assigning 2d array to type **arr doesn't work

I have a program that uses 2 2d arrays, grid1 and grid2. I have a 'bool which' that tells me which grid to use. I would like to be able to use 1 grid name throughout the program (as opposed to grid1 and grid2).. Here's what I tried, but it doesn't appear to be working. Any insight?

Code:

---

enum cell {DEAD, ALIVE};

const int WIDTH = 100;
const int HEIGHT = 100;

cell grid1[WIDTH][HEIGHT];
cell grid2[WIDTH][HEIGHT];

int main {
  bool which = true;
  ...
  cell grid[WIDTH][HEIGHT];
  if (which) {
      grid = grid1;
  }
  else {
      grid = grid2;
  }
  ...
}

---

It compiles fine, but the assignment seems to never take place. I also tried cell **grid = grid1, but that doesn't work either. Any help?

Thanks!

-Sean

Either copy the array element by element, or declare "grid" as a pointer to a pointer. Note, if you do the second option, changing "grid" will actually be changin "grid1" or "grid2"

So that would be...

cell **grid = grid1;

Or something similar to that?

I tried the above with gcc 2.95.2 (required for this assignment, can't use 3.4 or whatever it is) and received the following error...

life.cpp:197: initialization to `cell **' from `cell (*)[100]'


Copying the array element by element isn't an option since the 2d array may become larger and time is somewhat critical to this project (updating the screen).

Thanks again

when you assign gridx to grid - do you want a copy of gridx to be created - or do you just want a pointer to gridx?

Code:

---

enum cell {DEAD, ALIVE};

const int WIDTH = 100;
const int HEIGHT = 100;

cell grid1[WIDTH][HEIGHT];
cell grid2[WIDTH][HEIGHT];

int main {
  bool which = true;
  ...
  cell (*p_grid)[WIDTH][HEIGHT];
  if (which) {
      p_grid = &grid1;
  }
  else {
      p_grid = &grid2;
  }
  ...
}

---

note that in this case no copy would be created - thus when you use p_grid it will change the original grid.
instead of pointer you could also use references

[edit]
also note that [] has higher precedence than *.
thus the parenthesis in (*p_grid)[][] is neccessairy

Thanks, that works perfectly. I appreciate the help!

I know this problem is already solved, but I would just like to point out that a static 2d array is still a pointer, not a pointer to a pointer.

Or even

Code:

---

  cell (*p_grid)[HEIGHT];
  if (which) {
      p_grid = grid1;
  }
  else {
      p_grid = grid2;
  }

---

Then you can just use p_grid[row][col] right off the bat without any further pointer notation.

Quote:

---

Originally Posted by Salem

Or even

Code:

---

  cell (*p_grid)[HEIGHT];
  if (which) {
      p_grid = grid1;
  }
  else {
      p_grid = grid2;
  }

---

Then you can just use p_grid[row][col] right off the bat without any further pointer notation.

---

That's even better, thanks salem :)