C++ 中链表实现中的分段错误

Question

I am writing a function in C++ to add a "data" of type 'int' to the end of a linked list.

void insert_back()
{
 int no;
 node *temp;
 cout<<"\nEnter the number"<<"\n";
 cin>>no;
 temp = head;
 if(temp != NULL)
 {
         while(temp != NULL)
                    temp = temp->next;
 }

 temp->next = (node*)malloc(sizeof(node));
 temp = temp->next;
 temp->data = no;
 temp->next = NULL;

}

However, at the line, temp->next = (node*)malloc(sizeof(node)), I get an access violation error(segmentation fault). I do not find anything fundamentally wrong. Can you please enlighten me on the issue?

Answer 1

If you want to get the last node of the list, just check if the next member is null or not as the next member of the last node is null.

In your code, you check temp is null or not instead of temp->next .

while(temp != NULL)
    temp = temp->next;

will get the temp be null when the loop is over.

Besides, you should also consider the condition where the head is null.

void insert_back()
{
    int no;
    node *temp;
    cout<<"\nEnter the number"<<"\n";
    cin>>no;
    temp = head;
    if(temp != NULL)
    {
        while(temp->next != NULL)
            temp = temp->next;
        temp->next = (node*)malloc(sizeof(node));
        temp = temp->next;
        temp->data = no;
        temp->next = NULL;
    }else{
        head = (node*)malloc(sizeof(node));
        head->data = no;
        head->next = NULL;
    }

}

Answer 2

Just before that line executes, temp will be null. You then dereference it.

Answer 3

The temp you are referring doesn't exist, temp is NULL. To correct this, instead of using temp!=NULL in the while loop condition, use temp->next!= NULL.

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

Node* new_node = (Node*)malloc(sizeof(Node));

new_node->data = no;
new_node->next = NULL;
temp->next = new_node;

Answer 4

If anyone has this issue, just check if you have created a Default constructor for your List class or not. In that default constructor " Make your head = NULL ";

Code:

class List
{
public:
Node *head;
List()
 {
    head = NULL;
 }
}

Answer 5

Just try this:- while(temp->next =NULL) Instead of while(temp =NULL)

It's such a silly mistake I was facing it and beileve me it took me months to see such a silly fcking error.

Answer 6

while(temp != NULL)
    temp = temp->next;

The above code gets you to the last node in the list. So, you are suppose to add the node to temp itself rather than temp->next .

temp = (node*)malloc(sizeof(node));

And now the last node's child should be NULL.

temp->next = NULL;