Employee:Employee(const Employee& other):name(other.name), id(count) { +

Employee::Employee(const Employee& other):name(other.name), id(count) { ++co

C/C++ code

//为什么出现//undefined reference to `Employee::count'//.hclass Employee{    public:        Employee():name("NoName"), id(count)        {            ++count;        }        Employee(std::string strName):name(strName), id(count)        {            ++count;        }        virtual ~Employee();        Employee(const Employee& other);        Employee& operator=(const Employee& other);    protected:    private:        std::string name;        int id;        static int count;};//.cppEmployee::Employee(const Employee& other):name(other.name), id(count){    ++count;}