C++ Virtual Functions and Virtual Inheritance: Uncovering the Complexities of Multiple Inheritance

Virtual function: allows derived classes to override functions in base classes. When the base class pointer points to a derived class object, the virtual function of the derived class is called. Virtual inheritance: Solve the diamond inheritance problem in multiple inheritance. Ensure that only one instance of each base class exists in the derived class.

C Virtual functions and virtual inheritance: Revealing the complexity of multiple inheritance

Virtual functions

Virtual functions are a type of C A special type of member function that allows a derived class to override functions in a base class. When a base class pointer or reference points to a derived class object, the virtual function of the derived class will be called.

class Shape {
public:
  virtual double area() const = 0; // 纯虚函数
};

class Rectangle : public Shape {
public:
  Rectangle(double width, double height) : m_width(width), m_height(height) {}
  double area() const override { return m_width * m_height; } // 重写虚函数

private:
  double m_width;
  double m_height;
};

Virtual inheritance

Virtual inheritance is a technique used to solve the diamond inheritance problem that occurs in multiple inheritance (also known as the ambiguity of multiple inheritance).

class Animal {
public:
  virtual void speak() const { cout << "Animal speaks" << endl; }
};

class Dog : virtual public Animal { // 虚继承
public:
  void speak() const override { cout << "Dog barks" << endl; }
};

class Cat : virtual public Animal { // 虚继承
public:
  void speak() const override { cout << "Cat meows" << endl; }
};

class SiberianHusky : public Dog, public Cat { // 多重继承
public:
  void speak() const override { cout << "Siberian Husky howls" << endl; }
};

Virtual inheritance ensures that each base class (Animal) has only one instance in the derived class (SiberianHusky), thus avoiding the diamond inheritance problem.

Practical case

#include <iostream>

using namespace std;

class Shape {
public:
  virtual double area() const = 0;
};

class Rectangle : public Shape {
public:
  Rectangle(double width, double height) : m_width(width), m_height(height) {}
  double area() const override { return m_width * m_height; }

private:
  double m_width;
  double m_height;
};

class Circle : public Shape {
public:
  Circle(double radius) : m_radius(radius) {}
  double area() const override { return M_PI * m_radius * m_radius; }

private:
  double m_radius;
};

int main() {
  // 创建形状的父类指针
  Shape* shape;

  // 创建矩形对象并将其分配给父类指针
  shape = new Rectangle(5, 10);
  cout << "矩形面积：" << shape->area() << endl;

  // 创建圆形对象并将其分配给父类指针
  shape = new Circle(3);
  cout << "圆形面积：" << shape->area() << endl;

  return 0;
}

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