probleme avec singleton

Bonjour à tous !!

Je suis en train d'implementer un singleton de la façon suivante :

Code:

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#ifndef GLOBAL_STAT_YEAR_FILE_H #define GLOBAL_STAT_YEAR_FILE_H   #include <iostream>   class Player;   // GlobalStat implementation as a singleton   Header :   class GlobalStat {   public: ~GlobalStat();   // instanciates a GlobalStat static void init();   // retrieve the static created object static GlobalStat * getInstance();   // write the stat on the filestatic GlobalStat * _instance; void makeStat(Player * iPlayer, int iYear, const std::string & iNameFile="stat_year.txt");   private: GlobalStat(); GlobalStat(const GlobalStat&); GlobalStat& operator= (const GlobalStat&);   static GlobalStat * _instance;   };   #endif // GLOBAL_STAT_YEAR_FILE_H

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Et pour l'mplementation :

Code:

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#include "GlobalStat.h" #include "Player.h"   // pointer variable containing a GlobalStat intance GlobalStat * _instance = NULL;   GlobalStat::GlobalStat() { }   GlobalStat::~GlobalStat() { }   void GlobalStat::init() { if (_instance == NULL) _instance = new GlobalStat; }   GlobalStat * GlobalStat::getInstance() { return _instance; }   void GlobalStat::makeStat(Player * iPlayer, int iYear, const std::string & iNameFile) { std::cout << "This is the creation of a file" << std::endl; }

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Et je trouve les erreurs :bug: :

GlobalStat.o: In function `GlobalStat::getInstance()':
GlobalStat.cpp:(.text+0x1c): undefined reference to `GlobalStat::_instance'
GlobalStat.o: In function `GlobalStat::init()':
GlobalStat.cpp:(.text+0xc8): undefined reference to `GlobalStat::_instance'
GlobalStat.cpp:(.text+0xe8): undefined reference to `GlobalStat::_instance'
collect2: ld returned 1 exit status

Pourquoi ? Comment je peux l'éviter ?

Merci !

Code:

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GlobalStat* GlobalStat::_instance = NULL;

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