c++ - strange problem with polymorphism - cellular automaton

Question

Hello, I am making "game of life" implementation that, when cell has:

• two live neighbours I make object of class CCellB
  
• two live neighbours I make object of class CCellA
  
• when has >3 or <2 I make object of class CCellX (dead)
  

Class CCell is base of CCellA, CCellB, CCellX arr is previous state of game, temp will be new arr at the end. My problem is: That works fine, until I change new CCell(); to new CCellB();:

CCell ***temp = allocateArray();

for(int i = 0; i < n; i++)
{
    for(int j = 0; j < m; j++)
    {
        nAmount = arr[i][j]->countAliveNeighbor();

        if(nAmount == 3)
        {      
            temp[i][j] = new CCellA();
            temp[i][j]->alive = 1;

        }else if(nAmount == 2)
        {                     
            temp[i][j] = new CCell(); // HERE, WHEN I CHANGE IT TO CCELLB IT DON'T WORKS
            temp[i][j]->alive = arr[i][j]->alive;

        }else if((nAmount >= 4)||(nAmount < 2))
        {                     
            temp[i][j] = new CCellX();
        }   
    }
}

Then it seems don't work properly... Seems like neighbours are not count properly, Cell with 4,5 neighbours still alive alive var is member of base class - CCell, all is public, please help!

Answer 1

Replace your CCell ***temp with std::vector<boost::shared_ptr<CCell>> or std::vector<std::tr1::shared_ptr<CCell>> (for VS2008 or VS2010) and I think you will find your mistakes.

Answer 2

Why would you create a new object for every Cell in Conway's Game of Life? It wil lconsume massive amounts of memory and time, even if you carefully delete every object after each iteration.

Better search about better algorithms for it, like Hashlife.

Answer 3

I'll skip over the design issues (the use of new here does seem like it would cause a lot of avoidable churn )

Is your countAliveNeighbor function unique for CCell vs CCellA, B, etc? If so it should be virtual. If it isn't, when you assign a CCellB object to a CCell pointer, the code will execute CCell.countAliveNeighbor insted of your intended CCellB function.