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POCompiler error in declaring template friend class within a template class
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  1. POCompiler error in declaring template friend class within a template class
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    copied!<p>I have been trying to implement my own linked list class for didactic purposes.</p> <p>I specified the "List" class as friend inside the Iterator declaration, but it doesn't seem to compile.</p> <p>These are the interfaces of the 3 classes I've used:</p> <p><strong>Node.h:</strong></p> <pre><code>#define null (Node&lt;T&gt; *) 0 template &lt;class T&gt; class Node { public: T content; Node&lt;T&gt;* next; Node&lt;T&gt;* prev; Node (const T&amp; _content) : content(_content), next(null), prev(null) {} }; </code></pre> <p><strong>Iterator.h:</strong></p> <pre><code>#include "Node.h" template &lt;class T&gt; class Iterator { private: Node&lt;T&gt;* current; Iterator (Node&lt;T&gt; *); public: bool isDone () const; bool hasNext () const; bool hasPrevious () const; void stepForward (); void stepBackwards (); T&amp; currentElement () const; friend class List&lt;T&gt;; }; </code></pre> <p><strong>List.h</strong></p> <pre><code>#include &lt;stdexcept&gt; #include "Iterator.h" template &lt;class T&gt; class List { private: Node&lt;T&gt;* head; Node&lt;T&gt;* tail; unsigned int items; public: List (); List (const List&lt;T&gt;&amp;); List&amp; operator = (const List&lt;T&gt;&amp;); ~List (); bool isEmpty () const { return items == 0; } unsigned int length () const { return items; } void clear (); void add (const T&amp;); T remove (const T&amp;) throw (std::length_error&amp;, std::invalid_argument&amp;); Iterator&lt;T&gt; createStartIterator () const throw (std::length_error&amp;); Iterator&lt;T&gt; createEndIterator () const throw (std::length_error&amp;); }; </code></pre> <p>And this is the test program I've been trying to run:</p> <p><strong>trial.cpp</strong></p> <pre><code>using namespace std; #include &lt;iostream&gt; #include "List/List.cc" int main () { List&lt;int&gt; myList; for (int i = 1; i &lt;= 10; i++) { myList.add(i); } for (Iterator&lt;int&gt; it = myList.createStartIterator(); !it.isDone(); it.stepForward()) { cout &lt;&lt; it.currentElement() &lt;&lt; endl; } return 0; } </code></pre> <p>When I try to compile it, the compiler gives me the following errors:</p> <p><strong>Iterator.h:26: error: ‘List’ is not a template</strong></p> <p><strong>Iterator.h: In instantiation of ‘Iterator’:</strong></p> <p><strong>trial.cpp:18: instantiated from here</strong></p> <p><strong>Iterator.h:12: error: template argument required for ‘struct List’</strong></p> <p><strong>List.cc: In member function ‘Iterator List::createStartIterator() const [with T = int]’:</strong></p> <p><strong>trial.cpp:18: instantiated from here</strong></p> <p><strong>Iterator.h:14: error: ‘Iterator::Iterator(Node*) [with T = int]’ is private</strong></p> <p><strong>List.cc:120: error: within this context</strong></p> <p>Seems like it is not recognizing the friend declaration. Where did I go wrong?</p>
 

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