Unique pointer in Linked List - c++

Question

I was trying to create a Linked List by using unique pointer. However, my program does not compile due to some weird errors that I do not know how to fix it. Would anyone please help me out how to solve this problem ? Thank you.
ContactList.h
#pragma once
#include"Contact.h"
#include<memory>
using namespace std;
class ContactList
{
public:
ContactList();
~ContactList();
void addToHead(const std::string&);
void PrintList();
private:
//Contact* head;
unique_ptr<Contact> head;
int size;
};
ContactList.cpp
#include"ContactList.h"
#include<memory>
using namespace std;
ContactList::ContactList(): head(new Contact()), size(0)
{
}
void ContactList::addToHead(const string& name)
{
//Contact* newOne = new Contact(name);
unique_ptr<Contact> newOne(new Contact(name));
if(head == 0)
{
head.swap(newOne);
//head = move(newOne);
}
else
{
newOne->next.swap(head);
head.swap(newOne);
//newOne->next = move(head);
//head = move(newOne);
}
size++;
}
void ContactList::PrintList()
{
//Contact* tp = head;
unique_ptr<Contact> tp(new Contact());
tp.swap(head);
//tp = move(head);
while(tp != 0)
{
cout << *tp << endl;
tp.swap(tp->next);
//tp = move(tp->next);
}
}
These are the errors that I've got:
Error 1 error LNK2019: unresolved external symbol "public: __thiscall ContactList::~ContactList(void)" (??1ContactList##QAE#XZ) referenced in function "public: void * __thiscall ContactList::`scalar deleting destructor'(unsigned int)" (??_GContactList##QAEPAXI#Z) E:\Fall 2013\CPSC 131\Practice\Practice\Practice\ContactListApp.obj
Error 2 error LNK1120: 1 unresolved externals E:\Fall 2013\CPSC 131\Practice\Practice\Debug\Practice.exe 1

Answer 1

Your ContactList destructor has no implementation.
Add to ContactList.cpp
ContactList::~ContactList()
{
}
Or (since the destructor is trivial anyway), just remove the explicit destructor from the class definition:
class ContactList
{
public:
ContactList();
// no explicit destructor required
void addToHead(const std::string&);
void PrintList();
private:
unique_ptr<Contact> head;
int size;
};