Thread: Two dimentional array

Is it possible to make a two dimetional dynamic array?
It probably is, but I cant get it to work

Thanks in advance

example:

Code:

int i;
int sizeX = 10, sizeY = 20;
int **my2DArray;
my2DArray = malloc(sizeX * sizeof(*my2DArray));
// OR: my2DArray = malloc(sizeX * sizeof(*int));
for (i = 0; i < sizeX; i++)
{
    my2DArray[i] = malloc(sizeY * sizeof(**my2DArray));
    // OR: my2DArray[i] = malloc(sizeY * sizeof(int));
}

that should be:

Code:

vector<vector<int> > V(rows, vector<int>(cols));

I wouldn't use malloc in C++, and I wouldn't use new either because a container like vector is much better than dynamic allocation.

For one thing, whether you use malloc or new, KONI's example doesn't include the deletion code. The vector example is all you need for creation and cleanup.

Considering this is C++ new and delete are more used, but vectors are the way to go, really.

Code:

int **Allocate_2D_Array( int x, int y )
{
    int **Array = new int *[y];

    for ( int i=0; i<y; i++ )
        Array[i] = new int [x];

    return Array;
}



void Dealocate_2d_array ( int **Array, int y )
{
    for ( int i=0; i<y; i++ )
        delete []Array[i];

    delete []Array;
}



int main( void )
{
    int x, y;

    // Get your user defined array dimensions
    cout<< "Enter X: ";
    cin >> x;

    cout<< "Enter Y: ";
    cin >> y;

    // Allocate memory
    int **p_2d_array = Allocate_2D_Array( x, y );

    // Fill array with variables
    for ( int j=0; j<y; j++ )
        for ( int i=0; i<x; i++ )
            p_2d_array[j][i] = i+j;

    // print out array
    for ( int j=0; j<y; j++ )
    {
        for ( int i=0; i<x; i++ )
            cout<< p_2d_array[j][i] << " ";

        cout<< '\n';
    }

    // delete allocated memory
    Dealocate_2d_array( p_2d_array, y );

    return 0;
}

Should work OK if you need to use new/delete. I prefer to make functions to allocate and deallocate the memory cause it makes main() ... nicer.

Unless you are forced to do so because you are a student, I cannot think of any reason why you would pick that version over a vector. You are really just reinventing what a vector does for you, except your own version won't work as well.

My copy of the standard indicates it should be explicit (23.2.4.1), so I suspect gcc is wrong in this case.

Interestingly, in this this link Stroustrup indicates that this exact example was the catalyst for the rule in C++ allowing constructors to be declared explicit: http://www.research.att.com/~bs/dne_errata.html (scroll to pg80 for the second printing).

Thanks to all of you for your inputs. I think this forum is the one where most people get the most replies to there question.

I need the two dimentional array for holding the color of a computer generated picture so that I can pass it to my saveFileFunction (Work in progres).

Thanks again

>> You are really just reinventing what a vector does for you

Technically it's the other way around isn't it

You are really just doing what a vector reinvents for you ?

I'm not very good at logical inverses