Exiv2

        oss.copyfmt(os);

        char sign = value.toLong() < 0 ? '-' : '+';

        long h = long(abs(value.toFloat())/60.0);

        os << std::fixed << "UTC " << sign << std::setw(2) << std::setfill('0') << h << ":" 

           << std::setw(2) << std::setfill('0') << min;

        os.copyfmt(oss);