插入链表的末尾

Question

I am writing a simple function to insert at the end of a linked list on C++, but finally it only shows the first data. I can't figure what's wrong. This is the function:

node* Insert(node* head, int data)
{
    if (head == NULL) {
        head = new node();

        head->data = data;
        head->link = NULL;

        return head;
    }
    else {
        node* temp = head;
        while (temp != NULL) {
            temp = temp->link;
        }

        node* temp2 = new node();

        temp2->data = data;
        temp2->link = NULL;
        (temp->link) = temp2;

        return head;
    }
}

Answer 1

Change the condition in while construct from:

while (temp!=NULL) {
    temp=temp->link;
}

To

while (temp->link!=NULL) {
    temp=temp->link;
}

In statement, temp->link = temp2 , temp is a null pointer. You were dereferencing a NULL pointer.

To append a node at the back, temp pointer should point to the last node of the linked list. So, in the while loop, you need to just stop linked list traversal when you have reached the last node, ie, the node whose link member points to nothing ( has NULL ). while (temp->link!=NULL) will stop at the last node as last node will have link member pointing to NULL .

Answer 2

You can simplify your logic by doing this:

void Insert(node **pnode, int data)
{
    while (*pnode) {
        pnode = &(*pnode)->link;
    }
    *pnode = new node(data, NULL);
}

assuming you have a node constructor that initializes data and link from arguments.

Instead of calling it as

head = Insert(head, 42);

you'd now do

Insert(&head, 42);

Answer 3

node* Insert(node* head, int data)
{
    if (head == NULL) {
        head = new node();
    }
    else {
        while (head->link != NULL) {
            head = head->link;
        }
        head = head->link = new node();
    }
    head->data = data;
    head->link = NULL;
    return head;
}

Answer 4

将while（temp！= NULL）更改为while（temp-> link！= NULL）