设计一个类，该类不能被继承，且只能实例化3次

[cpp]
#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");
}

#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");
}

补充：软件开发 , C++ ,