2d array using pointers

[~Kyo~]

The problem is that I need a 2d matrix for a map which is defined in a config file. The map is not a set height or width so I need to have the ability to either make the map any size between 1x1 to 1000x1000. Is there some way to get around this or do I do what all the other games do and use a few sets of numbers for map sizes like 256x256 128x512 etc?

int **grid;
.
.
.
load>>x>>y>>input;	//get dimentions of the map
grid = new int[x][y];
.
.
.

errors:

  error C2540: non-constant expression as array bound

  '=' : cannot convert from 'int (*)[1]' to 'int ** '
  Types pointed to are unrelated; conversion requires reinterpret_cast, C-style cast or function-style cast

[kuphryn]

Correct. Dynamic memory allocation is one solution.

int **p = new int*[x];

You need to dynamically allocate memory for each element in the first dimension.

Kuphryn

[~Kyo~]

then what about the y dimention?

int **p = new int*[x];
//something here for y?

[Zach L.]

Use a loop:

int** p = new int*[x];
for(int i = 0; i != x; ++i)
   p[i] = new int[y];

Delete[] with a similar loop.

[~Kyo~]

Alright thnx.

[Daved]

Or... you could just use a vector of vectors which allows non-constant values on initialization:

std::vector<std::vector<int> > grid(x, std::vector<int>(y));

With vector you also don't have to remember to delete the memory when you are done with it.

[Zach L.]

And Daved's solution really is the prefered one.

If you do decide to use standard arrays, I really recommend encapsulating your functionality in a class, so that all initialization and cleanup is automatic.

Cheers

[~Kyo~]

O it is in a class was just a little confused about the ** thing this is just for loading anyways so I got my constructor doing grid = NULL since in my desructor I assumed that the best way to destruct this is by the following code:

Map::~Map()
{	if(tilesetpath)delete tilesetpath;
	if(grid)
	{
		for(int i = 0;i < y;i++)
		{
			delete grid[i];
		}
		delete grid*[x];
	}
 	if(npclist)delete npclist;
}

[Daved]

There is no need to check something against null before deleting it. You also need to use delete [] to delete arrays. The proper syntax of the destructor would be:

delete tilesetpath;
if(grid)
{
	for(int i = 0;i < x;i++)
	{
		delete [] grid[i];
	}
	delete [] grid;
}
delete npclist;

Also not that you should loop until x, not y, since x is the number of rows.

[~Kyo~]

It's microsoft vs.net it gets mad if I try to delete a NULL array so I gotta check it for whatever reason it's gay and they should change it even though the standard says you don't need to....

[Zach L.]

That rather surprises me. Is it perhaps a odd setting somewhere in VS.NET... I'd expect it to comply with the standard in this regard.

[Daved]

I didn't mean the two dimensional array, I meant the other things.

[~Kyo~]

Hey it's microsoft why do they need to adhear to a standard that wasn't written 100% by them? But anyways I check it just to make sure.

[~Kyo~]

I didn't mean the two dimensional array, I meant the other things.

so

Map::~Map()
{	if(tilesetpath)delete tilesetpath[];
	if(grid)
	{
		for(int i = 0;i < y;i++)
		{
			delete grid[i];
		}
		delete grid*[x];
	}
 	if(npclist)delete npclist[];
}

??

[Zach L.]

Use Daved's code for the destructor.