I am attempting to compile a new class template within the namespace cop4530. Do you have any idea why I am getting this back? These functions do exist and the compiler isn’t helping me by saying much about the specifics. I have done what this thread says already, but I still get undefined symbols
g++ -o proj2.x test_list.o
Undefined symbols for architecture x86_64:
"cop4530::List<int>::iterator::operator++(int)", referenced from:
_main in test_list.o
"cop4530::List<int>::iterator::operator*()", referenced from:
_main in test_list.o
"cop4530::List<int>::iterator::operator++()", referenced from:
_main in test_list.o
cop4530::List<int>::List(int, int const&)in test_list.o
"cop4530::List<std::basic_string<char, std::char_traits<char>, std::allocator<char> > >::iterator::operator++(int)", referenced from:
_main in test_list.o
"cop4530::List<std::basic_string<char, std::char_traits<char>, std::allocator<char> > >::iterator::operator*()", referenced from:
_main in test_list.o
"cop4530::List<std::basic_string<char, std::char_traits<char>, std::allocator<char> > >::iterator::operator++()", referenced from:
_main in test_list.o
cop4530::List<std::basic_string<char, std::char_traits<char>, std::allocator<char> > >::List(int, std::basic_string<char, std::char_traits<char>, std::allocator<char> > const&)in test_list.o
"cop4530::List<int>::iterator::iterator(cop4530::List<int>::Node*)", referenced from:
cop4530::List<int>::erase(cop4530::List<int>::iterator)in test_list.o
cop4530::List<int>::clear() in test_list.o
cop4530::List<int>::insert(cop4530::List<int>::iterator, int const&)in test_list.o
"cop4530::List<std::basic_string<char, std::char_traits<char>, std::allocator<char> > >::iterator::iterator(cop4530::List<std::basic_string<char, std::char_traits<char>, std::allocator<char> > >::Node*)", referenced from:
cop4530::List<std::basic_string<char, std::char_traits<char>, std::allocator<char> > >::erase(cop4530::List<std::basic_string<char, std::char_traits<char>, std::allocator<char> > >::iterator)in test_list.o
cop4530::List<std::basic_string<char, std::char_traits<char>, std::allocator<char> > >::clear()in test_list.o
cop4530::List<std::basic_string<char, std::char_traits<char>, std::allocator<char> > >::insert(cop4530::List<std::basic_string<char, std::char_traits<char>, std::allocator<char> > >::iterator, std::basic_string<char, std::char_traits<char>, std::allocator<char> > const&)in test_list.o
ld: symbol(s) not found for architecture x86_64
collect2: ld returned 1 exit status
make: *** [List_executable] Error 1
My header was written by textbook and nothing has been changed(or can be changed for this project), so the problem isn’t there. Same with the driver ‘test_list’. At the end of the header file there is an include (what the question [its not called a thread, I’m told] above said to do.)
Header anyway:
#ifndef DL_LIST_H
#define DL_LIST_H
#include <iostream>
namespace cop4530 {
template <typename T>
class List {
private:
// nested Node class
struct Node {
T data;
Node *prev;
Node *next;
Node(const T & d = T(), Node *p = NULL, Node *n = NULL)
: data(d), prev(p), next(n) {}
};
public:
//nested const_iterator class
class const_iterator {
public:
const_iterator(); // default zero parameter constructor
const T & operator*() const; // operator*() to return element
// increment/decrement operators
const_iterator & operator++();
const_iterator operator++(int);
const_iterator & operator--();
const_iterator operator--(int);
// comparison operators
bool operator==(const const_iterator &rhs) const;
bool operator!=(const const_iterator &rhs) const;
protected:
Node *current; // pointer to node in List
T & retrieve() const; // retrieve the element refers to
const_iterator(Node *p); // protected constructor
friend class List<T>;
};
// nested iterator class
class iterator : public const_iterator {
public:
iterator() {}
T & operator*();
const T & operator*() const;
// increment/decrement operators
iterator & operator++();
iterator operator++(int);
iterator & operator--();
iterator operator--(int);
protected:
iterator(Node *p);
friend class List<T>;
};
public:
// constructor, desctructor, copy constructor
List(); // default zero parameter constructor
List(const List &rhs); // copy constructor
// num elements with value of val
explicit List(int num, const T& val = T());
// constructs with elements [start, end)
List(const_iterator start, const_iterator end);
~List(); // destructor
// assignment operator
const List& operator=(const List &rhs);
// member functions
int size() const; // number of elements
bool empty() const; // check if list is empty
void clear(); // delete all elements
void reverse(); // reverse the order of the elements
T &front(); // reference to the first element
const T& front() const;
T &back(); // reference to the last element
const T & back() const;
void push_front(const T & val); // insert to the beginning
void push_back(const T & val); // insert to the end
void pop_front(); // delete first element
void pop_back(); // delete last element
void remove(const T &val); // remove all elements with value = val
// print out all elements. ofc is deliminitor
void print(std::ostream& os, char ofc = ' ') const;
iterator begin(); // iterator to first element
const_iterator begin() const;
iterator end(); // end marker iterator
const_iterator end() const;
iterator insert(iterator itr, const T& val); // insert val ahead of itr
iterator erase(iterator itr); // erase one element
iterator erase(iterator start, iterator end); // erase [start, end)
private:
int theSize; // number of elements
Node *head; // head node
Node *tail; // tail node
void init(); // initialization
};
// overloading comparison operators
template <typename T>
bool operator==(const List<T> & lhs, const List<T> &rhs);
template <typename T>
bool operator!=(const List<T> & lhs, const List<T> &rhs);
// overloading output operator
template <typename T>
std::ostream & operator<<(std::ostream &os, const List<T> &l);
// include the implementation file here
#include "List.cpp"
} // end of namespace 4530
#endif
Here is the .cpp file. Its not completely finished:
using namespace std;
// --------------------- CONST_ITERATOR --------------------- //
template <class T>
List<T>::const_iterator::const_iterator()
{ // default zero-parameter constructor. Set pointer current to NULL.
current = NULL;
}
template <class T>
const T& List<T>::const_iterator::operator*() const
{ // returns a reference to the corresponding element in the list by calling retrieve() member function.
return retrieve();
}
template <class T>
typename List<T>::const_iterator& List<T>::const_iterator::operator++()
{
current = current->next;
return *this;
}
template <class T>
typename List<T>::const_iterator List<T>::const_iterator::operator++(int)
{
const_iterator old = *this;
++( *this );
return old;
}
template <class T>
typename List<T>::const_iterator& List<T>::const_iterator::operator--()
{
current = current->prev;
return *this;
}
template <class T>
typename List<T>::const_iterator List<T>::const_iterator::operator--(int)
{
const_iterator old = *this;
--( *this );
return old;
}
template <class T>
bool List<T>::const_iterator::operator==(const const_iterator &rhs) const
{return current == rhs.current;}
template <class T>
bool List<T>::const_iterator::operator!=(const const_iterator &rhs) const
{return !( *this == rhs );}
template <class T>
T& List<T>::const_iterator::retrieve() const
{ // return a reference to the corresponding element in the list.
return current->data;
}
template <class T>
List<T>::const_iterator::const_iterator(Node *p)
{ // one-parameter constructor
// Set pointer current to the given node pointer p.
current = p;
}
// --------------------- ITERATOR --------------------- //
template <class T>
T& List<T>::iterator::operator*()
{
return retreive();
}
template <class T>
const T& List<T>::iterator::operator*() const
{
return retreive();
}
template <class T>
List<T>::iterator & List<T>::iterator::operator++()
{
current = current->next;
return *this;
}
template <class T>
List<T>::iterator List<T>::iterator::operator++(int)
{
const_iterator old = *this;
++( *this );
return old;
}
template <class T>
List<T>::iterator & List<T>::iterator::operator--()
{
current = current->prev;
return *this;
}
template <class T>
List<T>::iterator List<T>::iterator::operator--(int)
{
const_iterator old = *this;
--( *this );
return old;
}
template <class T>
List<T>::iterator::iterator(Node *p)
{ // one-parameter constructor
// Set current to the given node pointer p
current = p;
}
// --------------------- LIST --------------------- //
template <class T>
List<T>::List()
{ init(); }
template <class T>
List<T>::List( const List & rhs )
{ // Copy constructor
init();
*this = rhs;
}
template <class T>
List<T>::List(int num, const T& val)
{ //Constructs a list with num elements, all initialized with value val
init();
iterator itr = begin();
for (int i = 0; i < num; ++i)
{
insert(itr, val);
++itr;
}
}
template <class T>
List<T>::List(const_iterator start, const_iterator end)
{ // Constructs a List w/ elements from another List between
// start and end. [includes start, not end)
///////////
}
template <class T>
List<T>::~List()
{ // Destructor
clear();
delete head;
delete tail;
}
template <class T>
const typename List<T>::List& List<T>::operator=(const List &rhs)
{ // Assignment operator
List<T>::iterator ritr = rhs.first();
List<T>::iterator itr = begin();
if( this != &rhs )
{
clear();
for( ; !ritr.isPastEnd( ); ritr.advance( ), itr.advance( ) )
insert( ritr.retrieve( ), itr );
}
return *this;
}
template <class T>
int List<T>::size() const
{ // return the number of elements in the List
return theSize;
}
template <class T>
bool List<T>::empty() const
{ // check if list is empty
return head->next == NULL;
}
template <class T>
void List<T>::clear()
{ // delete all elements
while( !isEmpty( ) )
erase( begin().retreive() );
}
template <class T>
void List<T>::reverse()
{ // reverse the order of the elements
/////////////
}
template <class T>
T& List<T>::front()
{ // reference to the first element
return head->next->data;
}
template <class T>
T& List<T>::back()
{ // reference to the last element
return tail->prev->data;
}
template <class T>
void List<T>::push_front(const T & val)
{ // insert to the beginning
}
template <class T>
void List<T>::push_back(const T & val)
{ // insert to the end
}
template <class T>
void List<T>::pop_front()
{ // delete first element
}
template <class T>
void List<T>::pop_back()
{ // delete last element
}
template <class T>
void List<T>::remove(const T &val)
{ // remove all elements with value = val
}
template <class T>
void List<T>::print(std::ostream& os, char ofc) const
{ // print out all elements. ofc is deliminitor
}
template <class T>
typename List<T>::iterator List<T>::begin()
{ // iterator to first element
return List<T>::iterator( head->next );
}
template <class T>
typename List<T>::iterator List<T>::end()
{ // end marker iterator
return List<T>::iterator( tail->prev );
}
template <class T>
typename List<T>::iterator List<T>::insert( iterator itr, const T & x )
{
Node *p = itr.current;
theSize++;
return iterator( p->prev = p->prev->next = new Node( x, p->prev, p) );
}
template <class T>
typename List<T>::iterator List<T>::erase( iterator itr )
{
Node *p = itr.current;
iterator retVal( p->next );
p->prev->next = p->next;
p->next->prev = p->prev;
delete p;
theSize--;
return retVal;
}
template <class T>
typename List<T>::iterator List<T>::erase( iterator start, iterator end )
{
for( iterator itr = start; itr != end; )
itr = erase( itr );
return end;
}
template <class T>
void List<T>::init()
{ // Initaialize the member variables of a List
theSize = 0;
head = new Node;
tail = new Node;
head->next = tail;
tail->prev = head;
}
// --------- OVERLOADS --------- //
template <typename T>
bool operator==(const List<T> & lhs, const List<T> &rhs)
{
}
template <typename T>
bool operator!=(const List<T> & lhs, const List<T> &rhs)
{
}
template <typename T>
std::ostream & operator<<(std::ostream &os, const List<T> &l)
{
}
Let me just add that I appreciate any and all help given. I am a student and I am trying to learn.
Template class methods are instanced the first time they are used, so a definition for
List<int>andList<string>must be visible from the calling unit.Your textbook seems to assume compiler support for external template definitions, that GCC don’t support.
An easy fix is to copy-paste the List.cpp file content inside the compilation unit you are trying to fix.