2d array using pointers

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?

Code:

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

---

errors:

Code:

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  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

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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

then what about the y dimention?

Code:

---

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

---

Use a loop:

Code:

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

---

Delete[] with a similar loop.

Alright thnx.

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

Code:

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

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

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

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:

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;
}

---

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:

Code:

---

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.

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....

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.

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

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.

Quote:

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Originally Posted by Daved

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

---

so

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[];
}

---

??

Use Daved's code for the destructor.

The if(tilesetpath) and if(npclist) are what are unnecessary, so I removed them from the code I posted. If VC++ causes you trouble with that, then you are doing something wrong. (BTW, VC++ 7.1 is one of the most standards-conformant compilers available.) Of course, I was assuming that tilesetpath and npclist were not arrays but regular pointers. If they are arrays you should put the [] in front of them instead of behind.

To delete an array, you put the [] between the delete and the array name. Since you have a two-dimensional array, each value in the outer array is another array to be deleted. That is why I used delete [] grid[i];. The name of the array is grid[i] and you put delete [] in front of it. The outer array must also be deleted, and the outer array is just grid, so that is why I used delete [] grid;.

The only other change I made was to loop from 0 to x, which as I said is because you have x rows (i.e. x inner arrays).

While vectors have their own learning curve, you don't have to do anything with them in the destructor, their data will be cleaned up automatically.

Yea I found a friend who was kind enough to go over all the pointer stuff with me. Thanks for all the help though.... vectors might be a better way to go but for now I want to learn pointers.