c++ - Unique pointer in Linked List -

i trying create linked list using unique pointer. however, program not compile due weird errors not know how fix it. please me out how solve 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 errors 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 

your contactlist destructor has no implementation.

add contactlist.cpp

contactlist::~contactlist() { } 

or (since destructor trivial anyway), remove explicit destructor class definition:

class contactlist { public:     contactlist();     // no explicit destructor required     void addtohead(const std::string&);     void printlist();  private:     unique_ptr<contact> head;     int size; };