Question

I am somehow aware of returning by reference by this got me confused.

I have a function which returns a reference to a public field of class BoardNode, std::vector<BoardNode> _neighboursVector.

I also have a class Board which holds a std::vector<BoardNode>.

my member function goes like this:

const std::vector<BoardNode>& 
Board::getNeighboursVector(unsigned int x, unsigned int y) const
{
    BoardNode node = this->getBoardNode(x, y);
    //...
    node._neighboursVector.push_back(...);
    //...
    return node._neighboursVector;
}

While debugging on return line I get the correct values in the vector but outside of this function I get empty vector. Why ?

std::vector<BoardNode> v = b.getNeighboursVector(5,5);

EDIT

getBoardNode definitions

const BoardNode & Board::getBoardNode(unsigned int rowIdx, unsigned int colIdx) const
{
//...
}

BoardNode & Board::getBoardNode(unsigned int rowIdx, unsigned int colIdx)
{
//...
}

Answer 1

node is a local object. And by extension, node._neighborsVector is also a local object. As a local object, it gets destroyed at the end of the function. So you are returning a reference to a destroyed object. That’s undefined behavior.