check_dayofweek
if (check_dayofweek(date2, &len, &di->dayofweek)) {
check_dayofweek(p2, &len, &di->dayofweek)) {
if (check_dayofweek(p2, &len, &di->dayofweek)) {
static bool check_dayofweek(const char *s, size_t *len, int *dow);