设计一个类，该类不能被继承，且只能实例化3次

#include<iostream>

class finalclass
{
public: static int count;
public:
	static finalclass *getinstance()
	{
		if(count <= 0)
			return NULL;
		count--;
		return new finalclass;
	}
	static void setcount(int n)
	{
		count = n;
	}
/*	static void deleteinstance(finalclass *pinstance)
	{
		delete pinstance;
		pinstance = 0;
	}
*/
private:
	finalclass(){}
	~finalclass(){}
};
int finalclass::count = 0;
int main()
{
	finalclass::setcount(3);
	finalclass *f1 = finalclass::getinstance();
	finalclass *f2 = finalclass::getinstance();
	finalclass *f3 = finalclass::getinstance();
	if(f3 == NULL)
		printf("f3 NULL\n");
	else
		printf("f3 NOT NULL\n");
	finalclass *f4 = finalclass::getinstance();
	if(f4 == NULL)
		printf("f4 NULL\n");
	finalclass *f5 = finalclass::getinstance();
	if(f5 == NULL)
		printf("f5 NULL\n");
}