Thanks, SGaist.
QtSingleApplicaiton is an alternative solution to singleton , I will make a try.

@Chris-Kawa Thanks a lot your answer solve my dude thanks a lot. The system of resources of Qt is awesome and more easy to use so it's better. Anyways i was trying to understand more about windows api and with these explications i understand now thanks.

@Thynome
Hi,
Well, you're stuck with C when working with the WinApi. It sucks, I know, but you need to transfer the context (the object) through a global variable. You can look here for some inspiration - WindowsCtrlDispatcher::instance is the context that's transferred to the VOID WINAPI ServiceMain(DWORD, LPTSTR *) function. I hope that helps.

Kind regards.

@SGaist said:

Indeed, but I wouldn't be surprised if that changed at some point :D

Perhaps, perhaps. Although, judging from the time it took MS to introduce the x64 compiler, if it were to change, it'd take decades. And since it hasn't changed for over 30 years, I really doubt that it ever will. :D