virtual iter_type do_get_weekday(iter_type first, iter_type last,
ios_base& x, ios_base::iostate& st, tm *pt) const;The virtual protected member function endeavors to match sequential elements beginning at first in the sequence
[first, last) until it has recognized a complete, nonempty weekday input field. If successful, it converts this field
to its equivalent value as the component tm::tm_wday, and stores the result in pt->tm_wday. It returns an iterator
designating the first element beyond the weekday input field. Otherwise, the function sets ios_base::failbit in st.
It returns an iterator designating the first element beyond any prefix of a valid weekday input field. In either case, if the
return value equals last, the function sets ios_base::eofbit in st.
The weekday input field is a sequence that matches the longest of a set of locale-specific sequences, such as Sun,
Sunday, Mon, Monday. The converted value is the number of days since Sunday.