#include <iostream>
#include <string>

using namespace std;

class SObject
{
  static SObject* c_instance; // 定義標(biāo)識符指針；

  /* 不需用拷貝和賦值，在單例模式中，始終只有一個對象 */  
  SObject(const SObject&);
  SObject& operator= (const SObject&);
  
  SObject() // 私有的構(gòu)造函數(shù)
  {
  }
public:
  static SObject* GetInstance();  // 創(chuàng)建對象的入口
  
  void print()
  {
    cout << "this = " << this << endl;
  }
};

SObject* SObject::c_instance = NULL; // 靜態(tài)成員類內(nèi)聲明，類外定義

SObject* SObject::GetInstance() // 單例模式的關(guān)鍵
{
  if( c_instance == NULL )
  {
    c_instance = new SObject();
  }
  
  return c_instance;
}

int main()
{
  SObject* s = SObject::GetInstance();
  SObject* s1 = SObject::GetInstance();
  SObject* s2 = SObject::GetInstance();
  
  s->print();  // this = 0x940a008
  s1->print(); // this = 0x940a008
  s2->print(); // this = 0x940a008
  
  return 0;
}
// 注：單例模式中，對象的生命周期存在整個系統(tǒng)運行過程中，所以是絕對不釋放的；

 // 對上個單例模式實現(xiàn)代碼的改進(jìn)

// singleton.hpp 單例模式代碼
#ifndef SINGLETON_H
#define SINGLETON_H

template
< typename T >
class Singleton
{
  static T* c_instance;
public:
  static T* GetInstance();
};

template
< typename T >
T* Singleton<T>::c_instance = NULL;

template
< typename T >
T* Singleton<T>::GetInstance()
{
  if( c_instance == NULL )
  {
    c_instance = new T();
  }
  
  return c_instance;
}

#endif

// main.cpp 測試文件
#include <iostream>
#include <string>
#include "singleton.hpp"

using namespace std;

class SObject
{
  friend class Singleton<SObject>;  // 當(dāng)前類需要使用單例模式
  
  SObject(const SObject&);
  SObject& operator= (const SObject&);
  
  SObject()
  {
  }
public:
  
  void print()
  {
    cout << "this = " << this << endl;
  }
};

int main()
{
  SObject* s = Singleton<SObject>::GetInstance();
  SObject* s1 = Singleton<SObject>::GetInstance();
  SObject* s2 = Singleton<SObject>::GetInstance();
  
  s->print();  // 0xe63c20
  s1->print(); // 0xe63c20
  s2->print(); // 0xe63c20
  
  return 0;
}