Fucking pointers...

void prepare_lock (SDL_mutex ** global_lock)
{
SDL_mutex * lock = *global_lock;
if (lock == NULL)
{
// This works, obviously:
*global_lock = SDL_CreateMutex ();
// but this doesn't (so it's commented):
// lock = SDL_CreateMutex ();
}
}

When I run:

prepare_lock (&teh_lock);

How do I pointers?