# Multidimensional arrays

Discussion in 'C++' started by James, Aug 19, 2003.

1. ### JamesGuest

What's the best way of dynamically allocating a multidim array from the
following:

int **a = new int*[size];
a[0] = new int[size];
.... and so on

or:

int (*a)[10] = new int[10][10];

by the way, how do we pass arrays delcared by the second way to
functions? What really is the difference between (*a)[] and *a[]..
actually i kind of understand the difference but it doesn't hit me that
well.. I can't interpret what (*a)[] really means. Thanks!

James

James, Aug 19, 2003

2. ### BusterGuest

I should have said 'any dimension except the first'.

And here, 'every dimension except the first'.

Regards,
Buster.

Buster, Aug 19, 2003

3. ### Allan BruceGuest

I use a pointer to an array of pointers to an array of <type>, like this

int **array;

array = new int*[width];
for (int loop=0; loop<width; ++loop)
array[loop] = new int[height];

// do some things with it like
// array[3][4] = rand(); // or whatever

for (loop=0; loop<width; ++loop)
delete []array[loop];
delete [] array;

Allan

Allan Bruce, Aug 19, 2003
4. ### Mike WahlerGuest

Mike Wahler, Aug 19, 2003
5. ### AxterGuest

Here's a class that creates a 2 dimensional array very easily and
efficiently:

template < class T, int ROW_T = 0, int COL_T = 0 >

class dynamic_2d_array

{

public:

dynamic_2d_array(int row, int col):m_row(row),m_col(col),
m_data((row!=0&&col!=0)?new T[row*col]:NULL){}

dynamic_2d_array():m_row(ROW_T),m_col(COL_T), m_data(new
T[ROW_T*COL_T])

{if (!COL_T || !ROW_T) {int x[ROW_T] = {{ROW_T}};int y[COL_T] =
{{x[0]}};}}

~dynamic_2d_array(){if(m_data) delete []m_data;}

T* operator[](int i) {return (m_data + (m_col*i));}

T const*const operator[](int i) const {return (m_data + (m_col*i));}

private:

const int m_row;

const int m_col;

T* m_data;

};

The above class can be delcare and used in the following maner:

dynamic_2d_array < char > My_dynamic_2d_array(3, 20);

My_dynamic_2d_array[2][11] = 99;

cout << My_dynamic_2d_array[2][11] << endl;

You can also use a vector<vector<char> > type object.

http://axter.com/faq/topic.asp?TOPIC_ID=60&FORUM_ID=4&CAT_ID=9&Topi-
c_Title=How+to+create+dynamic+two%2Ddimensional+arrays&Forum_Title=-
C%2FC%2B%2B

Also check out the multidimensional class in the following link:

http://axter.com/faq/topic.asp?TOPIC_ID=61&FORUM_ID=4&CAT_ID=9&Topic-
_Title=How+to+create+dynamic+Multi%2Ddimensional+arrays&Forum_Title=-
C%2FC%2B%2B

Axter, Aug 19, 2003