I have been working on a C program for an assignment in my CS class, which compiles successfully but gets a segmentation fault error upon running. The assignment deals with linkedLists; we had to take methods described and declared in a header file called linkedlist.h and implement them a file called linkedlist.c. A file called listtest.c is provided and used to test the method.
My Code (linkedlist.c, the comments are from the header file we were given describing how the methods should work):
#include "linkedlist.h"
#include <stddef.h>
#include <stdio.h>
#include <stdlib.h>
/* Alloc a new node with given data. */
struct ListNode* createNode(int inputData)
{
struct ListNode *newNodeCN;
newNodeCN->data = inputData;
return newNodeCN;
}
/* Insert data at appropriate place in a sorted list, return new list head. */
struct ListNode* insertSorted(struct ListNode* head, int inputData)
{
printf("insertsorted started \n");
struct ListNode * nextIS = NULL;
struct ListNode * newNodeIS = NULL;
struct ListNode * currIS = head;
struct ListNode * listHeadIS = currIS;
if (currIS == NULL)
{
listHeadIS = createNode(inputData);
return listHeadIS;
}
while (currIS->next != NULL)
{
nextIS = currIS->next;
if (currIS->data < inputData)
{
if (nextIS->data >= inputData)
{
nextIS->next = createNode(inputData);
newNodeIS = nextIS->next;
if (newNodeIS->data > listHeadIS->data)
{
listHeadIS = newNodeIS;
}
}
}
currIS = currIS->next;
}
return listHeadIS;
}
/* Remove data from list pointed to by headRef, changing head if necessary.
* Make no assumptions as to whether the list is sorted.
* Memory for removed node should be freed.
* Return 1 if data was present, 0 if not found. */
int removeItem(struct ListNode** headRef, int data)
{
struct ListNode * tempRem = *headRef;
int filterVal = data;
while (tempRem->next != NULL)
{
if (tempRem->data == filterVal)
{
free(tempRem);
tempRem = tempRem->next;
return 1;
}
}
return 0;
}
/* Insert data at head of list, return new list head. */
struct ListNode* push(struct ListNode* head, int data)
{
printf("push started \n");
int dataPush = data;
struct ListNode * tempPush = (struct ListNode*)malloc(sizeof(struct ListNode));
tempPush->data = dataPush;
tempPush->next = head;
*head = *tempPush;
return tempPush;
}
/* Remove and return data from head of non-empty list, changing head.
* Memory for removed node should be freed. */
int pop(struct ListNode** headRef)
{
struct ListNode * tempPop = *headRef;
int tempData;
tempData = tempPop->data;
free(tempPop);
tempPop = tempPop->next;
return tempData;
}
/* Return length of the list. */
int listLength(struct ListNode* head)
{
int i;
while (head->next != NULL)
{
i++;
head = head->next;
}
return i;
}
/* Print list data on single line, separated with spaces. */
void printList(struct ListNode* head)
{
printf("PrintList Started \n");
if (head != NULL)
{
while (head->next != NULL)
{
printf("%d\n", head->data);
head = head->next;
}
}
}
/* Free memory used by the list. */
void freeList(struct ListNode* head)
{
while (head != NULL)
{
free(head);
head = head->next;
}
}
/* Reverse order of elements in the list */
void reverseList(struct ListNode** headRef)
{
struct ListNode * origRL = *headRef;
struct ListNode * nextRL = NULL;
struct ListNode * prevRL = NULL;
while (origRL->next != NULL);
{
nextRL = origRL->next;
prevRL = origRL;
origRL = nextRL;
origRL->next = prevRL;
}
}
The code from listtest.c (I did not write this):
#include <stdio.h>
#include <stdlib.h>
#include "linkedlist.h"
int main(int argc, char** argv)
{
int i, n;
struct ListNode* head = NULL;
struct ListNode* stack = NULL;
printf("empty list: ");
printList(head);
for(i = 0; i < 23; ++i)
{
n = (i*17+11) % 23;
head = insertSorted(head, n);
printf("sort succesful /n");
stack = push(stack, n);
}
printf("filled list: ");
printList(head);
printf("list length = %d\n", listLength(head));
printf("filled stack: ");
printList(stack);
printf("stack size = %d\n", listLength(stack));
for(i = -4; i < 25; i+=4)
{
n = removeItem(&head, i);
if(!n) printf("remove did not find %d\n", i);
}
printf("list after removes: ");
printList(head);
printf("list length = %d\n", listLength(head));
for(i = 0; i < 5; ++i)
{
printf("pop: %d\n", pop(&stack));
}
printf("stack after pops: ");
printList(stack);
printf("stack size = %d\n", listLength(stack));
reverseList(&head);
printf("list after reverse: ");
printList(head);
freeList(head);
head = NULL;
freeList(stack);
stack = NULL;
return 0;
}
According to both Valgrind and GDB the segmentation fault is being caused by something in main. Valgrind gives me the error:
Access not within mapped region at address 0x6FFFFFFE3
==6300== at 0x400953: main
My question is what exactly is causing the segmentation fault, how could I fix it, and could anything else in my code cause a segmentation fault? I am not allowed to edit listtest.c, so any changes will have to be in linkedlist.c. Thank You.
