How do I convert separate int values to hex byte array

Question

I need to do some (new to me) int/hex/byte work and I am struggling to get it right. The tcp server on the other side is expecting Little Endian.

I need to send a byte array consisting of HEX values.

6000 needs to be sent as:

0x70, 0x17

19 needs to be sent as:

0x13, 0x00, 0x00, 0x00

The resulting byte array should look like this.

**FROM THE MANUFACTURER**
Complete message should be: 

0x70, 0x17, 0x13, 0x00, 0x00, 0x00, 0x40, 0x42, 0x0f, 0x00, 0xA0, 0x86, 0x01, 0x00, 0x04, 0x01, 0x02, 0x03, 0x04

I can get the hex value of 6000 as 1770 by using: .ToString("x4") I can get the hex value of 19 as 00000013 by using: .ToString("x8")

I have two questions:

This (to my knowledge) is Big Endian. Short from chopping the string and manually rewriting it to reverse it, is there a .net routine that can do this for me?
Once I have it reversed, how do I get

7017

in a byte array of:

[0] = 0x70, [1] = 0x17

Thanks in advance.

in which format do you need it in the end? starting with 6000 it should endup in a byte[] {0x70, 0x17} ? — Mong Zhu
– Mong Zhu, Commented Jul 20, 2017 at 11:32
are you sending raw bytes? Then BitConverter.GetBytes(value); would by more suitable than strings. And once you have a byte array, just call Array.Reverse(bytes); to reverse your bytes. — fairtrax
– fairtrax, Commented Jul 20, 2017 at 11:34
@MongZhu and @fairtrax. Manufacturer message states final data on the wire should be a byte array that looks like: 0x70, 0x17, 0x13, 0x00, 0x00, 0x00, 0x40, 0x42, 0x0f, 0x00, 0xA0, 0x86, 0x01, 0x00, 0x04, 0x01, 0x02, 0x03, 0x04 — Louis van Tonder
– Louis van Tonder, Commented Jul 20, 2017 at 11:35
I was doing such staff in java with bit-wise operators, shifting each 8 bits of a number to the right, converting to byte etc, that was much more complicated :D but funny, just playing with bits. — fairtrax
– fairtrax, Commented Jul 20, 2017 at 11:36
do you send formatted strings, or bytes? 0x70, 0x17 etc is just human-readable form of the bytes, but the bytes "on the wire" take 1 byte per byte, instead of 4 (0x17 is 23 etc.) If you really format them and send a string separated by commas, use the code of Mong Zhu below. — fairtrax
– fairtrax, Commented Jul 20, 2017 at 11:43

Mong Zhu · Accepted Answer · 2017-07-20 11:55:52Z

2

You can use the BitConverter class to achieve the conversion. The result is actually already in the convention that you need. No Reversion is necessary

byte[] res6000 = BitConverter.GetBytes(6000);
byte[] res19 = BitConverter.GetBytes(19);

// TEST OUTPUT for example
Console.WriteLine(" 6000 -> : " + String.Join("", res6000.Select(x => x.ToString("X2"))));
Console.WriteLine("  19  -> : " + String.Join("", res19.Select(x=>x.ToString("X2"))));

Output:

6000 -> : 70170000
19 -> : 13000000

Here is a little method that does the job, with the amount of bytes that you desire:

public byte[] TransformBytes(int num, int byteLength)
{
    byte[] res = new byte[byteLength];

    byte[] temp = BitConverter.GetBytes(num);

    Array.Copy(temp, res, byteLength);

    return res;
}

Then you could call it and combine the result in a list like this:

List<byte> allBytesList = new List<byte>();

allBytesList.AddRange(TransformBytes(   6000, 2));
allBytesList.AddRange(TransformBytes(     19, 4));
allBytesList.AddRange(TransformBytes(1000000, 4));
allBytesList.AddRange(TransformBytes( 100000, 4));
allBytesList.AddRange(TransformBytes(      4, 1));

Console.WriteLine(" All -> : " + String.Join(" ", allBytesList.Select(x => x.ToString("X2"))));

Output:

All -> : 70 17 13 00 00 00 40 42 0F 00 A0 86 01 00 04

The List<byte> can be easily converted in the end to an array:

byte [] b_array = allBytesList.ToArray();

edited Jul 20, 2017 at 11:55

answered Jul 20, 2017 at 11:35

Mong Zhu

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2 Comments

Louis van Tonder Over a year ago

Thanks a stack for this very detailed answer! It is appreciated. At least now the server is returning some data. On to the next challenge of reading said data. Thanks

Mong Zhu Over a year ago

@LouisvanTonder You are welcome. Good luck with the server chit-chat ;)

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