C# - Convert hex string to byte array of hex values

Question

This question looks like a bunch of other questions, but none exactly match what I need. The problem with the other related questions seem to do an implicit conversion to decimal based on Visual Studio's IntelliSense.

Goal: Trying to convert hex string to byte array of hex values (not decimal values) in C#.

public static byte[] ConvertHexValueToByteArray() 
{
  string hexIpAddress = "0A010248"; // 10.1.2.72 => "0A010248"
  byte[] bytes = new byte[hexIpAddress.Length / 2];

  for (int i = 0; i < hexIpAddress.Length; i += 2)
  {
    string s2CharSubStr = hexIpAddress.Substring(i, 2);  // holds "0A" on 1st pass, "01" on 2nd pass, etc.

    if ((s2CharSubStr.IsAllDigit()) && (int.Parse(s2CharSubStr) < 10)) // fixes 0 to 9
      bytes[i / 2] = (byte) int.Parse(s2CharSubStr); // same value even if translated to decimal
    else if (s2CharSubStr.IsAllDigit()) // fixes stuff like 72 (decimal) 48 (hex)
      bytes[i / 2] = Convert.ToByte(s2CharSubStr, 10); // does not convert, so 48 hex stays 48 hex. But will not handle letters.
    else if (s2CharSubStr[0] == '0') // handles things like 10 (decimal) 0A (hex) 
      bytes[i / 2] = // ?????????????????????????????
    else // handle things like AA to FF (hex)
      bytes[i / 2] = // ?????????????????????????????
   }

   return bytes;
 }

Answers like the two below do implicit conversions (as viewed in Visual Studio's IntelliSense) from the hex to decimal AND/OR fail to handle the alpha part of the hex: 1)

bytes[i / 2] = (byte)int.Parse(sSubStr, NumberStyles.AllowHexSpecifier);

2)

bytes[i / 2] = Convert.ToByte(hex.Substring(i, 2), 16);

3) bytes[i / 2] = Convert.ToByte(hexIpAddress.Substring(i, 2));

So I would like the function to return the equivalent of this hard-coded byte array:

byte[] currentIpBytes = {0x0A, 01, 02, 0x48};

What is the difference between "decimal" and "hex values"? They are bytes, 0x01 is the same as 1, 0x0a is the same as 10 an so on, when you deal with binary data, not string data, the representation is indifferent of the underlying data. — Gusman
– Gusman, Commented Jan 31, 2017 at 17:14
But 2) is correct. A byte value is a byte value...so bytes[0] will be of value 10 (decimal) which is 0x0A. What other value do you want bytes[0] to have? — René Vogt
– René Vogt, Commented Jan 31, 2017 at 17:14
I would like the function to return the equivalent of this hard-coded byte array: byte[] currentIpBytes = {0x0A, 01, 02, 48}; — Eric Wood
– Eric Wood, Commented Jan 31, 2017 at 17:16
Yes, so bytes[i/2] = Convert.ToByte(hexIpAddress.Substring(i,2)); does exactly what you want. (though it's 0x48, not 48) — René Vogt
– René Vogt, Commented Jan 31, 2017 at 17:17
@Rene, public static byte[] ConvertHexValueToByteArray() { string hexIpAddress = "0A010248"; byte[] bytes = new byte[hexIpAddress.Length / 2]; for (int i = 0; i < hexIpAddress.Length; i += 2) { bytes[i / 2] = Convert.ToByte(hexIpAddress.Substring(i, 2)); } return bytes; } // returns error. I would be happy at 0x48 in the byte array. — Eric Wood
– Eric Wood, Commented Jan 31, 2017 at 17:20

René Vogt · Accepted Answer · 2017-01-31 17:33:20Z

3

string hexIpAddress = "0A010248"; // 10.1.2.72 => "0A010248"
byte[] bytes = new byte[hexIpAddress.Length / 2];

for (int i = 0; i < hexIpAddress.Length; i += 2)
    bytes[i/2] = Convert.ToByte(hexIpAddress.Substring(i, 2), 16);

This results in this array:

bytes = {0x0A, 0x01, 0x02, 0x48};

or represented as decimals:

bytes = {10, 1, 2, 72};

or as binaries 00001010, 000000001, 00000010, 01001000 (binary literals are still not supported in C#6).

The values are the same, there is no representation in any base in byte. You can only decide how the values should be represented when converting them to strings again:

foreach(byte b in bytes)
    Console.WriteLine("{0} {0:X}", b);

results in

edited Jan 31, 2017 at 17:33

answered Jan 31, 2017 at 17:23

René Vogt

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3 Comments

Eric Wood Over a year ago

Correction: "hex" needs to be "hexIpAddress" in your answer.

Eric Wood Over a year ago

Let me understand. So my core problem I have is a misunderstanding of what code insight shows {10, 1, 2, 72} it is really the hex values underneath {0x0A, 0x01, 0x02, 0x48} ? So when I send this to a device that wants my IP address in hex values, it will really be fine?

René Vogt Over a year ago

@EricWood well that depends on the device and who told you it "expects hex values", but I'm pretty sure it will be alright. Btw: if you're using Visual Studio, you can tell the debugger if it should show the values as hex or decimal (right click in the "Watch" window, I guess).

Lee Taylor · Accepted Answer · 2022-06-13 12:57:55Z

1

private string DateToHex(DateTime theDate)
{
    string isoDate = theDate.ToString("yyyyMMddHHmmss");

    string resultString = string.Empty;

    for (int i = 0; i < isoDate.Length ; i++)    // Amended
    {
        int n = char.ConvertToUtf32(isoDate, i);
        string hs = n.ToString("x");
        resultString += hs;
    }
    return resultString;
}

edited Jun 13, 2022 at 12:57

Lee Taylor

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answered Jun 13, 2022 at 12:41

payam purchi

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