C++如何实现单例模式 C++单例模式的设计与代码示例

#include <iostream>
#include <mutex>

class Singleton {
private:
    // 构造函数私有化，防止外部创建实例
    Singleton() {
        std::cout << "Singleton created." << std::endl;
    }

    // 拷贝构造和赋值运算符删除，防止拷贝和赋值
    Singleton(const Singleton&) = delete;
    Singleton& operator=(const Singleton&) = delete;

    static Singleton* instance; // 静态成员变量，存储唯一的实例
    static std::mutex mutex_; // 互斥锁，用于线程安全

public:
    // 静态方法，提供全局访问点
    static Singleton* getInstance() {
        std::lock_guard<std::mutex> lock(mutex_); // 加锁，保证线程安全
        if (instance == nullptr) {
            instance = new Singleton();
        }
        return instance;
    }

    // 示例方法
    void doSomething() {
        std::cout << "Singleton is doing something." << std::endl;
    }

    // 释放单例对象，避免内存泄漏
    static void destroyInstance() {
        std::lock_guard<std::mutex> lock(mutex_);
        if (instance != nullptr) {
            delete instance;
            instance = nullptr;
        }
    }
};

// 初始化静态成员变量
Singleton* Singleton::instance = nullptr;
std::mutex Singleton::mutex_;

int main() {
    Singleton* s1 = Singleton::getInstance();
    s1->doSomething();

    Singleton* s2 = Singleton::getInstance();
    s2->doSomething();

    if (s1 == s2) {
        std::cout << "Both pointers point to the same instance." << std::endl;
    }

    Singleton::destroyInstance(); // 释放单例对象

    return 0;
}

class Singleton {
private:
    Singleton() {}
    Singleton(const Singleton&) = delete;
    Singleton& operator=(const Singleton&) = delete;

public:
    static Singleton& getInstance() {
        static Singleton instance; // 静态局部变量，线程安全初始化
        return instance;
    }

    void doSomething() {
        std::cout << "Singleton is doing something." << std::endl;
    }
};