class CompanyA
{
    public:
        void sendClearMsg() { cout << "call company A sendClear " << endl;}
        void sendEncryptedMsg() { cout << "call company A sendEncryptedMsg " << endl;}

};

class CompanyB
{
    public:
        void sendClearMsg() { cout << "call company B sendClear " << endl;}
        void sendEncryptedMsg() { cout << "call company B sendEncryptedMsg " << endl;}

};

//首先定義了兩個類，用於表示各個公司自己傳送資訊的方式。

//CompanyC與上述兩個公司不一樣，只允許將資料加密之後再傳送

//companyC only send encrypted Msg
class CompanyC
{
    public:
        void sendEncryptedMsg() { cout << "call company C sendEncryptedMsg " << endl;}

};


//定義了一個傳送資訊的類，對於不同的公司，封裝了公司的傳送資訊的方式，取決於模板實參。

template
class MsgSender
{
    public:
        void sendClear()
        {
            cout << "call MsgSender sendClear ... " << endl;
            Company c;
            c.sendClearMsg();
        }
        void sendEncrypted()
        {
            cout << "call MsgSender sendEncrypted ... " << endl;
            Company c;
            c.sendEncryptedMsg();
        }
};


//針對CompanyC的特化版本的傳送資訊方式，即如果模板實參為CompanyC，那麼直接呼叫此模板類
template<>
class MsgSender
{
    public:
        void sendClear()
        {
            cout << "call MsgSender sendClear ... " << endl;
        }
        void sendEncrypted()
        {
            cout << "call MsgSender sendEncrypted ... " << endl;
        }
};

//在每次將資訊發出去時，記錄下發出的資訊。
//log the Message
template
class LogSendMsg : public MsgSender
{
public:
    void Log()
    {
        cout << "call LogSendMsg log ..." << endl;
    //    sendClear(); //錯誤！！因為LogSendMsg類不知道這個sendClear函式是什麼？甚至不知道是哪兒來的。
        //error: there are no arguments to 'sendClear' that depend on a template parameter, so a declaration of 'sendClear' must be available|
        cout << "call LogSendMsg log end... " << endl;

    }

};