multi dimensional vectors

Hi i was wondering if it was possible to set a specific value in a vector. ill explain what i mean in arrays, if you could please show me the vector equivelent.

first i declare my multidimensional array / vector

Tile tiles[50][50]; OR vector<vector<Tile> > tiles;

next i have a loop to loop thru each element and initialise it.

array version:

Code:

---

          for(int j = 0; j < mapHeight; j++){
              for(int i = 0; i < mapWidth; i++){
                  tiles[i][j].init();
              }
          }

---

how would i perform this action on a multidimensional vector. baring in mind that i need to set that specific x/y value.

i tried the above with vectors but it doesnt seam to work.

any help will be great as i cant find much on vectors containing objects on the internet.

rob

The for loop is the exact same assuming mapHeight and mapWidth are correct.

The problem might be in your constructor. Tile tiles[50][50]; is NOT the same as vector<vector<Tile> > tiles; because the vector constructor you are using creates an empty vector. If you aren't using push_back to add inner vectors, you are probably not getting the results you want.

There are many ways to solve this, but here is the equivalent of a 50 x 50 2-D vector of default constructed Tiles:

Code:

---

vector<vector<Tile> > tiles(50, vector<Tile>(50));

---

I have given an example to do what you want. In my comments below, I repeatedly ask, "Why not just call init() inside the Tile constructor?" That really is the best solution, but I show how to iterate over each element anyway using standard algorithms.

You might also consider writing a data structure to hold your vector< vector<Tile> >, so that you can make add, remove, etc. easier.

Code:

---

# include <vector>
# include <iostream>
# include <algorithm>
using namespace std;

class Tile {
    public:
    Tile() {
        // Why not call init here??
        init();
    }
    void init()
    {
        cout << "Init called!" << endl;
    }
};

void init_tile(Tile& t)

{
    /* Why not do it in the Tile constructor? */
    t.init();
}

void init_row(vector<Tile>& row)

{
    for_each(row.begin(), row.end(), init_tile);
}

int main()

{
    vector< vector<Tile> > tiles;

    /* Add some rows */
    tiles.push_back(vector<Tile>());
    tiles.push_back(vector<Tile>());
    tiles.push_back(vector<Tile>());

    /* Add some tiles */

    tiles.at(0).push_back(Tile());
    tiles.at(1).push_back(Tile());
    tiles.at(0).push_back(Tile());
    tiles.at(2).push_back(Tile());

    /* Initialize here, if for some reason you can't just
        do it in the constructor... */
    for_each(tiles.begin(), tiles.end(), init_row);
}

---

daveds method worked, thanks a lot! the reason i dont call init in the constructor is because i want to check whats returned.

cheers for all ur help

rob

Code:

---

for(int j = 0; j < mapHeight; j++){
              for(int i = 0; i < mapWidth; i++){
                  tiles[i][j].init();
              }
          }

---

Code:

---

unsigned long maxoffset=(mapHeight*mapWidth);

for (int i=0;i<maxoffset;i++)
{
  Tiles[i].init();
}

---

My advice. Don't use 2D vectors.