Thread: code problem

I am trying to do insertion sort with list (ADT), I wrote the function InsertionSortList in the sort.c file:

Code:

void
InsertionSortList(List L)
{
  Position P1, P2;
  ElementType temp;
  for(P1 = L; P1->Next != NULL; P1 = P1->Next)  //problem
    {
      temp = P1->Element; //problem
      for(P2 = P1; (P2->Last != NULL) && (P2->Last->Element < P2->Element); P2 = P2->Last) //problem
	P2->Element = P2->Last->Element; //problem
    }
}

while i am compling my programme, the gcc complier said:
dereferencing pointer to incomplete type
these problems happend at the lines which I indicate in the function

How can I deal with it? Thx a lot!