func Int2HexStr(num int) (hex string) {
	if num == 0 {
		return "0"
	}
	for num > 0 {
		r := num % 16
		c := "?"
		if r >= 0 && r <= 9 {
			c = string(r + '0')
		} else {
			c = string(r + 'a' - 10)
		}
		hex = c + hex
		num = num / 16
	}
	return hex
}