// Link list compare functionint compareUsername(void* pUsername1, void* pUsername2){ int result = 0; char username1[1]; char username2[1]; strncpy(username1, ((USER*)pUsername1)->username, 1); strncpy(username2, ((USER*)pUsername2)->username, 1); if (*username1 < *username2) result = -1; else if (*username1 > *username2) result = 1; else result = 0; return result; //return 0;}/* ============================ addNode ======================================== Inserts data into list. Pre pList is pointer to valid list dataInPtr is pointer to insertion data Post data inserted or error Return -1 if overflow 0 if successful 1 if dupe key =============================================================================*/int addNode (LIST* pList, void* dataInPtr){ int found; int success; NODE* pPre; NODE* pLoc; found = _search(pList, &pPre, &pLoc, dataInPtr); if (found) { // Duplicate keys not allowed return (+1); } success = _insert(pList, pPre, dataInPtr); if (!success) { // Overflow return (-1); } return 0;} //end addNode/* ============================= _insert ======================================= Inserts data pointer into a new node. Pre pList pointer to a valid list pPre pointer to a data's predecessor dataInPtr data pointer to be inserted Post data has been inserted in sequence Return boolean, 1 is successful, -1 if memory overflow===============================================================================*/static int _insert (LIST* pList, NODE* pPre, void* dataInPtr){ NODE* pNew; if (!(pNew = (NODE*) malloc(sizeof(NODE)))) { return FALSE; } pNew->dataPtr = dataInPtr; pNew->link = NULL; if (pPre == NULL) { // Adding before first nore or to empty list. pNew->link = pList->head; pList->head = pNew; if (pList->count == 0) { // Adding to empty list. Set rear. pList->rear = pNew; } } else { // Adding in middle or at end pNew->link = pPre->link; pPre->link = pNew; // Now check for add at end of list if (pNew->link == NULL) { pList->rear = pNew; } } (pList->count)++; return TRUE;} //end _insert/* ================== _search ================================================= Searches list and passes back address of node containing target and its logical predecessor. Pre pList pointer to initialized list pPre pointer variable to predecessor pLoc pointer variable to receive node pArgu pointer to key being sought Post pLoc points to first equal/greater key -or- null if target > key of last node pPre points to largest node < key -or- null if target < key of first node Return boolean true found; false not found ===============================================================================*/int _search (LIST* pList, NODE** pPre, NODE** pLoc, void* pArgu){// Macro Definition #define COMPARE \ ( ((* pList->compare) (pArgu, (*pLoc)->dataPtr)) )#define COMPARE_LAST \ ((* pList->compare) (pArgu, pList->rear->dataPtr)) int result; *pPre = NULL; *pLoc = pList->head; if (pList->count == 0) { return FALSE; } // Test for argument > last node in list if ( COMPARE_LAST > 0) { *pPre = pList->rear; *pLoc = NULL; return FALSE; } // if while ( (result = COMPARE) > 0 ) { // Have not found search argument location *pPre = *pLoc; *pLoc = (*pLoc)->link; } if (result == 0) { // argument found--success return TRUE; } else { return FALSE; }} // end _search