C++設計模式淺識備忘錄模式

備忘錄模式(Memento)：在不破壞封裝性的前提下，捕獲一個對象的內部狀態，並在該對象之外儲存這個狀態。這樣以後就可將該對象恢複到原先儲存的狀態。

模式實現：

[code]struct State{    wchar_t wcsState[260];};class Memento{public:    Memento(State *pState): m_pState(pState) {}    State *GetState() { return m_pState; }private:    friend class Originator;    State *m_pState;};class Originator{public:    Originator() : m_pState(NULL) {}    ~Originator(){        //Delete the storage of the state        if(m_pState){            delete m_pState;            m_pState = NULL;        }    }    void SetMemento(Memento *pMemento);    Memento * CreateMemento();    void SetValue(wchar_t *val){        memset(wcsValue, 0, 260 * sizeof(wchar_t));        wcscpy_s(wcsValue, 260, val);    }    void PrintState() { std::wcout << wcsValue << std::endl; } private:    State *m_pState; //To store the object's state    wchar_t wcsValue[260]; //This is the object's real data};Memento *Originator::CreateMemento(){    m_pState = new State;    if(m_pState == NULL)        return NULL;    Memento *pMemento = new Memento(m_pState);    wcscpy_s(m_pState->wcsState, 260, wcsValue);  //Backup the value    return pMemento;}void Originator::SetMemento(Memento *pMemento){    m_pState = pMemento->GetState();    //Recovery the data    memset(wcsValue, 0, 260 * sizeof(wchar_t));    wcscpy_s(wcsValue, 260, m_pState->wcsState);}//Manager the Mementoclass Caretaker{public:    Memento *GetMemento() { return m_pMemento; }    void SetMemento(Memento *pMemento){        //Free the previous Memento        if(m_pMemento){            delete m_pMemento;            m_pMemento = NULL;        }        //set the new Memento        m_pMemento = pMemento;    }private:    Memento *m_pMemento;};

用戶端：

[code]int main(){     Originator *pOriginator = new Originator();    pOriginator->SetValue(L"on");    pOriginator->PrintState();  //OutPut： on    //Now I backup the state    Caretaker *pCaretaker = new Caretaker();    pCaretaker->SetMemento(pOriginator->CreateMemento());    //Set the new state    pOriginator->SetValue(L"off");    pOriginator->PrintState(); //OutPut： off    //Recovery to the old state    pOriginator->SetMemento(pCaretaker->GetMemento());    pOriginator->PrintState(); //OutPut： on    if(pCaretaker)        delete pCaretaker;    if(pOriginator);        delete pOriginator;    return 0;}

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