boost::text::v1::transcode_to_utf8
// In header: <boost/text/transcode_algorithm.hpp> template<std::input_iterator I, std::sentinel_for< I > S, std::output_iterator< uint8_t > O> transcode_result< I, O > transcode_to_utf8(I first, S last, O out);
Copies the code points in the range [first, last) to out, changing the encoding to UTF-8.
[first, last)
out