C语言中使用递归的“填充函数”

Question

I'm working on a simple drawing application, i need to create a "fill" function where the user will enter x,y values, the function should assume 4 connected neighbors, I tried to use recursion to do that but the program suddenly stops. here is my function code :

---

void fill(int x, int y, struct pixels* screen)

{

int xx, yy, x1, y1;


    for (xx = -1; xx <= 1; xx++)
    {
        for (yy = -1; yy <= 1; yy++)
        {

            x1 = x + xx;
            y1 = y + yy;

            if ((x1 >= 0) && (x1 < screen->width))
            {
                if ((y1 >= 0) && (y1 < screen->height))
                {
                    if (screen->pixel[x1][y1] = '.')
                    {
                        screen->pixel[x1][y1] = '*';
                        fill(x1, y1, screen);
                    }
                }

            }
        }
    }
}

here's an image of how it should work when the user enters "fill 6 20"

Answer 1

The problem with your recursive approach is that larger images tend to cause stack overflow, because the highest number of recursive invocations is controlled by the size of the larges "frontier" to be filled.

One approach that could save you from stack overflow would be using a dynamically allocated queue of items. Each queue element would store an {X, Y} pair of coordinates. Initially you would put x , y passed into your function on the queue, and start the loop that goes on until the queue is empty.

Each time you extract the first element of the queue it becomes your current x , y . Then you do your two nested loops the same way, except that rather than calling fill(x1, y1, screen); you add {x1, y1} to the end of the queue.