C++虚函数与运行时多态

C虚函数与运行时多态虚函数通过虚函数表vtable和虚函数指针vptr实现运行时多态。当通过基类指针或引用调用虚函数时程序根据对象的实际类型动态分派到正确的函数实现。虚函数使用virtual关键字声明派生类使用override关键字明确重写意图。#include#include#include#includeclass Animal {public:virtual ~Animal() default;virtual void make_sound() const {std::cout Animal makes a generic sound\n;}virtual void move() const {std::cout Animal moves\n;}void describe() const {std::cout This is an animal\n;}};class Dog : public Animal {public:void make_sound() const override {std::cout Dog barks: Woof!\n;}void move() const override {std::cout Dog runs on four legs\n;}};class Cat : public Animal {public:void make_sound() const override {std::cout Cat meows: Meow!\n;}void move() const override {std::cout Cat walks gracefully\n;}};void polymorphism_demo() {std::vector animals;animals.push_back(std::make_unique());animals.push_back(std::make_unique());for (const auto animal : animals) {animal-make_sound();animal-move();std::cout ---\n;}}纯虚函数定义接口契约包含纯虚函数的类是抽象类不能实例化。class Shape {public:virtual ~Shape() default;virtual double area() const 0;virtual double perimeter() const 0;virtual void draw() const 0;};class Circle : public Shape {double radius_;public:explicit Circle(double r) : radius_(r) {}double area() const override {return 3.14159265358979 * radius_ * radius_;}double perimeter() const override {return 2.0 * 3.14159265358979 * radius_;}void draw() const override {std::cout Circle (radius radius_ )\n;}};class Rectangle : public Shape {double width_, height_;public:Rectangle(double w, double h) : width_(w), height_(h) {}double area() const override { return width_ * height_; }double perimeter() const override { return 2 * (width_ height_); }void draw() const override {std::cout Rectangle ( width_ x height_ )\n;}};void abstract_class_demo() {std::vector shapes;shapes.push_back(std::make_unique(5.0));shapes.push_back(std::make_unique(4.0, 6.0));double total 0;for (const auto s : shapes) {s-draw();total s-area();std::cout Area: s-area() \n;}std::cout Total area: total \n;}虚析构函数确保派生类正确析构。class Base {public:Base() { std::cout Base constructed\n; }virtual ~Base() { std::cout Base destroyed\n; }};class Derived : public Base {int* data_;public:Derived() : data_(new int[100]) {std::cout Derived constructed\n;}~Derived() override {delete[] data_;std::cout Derived destroyed\n;}};void virtual_destructor_demo() {Base* ptr new Derived();delete ptr;}dynamic_cast进行运行时类型转换。void dynamic_cast_demo() {std::vector animals;animals.push_back(std::make_unique());animals.push_back(std::make_unique());for (auto animal : animals) {if (Dog* dog dynamic_cast(animal.get())) {std::cout Found a dog\n;} else if (Cat* cat dynamic_cast(animal.get())) {std::cout Found a cat\n;}}}typeid获取运行时类型信息。void typeid_demo() {std::unique_ptr animal std::make_unique();std::cout Type name: typeid(*animal).name() \n;std::cout Is Dog: (typeid(*animal) typeid(Dog)) \n;std::cout Is Cat: (typeid(*animal) typeid(Cat)) \n;}final关键字防止继承和重写。class BaseFinal {public:virtual void func() final {std::cout Cannot override\n;}};多重接口继承。class Printable {public:virtual ~Printable() default;virtual void print() const 0;};class Serializable {public:virtual ~Serializable() default;virtual std::string serialize() const 0;};class Document : public Printable, public Serializable {std::string content_;public:explicit Document(const std::string c) : content_(c) {}void print() const override {std::cout content_ \n;}std::string serialize() const override {return DOC: content_;}};void multiple_interface_demo() {Document doc(Hello World);doc.print();std::cout Serialized: doc.serialize() \n;}协变返回类型。class Cloneable {public:virtual Cloneable* clone() const { return new Cloneable(*this); }};class CloneableDerived : public Cloneable {public:CloneableDerived* clone() const override {return new CloneableDerived(*this);}};虚函数是实现运行时多态的基础理解vtable机制有助于设计灵活的面向对象系统。