Question

I’m trying to implement a linked list class in C++ and I got problem. I have the += operator who adds new node.

the linked list class interface:

template <typename Type>

class LinkedList {
public:
    LinkedList<Type>* head;
//  linked list stracture
    Type data;
    LinkedList<Type>* next;
//  others ....
    size_t length;
public:
    LinkedList();
    ~LinkedList();
    void initializeHead(LinkedList<Type>* headPtr);
    size_t size() const;
    LinkedList& operator+=(const Type& add);
    void operator-=(const Type& remove);
    LinkedList<Type>& operator[] (const size_t index) const;
    bool operator== (const LinkedList<Type> &versus) const;
    friend ostream& operator<< (ostream& out,LinkedList& obj);
};

and here i have the += overload implement:

template <typename Type> LinkedList<Type>& LinkedList<Type>::operator +=(const Type& add) {
    // head ptr - :)
    LinkedList<Type>* p = head->next;
    // go to the end
    while(p) p = p->next;
    // now on end - create new..!!!
    try {
        p = new LinkedList<Type>;
    } catch (bad_alloc& e) {
        cout << "There\'s an allocation error....";
    } catch (...) {
        cout << "An unknown error.." << endl;
    }// fill and done
    p->data = add;
    p->next = NULL;
    // increment length .........
    ++head->length;
    // done ............
    return *p;
}

Additionally , I have “array” access overload method:

template <typename Type> LinkedList<Type>& LinkedList<Type>::operator [](const size_t index) const {
    if(index < 0 || index >= length) // invaild argument
        throw  exception();
    // continue
    LinkedList<Type>* p = head;
    for(size_t i = 0; i < index; ++i) p = p->next; // we are at what we want
    return *p;
}

All works correctly – I checked on the dibugger,

the problem is – += doesn’t save the new node in “head->next”, for some reason, after finish += method, head->next equal to null.

Do someone know why the new allocation don’t link to head->next?

Thanks a lot!!

Answer 1

after while(p) p = p->next; p is NULL

and next you do p = new LinkedList<Type>; but you don’t link the p into the head.