I think I have a memory leak? - c++

Question

I am trying to do the Knight's Tour using dynamic arrays because the user will be able to implement their own board size, and where they want to start the knight at in the board.
However, before I changed everything to dynamic arrays, I was able to perform my code just find using static arrays, but now that I switched to dynamic arrays whenever my code executes, I get a memory leak I believe and the program crashes. I was wondering if my deconstructor is not working properly? Or if there is a different way I have to delete the dynamic array?
I am also wondering if there is a way to make this code a little more efficient, more exactly make the Move() function a little more efficient. Thanks.
#include <iostream>
#include <iomanip>
#include "stdafx.h"
using namespace std;
class Knight
{
private:
int Tracker = 1;
int BoardSize;
int **Board = new int*[BoardSize];
public:
Knight(int s)
{
BoardSize = s;
for (int i = 0; i <= s -1; i++)
{
Board[i] = new int[s];
}
for (int i = 0; i <= s - 1; i++)
{
for (int j = 0; j <= s - 1; j++)
{
Board[i][j] = 0;
}
}
}
~Knight()
{
for (int i = 0; i <= BoardSize - 1; i++)
{
delete[] Board[i];
}
delete[] Board;
}
void MarkUp(int &val)
{
val = Tracker;
Tracker++;
}
void MarkDown(int &val)
{
val = 0;
Tracker--;
}
bool PossibleMove(int &val)
{
if (val == 0)
return 1;
else
return 0;
}
void Display()
{
for (int k = 0; k < (BoardSize * 5) + 1; k++)
{
cout << "-";
}
cout << endl;
for (int i = 0; i <= BoardSize - 1; i++)
{
cout << "| ";
for (int j = 0; j <= BoardSize - 1; j++)
{
cout << setw(2) << setfill('0') << Board[i][j] << " | ";
}
cout << endl;
for (int k = 0; k < (BoardSize * 5) + 1; k++)
{
cout << "-";
}
cout << endl;
}
cout << endl << endl;
}
bool Move(int x, int y)
{
if (Tracker > (BoardSize * BoardSize))
{
return true;
}
if (PossibleMove(Board[x][y])) {
if ((x - 2 >= 0) && (y + 1 <= (BoardSize - 1)))
{
MarkUp(Board[x][y]);
if (Move(x - 2, y + 1))
{
return true;
}
else
{
MarkDown(Board[x][y]);
}
}
if ((x - 2 >= 0) && (y - 1 >= 0))
{
MarkUp(Board[x][y]);
if (Move(x - 2, y - 1))
{
return true;
}
else
{
MarkDown(Board[x][y]);
}
}
if ((x - 1 >= 0) && (y + 2 <= (BoardSize - 1)))
{
MarkUp(Board[x][y]);
if (Move(x - 1, y + 2))
{
return true;
}
else
{
MarkDown(Board[x][y]);
}
}
if ((x - 1 >= 0) && (y - 2 >= 0))
{
MarkUp(Board[x][y]);
if (Move(x - 1, y - 2))
{
return true;
}
else
{
MarkDown(Board[x][y]);
}
}
if ((x + 2 <= (BoardSize - 1)) && (y + 1 <= (BoardSize - 1)))
{
MarkUp(Board[x][y]);
if (Move(x + 2, y + 1))
{
return true;
}
else
{
MarkDown(Board[x][y]);
}
}
if ((x + 2 <= (BoardSize - 1)) && (y - 1 >= 0))
{
MarkUp(Board[x][y]);
if (Move(x + 2, y - 1))
{
return true;
}
else
{
MarkDown(Board[x][y]);
}
}
if ((x + 1 <= (BoardSize - 1)) && (y + 2 <= (BoardSize - 1)))
{
MarkUp(Board[x][y]);
if (Move(x + 1, y + 2))
{
return true;
}
else
{
MarkDown(Board[x][y]);
}
}
if ((x + 1 <= (BoardSize - 1)) && (y - 2 >= 0))
{
MarkUp(Board[x][y]);
if (Move(x + 1, y - 2))
{
return true;
}
else
{
MarkDown(Board[x][y]);
}
}
}
return false;
}
};
int main()
{
int size = 0;
int Row, Col;
int opt = 0;
do
{
cout << "Welcome to Knights Tour!" << endl;
cout << "1) Start the Tour." << endl;
cout << "2) Quit." << endl;
cin >> opt;
switch (opt)
{
case 1:
{
cout << "Enter board size:" << endl;
cin >> size;
Knight K1(size);
cout << "Enter Row:" << endl;
cin >> Row;
cout << "Enter Column: " << endl;
cin >> Col;
if (K1.Move(Row, Col))
{
cout << "\nOperation was Successful." << endl;
cout << "Possible Solution:" << endl;
K1.Display();
}
else
{
cout << "\nThat is not Possible." << endl;
}
cout << endl;
break;
}
case 2:
{
exit(0);
break;
}
default:
{
cout << "Not a Valid Option." << endl;
cout << "Try Again Please." << endl;
cout << endl;
break;
}
}
} while (opt != 2);
return 0;
}

Answer 1

This code does not work as you think it does:
int BoardSize;
int **Board = new int*[BoardSize];
The value of BoardSize is going to be whatever happens to be in the memory that gets allocated for it, so the new is going to try to allocate an unknowable size array.
Don't use hand coded dynamic arrays for this. Use std::vector; That's what it's for. In real life production code, you should almost never ever use dynamically allocated arrays. You'll use one of the standard containers.

Answer 2

As noted in the comments by multiple people, memory leaks do not cause crashes (generally).
The issue is that inside the constructor you assign values to the Board array elements. However, you never allocate memory for the Board array itself. I.e. when you do Board[i] = new int[s];, Board points to some random address. This is because the line int **Board = new int*[BoardSize]; is not executed before the constructor starts.
So the following should work:
class Knight {
private:
int BoardSize;
int **Board;
public:
Knight (int s) {
BoardSize = s;
Board = new int*[BoardSize];
// Remainder of code
}
};
However, I really suggest you use std::vector for this instead. Then you won't have to deal with memory (de)allocation at all. That could look as concise as the following:
#include <vector>
class Knight {
private:
int BoardSize;
std::vector<std::vector<int>> Board;
public:
Knight (int s) : BoardSize(s), Board(s, std::vector<int>(s, 0)) { }
};
Note that I initialized the class members directory in the member initializer list.