How to pass file path to constructor?

Question

C++ / C#

I created a library, the constructor must accept a string (path to the file), but an error occurs at the compilation stage:

constructor code:

Grid::Grid(string path_to_grid_txt){

    ifstream grid_txt(path_to_grid_txt);

    grid_txt >> height;
    grid_txt >> width;

    grid_nodes = new node * [height];
    for(int i = 0; i < height; ++i){

        grid_nodes[i] = new node [width];

        for(int j = 0; j < width; ++j){

            grid_txt >> grid_nodes[i][j].pass;

            grid_nodes[i][j].coordinates.x = j;
            grid_nodes[i][j].coordinates.y = i;
            grid_nodes[i][j].n = i * width + j;
        }
    }
}

I pass it like this:

int main()
{
    string a;

    cin >> a;

    Grid st(a);

    return 0;
}