C虚函数与多态机制虚函数是C实现运行时多态的核心机制。通过虚函数表和虚函数指针C能够在运行时根据对象的实际类型调用相应的函数实现。虚函数的基本语法使用virtual关键字声明派生类可以重写基类的虚函数。#include#include#includeclass Animal {public:virtual ~Animal() default;virtual void make_sound() const {std::cout Animal makes a 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_basic() {std::vector animals;animals.push_back(std::make_unique());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;}}纯虚函数使用0语法声明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 3.14159 * radius_ * radius_;}double perimeter() const override {return 2 * 3.14159 * radius_;}void draw() const override {std::cout Drawing circle with 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 Drawing rectangle width_ x height_ \n;}};void abstract_class_example() {std::vector shapes;shapes.push_back(std::make_unique(5.0));shapes.push_back(std::make_unique(4.0, 6.0));double total_area 0;for (const auto shape : shapes) {shape-draw();total_area shape-area();std::cout Area: shape-area() , Perimeter: shape-perimeter() \n;}std::cout Total area: total_area \n;}虚函数表是编译器实现虚函数的机制每个包含虚函数的类都有一个虚函数表。class Base {public:virtual void func1() { std::cout Base::func1\n; }virtual void func2() { std::cout Base::func2\n; }virtual ~Base() default;};class Derived : public Base {public:void func1() override { std::cout Derived::func1\n; }void func3() { std::cout Derived::func3\n; }};void vtable_demonstration() {Base* ptr new Derived();ptr-func1();ptr-func2();delete ptr;std::cout Size of Base: sizeof(Base) \n;std::cout Size of Derived: sizeof(Derived) \n;}多重继承中的虚函数需要特别注意菱形继承问题。class Device {public:virtual ~Device() default;virtual void power_on() 0;virtual void power_off() 0;};class Printer : virtual public Device {public:void power_on() override {std::cout Printer powered on\n;}void power_off() override {std::cout Printer powered off\n;}virtual void print(const std::string doc) {std::cout Printing: doc \n;}};class Scanner : virtual public Device {public:void power_on() override {std::cout Scanner powered on\n;}void power_off() override {std::cout Scanner powered off\n;}virtual void scan() {std::cout Scanning document\n;}};class MultiFunctionDevice : public Printer, public Scanner {public:void power_on() override {std::cout Multi-function device powered on\n;}void power_off() override {std::cout Multi-function device powered off\n;}};void multiple_inheritance_example() {MultiFunctionDevice mfd;mfd.power_on();mfd.print(document.pdf);mfd.scan();mfd.power_off();}final关键字可以防止类被继承或虚函数被重写。class FinalClass final {public:virtual void func() {std::cout FinalClass::func\n;}};class BaseWithFinal {public:virtual void can_override() {std::cout BaseWithFinal::can_override\n;}virtual void cannot_override() final {std::cout BaseWithFinal::cannot_override\n;}};class DerivedFromBase : public BaseWithFinal {public:void can_override() override {std::cout DerivedFromBase::can_override\n;}};协变返回类型允许派生类的虚函数返回更具体的类型。class Product {public:virtual ~Product() default;virtual void use() const 0;};class ConcreteProduct : public Product {public:void use() const override {std::cout Using concrete product\n;}};class Factory {public:virtual ~Factory() default;virtual Product* create() const {return new Product();}};class ConcreteFactory : public Factory {public:ConcreteProduct* create() const override {return new ConcreteProduct();}};虚析构函数确保通过基类指针删除派生类对象时能正确调用派生类的析构函数。class ResourceBase {public:ResourceBase() {std::cout ResourceBase constructor\n;}virtual ~ResourceBase() {std::cout ResourceBase destructor\n;}};class ResourceDerived : public ResourceBase {int* data_;public:ResourceDerived() : data_(new int[100]) {std::cout ResourceDerived constructor\n;}~ResourceDerived() override {delete[] data_;std::cout ResourceDerived destructor\n;}};void virtual_destructor_example() {ResourceBase* ptr new ResourceDerived();delete ptr;}动态类型识别使用dynamic_cast和typeid实现。#includeclass Component {public:virtual ~Component() default;virtual void update() 0;};class GraphicsComponent : public Component {public:void update() override {std::cout Updating graphics\n;}void render() {std::cout Rendering graphics\n;}};class PhysicsComponent : public Component {public:void update() override {std::cout Updating physics\n;}void simulate() {std::cout Simulating physics\n;}};void rtti_example() {std::vector components;components.push_back(std::make_unique());components.push_back(std::make_unique());for (auto comp : components) {comp-update();if (auto* graphics dynamic_cast(comp.get())) {graphics-render();} else if (auto* physics dynamic_cast(comp.get())) {physics-simulate();}std::cout Type: typeid(*comp).name() \n;}}虚函数的性能开销主要来自间接调用和缓存未命中。#includeclass VirtualBase {public:virtual ~VirtualBase() default;virtual int compute(int x) const {return x * x;}};class VirtualDerived : public VirtualBase {public:int compute(int x) const override {return x * x x;}};class NonVirtual {public:int compute(int x) const {return x * x x;}};void performance_comparison() {const int iterations 10000000;VirtualBase* vptr new VirtualDerived();auto start std::chrono::high_resolution_clock::now();volatile int result 0;for (int i 0; i iterations; i) {result vptr-compute(i);}auto end std::chrono::high_resolution_clock::now();auto duration std::chrono::duration_cast(end - start);std::cout Virtual call: duration.count() ms\n;delete vptr;NonVirtual nv;start std::chrono::high_resolution_clock::now();for (int i 0; i iterations; i) {result nv.compute(i);}end std::chrono::high_resolution_clock::now();duration std::chrono::duration_cast(end - start);std::cout Non-virtual call: duration.count() ms\n;}虚函数与模板结合可以实现静态多态和动态多态的混合使用。templateclass Processor {public:void process(const T data) {pre_process();do_process(data);post_process();}virtual ~Processor() default;protected:virtual void pre_process() {std::cout Default pre-processing\n;}virtual void do_process(const T data) 0;virtual void post_process() {std::cout Default post-processing\n;}};class IntProcessor : public Processor {protected:void do_process(const int data) override {std::cout Processing int: data * 2 \n;}};虚函数是C面向对象编程的核心特性理解其实现机制和使用场景对于设计灵活的系统至关重要。
