c-hooks/linkedList.h

#define LINKED_LIST

struct listElement {
  void * data;
  struct listElement *next;
  struct listElement *previous;
};

typedef struct listElement LISTEL;

LISTEL * insertBefore(void *theData, LISTEL *place)
{
  LISTEL * element = malloc(sizeof(LISTEL));
  element->data = theData;
  if(place->previous == NULL)
    {
      element->next = place;
      place->previous = element;
    }
  else
    {
      LISTEL * previous = place->previous;
      previous->next = element;
      element->previous = previous;
      place->previous = place;
      element->next = place;
    }
  
  return element;
}

LISTEL * insertAfter(void *theData, LISTEL *place)
{
  LISTEL * element = malloc(sizeof(LISTEL));
  element->data = theData;
  if(place->next == NULL)
    {
      element->previous = place;
      place->next = element;
    }
  else
    {
      LISTEL * next = place->next;
      next->previous = element;
      element->next = next;
      place->next = element;
      element->previous = place;
    }
  return element;
}