单例模式

饿汉式单例模式

饿汉式单例模式在类加载时就初始化实例，线程安全

class Signleton{
    private:
        Signleton(){}
        static Signleton* instance;
    public:
        static Singleton* getInstance(){
            return instance;
        }
        void print(){
            std::count << "Hello Signleton..." << std::endl;
        }
}
// 静态成员变量初始化
Signleton* Signleton::instance = new Signleton();

int main(){
    Signleton::getInstance()->print();
    return 0;
}

懒汉式单例模式

懒汉式单例模式在第一次使用时初始化实例，懒加载，但需要考虑线程安全。

#include <iostream>
#include <mutex>

class Singleton {
private:
    static Singleton* instance;
    static std::mutex mutex;

    Singleton() {}

public:
    static Singleton* getInstance() {
        if (instance == nullptr) {
            std::lock_guard<std::mutex> lock(mutex);
            if (instance == nullptr) {
                instance = new Singleton();
            }
        }
        return instance;
    }

    void print() {
        std::cout << "Hello Singleton..." << std::endl;
    }
};

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

int main() {
    Singleton* singleton = Singleton::getInstance();
    singleton->print();
    return 0;
}