“抛出异常：读取访问冲突。 this->head 是 nullptr。”

Question

I'm writing code that removes every other element from a Linked List. It works when there are enough elements in the List. When there are not enough elements, I'm trying to still have the code run through a while loop for other options (add, remove, etc). However, an error pops up

Exception thrown: read access violation. this->head was nullptr.

How would I fix this? I provided the function below:

void removeEveryOtherNode() {
    Chunk* previous = head;
    Chunk* pointer = head->next; //error happens here

    if (head == NULL) {
        cout << "Linked List is empty...Nothing to delete" << endl;
    }

    else if (pointer == NULL) {
        cout << "Not enough elements to delete every other element." << endl;
    }

    while (previous != NULL && pointer != NULL) {
        previous->next = pointer->next;
        delete pointer;
        previous = previous->next;
        if (previous != NULL) {
            pointer = previous->next;
        }
    }
    cout << "Removed every other element. Press 4 to display" << endl;
}

Answer 1

You should check if head is valid before dereferencing it

if (head == NULL) {
     cout << "Linked List is empty...Nothing to delete" << endl;
     return;
}
if (head->next == NULL) {
     cout << "Not enough elements to delete every other element." << endl;
     return;
}

// then dereference
Chunk* pointer = head->next; 

Also, use nullptr instead of NULL .