Question

I have a written a C program to find the k nearest neighbors of all the points in a given set of points (randomly generated). The problem is when I increase the number of points(and consequently the array size) to 10000 the program gives segment violation error as soon as I call the function to find out the nearest neighbors. I am not able to get inside the function using the debugger. As soon as I do a “Step Into” the program crashes.

I have used code-blocks and Eclipse CDT (on Windows 7) and both give the error at the same point. In case of code-blocks it gives segment violation and in case of Eclipse it first shows – “No source available for __chkstk_ms() at 0x4039a7” and then the error comes from the OS itself – “KNN.exe has stopped working”
However the program runs fine on Linux(Ubuntu 32bit).

Here is the code snippet :

#define MAX_SIZE 10000

    int main()
    {
        int n = MAX_SIZE;
        int k = 3;
        int i;


        double points[MAX_SIZE*2];  //2-D array in row-major order
        double result[MAX_SIZE*3*2];

        srand(time(NULL));

        for(i=0; i < n; i++)
        {
            points[i*2] = (double)rand()/(double)RAND_MAX;
            points[i*2 + 1] = (double)rand()/(double)RAND_MAX;
        }


        seek(points,n,k,result);   //<---------- ERROR

        seek(points,n,k,result);   //<------------ NO ERROR 
   ....
  }

 void seek(const double * const points, int n, int k, double *result)
 {

  TreeNode qtree[MAX_SIZE];
  int order_array[MAX_SIZE];

  int num_nodes = build_quadtree(a, n, k, qtree,order_array);   
  ......
  }

struct tree_node
{
int id;
int num_points;
int start_order;
int end_order;
int parent;
int child[4];
struct rectangle rect;
enum boolean is_leaf;
};

struct point
{
double x;
double y;
};

struct rectangle
{
int id;
double xmin,xmax,ymin, ymax;
struct point midpt;
};

What is more confusing is that I have another function with the same arguments which is running without any problem.
Please provide suggestions on how to debug this.

EDIT:- . I have posted the first few lines of seek() function. As the replies have pointed out I am actually allocating a lot of memory on the seek function but I am wondering why it is not a problem in linux.

Answer 1

I think you’re exceeding your available stack (see the MSDN docs on _chkstk). Try allocating the arrays dynamically instead

int main()
{
    double* points = malloc(sizeof(double) * MAX_SIZE*2];
    double* result = malloc(sizeof(double) * MAX_SIZE*3*2];
    ...
    free(points);
    free(result);
}

The stack overflow is happening when you call seek. You haven’t posted code for it but may have to rework it also to reduce its stack use.