static成员函数、成员变量

class Cat
{
public:
         Cat(int age):itsAge(age){HowManyCats++;}
         virtual ~Cat(){HowManyCats--;}
         virtual int getAge(){return itsAge;}
         virtual void setAge(int age){itsAge=age;};
         static int HowManyCats;
private:
         int itsAge;
};
// int Cat::HowManyCats=0; //对静态成员数据如此赋值
int main()
{
 
         const int maxCats =5;
         int i;
         Cat *catHouse[maxCats];
 
         for(i=0; i<maxCats; i++)
                   catHouse[i]=new Cat(i);
         for(i=0; i<=maxCats; i++)
         {
                   cout<<"there are "<<Cat::HowManyCats<<" cats left.\n";
                   if(!Cat::HowManyCats) break;
 
                   cout<<"delete the cat which is "<<catHouse[i]->getAge()<<" years old."<<endl;
                   delete catHouse[i];
                   catHouse[i] = 0;
         }
         return 0;
}

上面程序的错误是定义了静态数据成员，但没有为之赋值！

对于私有静态数据成员：private:         static int HowManyCats;

可以用公有的静态成员函数访问：public: static int GetHowMany(){return HowManyCats;},也可以用非静态成员函数访问，用对象调用此成员函数。