Copy constructor of dynamic two-dimensional array

Question

I need help. Now i'm trying to make a class Matrix, but my program freezes every time I run it in Visual Studio 2013. I think there is some trouble with copy constructor. Here is the whole code. `

class Matrix
{
private:
    int** matrix;
    int X; // Matrix rows
    int Y; // Matrix columns
public:
    // Default Constructor
    Matrix()
    {
        X = 0;
        Y = 0;
        matrix = NULL;
    }
    // Constructor with parameters
    Matrix(int _X, int _Y)
    {
        srand(time(NULL));

        X = _X;
        Y = _Y;
        matrix = new int*[X];

        for (int i = 0; i < X; i++)
                matrix[i] = new int[Y];

        for (int i = 0; i < X; i++)
        {
            for (int j = 0; j < Y; j++)
            {
                matrix[i][j] = rand() % 100;
            }
        }

    }
    // Copy constructor
    Matrix(const Matrix& N)
    {
        X = N.X;
        Y = N.Y;

        matrix = new int*[X];

        for (int i = 0; i < X; i++)
            matrix[i] = new int[Y];

        for (int i = 0; i < X; i++)
        {
            for (int j = 0; j < Y; j++)
            {
                matrix[i][j] = N.matrix[i][j];
            }
        }
    }
    // Destructor
    ~Matrix()
    {
        for (int i = 0; i < X; i++)
            delete[] matrix[X];
    }
    //--------------------------------------
    void ShowMatrixOnScreen()
    {
        for (int i = 0; i < X; i++)
        {
            for (int j = 0; j < Y; j++)
                cout << matrix[i][j] << "   ";

            cout << endl << endl;
        }
    }
};

void main() 
{
    Matrix x(4, 2);
    x.ShowMatrixOnScreen();
}

`

Function "ShowMatrixOnScreen" prints matrix "x" on a screen, but then console freezes.

Answer 1

Your destructor has the statement delete[] matrix[X];

matrix[X] does not exist, so you are freeing memory which is not allocated to you, which is Undefined Behavior. It should be delete [] matrix[i] instead!

Moreover, as pointed by Vlad From Moscow, it is advisable to delete all the memory, so you shall also consider adding delete [] matrix, to delete the 1-D array of pointers which you allocated using matrix = new int*[X];