继承体制下二元操作符的重载

　　C++Primer上建议最好把重载二元操作符函数作为非成员函数，我试验了下，代码如下，但有个问题，恳求得到诸位的回复。

#include <iostream>
using namespace std;

class CPoint
{
public:
    CPoint(): fx(0) { }
    CPoint(float x): fx(x) { }
    ~CPoint() { }
protected:
    
public:
    float fx;
};

class CPoint2d: public CPoint
{
public:
    CPoint2d(): fy(0) { }
    CPoint2d(float x, float y): CPoint(x), fy(y) { }

    ~CPoint2d() { }
protected:
    
public:
    float fy;
};

inline bool operator==(const CPoint &lpt, const CPoint &rpt )
{
    cout <<"1d==" <<endl;
    return lpt.fx == rpt.fx ? true : false;
}

inline bool operator!=(const CPoint &lpt, const CPoint &rpt )
{
    return lpt == rpt ? false : true;
}

inline bool operator== (const CPoint2d &lpt, const CPoint2d &rpt )
{
    cout << "2d==" <<endl;
    if ( operator==(static_cast<CPoint>(lpt), static_cast<CPoint>(rpt) ) )
    {
        if ( lpt.fy == lpt.fy )
        {
            return true;
        }
    }

    return false;
//    return operator==(lpt, rpt) && lpt.fy == rpt.fy ? true : false;
}

int main()
{
    CPoint pt1;
    CPoint pt2(10);
    
    if ( pt2 == pt1 )
    {
        cout << "1d: Yes == " <<endl;
    }
    else 
    {
        cout << "1d: No != " <<endl;
    }

    CPoint2d pt2D;
    CPoint2d pt2D2(5, 10);

    if ( pt2D == pt2D2 )
    {
        cout << "2d: Yes == " <<endl;
    }
    else
    {
        cout << "2d: No != " <<endl;
    }

    cout << pt2D.fx << " " <<pt2D.fy << " " << pt2D2.fx << " "<< pt2D2.fy <<endl;
    return 0;
}

 

　　输出如下：

1d==

1d:No !=

2d==

1d==

2d: No !=

0 0 5 10

Press any key to continue 

 　　我的问题在于给CPoint2d重载==操作符时，比较基类的部分，我想调用基类的==重载函数，但现在它不是成员函数，无法用CPoint::来指定调用基类，我想请问，有没有其他更好的方法使它跟是成员函数时一样好用？希望各位不吝赐教，可以讨论下你们的做法，O(∩_∩)O~，谢谢啦！