class IDownloadSink{public:    virtual void OnDownloadFinished(const char* pURL, bool bOK) = 0;};class CMyDownloader{public:    CMyDownloader(IDownloadSink* pSink)        :m_pSink(pSink)    {    }    void DownloadFile(const char* pURL)    {        cout << "downloading: " << pURL << "" << endl;        if(m_pSink != NULL)        {            m_pSink->OnDownloadFinished(pURL, true);        }    }private:    IDownloadSink* m_pSink;};class CMyFile: public IDownloadSink{public:    void download()    {        CMyDownloader downloader(this);        downloader.DownloadFile("www.baidu.com");    }    virtual void OnDownloadFinished(const char* pURL, bool bOK)    {        cout << "OnDownloadFinished, URL:" << pURL << "    status:" << bOK << endl;    }};