设计一个类只能生成该类的一个实例

class Singleton{public:    Singleton()    {        if (_count == 0)        {            cout << "进行构造函数" << endl;            _count++;        }        else        {            cout << "构造失败" << endl;        }    }private:    static int _count;};int Singleton::_count=0;void test(){    Singleton t1;    Singleton t2;}int main(){    test();    system("pause");    return 0;}

//只适用于单线程,多线程需要加锁class Singleton{public:    static Singleton* GetConstuct()    {        if (instance == NULL)        {            instance = new Singleton();            return instance;        }        return NULL;    }private:    static Singleton* instance;    Singleton()    {            cout << "进行构造函数" << endl;    }};Singleton* Singleton::instance = NULL;void test(){    Singleton* t1 = Singleton::GetConstuct();    Singleton* t2= Singleton::GetConstuct();}int main(){    test();    system("pause");    return 0;}

利用静态构造函数，初始化静态变量的时候创建实例class Singleton{public:    static Singleton* GetConstuct()    {        return instance;    }private:    Singleton()    {        cout << "进行构造函数" << endl;    }    static Singleton* instance;};Singleton* Singleton::instance = new Singleton();void test(){    Singleton* t1 = Singleton::GetConstuct();    Singleton* t2 = Singleton::GetConstuct();}int main(){    test();    system("pause");    return 0;}