The secret of C++ virtual functions revealed

Virtual functions use dynamic binding to determine the function to be called at runtime to achieve polymorphism. Its advantages include scalability and reusability, but it also introduces overhead and complexity. Virtual functions are often used to implement methods of different types of objects in a uniform way.

The secret of C virtual functions revealed

Virtual functions are a powerful tool in C that allow you to create methods that can be overridden by derived classes. This means you can write base class code and then customize it as needed in the derived classes.

How virtual functions work

Virtual functions use a technology called dynamic binding (also known as late binding). Unlike static binding (also known as early binding), which determines the function to be called at compile time, dynamic binding is determined at runtime.

This means that when you call a virtual function, the compiler generates a pointer to the virtual function table. This table contains pointers to functions implemented by each derived class. At run time, this pointer is used to select the function to call.

Advantages of virtual functions

Advantages of virtual functions include:

• Extensibility:You can add new functionality to existing code , without having to modify the base class code.
• Reusability: You can share common code while still allowing derived classes to customize behavior.
• Polymorphism: Virtual functions are the basis for achieving polymorphism, so objects can call methods in a uniform way, even if they are objects of different types.

Disadvantages of virtual functions

Virtual functions also have some disadvantages, including:

• ##Overhead:Create and look up the virtual function table It will bring some runtime overhead.
• Complexity: Understanding and debugging the code for virtual functions can be complex.

Practical case

Consider the following example:

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

class Circle : public Shape {
public:
    Circle(double radius) : _radius(radius) {}
    double area() override { return M_PI * _radius * _radius; }
    double perimeter() override { return 2 * M_PI * _radius; }

private:
    double _radius;
};

class Square : public Shape {
public:
    Square(double side) : _side(side) {}
    double area() override { return _side * _side; }
    double perimeter() override { return 4 * _side; }

private:
    double _side;
};

int main() {
    Shape* shapes[] = { new Circle(5), new Square(3) };

    for (Shape* shape : shapes) {
        std::cout << "Area: " << shape->area() << std::endl;
        std::cout << "Perimeter: " << shape->perimeter() << std::endl;
    }

    delete[] shapes;
    return 0;
}

In this example, the

Shape class declares two pure virtual functionsarea() and perimeter(). Circle and Square derived classes override these functions, providing specific implementations for each shape.

main() The function uses dynamic binding to call different virtual functions, depending on the type of the current object. This allows us to use a unified interface to handle different shapes.

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