Question

我正在构建一个使用OpenCV Mat的搜索算法，我将Mat转换为灰色图像，然后检查像素以使其坐标可行走或不可行走。我用vector＆gt;网格。当我尝试从网格中打印nodeID时，程序突然关闭（例如grid.grid[10][10]->NodeID）。

using namespace std;
int gridZise;
class location{
public:
    int x;
    int y;

};

class Node{
public:
    int gridX;
    int gridY;
    bool walkable;
    location worldPosition;
    int NodeID;


    int gCost;
    int hCost;
    Node *parent;

    Node(bool _walkable, int _gridX, int _gridY)
        {
            walkable = _walkable;
            gridX = _gridX;
            gridY = _gridY;
            NodeID = gridY * gridZise + gridX;
        }
    Node(int _gridX, int _gridY){
        gridX = _gridX;
        gridY = _gridY;
        NodeID = gridY * gridZise + gridX;
    }

    int fCost(){
        return gCost + hCost;
    }

};

class Grid{

public:
    cv::Mat map;
    vector<vector<Node*> > grid;
    int gridx;
    int gridy;


    Grid(cv::Mat _map){
        map = _map;
        gridx = map.cols;
        gridy = map.cols;
        gridZise = map.cols;
    }

    void CreateGrid(){
        // Set up sizes. (HEIGHT x WIDTH)
          grid.resize(gridy);
          for (int i = 0; i < gridy; ++i)
            grid[i].resize(gridx);

          // build up the grid
          for(int i=0; i <gridx;i++){
              for(int j=0; j < gridy;j++){
                  int pixel_val = map.at<int>(i,j);
                  bool _walkable = false;
                  if(pixel_val > 120){//if the value of the pixel is bigger than 120 is walkable
                       _walkable = true;
                  }
                  grid[i][j]->walkable = _walkable;
                  grid[i][j]->gridX = i;
                  grid[i][j]->gridY = j;
              }
          }
    }

    void PrintGrid(){
        for(int i=0; i <gridx;i++){
            for(int j=0; j < gridy;j++){
                cout << grid[i][j]->NodeID <<endl;
            }
        }
    }

    vector<Node> GetNeighbours(Node node)
        {
            vector<Node> neighbours;

            for (int x = -1; x <=1; x++)
            {
                for (int y = -1; y <= 1; y++)
                {
                    if (x == 0 && y == 0)
                        continue;

                    int checkX = node.gridX + x;
                    int checkY = node.gridY + y;

                    if(checkX >=0 && checkX < gridx && checkY >=0 && checkY < gridy)
                    {
                        Node neighbour(checkX,checkY);
                        neighbours.push_back(neighbour);
                    }
                }
            }
            return neighbours;
        }

    Node nodeFromLocation(location _node){
        Node currentNode = *grid[_node.x][_node.y];
        return currentNode;
    }

};


using namespace cv;
int main()
{
    cv::Mat img;
    img = imread("C:\\Users\\abdulla\\Pictures\\maze.jpg");

    if(img.empty()){
        cout<<"image not load "<<endl;
        return -1;
    }
    cvtColor(img,img,CV_BGR2GRAY);
    imshow("image",img);
    waitKey();
    Grid grid(img);

    grid.PrintGrid();

    return 0;
}

谢谢。

Answer 1

首先，摆脱using namespace std;。虽然它看起来很方便，但您可能会遇到一些令人讨厌的惊喜（请参阅this问题）。

Grid的构造函数使用Grid::grid的默认构造函数，它创建一个空向量。

在PrintGrid中，您会得到未定义的行为。

grid; // ok, grid is a member of Grid
grid[0]; // Returns a reference. No bounds checking is performed.
grid[0][0]; // undefined behaviour. grid[0] is outside of bounds.

方法CreateGrid与此无关，因为您从不称呼它。但是我们假设你已经打过电话了。那么PrintGrid会像这样工作：

grid; // ok, grid is a member of Grid
grid[0]; // ok
grid[0][0]; // ok, return a pointer to a Node. Which you never initialized.
grid[0][0]->NodeID; // Undefined behaviour. You're trying to access a random memory location.

你真的需要将节点存储为指针吗？你也可以使用vector<vector<Node>>。这样，某人（std::vector<...）将负责分配和删除节点。您仍然可以使用指针指向父节点，只要指针用作引用而不是所有权，那就没问题。

如果您确实需要存储指针，make use of smart pointers。这样，有人会负责删除节点。

最后，班级Grid负责维持适当的状态。总是。所以构造函数应该已经完成了CreateGrid所做的事情。问题是你不能从构造函数中调用CreateGrid，因为那时你将调用一个生命尚未开始的对象的方法（如果我错了那个人就会纠正我）。如果你想把它作为一个单独的函数，你可以使CreateGrid静态：

class Grid {
    Grid(cv::Mat _map):
           map(_map),
           gridx(_map.cols),
           gridy(_map.cols),
           gridZise(_map.cols),
    {
        GreateGrid(grid, map, gridx, gridy);
    }

//...
    static void CreateGrid(std::vector<std::vector<Node>> & grid, cv::Mat map, int gridx, int grid y) {
    //...
    }
//...
};

创建opencv Mat到2d网格

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