Question

I’ve got class similar to this:

class Krzyzowka
{
    protected:
    char model[40][40];
    int x, y;

    public:
        Krzyzowka() { }

            Krzyzowka(char model[][40], int x, int y)
            {
                this->model=model;
            }
};

Now, I declare in main():

char array[10][10];

and want to pass it to the:

Krzyzowka(char model[][40], int x, int y)

I’m doing it this way:

Krzyzowka obj(array, 10, 10);

But then I want to set the model 2D array with the passed array:

this->model=model;

But compiler returns two errors:

error: no matching function for call to ‘Krzyzowka::Krzyzowka(char [10][10], int, int)’

error: incompatible types in assignment of ‘char (*)[40]’ to ‘char [40][40]’

How can I do this correctly? Thanks in advance for help.

Answer 1

There is no operation available that automatically assigns an array to another array.

Possible workarounds that come to mind:

---

Manually copy-assign the data to your internal array using a loop (make sure to keep track of the effective nrows and ncols). For circumventing the compiler complaints you could use a template (assuming the size is known at compile time):

    template<int NROWS, int NCOLS>
    Krzyzowka(char (&model)[NROWS][NCOLS])
    {
        nrows = NROWS > nrows ? nrows : NROWS;
        ncols = NCOLS > ncols ? ncols : NCOLS;
        for (int row = 0; row < nrows; row++)
          for (int col = 0; col < ncols; col++) 
            this->model[row][col] = model[row][col];
    }

Now you can create the object like:

char array[][2] = {{'a', 'b'}, {'c', 'd'}};
Krzyzowka k(array);

---

If the dimensions of the array are only known at run time (e.g. based on user input, and char** array dynamically allocated by nested new[]), you may need to adopt the approach given here or switch to the following.

---

Even better would probably be to use some standard array type, like std::vector (which you can swap or assign). Then you have no problem with the compiler type incompatility complaints either.

std::vector<std::vector<char> > array(nrows, std::vector<char>(ncols));
std::vector<std::vector<char> > model;
model = array; // or model.swap(array); if you don't need the copy