定义：状态模式（State Pattern）是一种行为设计模式，它允许对象在内部状态改变时改变它的行为，对象看起来似乎修改了它的类。状态模式将状态相关的行为封装到单独的类中，并将这些对象组合成状态模式，允许状态对象在运行时改变行为。

        代码：

class TicketMachine;
// 状态接口
class State {
public:virtual ~State() = default;virtual void handle(std::shared_ptr<TicketMachine> machine) = 0;virtual std::string getStateName() const = 0;
};// 上下文：售票机
class TicketMachine : public std::enable_shared_from_this<TicketMachine> {
public:TicketMachine() {}void insertMoney() {std::cout << "Money inserted." << std::endl;handle();}void setState(std::shared_ptr<State> newState) {state = newState;std::cout << "State changed to: " << state->getStateName() << std::endl;}std::string getCurrentState() const {return state->getStateName();}private:void handle() {state->handle(shared_from_this());}std::shared_ptr<State> state;
};// 具体状态：票已售罄
class SoldOutState : public State {
public:void handle(std::shared_ptr<TicketMachine> machine) override {std::cout << "Sorry, tickets are sold out." << std::endl;}std::string getStateName() const override {return "SoldOut";}
};// 具体状态：可以售票
class AvailableState : public State {
public:void handle(std::shared_ptr<TicketMachine> machine) override {std::cout << "Ticket is available. Selling one ticket." << std::endl;machine->setState(std::make_shared<SoldOutState>()); // 改变状态}std::string getStateName() const override {return "Available";}
};int main() {auto machine = std::make_shared<TicketMachine>();machine->setState(std::make_shared<AvailableState>());machine->insertMoney(); // Ticket is available. Selling one ticket. State changed to: SoldOutmachine->insertMoney(); // Sorry, tickets are sold out.return 0;
}