I've used an ugly line for now, that only allows letters and numbers:
Code:
(47 < str_getchar(str_in,pos) && str_getchar(str_in,pos) < 58) || (64 < str_getchar(str_in,pos) && str_getchar(str_in,pos) < 91) || (96 < str_getchar(str_in,pos) && str_getchar(str_in,pos) < 123) ? (