Main Application class as singleton

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Is using a singleton as a main application class in a framework a good idea? I presume that these "problems" are at least an indication that a better solution surely exists, but what would that alternative be?

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The problem here is that to be able to instantiate the subclass, you need to make its constructor public

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Where is the problem in the first place?

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Why must an application be a singleton? Is there an advantage to be gained from limiting it to one single instance, with no life-cycle management?

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What about "protected"? And while I don't know the details, why does there need to be setInstance method? This smells like someone used singletons, then ran into a problems due to restrictions, and worked around them.

// ---------------// Application.cpp// ---------------// [...]void CApplication::SetApplication(CApplication* pTheApp){	if(s_pTheApplication!=NULL)	{		fprintf(stderr,"More than one CApplication created!\n");		exit(1);	}	s_pTheApplication=pTheApp;}CApplication::CApplication():CMessageHandler(NULL){	SetApplication(this);	if(SDL_Init(SDL_INIT_EVERYTHING)==-1)	{		fprintf(stderr,"Failed to Init SDL:%s\n",SDL_GetError());		exit(1);	}	atexit(SDL_Quit);}// [...]

// Implementation of TestApplication's methods...// [...]//declare application variableCTestApplication TheApp;

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There is no "right" or "wrong" way to design an application. But at the same time - is there any need whatsoever for Application to be singleton?

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That's actually what my question was in my first post; is there a better solution, if yes then what would that be. Sorry if I didn't make myself clear.

int main( ... ){  Application app;  app.run();}

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Original post by XezekielX Souldn't main() also be "hidden" inside the framework?

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Then how could I "tell" the compiler to use my subclass? (other than doing main(...) { MyApplication myApp; myApp.run(); }, which obviously isn't an acceptable solution)

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Original post by Spoonbender Quote: Original post by XezekielX Souldn't main() also be "hidden" inside the framework? Should it? Depends on your preferences. Personally, I'd hate it. If I'm writing a game using your program, then I expect to write an application that uses the functionality you expose in your library. I don't expect it to be the other way around. I don't expect to run your application, and then have to wait for *it* to ask me what I'd like to do next. The thing is, if I'm a C++ programmer, I already know how to write a main function, and I know that is where execution starts. If I don't have one of those, I have to start digging through documentation just to figure out *which code is actually executed*

class application // base class for all applications{  // we are going to store a pointer to the user application   // object in a hidden global variable  static application* the_app;public:  // gives access to the user application object  static application& get_app() { return *the_app; }  // construct the app object  application()  {    // don't forget to initialize the hidden application variable    the_app = this;  }};// in main:int main(){  application& app = application::get_app();  app.run();}

// first, the main function - which is in the framework#undef mainint main(int ac, const char* av[]){  framework::do_init();  // call the main() writtent by the programmer:  framework_main(ac, av);  framework::do_uninit();}// the user code#include "framework.h"  // contains #define main framework_mainint main(int ac, const char* av[]){  my_application app;  app.run();}

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Original post by Emmanuel Deloget You can also give a look to the MFC - WinMain() is implemented in the framework, and when you see how complex it is, that's a pretty good thing [smile].

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Original post by XezekielX The problem here is that to be able to instantiate the subclass, you need to make its constructor public; doesn't that destroy the "protection" provided by the singleton pattern?

class Singleton{public:  Singleton * getInstance();private:  Singleton();  Singleton(Singleton *);  static Singleton * instance;};

class MyApplication : public Application{public:  virtual MyApplication * getInstance()  {    if(instance)      return instance;    return new MyApplication();  }private:  MyApplication();  MyApplication(MyApplication *);};