Question

我基本上是在尝试编写比较器函数，以x和y的顺序排列对象P1和Pt2的值，按升序和降序排列。

现在我遇到了x和y受保护的错误，但是如何在排序中正确使用getter呢？我还是很困惑。我尝试使用它但不起作用。

bool Line2D::sortLine2DPtAsc (const Point2D& left, const Point2D& right) 
{
    return (left.pt1.getX() < right.pt1.getX()) || ((left.pt1.getX() == right.pt1.getX()) && (left.pt1.getY() < right.pt1.getY()));
}

使用getter时出错：

Line2D.cpp:25:15: error: ‘const class Point2D’ has no member named ‘pt1’
Line2D.cpp:25:34: error: ‘const class Point2D’ has no member named ‘pt1’
Line2D.cpp:25:56: error: ‘const class Point2D’ has no member named ‘pt1’
Line2D.cpp:25:76: error: ‘const class Point2D’ has no member named ‘pt1’
Line2D.cpp:25:97: error: ‘const class Point2D’ has no member named ‘pt1’
Line2D.cpp:25:116: error: ‘const class Point2D’ has no member named ‘pt1’

这是我的代码：

class Line2D
{

    private:    
        Point2D pt1;
        Point2D pt2;

    public:
        //Constructor
        Line2D ();
        Line2D (Point2D pt1, Point2D pt2);

        //Accessors
        Point2D getPt1();
        Point2D getPt2();
        double getScalarValue();    //returns the value of attribute length

        //Mutators
        void setPt1 (Point2D pt1);
        void setPt2 (Point2D pt2);

        static bool sortLine2DPtAsc (const Point2D& left, const Point2D& right) ;
}


bool Line2D::sortLine2DPtAsc (const Point2D& left, const Point2D& right) 
{
    return (left.x < right.x) || ((left.x == right.x) && (left.y < right.y));
}

Answer 1

将该版本与getter一起使用，但将left.pt1.getX()替换为left.getX()等。

我猜你在Point2D课程中需要改变

double getX();

到

double getX() const;

同样适用于getY。

传递const Point2D& left, const Point2D& right，您承诺不修改这些对象中的任何值。您只能调用声明为const的成员函数（它们不会更改对象）。

Answer 2

bool Line2D::sortLine2DPtAsc (const Point2D& left, const Point2D& right)
您的参数属于Point2D类型，也许您打算使用Line2D类型的参数如果函数是排序线，你为什么要传递点;）
pt1和pt2是Line2D课程的成员而不是您的Point2D课程

从比较函数访问成员变量/ getter

2 个答案: