代码示例中的友元运算符？C++头文件，朋友在这里做什么？

Question

我正在查看一些代码，我想知道友元运算符在这个类头文件中做了什么。

这是否只需要说“当我使用这个运算符并且两个输入都是 CSegment3D 类型时，我按照函数实现中定义的方式对它们进行操作”？

class CSegment3D : public CObject
{
public:
    CSegment3D& operator*=(const double& factor);//  multiply by a scalar factor & assign
    CSegment3D& operator/=(const double& factor);//  divide by a scalar factor & assign
    CSegment3D& operator+=(const CSegment3D& other);// vector addition
    CSegment3D& operator-=(const CSegment3D& other);// vector subtraction
    friend CSegment3D GetMidpoint(const CSegment3D& ptA, const CSegment3D& ptB);
    friend CSegment3D GetNormal( CSegment3D *pSeg1, CSegment3D *pSeg2, CSegment3D *pSeg3 ); // Return a point normal to the surface defines by the tree point passed in.
    friend double operator*(const CSegment3D& vectorA, const CSegment3D& vectorB); // dot product
    friend CSegment3D operator*(const double& factor, const CSegment3D& vectorA); // multiply by a scalar
    friend CSegment3D operator/(const CSegment3D& vectorA, const double& factor); // divide by a scalar
    friend CSegment3D operator+(const CSegment3D& vectorA, const CSegment3D& vectorB);// vector addition
    friend CSegment3D operator-(const CSegment3D& vectorA, const CSegment3D& vectorB );// vector subtraction
    friend CSegment3D operator^(const CSegment3D& vectorA, const CSegment3D& vectorB); // cross product
    friend CSegment3D operator%(CSegment3D vectorA, const CSegment3D& vectorB); // projection of vectorB onto vectorA
};

Answer 1

正如我总是喜欢告诉我的学生的那样，朋友就像女朋友：带有朋友关键字的函数不是家庭，但仍然可以访问您最心爱的东西，在这种情况下，您的“私有”属性