Pointer is not being passed during a linked list swap

Question

This will most likely seem like I am missing something obvious but when I try to pass a Linked List pointer to my Selection sort I get a NULL pointer problem. In my C code I have this as my linked list:

typedef struct iorb
{
    int base_pri;
    struct iorb *link;
    char filler[100];
} IORB;

Then I pass my new linked list into this function after creating it:

void swapNodes(POINTER *head, POINTER CurrentHead, POINTER CurrentMinimum, POINTER TempSwap);

POINTER SortList(POINTER *head, char *SortMethod[])
{
    POINTER TempHead = *head;

    //Only one node, no need to sort.
    if (TempHead->link == NULL)
    {
        return head;
    }

    //Store node with the new minimum value.
    POINTER TempMin = *head;

    //Store curent node for swapping
    POINTER TempSwap = *head;

    //Transverse the list.
    POINTER TempCurrent;
    for (TempCurrent = *head; TempCurrent->link != NULL; TempCurrent = TempCurrent->link)
    {
        //Check if this node has a lower priority than the current minimum and if so, swap them.
        if (TempCurrent->link->base_pri < TempMin->base_pri)
        {
            TempMin = TempCurrent->link;
            TempSwap = TempCurrent;
        }
    }

    //Swap nodes if the head is not the same as the minimum.
    if (TempMin != TempHead)
    {
        swapNodes(&TempHead, TempHead, TempMin, TempSwap);
    }   

    //Recursively sort the rest of the list.

    //FOR SOME REASON THE NODE POINTER IS NOT BEING PASSED HERE (EMPTY)
    TempHead->link = SortList(TempHead->link, *SortMethod);

    return head;

}

void swapNodes(POINTER *head, POINTER CurrentHead, POINTER CurrentMinimum, POINTER TempSwap)
{
    //Set new head as the minimum.
    *head = CurrentMinimum;

    //Link the current temp swap to the head.
    TempSwap->link = CurrentHead;

    //Swap pointers.
    POINTER temp = CurrentMinimum->link;
    CurrentMinimum->link = CurrentHead->link;
    CurrentHead->link = temp;
}

I am not sure why it is isn't being passed back into the same function, when I debug the linked list seems okay. I suspect that I am missing something in the swap node function, but I don't quite understand what this is. Can someone please offer some insight as to how this code should go for swapping the nodes around?

If you need additional information please let me know.

Answer 1

SortList(TempHead->link, *SortMethod); needs to be listed as SortList(&TempHead, *SortMethod);

To correctly pass the pointer.