初始化static成员

//Cat.h

class Cat

{

public:

Cat(int age):its_age(age) {

HowManyCats++;

}

virtual ~Cat() {

HowManyCats--;

virtual int get_age();

virtual void set_age(int);

static int get_how_many() {return HowManyCats;}

private:

int its_age;

static int HowManyCats;

};

//Cat.cpp

#include "Cat.h"

int Cat::get_age()

return its_age;

void Cat::set_age(int age)

its_age=age;

int Cat::HowManyCats = 0; //初始化 static 成员