Pretty much the only standard way to do this involves something like "void (fp)(void arg)" or "void (*fp)(va_list ap)" and generous casting. That said, this is

Pretty much the only standard way to do this involves something like "void (fp)(void arg)" or "void (*fp)(va_list ap)" and generous casting. That said, this is not that likely to be a problem in practice on Unix machines (Windows has more than one calling convention - I have no idea how much of a problem that is.)