How to convert decimal string value to hex byte array in C#?

Question

I have an input string which is in decimal format:

var decString = "12345678"; // in hex this is 0xBC614E

and I want to convert this to a fixed length hex byte array:

byte hexBytes[] // = { 0x00, 0x00, 0xBC, 0x61, 0x4E }

I've come up with a few rather convoluted ways to do this but I suspect there is a neat two-liner! Any thoughts? Thanks

UPDATE:

OK I think I may have inadvertently added a level of complexity by having the example showing 5 bytes. Maximum is in fact 4 bytes (FF FF FF FF) = 4294967295. Int64 is fine.

Do you know the maximum and minimum values you will have to deal with? — hatchet - done with SOverflow
– hatchet - done with SOverflow, Commented Jan 22, 2015 at 14:04

Sergey Kalinichenko · Accepted Answer · 2015-01-22 16:13:26Z

5

If you have no particular limit to the size of your integer, you could use BigInteger to do this conversion:

var b = BigInteger.Parse("12345678");
var bb = b.ToByteArray();
foreach (var s in bb) {
    Console.Write("{0:x} ", s);
}

This prints

4e 61 bc 0

If the order of bytes matters, you may need to reverse the array of bytes.

Maximum is in fact 4 bytes (FF FF FF FF) = 4294967295

You can use uint for that - like this:

uint data = uint.Parse("12345678");
byte[] bytes = new[] {
    (byte)((data>>24) & 0xFF)
,   (byte)((data>>16) & 0xFF)
,   (byte)((data>>8) & 0xFF)
,   (byte)((data>>0) & 0xFF)
};

Demo.

edited Jan 22, 2015 at 16:13

answered Jan 22, 2015 at 14:09

Sergey Kalinichenko

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4 Comments

Jon Over a year ago

And Array.Reverse since it seems big-endian output is desired.

Christoph Fink Over a year ago

Where does this generate the fixed length array (I want to convert this to a fixed length hex byte array)?

Sergey Kalinichenko Over a year ago

@ChrFin This gives OP a variable-size array which he is free to extend. The important thing is that this approach would not truncate his data or throw an exception, no matter how many decimal digits is supplied.

Mark Chidlow Over a year ago

Thanks @dasblinkenlight nice two-line answer - and thanks for demo!

Dmitrii Bychenko · Accepted Answer · 2023-05-19 15:39:46Z

4

You can use Linq:

  String source = "12345678";

  // "BC614E"
  String result = String.Concat(BigInteger
    .Parse(source)
    .ToByteArray()
    .Reverse()
    .SkipWhile(item => item == 0)
    .Select(item => item.ToString("X2")));

In case you want Byte[] it'll be

   // [0xBC, 0x61, 0x4E]
   Byte[] result = BigInteger
     .Parse(source)
     .ToByteArray()
     .Reverse()
     .SkipWhile(item => item == 0)
     .ToArray();

edited May 19, 2023 at 15:39

answered Jan 22, 2015 at 14:37

Dmitrii Bychenko

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Comments

Christoph Fink · Accepted Answer · 2015-01-22 14:14:47Z

3

To convert the string to bytes you can use BitConverter.GetBytes:

var byteArray = BitConverter.GetBytes(Int32.Parse(decString)).Reverse().ToArray();

Use the appropriate type instead of Int32 if the string is not allways an 32 bit integer.
Then you could check the lenght and add padding bytes if needed:

if (byteArray.Length < 5)
{
    var newArray = new byte[5];
    Array.Copy(byteArray, 0, newArray, 5 - byteArray.Length, byteArray.Length);
    byteArray = newArray;
}

edited Jan 22, 2015 at 14:14

answered Jan 22, 2015 at 14:09

Christoph Fink

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3 Comments

hatchet - done with SOverflow Over a year ago

Assuming the decimal string represents a value that fits in a 32-bit int.

Mark Chidlow Over a year ago

Thanks - that's certainly an improvement on my attempt! I'll give it a short while before accepting as best answer - as you never know ;-)

Matthew Watson Over a year ago

Can skip 3 bytes to give the same result as the OP: var result = BitConverter.GetBytes(ulong.Parse(decString)).Reverse().Skip(3).ToArray();

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