Function l_checkmode

3rd/lua-5.4.3/src/liolib.c:40–44

Check whether 'mode' matches '[rwa]%+?[L_MODEEXT]*' */

/* Check whether 'mode' matches '[rwa]%+?[L_MODEEXT]*' */
static int l_checkmode (const char *mode) {
  return (*mode != '\0' && strchr("rwa", *(mode++)) != NULL &&
         (*mode != '+' || ((void)(++mode), 1)) &&  /* skip if char is '+' */
         (strspn(mode, L_MODEEXT) == strlen(mode)));  /* check extensions */
}

#endif