#include <iostream>using namespace std;#define DESTROY_POINTER(ptr) if (ptr) { delete ptr; ptr = NULL; }class Context;class DbState{public:    DbState(Context* pContext) { m_pContext = pContext; }    virtual void Open()=0;    virtual void Close()=0;    virtual void Read()=0;    virtual void Write()=0;protected:    Context* m_pContext;};class OpenState : public DbState{public:    OpenState(Context* pContext) : DbState(pContext) {}        void Open() { cout<<"Already open!"<<endl; }    void Close();    void Read() { cout<<"Finish Reading"<<endl; }    void Write() { cout<<"Finish Writing"<<endl; }};class CloseState : public DbState{public:    CloseState(Context* pContext) : DbState(pContext) {}        void Open();    void Close() { cout<<"Already Closing"<<endl; }    void Read() { cout<<"Already Closing, Can‘t read"<<endl; }    void Write() { cout<<"Already Closing, Can‘t write"<<endl; }};class ReadingState : public DbState{public:    ReadingState(Context* pContext) : DbState(pContext) {}        void Open() { cout<<"Already Open"<<endl; }    void Close();    void Read() { cout<<"Reading, Try again"<<endl; }    void Write() { cout<<"Reading, Can‘t write"<<endl; }};class WritingState : public DbState{public:    WritingState(Context* pContext) : DbState(pContext) {}        void Open() { cout<<"Already Open"<<endl; }    void Close();    void Read() { cout<<"Writing, Can‘t read"<<endl; }    void Write() { cout<<"Writing, Try again"<<endl; }};class BusyState : public DbState{public:    BusyState(Context* pContext) : DbState(pContext) {}        void Open() { cout<<"Already Open"<<endl; }    void Close() { cout<<"Busy, Can‘t Close"<<endl; }    void Read() { cout<<"Busy, Can‘t read"<<endl; }    void Write() { cout<<"Busy, Can‘t write"<<endl; }};class Context{public:    Context() : m_pState(NULL) {}    ~Context() { DESTROY_POINTER(m_pState); }    void SetState(DbState* pState) { DESTROY_POINTER(m_pState); m_pState = pState; }        void Open() { m_pState->Open(); }    void Close() { m_pState->Close(); }    void Read() { m_pState->Read(); }    void Write() { m_pState->Write(); }    private:    DbState* m_pState;};void OpenState::Close() { cout<<"Finish closing"<<endl; m_pContext->SetState(new CloseState(m_pContext)); }void CloseState::Open() { cout<<"Finish Opening"<<endl; m_pContext->SetState(new OpenState(m_pContext)); }void ReadingState::Close() { cout<<"Finish Closing"<<endl; m_pContext->SetState(new CloseState(m_pContext)); }void WritingState::Close() { cout<<"Finish Closing"<<endl; m_pContext->SetState(new CloseState(m_pContext)); }int main(int argc, char *argv[]){    Context context;    context.SetState(new OpenState(&context));    context.Open();    context.Close();        context.Open();    context.Read();    context.Write();        context.Close();    context.Write();        context.Open();    context.Write();        return 0;}