Question

I want to create a class which has several pointers to other instances of this class. I want to create game of life where I can set the neighbour cells.

The problem that I have is that I can’t assign a reference to my const pointer member variables.

class Cell {

            ...
        const Cell* left;
            ...

        void setLeft(const Cell & left) {
        this->left = left;
    }
}

I had the idea to save all cells in a vector something like this

std::vector<Cell::Cell> cells;

and then access and set them like this cells[pos].setLeft(cells[left]);(pos and left would be integers)

I get the following error msg. Can't convert const cell to const cell* in assignment.
Also it can’t find the method setLeft

I come from a java/net background so maybe I just made a huge mistake.

Answer 1

You’re mixing up pointers and references (which is understandable when you’re comming from java/net). In C++, there is a clear distinction between:

1. Cell x;, an object (instance) of class Cell
2. Cell *x;, a pointer to an instance of Cell
3. Cell &x;, a reference (“another name”) to an instance of Cell

Java “references” are equivalent to C++ pointers.

In your case, there are several issues. First, setLeft() needs to get the address of its argument, like this:

void setLeft(const Cell & left) {
  this->left = &left;
}

Second, unless the class Cell is defined in a namespace Cell, the vector would have to be typed just std::vector<Cell> cells;.

However, even more dangerous is the fact that your vector contains statically allocated Cell objects (its template argument is a class type, not a pointer). std::vector is allowed to move objects around in memory when it’s added to, so once this happens, all existing pointers to objects stored in cells will become dangling. What you should do is store pointers in the vector instead:

std::vector<Cell*> cells;
cells[pos]->setLeft(*cells[left]); //assuming setLeft() still takes a reference

It might actually be even better to use smart pointers (std::shared_ptr and std::weak_ptr) instead of raw pointers, but that’s a separate topic.