Method encode_utf8

tests/autotester/json11.hpp:664–683

encode_utf8(pt, out) * * Encode pt as UTF-8 and add it to out. */

     * Encode pt as UTF-8 and add it to out.
     */
    void encode_utf8(long pt, string & out) {
        if (pt < 0)
            return;

        if (pt < 0x80) {
            out += static_cast<char>(pt);
        } else if (pt < 0x800) {
            out += static_cast<char>((pt >> 6) | 0xC0);
            out += static_cast<char>((pt & 0x3F) | 0x80);
        } else if (pt < 0x10000) {
            out += static_cast<char>((pt >> 12) | 0xE0);
            out += static_cast<char>(((pt >> 6) & 0x3F) | 0x80);
            out += static_cast<char>((pt & 0x3F) | 0x80);
        } else {
            out += static_cast<char>((pt >> 18) | 0xF0);
            out += static_cast<char>(((pt >> 12) & 0x3F) | 0x80);
            out += static_cast<char>(((pt >> 6) & 0x3F) | 0x80);
            out += static_cast<char>((pt & 0x3F) | 0x80);
        }
    }

    /* parse_string()
     *