C++: creating an instance of an iterator nested class

Question

I have a class called OrderedList in a namespace MYLIB. In it I have a nested class called iterator which will be used as an iterator for the OrderedList class.

Following is the snippet of my code where I create OrderedList and iterator classes:

    template<class T>
    class OrderedList
    {
        private:
            ListNode<T>* head;
            ListNode<T>* tail;
            int total;
        public:
            OrderedList(T[],int);
            ~OrderedList();
            void insert(const T&);
            void sort(int);
            void output();
            class iterator
            {
                private:
                    ListNode<T>* curr;
                    int current;
                    OrderedList& order;
                public:
                    iterator(OrderedList& ord, bool is_end)
                    {
                        this->order = ord; //problem is here
                        if(is_end == false)
                        {...

Snippet of my main function:

int main()
{
    int one[5] = {9,7,5,4,1};
    MYLIB::OrderedList<int> odd(one,5);
    odd.output();

    MYLIB::OrderedList<int>::iterator starter(odd,false);

When I compile it gives me the following error:

OrderedList.cpp: In instantiation of ‘MYLIB::OrderedList<T>::iterator::iterator(MYLIB::OrderedList<T>&, bool) [with T = int]’:
OrderedList.cpp:215:53:   required from here
OrderedList.cpp:47:6: error: uninitialized reference member ‘MYLIB::OrderedList<int>::iterator::order’ [-fpermissive]
      iterator(OrderedList& ord, bool is_end)
      ^

Every time a picture of code is posted, somewhere a kitten dies. Please, please don't do that. — WhozCraig
– WhozCraig, Commented May 24, 2015 at 6:24
Lol @WhozCraig. I believe posting picture is much more clear than the text since you can refer to the line numbers as well :) — Fahad Ur Rehman
– Fahad Ur Rehman, Commented May 24, 2015 at 6:31
@FahadUrRehman And its impossible to copy/paste posted code to reproduce problems, a highly desired and to-be-considered mandetory goal of an MCVE. Leave both the line numbers and pictures at home. If there is a line of code that is causing you grief, clearly mark it with a comment. if the grief is an error message saying "line XXXX", then mark said-line with a comment to the effect // line XXXX HERE. Make it as easy as possible for people to test your problem and produce a solution. — WhozCraig
– WhozCraig, Commented May 24, 2015 at 6:39

6502 · Accepted Answer · 2015-05-24 06:23:10Z

1

In C++ a reference must be initialized in the member initialization list, it cannot be initialized in the coustructor body.

You need to change your code to

iterator(OrderList& ord, bool is_end) : order(ord) {
    if (is_end == false) {
        ...
    }
}

instead of using an assignment.

Assignment on a reference does a different thing (it assigns the original object the reference is referencing). You cannot change what a reference is bound to.

PS: Why stopping there and not going for if ((is_end == false) == true) ? ;-)

answered May 24, 2015 at 6:23

6502

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1 Comment

Fahad Ur Rehman Over a year ago

Thanks heaps it works :) Well, yes I can do that but I like my code to be spread out, so that it is clear for future reference. That notation can be unclear at times, especially if you haven't done c++ for a while and then referring back to this code after a while will be a bit hard.

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