In Unity, why does my IndexOutOfRange exception disappear when trying to debug it?

Question

I don't get errors when playing from Unity "Game" tab. But when I build an executable (development or not) it stucks. I get "IndexOutOfRange" exception. Which also magically disappears (yes) when I add some debug lines:

This does not work:

for (int i = x1; i <= x2; i++)
for (int j = y1; j <= y2; j++)
{
    int a, b;
    a = 7 + i; // Out of range
    b = 7 + j; // Out of range

    submap[a, b] = world.WalkableMap[(int)CurrentWalkableTile.x + i, (int)CurrentWalkableTile.y + j];
}

This works:

for (int i = x1; i <= x2; i++)
for (int j = y1; j <= y2; j++)
{
    int a, b;
    a = 7 + i;
    b = 7 + j;

    if (a < 0 || a > 15) // now with this never gets out of range
        Debug.Log("A out of range: " + a);

    if (b < 0 || b > 15) // now with this never gets out of range
        Debug.Log("B out of range: " + b);

    submap[a, b] = world.WalkableMap[(int)CurrentWalkableTile.x + i, (int)CurrentWalkableTile.y + j];
}

I can't find any sense. The exception literally hides from me

Additional info maybe is useful:

x1 = (CurrentWalkableTile.x - 7) >= 0 ? -7 : -(int)CurrentWalkableTile.x;
x2 = (CurrentWalkableTile.x + 7) < world.wmap_x_size ? 7 : (world.wmap_x_size - (int)CurrentWalkableTile.x - 1);

y1 = (CurrentWalkableTile.y - 7) >= 0 ? -7 : -(int)CurrentWalkableTile.y;
y2 = (CurrentWalkableTile.y + 7) < world.wmap_y_size ? 7 : (world.wmap_y_size - (int)CurrentWalkableTile.y - 1);

I'd like to post more information, but I can't even debug to find the problem.

Answer 1

if (a < 0 || a > 15) // now with this never gets out of range
            Debug.Log("A out of range: " + a);

if (b < 0 || b > 15) // now with this never gets out of range
            Debug.Log("B out of range: " + b);

submap is bool[15,15] (according to comments)

then that should be

if (b < 0 || b >= 15)

or

if (b < 0 || b > 14)

index 15 would be already outside of bounds (size 15, indizes 0 - 14)

Since you couldn't trace your bug with the current if statement this leads to the conclusion your invalid index causing the exception is 15 and not a negative index.

---

Since part one didn't find the problem the next chance is to not check the submap[a][b] array but the world.WalkableMap[] array.

Just do the same as with a b.

int c = (int)CurrentWalkableTile.x + i;
int d = (int)CurrentWalkableTile.y + j;

if (c < 0 || c >= world.WalkableMap.length) Debug.Log("C out of range: " + c); 

if (d < 0 || d >= world.WalkableMap[0].length) Debug.Log("d out of range: " + d);

Because you are using two arrays but so far you haven't excluded one causing the IndexOutOfBoundsException.