size_type
find_first_of(const basic_string& str,
size_type pos = 0) const noexcept;
Returns: xpos if the function can determine such a value for xpos. Otherwise, returns npos.
Remarks: Uses traits::eq().
size_type
find_first_of(const charT* s, size_type pos, size_type n) const;
Returns: find_first_of(basic_string(s, n), pos).
size_type find_first_of(const charT* s, size_type pos = 0) const;
Requires: s points to an array of at least traits::length(s) + 1 elements of charT.
Returns: find_first_of(basic_string(s), pos).
size_type find_first_of(charT c, size_type pos = 0) const;
Returns: find_first_of(basic_string(1,c), pos).