とりあえずwinなら

if (size == 1) {
 c = *(char*)x;
} else if (size == 2) {
 s = *(short*)x;
} else if (size == 4) {
 i = *(int*)x;
 l = *(long*)x;
 f = *(float*)x;
}

こんな感じにすれば?