c++ - 嵌套类 : how to access the member variable in enclosed class

Question

以下代码片段旨在将所有点存储在封闭类Solution的成员函数mainFunc中的priority_queue中(即 pq), 这样所有的 points 都按照它们到 origin 的距离排序。但是，编译器报错:

error: invalid use of non-static data member 'Solution::ori'

然后我将 Point ori 的第 3 行更改为 static Point ori 并将 ori 更改为 Solution::ori在distance(Point p)函数中，出现链接错误:

undefined reference to 'Solution::ori'

谁能帮我解决这个问题？提前致谢!

/**
 * Definition for a point.
 * struct Point {
 *     int x;
 *     int y;
 *     Point() : x(0), y(0) {}
 *     Point(int a, int b) : x(a), y(b) {}
 * };
 */

class Solution {
private:
    Point ori;
    class Comparator {
    public:
        // calculate the euclidean distance between p and ori
        int distance(Point p) {
            return pow(p.x-ori.x, 2) + pow(p.y-ori.y, 2);
        }
        // overload the comparator (), the nearest point to 
        // origin comes to the first
        bool operator() (Point l, Point r) {
            if (distance(l) > distance(r)) {
                return true;
            }
        }        
    };

public:
    /*
     * @param points: a list of points
     * @param origin: a point
     */
    void mainFunc(vector<Point> points, Point origin) {
        ori = origin;
        priority_queue<Point, vector<Point>, Comparator> pq;
        for (int i = 0; i < points.size(); i++) {
            pq.push(points[i]);
        }
    }
};

Answer 1

您可以修改您的 Comparator 声明以在其构造函数中采用特定的 Point 值:

class Solution {
private:
    Point ori;
    class Comparator {
    public:
        // Save the value in the functor class
        Comparator(const Point& origin) : origin_(origin) {}

        // calculate the euclidean distance between p and origin
        int distance(Point p) {
            return pow(p.x-origin_.x, 2) + pow(p.y-origin_.y, 2);
        }
        // overload the comparator (), the nearest point to 
        // origin comes to the first
        bool operator() (Point l, Point r) {
            if (distance(l) > distance(r)) {
                return true;
            }
        }        
    private:
         Point origin_;
    };

public:
    /*
     * @param points: a list of points
     * @param origin: a point
     */
    void mainFunc(vector<Point> points, Point origin) {
        ori = origin;
        priority_queue<Point, vector<Point>> pq(Comparator(ori));
                                             // ^^^^^^^^^^^^^^^ 
                                             // Pass an instance of 
                                             // the functor class
        for (int i = 0; i < points.size(); i++) {
            pq.push(points[i]);
        }
    }
};