CODEWITHSUNDEEP
c++pointerslinked-listpass-by-reference
user906357
user906357

Reputation: 4685

C++ pass by reference then set a pointer to the object

I am creating a class LinkedList. I am having difficulty adding another node to my list.

Here is what I have so far:

template<typename T>
class LinkedList
{
private:
    T element;
    T *next;

public:    
    LinkedList();
    LinkedList(T element);

    void add(LinkedList<T> &otherList);
    void print();
};

template<typename T>
LinkedList<T>::LinkedList()
{
    next = NULL;
}

template<typename T>
LinkedList<T>::LinkedList(T element)
{
    this->element = element;
    next = NULL;
}

template<typename T>
void LinkedList<T>::add(LinkedList<T> &otherList)
{
    next = &otherList;
}


template<typename T>
void LinkedList<T>::print()
{
    LinkedList<T> *current = this;
    while (current != NULL)
    {
        std::cout << current->element;
        current = current->next;
    }
}

int main()
{    
    LinkedList<std::string> myFirst("First");
    LinkedList<std::string> mySecond("Second");    
    myFirst.add(mySecond);
    myFirst.print();    

    return 0;
}

This works however if I make the change:

void add(const LinkedList<T> &otherList);

template<typename T>
void LinkedList<T>::add(const LinkedList<T> &otherList)
{
    next = &otherList; //now an error right here
}

Then I get an error stating:

Assigning to 'LinkedList<std::__1::basic_string<char> > *' from incompatible type 'const LinkedList<std::__1::basic_string<char> > *'

Why is it I get this error?

Upvotes: 0

Views: 117

Answers (1)

Lightness Races in Orbit
Lightness Races in Orbit

Reputation: 385194

next is a T*, and you're trying to assign a const LinkedList<T>* to it.

I suppose you meant something like next = &(otherList.element) (though even then I think your list semantics are somewhat broken — elements shouldn't typically be shared by multiple containers unless you're very, very clear about the ownership semantics).

Contrary to your claims, your first program doesn't work either for the same reason.

Upvotes: 4

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