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How to access null pointer of struct listnode?
member access within null pointer of type ‘struct ListNode’. struct ListNode { int val; ListNode *next; ListNode (int x) : val (x), next (NULL) {} }; class Solution { public: bool hasCycle (ListNode *head) { if (head == NULL) return false; ListNode* walker = head; ListNode* runner = head; while
How to know if a pointer to node is null?
Your parameter n is an independent variable, initialised to whatever you pass to alloc_memory. So any changes to n won’t be reflected in the calling code. Return the pointer, not a boolean. If the pointer returned is NULL, you know something went wrong. Make the parameter a pointer to pointer to node.
What is runtime error member access within null pointer?
Line 36: Char 18: runtime error: member access within null pointer of type ‘ListNode’ (solution.cpp) SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior prog_joined.cpp:45:18 Know someone who can answer? Share a link to this question via email, Twitter, or Facebook.
Why does my struct have a null pointer?
The problem is that you forgot to malloc new elements for the new list (aka start / temp3) inside the loops. you allocate one struct ListNode but inside for instance this loop: temp3 will become NULL in the first iteration so the next time you do: you dereference a NULL pointer and get a crash. You’ll need to malloc a new element in each loop.
Is it legal to declare struct node as head in C?
I think you meant, in LIST ‘s definition, that struct NODE* head; should be NODE* head;. There is no warning generated on that line, because in C it’s legal to implicitly declare a struct type just by mentioning it (i.e. this line declares the new type struct NODE also).
When to use the struct keyword before node?
There is code repetition in your insert function. You should not use the struct keyword before NODE in the second typedef statement because NODE is already an alias for the type struct node. That’s why you are getting the warning mentioned in your question. Also, you should not cast the result of malloc.