operator << 做为 virtual 重载问题

#include <iostream>

using namespace std;

class fig2d
{
    int dim1;
    int dim2;
public:
    fig2d(){dim1 = 5,dim2 = 6;}
    virtual void operator <<(ostream &rsh);
};

void fig2d::operator <<(ostream &rsh)
{
    rsh<<this->dim1 <<"  "<<this->dim2<<" ";
}

class fig3d : public fig2d
{
    int dim3;
public:
    fig3d(){dim3=7;}
    virtual void operator <<(ostream &rsh);
};

void fig3d::operator <<(ostream &rsh)
{
    fig2d::operator <<(rsh);
    rsh<<this->dim3;
}


void main()
{
    fig2d obj1;
    fig2d obj2;
    obj1 << cout;
    cout <<endl;
    obj2 << cout;
    return ;
}