C++实现单例模式

#include<stdio.h>
#include<iostream>

class Singleton
{
private:
Singleton(){}
static Singleton* instance;
public:
static Singleton* GetInstance()
{
if(instance == NULL)
{
instance = new Singleton();
}
return instance;
}
};
Singleton* Singleton::instance = NULL;

int main()
{
Singleton* mySingle1 = Singleton::GetInstance();
Singleton* mySingle2 = Singleton::GetInstance();
if(mySingle1 == mySingle2)
std::cout<<"mySingle1=mySingle2"<<std::endl;
if(mySingle1 == NULL)
std::cout<<"mySingle=NULL"<<std::endl;
return 0;
}

class Singleton
{
private:
Singleton(){}
static Singleton* instance;
static pthread_mutex_t mutex;
public:
static Singleton* GetInstance()
{
if(instance == NULL)
{
pthread_mutex_lock(&mutex);
if(instance == NULL)
{
instance = new Singleton();
}
pthread_mutex_unlock(&mutex);
}
return instance;
}
};

pthread_mutex_t Singleton::mutex=PTHREAD_MUTEX_INITIALIZER;
Singleton* Singleton::instance = NULL;