Thread: Undefined Reference

This problem has me absolutely stumped. As far as I can tell it's an include issue, but I don't know why.

perimosMain.cpp

Code:

      1 #include "perimosDatabase.hpp"
      2 
      3 class Client
      4 {
      5 public:
      6   Client();
      7   ~Client();
      8   Window parentID;
      9   Window windowID;
     10 };
     11 
     12 Client::Client(){}
     13 Client::~Client(){}
     14 
     15 int main()
     16 {
     17   perimos::database<Client>* pDB = new perimos::database<Client>;
     18   Client c;
     19 
     20   for (int a=1;a<10;++a) {
     21     c.windowID = a;
     22     pDB->add_entry(c.windowID,c);
     23   }
     24 
     25   Window wid = 3;
     26   pDB->remove_entry(wid);
     27 
     28   delete pDB;
     29   return 0;
     30 }

perimosDatabase.hpp

Code:

      1 #include <iostream>
      2 #include <map>
      3 
      4 /*extern "C" {
      5   #include <X11/Xlib.h> // Window definition
      6 }*/
      7 typedef unsigned long int Window;
      8 namespace perimos
      9 {
     10   template<class T> // T is the client type.
     11   class database
     12   {
     13   private:
     14     std::map<Window,T> db;
     15     typename std::map<Window,T>::iterator pEntry;
     16     bool locate(Window&);
     17   public:
     18     database();
     19     ~database();
     20     bool add_entry(Window&,T&);
     21     bool remove_entry(Window&);
     22     T& get_entry(Window&);
     23     void print();
     24   };
     25 } // namespace

perimosDatabase.cpp

Code:

      1 #include "perimosDatabase.hpp"
      2 
      3 template<class T>
      4 perimos::database<T>::database()
      5 {
      6 }
      7 template<class T>
      8 perimos::database<T>::~database()
      9 {
     10 }
     11 /*********************************************************
     12 ** Prototype:   locate(Window&)
     13 ** Parameters:  1
     14 *** Window&:    The window identity of the client.
     15 ** Returns:     True if the entry was found and false otherwise.
     16 ** Comments:    Private function.
     17 */
     18 template<class T>
     19 bool perimos::database<T>::locate(Window& wID)
     20 {
     21   pEntry = db.find(wID);
     22   if (pEntry != db.end())
     23     return true;
     24   return false;
     25 }
     26 /*********************************************************
     27 ** Prototype:   add_entry(Window&,T&)
     28 ** Parameters:  2
     29 *** Window&:    The window identity of the client.
     30 *** T&:         The client object.
     31 ** Returns:     True if the entry was added and false otherwise.
     32 ** Comments:    If false is returned, then the window identity was more than
     33                 likely a duplicate.
     34 */
     35 template<class T>
     36 bool perimos::database<T>::add_entry(Window& wID,T& c)
     37 {
     38   if (db.insert(std::make_pair(wID,c)).second)
     39     return true;
     40   std::cout<<""<<std::endl;
     41   return false;
     42 }
     43 /*********************************************************
     44 ** Prototype:   remove_entry(Window&)
     45 ** Parameters:  1
     46 *** Window&:    The window identity of the client
     47 ** Returns:     True if the entry was removed and false otherwise.
     48 ** Comments:    If false is returned, then the window identity didn't exist.
     49 */
     50 template<class T>
     51 bool perimos::database<T>::remove_entry(Window& wID)
     52 {
     53   if (locate(wID)) {
     54     db.erase(pEntry);
     55     return true;
     56   }
     57   return false;
     58 }
     59 /*********************************************************
     60 ** Prototype:   get_entry(Window&)
     61 ** Parameters:  1
     62 *** Window&:    The window identity of the client.
     63 ** Returns:     A reference to the client object stored in the database.
     64 ** Comments:    If the window identity does not exist, then the `windowID' of
     65                 returned object will equal zero (0). Ensure this is checked!
     66 */
     67 template<class T>
     68 T& perimos::database<T>::get_entry(Window& wID)
     69 { 
     70   locate(wID);
     71   return pEntry->second;
     72 }
     73 /*********************************************************
     74 ** Prototype:   print()
     75 ** Parameters:  0
     76 ** Returns:     void
     77 ** Comments:    For debugging purposes only.
     78 */
     79 template<class T>
     80 void perimos::database<T>::print()
     81 { 
     82   for (pEntry = db.begin();pEntry!=db.end();++pEntry)
     83     std::cout<<pEntry->second.windowID<<":"<<&pEntry->second<<std::endl;
     84 }

The problem is: when I compile, below is the error I get:

Command:

Code:

g++ perimosMain.cpp perimosDatabase.cpp -o perimos

Error:

Code:

/var/tmp//ccFSVViv.o: In function `main':
/var/tmp//ccFSVViv.o(.text+0x4c): undefined reference to `perimos::database<Client>::database()'
/var/tmp//ccFSVViv.o(.text+0xbf): undefined reference to `perimos::database<Client>::add_entry(unsigned long&, Client&)'
/var/tmp//ccFSVViv.o(.text+0xdf): undefined reference to `perimos::database<Client>::remove_entry(unsigned long&)'
/var/tmp//ccFSVViv.o(.text+0xf9): undefined reference to `perimos::database<Client>::~database()'

However, if in perimosMain.cpp I change #include "perimosDatabase.hpp" to #include "perimosDatabase.cpp" it compiles.

Could some please shed some light on my problem here?

Sure it does:

Code:

      3 template<class T>
      4 perimos::database<T>::database()
      5 {
      6 }
      7 template<class T>
      8 perimos::database<T>::~database()
      9 {
     10 }

I not long ago worked out the problem was with the template, yet I'm still not quite sure what. Could you explain it some more please?

Do you mean that what's in perimosDatabase.cpp should be merged into perimosDatabase.hpp?

I understand. Thanks, CornedBee.