What is wrong with this sort function? (linked list)

the list stores a group of terms in a polynomial

Code:

struct term
{
  int co;    //coefficient of a term
  int exp;  //exponent of a term
  term* link;
};

typedef term* termptr;

class Polynomial
{
  public:
    void sort();
    friend istream& operator >> (istream& ins, Polynomial& p1);
    //other random stuff you don't need to know for this
  private:
    termptr head;
};

I'm trying to sort them once they've been inputted in order of exponent from greatest to least. here's what my sort function looks like:

Code:

void Polynomial::sort()
{
  termptr cursor, current, prev;
  int largest = 0;

  current = head;
  cursor =  current->link;
  prev = current;
  for (termptr ptr = head; ptr != NULL; ptr = ptr->link)
  {
    largest = current->exp;
    while (cursor)
    {
      if (cursor->exp > largest)
      {
        largest = cursor->exp;
        prev->link = cursor->link;
        ptr = cursor;
        current = cursor;
        cursor = prev;
        cursor = cursor->link;
      }else
      {
        prev = prev->link;
        cursor = cursor->link;
      }
    }
    current = current->link
    prev = current
    cursor = current->link;
  }
}

istream& operator >> (istream& ins, Polynomial& p1)
{
   char x;
   string line;
   termptr new_term, current;

  new_term = new term;
  new_term->link = NULL;
  p1.set_head(new_term);
  current = new_term;

  getline(ins, line);

  if (ins)
  {
    line.erase(remove(line.begin(), line.end(), ' '), line.end());
    stringstream ss(line);

    while (ss>>current->co >> x >> current->exp)
    {
      new_term = new term;
      new_term->link = NULL;
      current->link = new_term;
      current = current->link;
    }
  }
  current->link = NULL;
  return ins;
}

//here's my application file

int main()
{
  Polynomial poly1;

  cout << "Enter a polynomial: ";
  cin >> poly1;
  cout << endl;
  poly1.sort();

  cout << poly1 << endl;

  return 0;
}

it compiles fine, but when I try to call it in my application file I get a segmentation fault and I can't figure out why

Well, let's see. The last time you dereferenced a null pointer, so I'll go with that. Like I said before, when you typedef away the pointer notation, it obscures when you are doing that.

I'd love to try and compile this, but I'd prefer to have a bit more code, such as Polynomial::set_head and Polynomial::operator<<.

edit: Some sample input would be nice, too.