Return the starting position of the last occurrence of the specified substring within this string, if such a sequence can be found in this string (on or before the optionally specified position if such a position is specified) using CHAR_TRAITS::eq to compare characters, and return npos otherwise.
Declared in <bslstl_string.h>
size_type
rfind(
basic_string<char8_t> const& substring,
size_type position = npos) const noexcept;