Question

I am getting the following when trying to compile the code below:

preallocarray.h: In member function 'void PreallocArray<T>::push_back(const T&)':
preallocarray.h:82: error: expected `;' before 'itr'

I have a nested const_iterator class inside of my LinkedList class I created. It’s been many years since I’ve done C++, so this is probably caused by something silly, but I’ve been hacking around and googling for an hour with no luck…

Here’s my linked list class definition, decared in linklist.h:

template <typename T> 
class LinkedList 
{
    <snip...>
    public:
        class const_iterator
        {
        <snip...>
        };
    <snip...>
};

Then I have a second class, declared in preallocarray.h, as follows:

#include "linklist.h"
template <typename T>
class PreallocArray
{
    <snip...>
    public:
        void push_back( const T & newValue )
        {
            if (capacity == size)
            {
                allocateNode( capacity / 2 );
            }
            LinkedList<Node>::const_iterator itr; // error occurs here
            theList.end();
        }
    <snip...>

    private:
        LinkedList<Node> theList; // the linked list of nodes
    <snip...>
};

Answer 1

LinkedList<Node>::const_iterator itr; // error occurs here

Based on the fact the enclosing class is actually a class template, I suspect that you intended to write T instead of Node. What is Node by the way? And where is it defined?

If you really wanted to write T, then you’ve to write it as:

typename LinkedList<T>::const_iterator itr; 

Don’t forget to write typename as I’ve written above. If you’ve to write typename even if the template parameter is Node but its definition depends on T in some way:

typename LinkedList<Node>::const_iterator itr;//if Node depends on T

To know why typename is needed, see this answer by @Johannes Schaub:

• Where and why do I have to put the "template" and "typename" keywords?