typedef struct sysstate; //假设的一个空结构，用来代表系统状态

//还原点
class Memento
{
public:
 Memento(sysstate &statein)
 {
  state = statein;
 }
 sysstate& getstate(){ return state}
private:
 sysstate state;
};

//运行系统
class system
{
public:
 void recovery(Memento* pMem)
 {
  if (pMem)
  {
   state = pMem->getstate();
  }  
 }
 Memento* backup()
 {
  return new Memento(state);
 }
private:
 sysstate state;
};

//还原控制器
class recoveryControl
{
public:
 ~recoveryControl()
 {
  map::iterator iter; 
  for ( iter = m_mementos.begin(); iter != m_mementos.end(); iter++)
  {
   delete iter.second;
  }
 }
 long addRecoveryPoint(Memento* pMem)
 {
  long t = clock();
  m_mementos.instert(pair(t, pMem));
  return t;
 }
 Memento* GetRecoveryPoint(long time)
 {
  map::iterator iter; 
 
  iter = m_mementos.find(time); 
 
  if(iter != m_mementos.end()) 
   return iter->second; 
  return NULL;
 }
 void DelRecoveryPoint(long time)
 {
  Memento* pMem = GetRecoveryPoint(time);
  m_mementos.erase(time);  
  delete pMem;
 }
private:
 map m_mementos;
};

int main()
{
 system Sys;
 recoveryControl controler;
 //备份系统并存入备份管理器中
 long time1 = controler.addRecoveryPoint(Sys.backup());
 long time2 = controler.addRecoveryPoint(Sys.backup());

 //将系统恢复到time1状态
 Sys.recovery(controler.GetRecoveryPoint(time1));

 //将系统恢复到time2状态
 Sys.recovery(controler.GetRecoveryPoint(time2));

}