CODEWITHSUNDEEP
c++functionpointersmultidimensional-arraydynamic-memory-allocation
Em Rul
Em Rul

Reputation: 57

How can I find the size of a matrix which passed to function?

In this C++ code sizeof (ar) doesn't help me to find cols and rows variables and always gives me the same wrong cols and rows. How can I find the size of the matrix without passing sizeX and sizeY variables to the IsMagicSquare(arr) function? Can you help me to understand this problem and find a way to solve it? 

int main()
{
    int sizeX, sizeY;
    cout << "Size of Matrix:";
    cin >> sizeX >> sizeY;

    int** arr = new int* [sizeY];
    for (int i = 0; i < sizeY; ++i)
    {
        arr[i] = new int[sizeX];
    }

    cout << "Elements of the Matrix:";
    for (int i = 0; i < sizeX; i++)
        for (int j = 0; j < sizeY; j++)
            cin >> arr[i][j];

    if (IsMagicSquare(arr))
    {
        for (int i = 0; i < sizeX; i++)
        {
            cout << "\n";
            for (int j = 0; j < sizeY; j++)
                cout << arr[i][j];
        }
    }
    else
    {
        for (int i = 0; i < sizeY; i++)
        {
            delete[] arr[i];
        }
        delete[] arr;
    }


    return 0;
}

bool IsMagicSquare(int** ar)
{
    int rows = sizeof (ar)/ sizeof (ar[0]);
    int cols = sizeof (ar[0]) / sizeof(int); 
    cout << rows << cols;
    if (rows == cols)
    {
        int* ver = new int[rows]();
        int* hor = new int[cols]();
        int cross0=0;
        int cross1=0;

        for (int i = 0; i < rows; i++)
        {
            for (int j = 0; j < cols; j++)
            {
                hor[i] += ar[i][j];
                ver[j] += ar[i][j];
                if (i == j)
                    cross0 += ar[i][j];
                else if ((i+j) == cols)
                    cross1 += ar[i][j];
            }
        }
        if (cross0 != cross1)
            return false;
        else
        {
            for (int i = 0; i < rows; i++)
                if ((cross0 != ver[i]) || (cross1 != hor[i]))
                    return false;
        }
    }
    else
        return false;

    return true;
}

Upvotes: 1

Views: 121

Answers (1)

Dietmar K&#252;hl
Dietmar K&#252;hl

Reputation: 153850

Just sum the allocations you are making for a reasonable estimate:

  • The outer array: sizeY * sizeof(int*).
  • The inner arrays: sizeY * sizeX * sizeof(int)

Of course, the size calculations you got in IsMagicSquare() won’t work: sizeof operates on the types rather than the actual allocated memory. That information is lost and can’t be recovered from the pointers. You are best off to use, e.g., a std::vector<std::vector<int>>. That deals with automatic memory allocation and it tracks the sizes of the structure.

Upvotes: 1

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