C ++链接列表指向结构崩溃的指针

Question

When I call the default constructor for my class LinkedList I attempt to assign values to the head node of the linked list before any other operations occur. I have isolate the error, via debugging, to the instructions in the default constructor. As soon as

    head -> next = NULL;
    head -> RUID = 0;
    head -> studentName = "No Student in Head";

are called the program crashes. This occurs when I call the default constructor in main. Here is my class declaration and my struct declaration along with the default constructor:

struct Node
{
    string studentName;
    int RUID;
    Node* next;
};

class LinkedList
{
private:

    // Initialize length of list 
    int listLength;

public:
    // Head of the list, which points to no data yet
    Node *head;
    LinkedList();
    bool insertNode(Node* newNode, int position);
    int generateRUID(); 

};


LinkedList::LinkedList()
{

    head -> next = NULL;
    head -> RUID = 0;
    head -> studentName = "No Student in Head";

    listLength = 0; 
}

I believe this all of the relevant code to this issue. If someone could shed light on this it would be much appreciated.

Answer 1

LinkedList::head is a Node* , not a Node and you don't initialize it, so the object (binary, in-memory) representation is undefined and is therefore dangerous to dereference.

Change your LinkedList to explicitly initialize the head member. I recommend storing it by-value (as Node ) rather than as a heap-allocated value ( Node* ) for simplicitly, unless you know you'll need to reparent nodes.

Using Node* :

LinkedList::LinkedList() :
    head( Node() ),
    listLength( 0 )
{
    this->head->next = nullptr;
    this->head->RUID = 0;
    this->head->studentName = "No Student in Head";
}