[Openal] Initializing effects extension

[Chris Robinson]

On Thursday 09 April 2009 12:36:50 pm Margin Marh wrote:
> You was right it fixed the error but before i go to tutorial 2 i don't
>
> understand 2 parts in the code...What does this part means :
> > alGenEffects    = (LPALGENEFFECTS)alGetProcAddress("alGenEffects");
> >         alDeleteEffects =
> > (LPALDELETEEFFECTS)alGetProcAddress("alDeleteEffects");
> >         alIsEffect      = (LPALISEFFECT)alGetProcAddress("alIsEffect");
>
> I dont understand that part very well so some explanation would be welcomed
>
> :)

alGenEffects (and alDeleteEffects and the others) are pointers to the 
functions you want to use. alGetProcAddress will return the pointer to the 
named function as a void*. By itself, just
alGenEffects = alGetProcAddress("alGenEffects");
would be sufficient, except most C/C++ compilers won't let that work without 
warnings or errors (they don't like implicitly casting void* to function 
pointer types).

So, you have to explicitly cast the void* to the function pointer type when 
assigning it. LPALGENEFFECTS is a typedef defined by efx.h as a pointer type 
to the alGenEffects function.

alGenEffects = (LPALGENEFFECTS)alGetProcAddress("alGenEffects");
  ^     ^        ^    ^     ^         ^    ^     ^     ^    ^
func pointer  cast to func pointer  returns func pointer as void*

So alGetProcAddress returns the pointer to alGenEffects as a void*, which is 
then cast to the LPALGENEFFECTS type, and then assigned to your function 
pointer.

Hope that clarifies. :)