我的 C++ 设计模式整理：23 种模式的实现与建议

抽象工厂模式

创建一整套相关的对象，比如一套 UI 控件，保证它们风格统一。

class AbstractProductA {
public:
    virtual ~AbstractProductA() {}
    virtual void operationA() = 0;
};

class AbstractProductB {
public:
    virtual ~AbstractProductB() {}
    virtual void operationB() = 0;
};

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

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

建造者模式

复杂对象的构建和表示分开，同样的构建步骤能产出不同的表示。

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

原型模式

拷贝已有对象来创建新对象，适合创建成本高的场景。

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 {
        std::cout << "Data: " << data << std::endl;
    }
};

结构型模式

处理类和对象的组合方式，让它们能协同工作。

适配器模式

把不兼容的接口转成客户想要的，让原本不能一起工作的类可以合作。

class Target {
public:
    virtual ~Target() {}
    virtual void request() {
        std::cout << "Target request" << std::endl;
    }
};

class Adaptee {
public:
    void specificRequest() {
        std::cout << "Adaptee specific request" << std::endl;
    }
};

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

桥接模式

抽象和实现解耦，两者都能独立变化。

class Implementor {
public:
    virtual ~Implementor() {}
    virtual void operationImpl() = 0;
};

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

组合模式

用树形结构表示部分-整体关系，单个对象和组合对象被统一对待。

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 {
        std::cout << "Leaf operation" << std::endl;
    }
};

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

装饰器模式

动态给对象加职责，比继承更灵活。

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

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

外观模式

给子系统提供一个统一的高层接口，简化调用。

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

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

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

享元模式

共享细粒度对象，减少内存占用。

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 {
        std::cout << "Intrinsic: " << intrinsicState << ", Extrinsic: " << extrinsicState << std::endl;
    }
};

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

代理模式

控制对象访问，比如延迟加载或权限检查。

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

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

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

行为型模式

关于算法和职责分配，决定对象之间怎么通信。

责任链模式

多个对象都有机会处理请求，发送者不关心谁会处理。

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) {
            std::cout << "Handler1 handled request " << request << std::endl;
        } else if (successor != nullptr) {
            successor->handleRequest(request);
        }
    }
};

命令模式

把请求封装成对象，支持参数化和撤销。

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

解释器模式

定义一个语言的文法并解释句子，不常见，但编译原理相关。

class Context {};

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;
    }
};

迭代器模式

顺序访问聚合对象元素，不暴露内部结构。

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

中介者模式

用一个中介对象封装对象间的交互，减少直接依赖。

class Colleague;
class Mediator {
public:
    virtual ~Mediator() {}
    virtual void notify(Colleague* sender, std::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");
    }
};

备忘录模式

保存对象内部状态，方便恢复，且不破坏封装。

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

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

观察者模式

一对多依赖，状态变化时所有观察者接到通知。

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

class Subject {
private:
    std::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 {
        std::cout << "Temperature updated: " << temperature << std::endl;
    }
};

状态模式

对象内部状态改变时改变行为，好像换了类。

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;
};

策略模式

算法族封装，运行时随意切换。

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

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

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

模板方法模式

算法骨架放在父类，子类填补具体步骤。

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 {
        std::cout << "Concrete operation 1" << std::endl;
    }
    void primitiveOperation2() override {
        std::cout << "Concrete operation 2" << std::endl;
    }
};

访问者模式

在不改变元素类的前提下定义新操作。

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() {
        std::cout << "Operation A" << std::endl;
    }
};

实际运用建议

23 种模式全记住没必要，我实际工作中经常打交道的就那几个：

• 单例：全局配置、日志，注意线程安全。
• 工厂方法：解耦创建，新类型扩展方便。
• 观察者：事件通知、消息总线的基础。
• 策略：避免 if-else 堆砌，让算法独立变化。
• 装饰器：给对象动态加功能，比改类继承好使。

再往下，适配器、代理、模板方法、命令、外观也比较常见。剩下的了解即可，真遇到场景再翻。

几个实在的提醒：

• 先搞清楚场景，再套模式，别为了模式而模式。
• 设计模式是帮助减少耦合的，但如果滥用，代码会更绕。
• C++11 之后的智能指针、Lambda 能简化很多实现，比如观察者用 std::function 替换虚接口，代码量少一半。

模式是活的，代码是死的，理解意图比背结构重要。