C++ 设计模式概述及常用模式

C++ 设计模式概述

本文介绍了C++中23种设计模式的分类及实现示例，主要分为三大类：

创建型模式（5个）：单例模式（常用）、工厂方法模式（常用）、抽象工厂模式（常用）、建造者模式和原型模式。这些模式专注于对象的创建机制。

结构型模式（7个）：适配器模式（常用）、桥接模式、组合模式和装饰器模式（常用）等。这些模式处理类和对象的组合方式。

行为型模式：未完整列出，但包含观察者模式等（未展示完整代码）。

文章通过简洁的C++代码示例展示了常用设计模式的实现方法，如单例模式通过私有构造函数和静态方法确保唯一实例，工厂方法模式通过抽象工厂类创建产品等。这些模式为解决特定设计问题提供了可重用的解决方案。

C++ 设计模式概述及常用模式

设计模式可分为三大类：创建型、结构型、行为型。以下是23个设计模式的分类及代码示例：

一、创建型模式（5个）

1. 单例模式（Singleton）⭐ 常用

cpp 复制代码

class Singleton {
private:
    static Singleton* instance;
    Singleton() {} // 私有构造函数
    
public:
    static Singleton* getInstance() {
        if (instance == nullptr) {
            instance = new Singleton();
        }
        return instance;
    }
    
    // 删除拷贝构造和赋值操作符
    Singleton(const Singleton&) = delete;
    Singleton& operator=(const Singleton&) = delete;
};

2. 工厂方法模式（Factory Method）⭐ 常用

cpp 复制代码

// 产品接口
class Product {
public:
    virtual ~Product() {}
    virtual void operation() = 0;
};

// 具体产品
class ConcreteProductA : public Product {
public:
    void operation() override {
        cout << "Product A operation" << endl;
    }
};

// 工厂接口
class Creator {
public:
    virtual ~Creator() {}
    virtual Product* factoryMethod() = 0;
};

// 具体工厂
class ConcreteCreatorA : public Creator {
public:
    Product* factoryMethod() override {
        return new ConcreteProductA();
    }
};

3. 抽象工厂模式（Abstract Factory）⭐ 常用

cpp 复制代码

// 抽象产品A
class AbstractProductA {
public:
    virtual ~AbstractProductA() {}
    virtual void operationA() = 0;
};

// 抽象产品B
class AbstractProductB {
public:
    virtual ~AbstractProductB() {}
    virtual void operationB() = 0;
};

// 抽象工厂
class AbstractFactory {
public:
    virtual AbstractProductA* createProductA() = 0;
    virtual AbstractProductB* createProductB() = 0;
};

// 具体工厂1
class ConcreteFactory1 : public AbstractFactory {
public:
    AbstractProductA* createProductA() override {
        return new ConcreteProductA1();
    }
    AbstractProductB* createProductB() override {
        return new ConcreteProductB1();
    }
};

4. 建造者模式（Builder）

cpp 复制代码

class Product {
private:
    string partA;
    string partB;
    
public:
    void setPartA(const string& a) { partA = a; }
    void setPartB(const string& b) { partB = b; }
};

class Builder {
public:
    virtual ~Builder() {}
    virtual void buildPartA() = 0;
    virtual void buildPartB() = 0;
    virtual Product* getResult() = 0;
};

class Director {
private:
    Builder* builder;
    
public:
    Director(Builder* b) : builder(b) {}
    
    void construct() {
        builder->buildPartA();
        builder->buildPartB();
    }
};

5. 原型模式（Prototype）

cpp 复制代码

class Prototype {
public:
    virtual ~Prototype() {}
    virtual Prototype* clone() const = 0;
    virtual void print() const = 0;
};

class ConcretePrototype : public Prototype {
private:
    int data;
    
public:
    ConcretePrototype(int d) : data(d) {}
    
    Prototype* clone() const override {
        return new ConcretePrototype(*this);
    }
    
    void print() const override {
        cout << "Data: " << data << endl;
    }
};

二、结构型模式（7个）

6. 适配器模式（Adapter）⭐ 常用

cpp 复制代码

// 目标接口
class Target {
public:
    virtual ~Target() {}
    virtual void request() {
        cout << "Target request" << endl;
    }
};

// 需要适配的类
class Adaptee {
public:
    void specificRequest() {
        cout << "Adaptee specific request" << endl;
    }
};

// 适配器
class Adapter : public Target {
private:
    Adaptee* adaptee;
    
public:
    Adapter(Adaptee* a) : adaptee(a) {}
    
    void request() override {
        adaptee->specificRequest();
    }
};

7. 桥接模式（Bridge）

cpp 复制代码

// 实现接口
class Implementor {
public:
    virtual ~Implementor() {}
    virtual void operationImpl() = 0;
};

// 抽象类
class Abstraction {
protected:
    Implementor* impl;
    
public:
    Abstraction(Implementor* i) : impl(i) {}
    virtual ~Abstraction() {}
    
    virtual void operation() {
        impl->operationImpl();
    }
};

8. 组合模式（Composite）

cpp 复制代码

class Component {
public:
    virtual ~Component() {}
    virtual void operation() = 0;
    virtual void add(Component*) {}
    virtual void remove(Component*) {}
    virtual Component* getChild(int) { return nullptr; }
};

class Leaf : public Component {
public:
    void operation() override {
        cout << "Leaf operation" << endl;
    }
};

class Composite : public Component {
private:
    vector<Component*> children;
    
public:
    void operation() override {
        cout << "Composite operation" << endl;
        for (auto child : children) {
            child->operation();
        }
    }
    
    void add(Component* c) override {
        children.push_back(c);
    }
};

9. 装饰器模式（Decorator）⭐ 常用

cpp 复制代码

class Component {
public:
    virtual ~Component() {}
    virtual void operation() = 0;
};

class ConcreteComponent : public Component {
public:
    void operation() override {
        cout << "ConcreteComponent operation" << endl;
    }
};

class Decorator : public Component {
protected:
    Component* component;
    
public:
    Decorator(Component* c) : component(c) {}
    
    void operation() override {
        component->operation();
    }
};

class ConcreteDecorator : public Decorator {
public:
    ConcreteDecorator(Component* c) : Decorator(c) {}
    
    void operation() override {
        Decorator::operation();
        addedBehavior();
    }
    
    void addedBehavior() {
        cout << "Added behavior" << endl;
    }
};

10. 外观模式（Facade）⭐ 常用

cpp 复制代码

class SubsystemA {
public:
    void operationA() {
        cout << "Subsystem A operation" << endl;
    }
};

class SubsystemB {
public:
    void operationB() {
        cout << "Subsystem B operation" << endl;
    }
};

class Facade {
private:
    SubsystemA* a;
    SubsystemB* b;
    
public:
    Facade() : a(new SubsystemA()), b(new SubsystemB()) {}
    
    void operation() {
        a->operationA();
        b->operationB();
    }
};

11. 享元模式（Flyweight）

cpp 复制代码

class Flyweight {
public:
    virtual ~Flyweight() {}
    virtual void operation(int extrinsicState) = 0;
};

class ConcreteFlyweight : public Flyweight {
private:
    int intrinsicState;
    
public:
    ConcreteFlyweight(int state) : intrinsicState(state) {}
    
    void operation(int extrinsicState) override {
        cout << "Intrinsic: " << intrinsicState 
             << ", Extrinsic: " << extrinsicState << endl;
    }
};

class FlyweightFactory {
private:
    unordered_map<int, Flyweight*> flyweights;
    
public:
    Flyweight* getFlyweight(int key) {
        if (flyweights.find(key) == flyweights.end()) {
            flyweights[key] = new ConcreteFlyweight(key);
        }
        return flyweights[key];
    }
};

12. 代理模式（Proxy）⭐ 常用

cpp 复制代码

class Subject {
public:
    virtual ~Subject() {}
    virtual void request() = 0;
};

class RealSubject : public Subject {
public:
    void request() override {
        cout << "RealSubject request" << endl;
    }
};

class Proxy : public Subject {
private:
    RealSubject* realSubject;
    
public:
    Proxy() : realSubject(nullptr) {}
    
    void request() override {
        if (realSubject == nullptr) {
            realSubject = new RealSubject();
        }
        realSubject->request();
    }
};

三、行为型模式（11个）

13. 责任链模式（Chain of Responsibility）

cpp 复制代码

class Handler {
protected:
    Handler* successor;
    
public:
    Handler() : successor(nullptr) {}
    virtual ~Handler() {}
    
    void setSuccessor(Handler* s) {
        successor = s;
    }
    
    virtual void handleRequest(int request) = 0;
};

class ConcreteHandler1 : public Handler {
public:
    void handleRequest(int request) override {
        if (request < 10) {
            cout << "Handler1 handled request " << request << endl;
        } else if (successor != nullptr) {
            successor->handleRequest(request);
        }
    }
};

14. 命令模式（Command）⭐ 常用

cpp 复制代码

class Receiver {
public:
    void action() {
        cout << "Receiver action" << endl;
    }
};

class Command {
public:
    virtual ~Command() {}
    virtual void execute() = 0;
};

class ConcreteCommand : public Command {
private:
    Receiver* receiver;
    
public:
    ConcreteCommand(Receiver* r) : receiver(r) {}
    
    void execute() override {
        receiver->action();
    }
};

class Invoker {
private:
    Command* command;
    
public:
    void setCommand(Command* c) {
        command = c;
    }
    
    void executeCommand() {
        command->execute();
    }
};

15. 解释器模式（Interpreter）

cpp 复制代码

class Context {
    // 上下文信息
};

class Expression {
public:
    virtual ~Expression() {}
    virtual bool interpret(Context& context) = 0;
};

class TerminalExpression : public Expression {
public:
    bool interpret(Context& context) override {
        // 终结符解释逻辑
        return true;
    }
};

16. 迭代器模式（Iterator）⭐ 常用

cpp 复制代码

template<typename T>
class Iterator {
public:
    virtual ~Iterator() {}
    virtual T next() = 0;
    virtual bool hasNext() = 0;
};

template<typename T>
class ConcreteIterator : public Iterator<T> {
private:
    vector<T> collection;
    size_t position;
    
public:
    ConcreteIterator(const vector<T>& col) : collection(col), position(0) {}
    
    T next() override {
        return collection[position++];
    }
    
    bool hasNext() override {
        return position < collection.size();
    }
};

17. 中介者模式（Mediator）

cpp 复制代码

class Colleague;
class Mediator {
public:
    virtual ~Mediator() {}
    virtual void notify(Colleague* sender, string event) = 0;
};

class Colleague {
protected:
    Mediator* mediator;
    
public:
    Colleague(Mediator* m = nullptr) : mediator(m) {}
    void setMediator(Mediator* m) { mediator = m; }
};

class ConcreteColleague1 : public Colleague {
public:
    void doSomething() {
        // ... 自己的逻辑
        mediator->notify(this, "event1");
    }
};

18. 备忘录模式（Memento）

cpp 复制代码

class Memento {
private:
    string state;
    
public:
    Memento(const string& s) : state(s) {}
    string getState() const { return state; }
};

class Originator {
private:
    string state;
    
public:
    void setState(const string& s) { state = s; }
    string getState() const { return state; }
    
    Memento* createMemento() {
        return new Memento(state);
    }
    
    void restoreMemento(Memento* m) {
        state = m->getState();
    }
};

19. 观察者模式（Observer）⭐ 常用

cpp 复制代码

class Observer {
public:
    virtual ~Observer() {}
    virtual void update(float temperature) = 0;
};

class Subject {
private:
    vector<Observer*> observers;
    
public:
    void attach(Observer* o) {
        observers.push_back(o);
    }
    
    void detach(Observer* o) {
        // 移除观察者逻辑
    }
    
    void notify(float temperature) {
        for (auto observer : observers) {
            observer->update(temperature);
        }
    }
};

class ConcreteObserver : public Observer {
public:
    void update(float temperature) override {
        cout << "Temperature updated: " << temperature << endl;
    }
};

20. 状态模式（State）

cpp 复制代码

class Context;

class State {
public:
    virtual ~State() {}
    virtual void handle(Context* context) = 0;
};

class Context {
private:
    State* state;
    
public:
    Context(State* s) : state(s) {}
    
    void setState(State* s) {
        state = s;
    }
    
    void request() {
        state->handle(this);
    }
};

class ConcreteStateA : public State {
public:
    void handle(Context* context) override;
};

21. 策略模式（Strategy）⭐ 常用

cpp 复制代码

class Strategy {
public:
    virtual ~Strategy() {}
    virtual void algorithm() = 0;
};

class ConcreteStrategyA : public Strategy {
public:
    void algorithm() override {
        cout << "Strategy A algorithm" << endl;
    }
};

class Context {
private:
    Strategy* strategy;
    
public:
    Context(Strategy* s) : strategy(s) {}
    
    void setStrategy(Strategy* s) {
        strategy = s;
    }
    
    void executeStrategy() {
        strategy->algorithm();
    }
};

22. 模板方法模式（Template Method）⭐ 常用

cpp 复制代码

class AbstractClass {
public:
    virtual ~AbstractClass() {}
    
    void templateMethod() {
        primitiveOperation1();
        primitiveOperation2();
    }
    
    virtual void primitiveOperation1() = 0;
    virtual void primitiveOperation2() = 0;
};

class ConcreteClass : public AbstractClass {
public:
    void primitiveOperation1() override {
        cout << "Concrete operation 1" << endl;
    }
    
    void primitiveOperation2() override {
        cout << "Concrete operation 2" << endl;
    }
};

23. 访问者模式（Visitor）

cpp 复制代码

class ConcreteElementA;
class ConcreteElementB;

class Visitor {
public:
    virtual ~Visitor() {}
    virtual void visit(ConcreteElementA* element) = 0;
    virtual void visit(ConcreteElementB* element) = 0;
};

class Element {
public:
    virtual ~Element() {}
    virtual void accept(Visitor* visitor) = 0;
};

class ConcreteElementA : public Element {
public:
    void accept(Visitor* visitor) override {
        visitor->visit(this);
    }
    
    void operationA() {
        cout << "Operation A" << endl;
    }
};

四、最常用的设计模式（建议优先掌握）

必须掌握的5个核心模式：

单例模式 - 全局唯一实例，如配置管理器、日志管理器
工厂方法模式 - 对象创建解耦，易于扩展
观察者模式 - 事件处理、消息通知系统
策略模式 - 算法封装，运行时切换
装饰器模式 - 动态添加功能

次常用的5个模式：

适配器模式 - 接口转换
代理模式 - 访问控制、延迟加载
模板方法模式 - 算法框架定义
命令模式 - 命令封装、撤销/重做
外观模式 - 简化复杂子系统接口

学习建议：

先从单例、工厂、观察者、策略开始学习
理解每种模式的应用场景而不仅仅是代码
避免过度设计，只在必要时使用设计模式
C++11/14/17的现代特性（智能指针、lambda等）可以简化某些模式的实现

这些模式提供了经过验证的解决方案，能帮助你构建更灵活、可维护的软件系统。