Confused about references and pointers in my BFS tile class

Question

I am currently coding a Tile class to be used in my BFS algorithm. I need a cameFrom variable that will keep track of where the tiles came from as I traverse a grid. It should not be initialized at the start as we do not know where it came from at the start. As I run through my BFS algorithm, it will continuously update.

Error 1 error C2758: 'Tile::cameFrom' : a member of reference type must be initialized

Anyone know what is wrong?

Here is my Tile.hpp:

#ifndef _TILE_H
#define _TILE_H

class Tile
{
    public:

        Tile(int x, int y);

        ~Tile();

        int GetX();

        int GetY();

        bool IsWall();

        bool IsVisited();

        void SetCameFrom(Tile& cameFrom);

        Tile& GetCameFrom();

        void ToggleWall();

        void ToggleVisited();

    private:

        int x;
        int y;
        bool isWall;
        bool isVisited;
        Tile& cameFrom;

};

#endif

My Tile.cpp:

#include "Tile.hpp"


Tile::Tile(int x, int y) {

    this->x = x;
    this->y = y;
    this->isWall = false;
    this->isVisited = false;

}

Tile::~Tile() {}

int Tile::GetX() {

    return x;

}

int Tile::GetY() {

    return y;

}

bool Tile::IsWall() {

    return isWall;

}

bool Tile::IsVisited() {

    return isVisited;

}

void Tile::SetCameFrom(Tile& cameFrom) {

    this->cameFrom = cameFrom;

}

Tile& Tile::GetCameFrom() {

    return cameFrom;

}

void Tile::ToggleWall() {

    isWall = !isWall;

}

void Tile::ToggleVisited() {

    isVisited = true;

}

Answer 1

Firstly reference must be initialized, so you would have to set it in the constructor. Secondly you can't re-assign reference, so your SetCameFrom function won't work. Use pointers for this.

Tile * cameFrom;

But it's also good to initialize pointer to 0 (or nullptr in C++11) in the constructor.

Tile::Tile(int p_x, int p_y):
    x(p_x), 
    y(p_y),
    cameFrom(0),
    isWall(false),
    isVisited(false)
{
}