Is it possible to use iterators on 3D matrix in a template class?(c++)

Question

i'm trying to use iterators on a 3d matrix allocated dynamically.

   matrix = new T**[height];
        for(int i =0; i<height; i++){
            matrix[i] = new T*[col];
            for(int j =0; j<col; j++){
                matrix[i][j] = new T[row];


            }
        }

Is it possible to iterate over this matrix using iterators? Or is better to choose a different solution using iterators? (no vector solution)

If it's possible, how can I implement them?

Answer 1

Every pointer meets the criteria for an iterator, too. So you can iterate as follows:

for(T*** begin1 = matrix, end1 = matrix + height; begin1 != end1; ++begin1)
{
    for(T** begin2 = *begin1, end2 = *begin1 + col; begin2 != end2; ++begin2)
    {
        for(T* begin3 = *begin2, end3 = *begin2 + row; begin3 != end3; ++begin3)
        {
            begin3->doSomething();
        }
    }
}

This works with standard library algorithms as well:

std::for_each
(
    matrix, matrix + height, [](T** t)
    {
        std::for_each
        (
            t, t + col, [](T* t)
            {
                std::for_each
                (
                    t, t + row, [](T& t)
                    {
                         t.doSomething();
                    }
                );
            }
        );
    }
);

Untested code, if you find a bug, please fix it yourself.

You are likely better off with std::vector , though, this relieves you from all the manual memory management and additionally allows for much simpler construction:

std::vector<std::vector<std::vector<T>>> v
(
    height, std::vector<std::vector<T>>(col, std::vector<T>(row)
);

If you do not need jagged arrays for whatever reason, you will get more efficient code if you place all the values into a one-dimensional array/vector and do the index calculations on your own, then [x][y][z] corresponds to [(x * col + y) * row + z] .