C++ 设计一个类，只能生成一个对象

#include<iostream>using namespace std;class singleton{public:    static singleton* getpsin()    {        if(psin == NULL)        {            psin = new singleton();        }        return psin;    }    static void relice()    {        if(psin != NULL)        {            delete psin;        }        psin = NULL;    }private:    singleton()    {cout<<"+++++"<<endl;}    static singleton* psin;};singleton* singleton::psin = NULL;int main(){    singleton* p = singleton::getpsin();    return 0;   }