Function std::gui_utf8_next

unsigned int gui_utf8_next([]const char s, &unsigned long i)

gui_utf8_next() decodes the codepoint starting at byte *i of s[0..len) and advances *i past it (malformed or truncated sequences, overlongs and surrogates decode as U+FFFD, one byte at a time); gui_utf8_encode() writes cp's 1-4 bytes to out[0..4) and returns how many; gui_utf8_prev() returns the start of the codepoint before byte i (0 at the start).