vovoida siph323csgw程序入口体现的多态

通过带C++语法高亮的editor软件阅读，将提高可读性和效率。这种editor软件有
(Win32)EditPlus2,UltraEdit32,Source Insigt;
(GNU/Linux)kedit, vim等。

类的关系：
Runnable <-- Application <-- SipToH323CallSigGW (箭头所指者为基类)
ApplicationCreator <-- SipToH323CallSigGWCreator

纯虚函数：
Runnable有run(),
ApplicationCreator有create()[@more@]//代码开始
ApplicationCreator* Application::myCreator = 0;
Application* Application::myApplication = 0;

int main() {
    using namespace std;
    
    cout << "Starting..." << endl;

    SipToH323CallSigGWCreator creator;
    Application::creator(&creator);
    return ( Application::main() );
}
//代码结束

//代码开始
const int SUCCESS = 0;
typedef int ReturnCode;
//Application类
class Application : public Runnable {
    private:
        static Application* myApplication;
        static ApplicationCreator* myCreator;
    protected:
        virtual ReturnCode init();
    public:
        static void creator(ApplicationCreator*);
        static Application& instance();
        static ReturnCode main();
};
//代码结束

//代码开始
void Application::creator(ApplicationCreator* creator) {
    myCreator = creator;
}

Application& Application::instance() {
    if ( !myApplication ) {
        if ( myCreator != 0 ) {
            myApplication = myCreator->create();
        }
        else {
            throw "No ApplicationCreator";
        }
    }   
    return ( *myApplication );
}

ReturnCode Application::init() {
    return SUCCESS;
}

ReturnCode Application::main() {
    Application& app = Application::instance();
    ReturnCode rc = 0;
    try {
        rc = app.init();
    }
    catch ( ... ) {
        cerr << "Unhandled exception from Application::init()." << endl;
        return 1;
    }
    if ( rc != 0 ) {
        return rc;
    }

    try {
        rc = app.run();
    }
    catch ( ... ) {
        cerr << "Unhandled exception from Application::run()." << endl;
        return 1;
    }
    return rc;
}

ReturnCode ServiceApplication::run() {
    string fn ("ServiceApplication::Run");
    cout << fn << endl;
    ReturnCode rc = SUCCESS;
    return rc;
}

ReturnCode ServiceApplication::init() {
    cout << "ServiceApplication::init()" << endl;
    ReturnCode rc = SUCCESS;
    return rc;
}

Application* SipToH323CallSigGWCreator::create() {
    return ( new SipToH323CallSigGW );
}
//代码结束

//代码重现开始
int main() {
    using namespace std;
   
    cout << "Starting..." << endl;

    SipToH323CallSigGWCreator creator;
    Application::creator(&creator);
    return ( Application::main() );
}
//代码重现结束

通过Application::creator()，&creator传递给Applicaion::myCreator，myCreator指向creator(SipToH323CallSigGWCreator的实例)
在Appliation::main()中，先调用Application::instance()，
在Application::instance()中，调用myCreator->create()。由于myCreator指向creator，将调用creator的create()方法，该方法返回
一个SipToH323CallSigGW实例。而在Application::main()中，Application::instance()还将返回*myApplication，此时myApplication指
向生成的SipToH323CallSigGW实例，因而局部Application引用app也指向该实例。app.run()和app.init()调用的是ServiceApplication的
同名方法(多态^-^)。

欢迎通过[e-mail]交流、赐教。也可提供与本帖相关的源文件和GNU Makefile。
vovida的开源软件通过可了解更多。

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