ref: 4c09eaec1c1f81e175b6e8b6266e8a2c9aa7afaa dir: /lib/c/isalnum.c/
#define __USE_MACROS #include <ctype.h> #undef isalnum int isalnum(int c) { return (__ctype+1)[c] & (_U|_L|_D); }