dog).

Output:

Siamese siamese;
siamese.makeSound(); // Cat meows

In the above example, the

Siamese class inherits the makeSound class from the Cat class () method because it is the first base class derived from the Animal class.

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