单例模式

饿汉模式(线程安全，嵌套类析构)

class Singleton
{
private:
	Singleton(){}
	static Singleton* instance;
public:
	static Singleton* GetInstance()//类加载的时候已经new了，可以直接返回
	{
		return instance;
	}
private:
	class GC
	{
	public:
		~GC()
		{
			if(Singleton::instance)
			{
				delete Singleton::instance;
				Singleton::instance = nullptr;
				cout << "单例模式析构啦" << endl;
				system("pause");
			}			
		}
	};
	static GC gc;
};

Singleton* Singleton::instance = new Singleton();
Singleton::GC Singleton::gc;

懒汉模式（互斥锁，线程安全，嵌套类析构）

class Singleton
{
private:
	Singleton(){}
	static Singleton* instance;
	static mutex mtx;
public:
	static Singleton* GetInstance()//类加载的时候已经new了，可以直接返回
	{
		if (!instance)
		{
			mtx.lock();
			Singleton* temp = new Singleton();
			instance = temp;
			mtx.unlock();
		}
		return instance;
	}
private:
	class GC
	{
	public:
		~GC()
		{
			if(Singleton::instance)
			{
				delete Singleton::instance;
				Singleton::instance = nullptr;
				cout << "单例模式析构啦" << endl;
				system("pause");
			}			
		}
	};
	static GC gc;
};

Singleton* Singleton::instance = nullptr;
mutex Singleton::mtx;
Singleton::GC Singleton::gc;

静态变量（互斥锁，无需析构）

class Singleton
{
private:
	Singleton(){}
	static mutex mtx;
public:
	static Singleton* GetInstance()
	{
		mtx.lock();
		static Singleton instance;
		mtx.unlock();
		return &instance;
	}
};
mutex Singleton::mtx;