Storing pixels in a 2D Array (in a matrix form)

Question

I want to store the total number of horizontal pixels and vertical pixels in an image in a 2D Array. What should be the syntax to carry this out in c++ using opencv? This is my code in C++ using opencv libraries.

using namespace std;
using namespace cv;

Mat image=imread("task1-1.png");

const int IDIM = image.rows; // horizontal size of the squares
const int JDIM = image.cols; // vertical size size of the squares                                                                                                                                   

int squares[IDIM][JDIM];

It gives me an error stating:

array bound is not an integer constant before ‘]’ token int squares[IDIM][JDIM]; ^ array bound is not an integer constant before ']' token int squares[IDIM][JDIM]; ^

What should be the correct way to carry this out?

Why do you want to use a 2D array, you already have a `Mat`. Do you really need it or do you think you need it? — smttsp, Mar 02 '17 at 16:53
Actually I need to obtain all the nodes in obstacles, start point, end point, movable area in order to find shortest path using A* algorithm. — maVerik, Mar 02 '17 at 17:21

score 2 · Accepted Answer · edited May 23 '17 at 12:17

Your error is because the values of IDIM and JDIM are not compile-time constant. So you must either dynamically allocate your array squares or use an alternative approach, such as a vector.

Dynamically Allocated Array

// Allocate

int** squares = new int*[image.rows];

for(int x = 0; x < image.rows; ++x)
{
    squares[x] = new int[image.cols];

    for(int y = 0; y < image.cols; ++y)
    {
        squares[y] = 0;
    }
}

// Use

squares[0][1] = 5;

// Clean up when done

for(int x = 0; x < image.rows; ++x)
{
    delete[] squares[x];
}

delete[] squares;
squares = nullptr;

Vector

// Allocate

std::vector<std::vector<int>> squares(image.rows, std::vector<int>(image.cols, 0));

// Use

squares[0][1] = 5;

// Automatically cleaned up

See How do I declare a 2d array in C++ using new?

Storing pixels in a 2D Array (in a matrix form)

1 Answers1