Variable changing for unknown reason

Question

I have these two methods called one after another;

m_Fence.Initialise(7);
m_Fence.CreateSquareFence();    

Here's each of their details;

void CFence::Initialise(int size)
{
    m_square_size = size;
}

void CFence::CreateSquareFence()
{
    int l_Vector_Pos = 0;

    //Set initial vector at origin and start of first fence
    CVector3f l_Fence_Position = CVector3f(0.0f,0.0f,0.0f);

    int l_side = 0; // Makes sure only 4 sides get created
    std::string bools[4] = {"plus_z", "plus_x", "minus_z", "minus_x"};
        //Draw 1st fence on 0 x-axis
        while(l_side < 4)
            {
                for(int i=0 ; i<=m_square_size ; i++)
                    {                   
                    //Find which direction it's going and set Fence position and add to vector
                    if(bools[l_side] == "plus_z" &&  i>0)
                        l_Fence_Position += CVector3f(0.0,0.0,beamLength);
                    else if(bools[l_side] == "plus_x" && i>0)
                        l_Fence_Position += CVector3f(beamLength,0.0,0.0);
                    else if(bools[l_side] == "minus_z" && i>0)
                        l_Fence_Position += CVector3f(0.0,0.0,-beamLength);
                    else if(bools[l_side] == "minus_x" && i>0)
                        l_Fence_Position += CVector3f(-beamLength,0.0,0.0);

                    fences[l_Vector_Pos].setPosition(l_Fence_Position);
                    l_Vector_Pos++;

                    //Increase this int to let it know what side we're creating
                    if(i == m_square_size) 
                        {
                            l_side++;
                    }
                }
            }
}

I pass the 7 through and it initially changes the m_square_size variable to 7 but when I call the CreateSquareFence method it ends up becoming 0 and I'm struggling to see why.

Answer 1

Turning my comment into an answer

Make sure fences is big enough so that you don't reach out of bounds and trump neighbouring mnemory (more generally, invoke Undefined Behaviour).

---

On a side note, that code seems way too complex. You could simplify it like this:

void CFence::CreateSquareFence()
{
  int l_Vector_Pos = 0;

  //Set initial vector at origin and start of first fence
  CVector3f l_Fence_Position = CVector3f(0.0f, 0.0f, 0.0f);

  CVector3f offsets[4] = {
    CVector3f(0.0, 0.0, beamLength),
    CVector3f(beamLength, 0.0, 0.0),
    CVector3f(0.0, 0.0, -beamLength),
    CVector3f(-beamLength, 0.0, 0.0)
  };
  for (int l_side = 0; l_side < 4; ++l_side) {
    for (int i = 0; i <= m_square_size; ++i) {
      if (i>0)
        l_Fence_Position += offsets[l_side];
      fences[l_Vector_Pos].setPosition(l_Fence_Position);
      ++l_Vector_Pos;
    }
  }
}