invalid use of non-static member function ‘void Date::init(int, int, int)’

#include
using namespace std;

class Date
{
 public:
 int day,month,year;
 void init(int,int,int);
 void print_ymd();
};

void Date::init(int yy, int mm, int dd)
{
 year = yy;
 month = mm;
 day = dd;
}

void Date::print_ymd()
{
 std::cout << year << "-" << month << "-" << day << std::endl;
}
int main()
{
 Date date1;
 Date *p1 = &date1;            //指向对象的指针
 p1->init(2006, 3, 28);
 p1->print_ymd();
 int *p2;
 p2 = &date1.year;             //指向对象数据成员的指针
 std::cout << *p2 << std::endl;
 void (Date:: * p3)(int,int,int);   //指向对象成员函数的指针
 void (Date:: * p4)();              //指向对象成员函数的指针
 p3 = Date::init;
 p4 = Date::print_ymd;
 (date1.*p3)(2006, 4, 8);
 (date1.*p4)();
 return 0;
}

编译的时候会报错:

35:13: error: invalid use of non-static member function ‘void Date::init(int, int, int)’
  p3 = Date::init;

36:13: error: invalid use of non-static member function ‘void Date::print_ymd()’
  p4 = Date::print_ymd;

将p3= Date::init;改为：

   p3 = &Date::init;

 将p4 = Date::init;改为:

   p4 = &Date::print_ymd;

C++的非静态成员函数在未实例化之前地址是不确定的，所以要将Date的两个成员函数

的地址指明之后才能进行赋值操作。