有如下程序：
include ＜iostream＞
using namespace std;
class ONE
{
public:
virtual void f() { cout ＜＜ "1"; }
};
class TWO: public ONE
{
public:
TWO() { cout ＜＜ "2"; }
};
class THREE: public TWO
{
public:
virtual void f() {TWO::f(); cout ＜＜ "3"; }
};
int main()
{
ONE aa, *p;
TWO bb;
THREE cc;
p=&cc;
P-＞f();
return 0;
}
执行上面程序的输出是【 】。