typedef struct sysstate; //假設的一個空結構，用來代表系統狀態//還原點class Memento{public: Memento(sysstate &statein) {  state = statein; } sysstate& getstate(){ return state}private: sysstate state;};//運行系統class system{public: void recovery(Memento* pMem) {  if (pMem)  {   state = pMem->getstate();  }   } Memento* backup() {  return new Memento(state); }private: sysstate state;};//還原控制器class recoveryControl{public: ~recoveryControl() {  map<long,Memento*>::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<long,Memento*>(t, pMem));  return t; } Memento* GetRecoveryPoint(long time) {  map<long,Memento*>::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<long,Memento*> m_mementos;};int main(){ system Sys; recoveryControl controler; //備份系統并存入備份管理器中 long time1 = controler.addRecoveryPoint(Sys.backup()); long time2 = controler.addRecoveryPoint(Sys.backup()); //將系統恢復到time1狀態 Sys.recovery(controler.GetRecoveryPoint(time1)); //將系統恢復到time2狀態 Sys.recovery(controler.GetRecoveryPoint(time2));}