[SOLVED] Dynamic Multidimension array?

[Zeotronic]

C++: Recently, I have come to need (or at least think I do) to put a resizable multidimensional array into a class. Now I know that using vector arrays isn't a good way to do this... what would be a good way to do this?

[hod139]

C++: Recently, I have come to need (or at least think I do) to put a resizable multidimensional array into a class.

First step is to know what you need.

Now I know that using vector arrays isn't a good way to do this... what would be a good way to do this?

I would always suggest using STL vectors instead of C style arrays, so I don't know what you mean here. For an example:

template <typename T>
class Matrix{
  private:
     std::vector<std::vector<T> > multiArray;  
}; 

[Zeotronic]

I would always suggest using STL vectors instead of C style arrays, so I don't know what you mean here. For an example:

I've searched the subject rather thoroughly trying to solve my problem myself, and I'm pretty sure your example turns out like crap. Each array contained in an array (in your example) would have to be resized to the proper size to have a standard sized second dimension, would they not? And I need to work with up to 3 or 4 dimensions, so this approach simply would not do.

But that is... as I said... to my knowledge.

[hundredwatt]

C++: Recently, I have come to need (or at least think I do) to put a resizable multidimensional array into a class. Now I know that using vector arrays isn't a good way to do this... what would be a good way to do this?

Perhaps something like this:

//create 5x5 array
int** array = new int*[5];
int row1[5] = {1,2,3,4,5};
int row2[5] = {6,7,8,9,10};
...
array[0]= &row1[0];
array[1] = &row2[0];

cout << array[0][1]; //2
cout << array[1][2]; //8

//change to 6x6 array;
int** temp = array;
delete[] array;
array = new int*[6];
...//copy data

Does this help? With this model, its easy to make a 5 dimensional array where each branch is a different length. You can also generalizes this to more dimensions with int*** array or int**** array:

int*** array = new int**[5];
int** branch1 = new int*[5];
int branch1row1[5] = {1,2,3,4,5};
branch1[0] = &branch1row1[0];
array[0] = &branch1[0];
cout << array[0][0][2]; //3

[Wybiral]

How about a hashtable that takes some two-value X,Y object as keys? In this case, you could expand it indefinitely, and you can just assume some default value for all the keys that aren't set.

[escapee]

What are you doing that you think you need 3-4 dimensions for? If you let us know what it is that you're aiming for we can likely be of more help to you.

And the thing with vectors is that they resize themselves, you don't have to manage it. If you need another item, push it on.

[dwhitney67]

I've searched the subject rather thoroughly trying to solve my problem myself, and I'm pretty sure your example turns out like crap.

Ouch; tough remark to make to someone considering that person was trying to help you.

[dwhitney67]

The easiest solution when dealing with multidimensional arrays is to use the array type as defined in the boost libraries.

Here's an example:

#include <boost/array.hpp>
#include <iostream>

int main()
{
  typedef boost::array<int,    3> OneD;
  typedef boost::array<OneD,   3> TwoD;
  typedef boost::array<TwoD,   3> ThreeD;
  typedef boost::array<ThreeD, 3> FourD;

  FourD array4D;

  array4D[0][0][0][0] = 10;
  array4D[1][1][1][1] = 20;
  array4D[2][2][2][2] = 30;

  std::cout << "array4D[0][0][0][0] = " << array4D[0][0][0][0] << std::endl;
  std::cout << "array4D[1][1][1][1] = " << array4D[1][1][1][1] << std::endl;
  std::cout << "array4D[2][2][2][2] = " << array4D[2][2][2][2] << std::endl;

  return 0;
} 

[Zeotronic]

Ouch; tough remark to make to someone considering that person was trying to help you.

I'm sorry I'm so blunt.

But am I not correct in that, using so may vector arrays just to get a 3 dimensional array would incur vast amounts of waste? We're talking all the extra data required by a vector, multiplied by what?

What are you doing that you think you need 3-4 dimensions for?

As far as the 3 dimensions goes. I'm storing voxel information... I think I've taken the instance where I needed 4 dimensions out of my code.

How about a hashtable that takes some two-value X,Y object as keys?

I'm not familiar with hashtables.

Perhaps something like this:

I'll toy around with that, but wouldn't "int** temp = array;" merely point to what's contained by array, and then, of course, it would be deleted in the next line?

The easiest solution when dealing with multidimensional arrays is to use the array type as defined in the boost libraries.

Array handles multidimensional arrays? I thought only Multi_Array did!.. and I couldn't get that to work in a structure... this will work?

...Oh wait... I see. Wouldn't that be almost as bad as vector?

[Wybiral]

I'm not familiar with hashtables.

You can use std::map as the hashtable, and std:air for the keys of a 2-dimensional table.

#include <map>
#include <iostream>

typedef std::pair<int,int> vec2;

int main() {
	std::map<vec2, int> grid;
	grid[vec2(10, 10)] = 10;
	grid[vec2(10000, 10000)] = 7;
	std::cout << grid[vec2(10, 10)] << std::endl;
	std::cout << grid[vec2(10000, 10000)] << std::endl;
	return 0;
}

For larger dimensions you can just make your own key class or use something like boosts tuple.