类到对象的 实例化的个数

#include <iostream>

using namespace std;

class cat

{public:

    cat()

    {num++;}

    static int getNumOfCats()

    { return num;}

    ~cat(){num--;}

private:

    static int num;

};

int cat::num=0;

int main()

{   cat c;//1个对象

    cout<<"num:"<<cat::getNumOfCats()<<endl;//num是1

    cat cArray[4];//再来4个对象

    cout<<"num:"<<cat::getNumOfCats()<<endl;//num是5

    cout << "Hello World!" << endl;

    return 0;

}