21std::uint8_t
utf8_decode_step(std::uint8_t state, std::uint8_t octet, std::uint32_t* cpp);
std::u32string utf8_to_utf32(const std::string &str)
std::uint8_t utf8_decode_step(std::uint8_t state, std::uint8_t octet, std::uint32_t *cpp)
bool is_valid_utf8_code_unit(const std::string &str)