CODEWITHSUNDEEP
cvalgrind
Nick
Nick

Reputation: 25

I'm receiving Invalid read of size 8 when running Valgrind in C

I've written a C linkedlist program and am running a simple test harness to ensure that all functions are working optimally. However, despite there being no memory leaks, according to Valgrind I'm having two issues with my code, these being

Header file: LinkedList.h

typedef struct LinkedListNode
{
    void* data;
    struct LinkedListNode* next;
    struct LinkedListNode* previous;
} LinkedListNode;

typedef struct
{
    LinkedListNode* head;
    LinkedListNode* tail;
    int size;
} LinkedList;

The removeStart function in linkedlist.c

void* removeStart(LinkedList* list)
{
    LinkedListNode* curr = list->head;

    void* ptr;

    if (curr->next == NULL)
    {
        free(curr);
        list->head = NULL;
    }
    if (curr->next != NULL)    //This is where the Invalid read of size 8 error occured
    {
        ptr = curr -> data;

        list -> head = curr -> next;

        free(curr);
        curr = NULL;

        list -> head -> previous = NULL;
        list->size--;
    }
 
 
    return ptr;
}

The removeLast function

void* removeLast(LinkedList* list)
{
    LinkedListNode* curr = list -> head;
    LinkedListNode* secondLast;

    void* ptr;

    if (isEmpty(list) == 0)
    {
        printf("List is empty");
    }
    else
    {
        while (curr->next != NULL)
        {
            secondLast = curr;
            curr = curr->next;
        }

        if (curr == list->head)
        {
            list -> head = NULL;
        }

    }

    ptr = curr->data;
    list->size--;
    list -> tail = secondLast;
    secondLast->next = NULL;        //This is where Use of uninitialised value of size 8 occured

    free(curr);
    curr = NULL;
    return ptr;
}

Upvotes: 0

Views: 183

Answers (1)

John3136
John3136

Reputation: 29265

In removeStart if curr->next == NULLthen you free curr but use it again 2 lines down.

In removeLast if the list is empty then secondLast is never set.

Upvotes: 1

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