Circular double linked list issue ..need help
Hi , I am implementing a circular linkedlist. I have got all the basic functions working but facing some issue in the ringMove function. Eventhough it is working fine ,I am getting valgrind error.Please see if there is some error.
Code:
#ifndef TKK_AS_C_RINGLIST_H
#define TKK_AS_C_RINGLIST_H
#include <stddef.h>
// TODO: RingNode definition
// Required variables:
// - data: array of 101 characters (max. 100 + terminating NUL)
// - prev and next: pointers to previous/next nodes
typedef struct RingNode_s {
char data[101];
struct RingNode_s *next;
struct RingNode_s *prev;
}RingNode;
/** Construct a new node.
* @param pos if NULL, a new ring is created, otherwise the new node is inserted after node pos.
* @param data a C string used to initialize the data (undefined behavior for strings longer than 100 characters).
* @return the new node (connected to the old ring if pos was provided).
**/
RingNode* ringAdd(RingNode* pos, char const* data);
/** Move a set of nodes to another position. O(1).
* Takes a range of nodes [first, last] and moves them to a new position. The new
* position may be within another ring or in the same ring as the range, but the
* behavior is undefined if the destination is within the range to be moved.
* @param first the first node to move.
* @param last the last node to move.
* @param pos the destination: the moved nodes are inserted after node pos.
* @return first
**/
RingNode* ringMove(RingNode* first, RingNode* last, RingNode* pos);
#endif
Code:
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include "ringlist.h"
RingNode* ringAdd(RingNode* pos, char const* data) {
RingNode *newring = malloc(sizeof (RingNode));
strcpy(newring->data, data);
if (pos) {
newring->prev = pos;
newring->next = pos->next;
pos->next = newring;
(newring->next)->prev = newring;
} else {
newring->next = newring;
newring->prev = newring;
}
return newring;
}
RingNode* ringMove(RingNode* first, RingNode* last, RingNode* pos) {
RingNode *item = first;
RingNode *final = last;
while (item->next != final) // valgrind error Invalid read of size 8
{
item = item->next;
if (item == pos)
return first;
}
(first->prev)->next = last->next;
(last->next)->prev = first->prev;
last->next = pos->next;
(pos->next)->prev = last;
pos->next = first;
first->prev = pos;
return first;
}
Code:
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include "ringlist.h"
int main() {
RingNode* ringitem1 = ringAdd(NULL, "ringitem1");
RingNode* ringitem2 = ringAdd(ringitem1, "ringitem2");
RingNode* ringitem3 = ringAdd(ringitem2, "ringitem3");
RingNode* ringitem4 = ringAdd(ringitem3, "ringitem4");
RingNode* ringitem5 = ringAdd(ringitem4, "ringitem5");
RingNode* ringitem6 = ringAdd(ringitem5, "ringitem6");
RingNode* ringitem7 = ringAdd(ringitem6, "ringitem7");
RingNode* ringitem8 = ringAdd(ringitem7, "ringitem8");
RingNode* ringitem9 = ringAdd(ringitem8, "ringitem9");
ringMove(ringitem5, ringitem8, ringitem9);
return 0;
}
Please sujjest what might be the issue. For clarity and simplicity i have not added the other functions here.
