单例模式

#include<iostream>
#include <pthread.h>
using namespace std;

//该实例一直存在
class Singleton
{
private:
    Singleton(){}
    Singleton(const Singleton&){}
    Singleton& operator=(const Singleton&){}
public:
    static Singleton& GetInstance()
    {
        static Singleton s_instance;
        return s_instance;
    }
};
//用时创建，不用时销毁
class Singleton2
{
private:
    Singleton2(){}
    Singleton2(const Singleton2&){}
    Singleton2& operator=(const Singleton2&){}
    static Singleton2* s_instance;
    static int s_counter;
    static pthread_mutex_t s_mutex;
public:
    static Singleton2& GetInstance()
    {
        pthread_mutex_lock(&s_mutex);
        if(!s_instance) s_instance = new Singleton2();
        ++s_counter;
        pthread_mutex_unlock(&s_mutex);
        return *s_instance;
    }
    void ReleaseInstance(void)
    {
        pthread_mutex_lock(&s_mutex);
        if(s_counter&&--s_counter==0)
            delete this;
        pthread_mutex_unlock(&s_mutex);
    }
};
Singleton2 Singleton2::*s_instance = NULL;
int Singleton2::s_counter = 0;
pthread_mutex_t Singleton2::s_mutex = PTHREAD_MUTEX_INITIALIZER;

int main()
{
    Singleton2& s1 = Singleton2::GetInstance();
    Singleton2& s2 = Singleton2::GetInstance();
    s1.ReleaseInstance();
    s2.ReleaseInstance();

    return 0;
}

注：主要看思想，windows下好像不能编译。