C++中23种设计模式的实现速览

抽象工厂模式

提供一个创建一系列相关或依赖对象的接口，无需指定它们具体的类。适合产品族一起变化的情况。

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

分步骤构建一个复杂对象，同样的构建过程可以创建不同的表示。当你需要一步步设置参数再产出对象时很有用。

class Product {
private:
    string partA, 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();
    }
};

原型模式

通过克隆现有实例来创建新对象，避免重复初始化。核心是写一个clone虚函数。

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; }
};

结构型模式 (7个)

适配器模式

让不兼容的接口能一起工作。比如要把一个老接口包装成新接口暴露出去。

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

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

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

桥接模式

将抽象部分与实现部分分离，让它们可以独立变化。典型的用组合替代继承的场景。

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

把对象组织成树形结构，使得单个对象和组合对象对外接口一致。操作单个和操作组合没有区别。

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); }
};

装饰器模式

动态地给对象添加功能，比生成子类更灵活。常用于在不修改原有类的情况下增强行为。

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; }
};

外观模式

为子系统中的一组接口提供一个统一的高层接口。简化外部调用，隐藏内部复杂性。

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();
    }
};

享元模式

运用共享技术有效支持大量细粒度对象。把不变的状态放在内部共享，变的外部传入。

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];
    }
};

代理模式

为另一个对象提供一个替身或占位符，以控制对它的访问。常见的有延迟加载、权限控制等。

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();
    }
};

行为型模式 (11个)

责任链模式

多个处理器依次尝试处理请求，直到某个处理器处理为止。解耦发送者和接收者。

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);
        }
    }
};

命令模式

将请求封装成对象，以便参数化客户端、记录操作日志或实现撤销。

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(); }
};

解释器模式

给定一个语言，定义其文法表示，并构建解释器来解释句子。实际项目中不太常用。

class Context {};

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

class TerminalExpression : public Expression {
public:
    bool interpret(Context& context) override {
        return true;
    }
};

迭代器模式

提供一种方法顺序访问聚合对象中的各个元素，而无需暴露其内部结构。C++标准库的迭代器用得很多。

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(); }
};

中介者模式

用一个中介对象封装一系列对象的交互，减少对象之间的直接引用。对象只需知道中介者。

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() {
        mediator->notify(this, "event1");
    }
};

备忘录模式

在不破坏封装的前提下，捕获并保存一个对象的内部状态，以便后续恢复。

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(); }
};

观察者模式

定义对象间一对多的依赖关系，当一个对象状态改变时，所有依赖它的对象都会收到通知。事件驱动的基础。

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;
    }
};

状态模式

允许对象在其内部状态改变时改变它的行为，看起来好像修改了它的类。

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

定义一系列算法，把它们封装起来，并且可以相互替换。可以避免大量 if-else 或 switch。

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(); }
};

模板方法模式

在一个方法中定义算法的骨架，将某些步骤延迟到子类中实现。子类可以改变某些步骤，但不能改变整体流程。

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; }
};

访问者模式

表示一个作用于某对象结构中的各元素的操作，使你可以在不改变元素类的前提下定义作用于这些元素的新操作。

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

实际开发中优先掌握的

上面23种模式看起来不少，但高频出现的也就那么几个。下面这些最好先弄熟：

• 单例模式：全局唯一实例，配置、日志都离不开它。
• 工厂方法：解耦对象创建，简单扩展。
• 观察者模式：事件通知、消息机制的基础。
• 策略模式：算法替换，干掉大片条件判断。
• 装饰器模式：运行时动态加功能，比继承灵活。

其次适配器、代理、模板方法、命令和外观也经常遇到。理解每种模式适合的场景比背代码重要，过度设计反而是负担。有些实现可以用C++11/14/17的特性简化，比如智能指针、lambda配合命令模式，或者用局部静态变量实现线程安全的单例。这些模式本身是思想，C++的具体写法可以很现代。