How to detect an infinite loop in a recursive call?

Question

I have a function that is recursively calling itself, and i want to detect and terminate if goes into an infinite loop, i.e - getting called for the same problem again. What is the easiest way to do that?

EDIT: This is the function, and it will get called recursively with different values of x and y. i want to terminate if in a recursive call, the value of the pair (x,y) is repeated.

int fromPos(int [] arr, int x, int y)

Answer 1

One way is to pass a depth variable from one call to the next, incrementing it each time your function calls itself. Check that depth doesn't grow larger than some particular threshold. Example:

int fromPos(int [] arr, int x, int y)
{
    return fromPos(arr, x, y, 0);
}

int fromPos(int [] arr, int x, int y, int depth)
{
    assert(depth < 10000);

    // Do stuff

    if (condition)
        return fromPos(arr, x+1, y+1, depth + 1);
    else
        return 0;
}