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.

Answer 1

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.