Timer Callback

[Ryan Binns]

The function must be declared as static Hope this helps,

Ryan

"Punctuality is only a virtue for those who aren't smart enough to think of good excuses for being late" John Nichol "Point Of Impact"

[LittleYellowBird]

Thanks for the suggestion. In fact I have got my code working like that at the moment, but I have several timers and I wanted to assign each one its own handling function. Thanks anyway :) Ali

[ivor bigun]

Haha, yes the declaration should be static void CALLBACK etc. well done ryan :)

[Phil Speller]

To expand on Ryan's post - it's all to do with pointers to member functions. Take a look at this[^] site - it will explain all! Phil

[LittleYellowBird]

Thanks, the link looks really helpful, looks like I need to do some reading! :) Ali

[LittleYellowBird]

You're right changing the funstionto static gets rid of the compiler error. However, now I have more errors calling functions from the timer function. Looks like I need to read up on static functions! Thanks for the help, much appreciated :) Ali

[Ryan Binns]

You're welcome :) Alison Pentland wrote: However, now I have more errors calling functions from the timer function. Looks like I need to read up on static functions! Good idea ;) Your errors at the moment are probably because you're calling non-static members from your static function. You can't do that :). The general way of using static functions as callbacks is to pass a pointer to the object as the lParam value that gets passed to the callback function, and then using that pointer to access the other class members.

Ryan

"Punctuality is only a virtue for those who aren't smart enough to think of good excuses for being late" John Nichol "Point Of Impact"

[Vitali Halershtein]

Hi Alison, I am not sure that "static" is right method. See following: The citation: -The lpfnTimer callback function need not be named TimerProc, but it must be defined as follows: -void CALLBACK EXPORT TimerProc( - HWND hWnd, // handle of CWnd that called SetTimer - UINT nMsg, // WM_TIMER - UINT nIDEvent // timer identification - DWORD dwTime // system time -); So, TimerProc should be a function insted class method.

[Phil Speller]

Declaring a member function of class as static will remove the need for an instance of the class to be associated with it - i.e. no this pointer. What this means is that it can't access any of the normal member functions/variables - precisely because there is no associated this pointer. However, supply the static function with a pointer to an instance of the class and you can access all functions/variables (even private ones) via that pointer - because the static function is still declared in the scope of the class. In terms of pointers to functions, because a static member function has no associated this pointer you can obtain it's address directly (just like a C function) - this is why Ryan's suggestion worked. Any normal member function must have an associated this pointer with it, so even when you take the address of a member function you must still use it with a pointer to an instance of the class as well. class CMyClass { public: void MyFn (void); static void MyStaticFn (CMyClass *); }; typedef void(* FnPtr)(CMyClass*); // C style fn pointer typedef void(CMyClass::* MemberFnPtr)(); // C++ style fn pointer CMyClass* pMyClass = new CMyClass; MemberFnPtr pMFn = &CMyClass::MyFn; pMyClass->MyFn(); // Calling as normal pMyClass->*pMFn(); // Calling via pointer to member fn FnPtr pFn = &CMyClass::MyStaticFn; (*pFn)( pMyClass ); // Calling static member fn [edit] You could try using the nIDEvent parameter of SetTimer to hold the pointer to your class instance - cast it back to the correct type and use within your static fn. [/edit] Hope this helps, Phil

[Ryan Binns]

Talik wrote: So, TimerProc should be a function insted class method. There is nothing wrong with using a static member. The compiler treats functions and static members in exactly the same way.

Ryan

"Punctuality is only a virtue for those who aren't smart enough to think of good excuses for being late" John Nichol "Point Of Impact"