template<class T>
size_type rfind(const T& t, size_type pos = npos) const;
size_type rfind(const basic_string& str, size_type pos = npos) const noexcept;
size_type rfind(const charT* s, size_type pos, size_type n) const;
size_type rfind(const charT* s, size_type pos = npos) const;
size_type rfind(charT c, size_type pos = npos) const;