“拋出異常：讀取訪問沖突。 this->head 是 nullptr。”

Question

我正在編寫從鏈接列表中刪除所有其他元素的代碼。 當列表中有足夠的元素時，它會起作用。 當沒有足夠的元素時，我仍然試圖讓代碼通過while循環運行其他選項（添加、刪除等）。 但是，會彈出一個錯誤

拋出異常：讀取訪問沖突。 this->head 是 nullptr。

我將如何解決這個問題？ 我在下面提供了 function：

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

您應該在取消引用之前檢查 head 是否有效

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; 

此外，使用nullptr代替NULL 。