Don't know why valgrind gives me Conditional jump or move depends on uninitialised value(s) error?

Question

My code below successfully converts a Binary search tree to a linked list however valgrind has been giving me "Conditional jump or move depends on uninitialised value(s)" errors. Yet after looking at my code, I don't see where I have that?

ListNodePtr convertBSTtoLinkedList(TreeNodePtr root)
{
    ListNodePtr list,head;
    list = malloc(sizeof(struct ListNode));
    list->key = root->key;
    if (root->right != NULL)
    {
        list->next = convertBSTtoLinkedList(root->right);    //line 80
    }
    if (root->left != NULL)  
    {
    ListNodePtr tail;
    head = convertBSTtoLinkedList(root->left);   //line 85
    tail = head;
    while (tail->next != NULL) {        //Line 87
        tail = tail->next;
    }
    tail->next = list;
    return head;
    }
    return list;
}

This is my valgrind error, it repeats itself a few times.

==3076== Conditional jump or move depends on uninitialised value(s)
==3076==    at 0x108AF2: convertBSTtoLinkedList (bst.c:87)
==3076==    by 0x108AC8: convertBSTtoLinkedList (bst.c:80)
==3076==    by 0x108ADD: convertBSTtoLinkedList (bst.c:85)
==3076==    by 0x108ADD: convertBSTtoLinkedList (bst.c:85)
==3076==    by 0x108ADD: convertBSTtoLinkedList (bst.c:85)
==3076==    by 0x108AC8: convertBSTtoLinkedList (bst.c:80)
==3076==    by 0x108AC8: convertBSTtoLinkedList (bst.c:80)
==3076==    by 0x108754: main (main_bst.c:28)

Do you mean if a NULL root was passed to the function? If so, I added a check and it did not fix the errors. — TheShield

aschepler aschepler · Accepted Answer · 2017-11-16T04:16:47

malloc gives you a pointer to uninitialized memory. So unless you set each member of your ListNode struct, trying to access that member later is a bad idea.

When your convertBSTtoLinkedList function processes any node of the BST which does not have a right child, it fails to set next on the created list node. So the next time after that a higher level in the recursion attempts to find the end of the returned sublist, it walks to the end of the sublist, checks that uninitialized next pointer, and valgrind complains.

Don't know why valgrind gives me Conditional jump or move depends on uninitialised value(s) error?

1 Answers