[c#] Write bytes to file

I have a hexadecimal string (e.g 0CFE9E69271557822FE715A8B3E564BE) and I want to write it to a file as bytes. For example,

Offset      0  1  2  3  4  5  6  7   8  9 10 11 12 13 14 15
00000000   0C FE 9E 69 27 15 57 82  2F E7 15 A8 B3 E5 64 BE   .þži'.W‚/ç.¨³åd¾

How can I accomplish this using .NET and C#?

Try this:

private byte[] Hex2Bin(string hex) 
{
 if ((hex == null) || (hex.Length < 1)) {
  return new byte[0];
 }
 int num = hex.Length / 2;
 byte[] buffer = new byte[num];
 num *= 2;
 for (int i = 0; i < num; i++) {
  int num3 = int.Parse(hex.Substring(i, 2), NumberStyles.HexNumber);
  buffer[i / 2] = (byte) num3;
  i++;
 }
 return buffer;
}

private string Bin2Hex(byte[] binary) 
{
 StringBuilder builder = new StringBuilder();
 foreach(byte num in binary) {
  if (num > 15) {
   builder.AppendFormat("{0:X}", num);
  } else {
   builder.AppendFormat("0{0:X}", num); /////// ?? 15 ???? 0
  }
 }
 return builder.ToString();
}

You convert the hex string to a byte array.

public static byte[] StringToByteArray(string hex) {
return Enumerable.Range(0, hex.Length)
                 .Where(x => x % 2 == 0)
                 .Select(x => Convert.ToByte(hex.Substring(x, 2), 16))
                 .ToArray();
}

Credit: Jared Par

And then use WriteAllBytes to write to the file system.

The simplest way would be to convert your hexadecimal string to a byte array and use the File.WriteAllBytes method.

Using the StringToByteArray() method from this question, you'd do something like this:

string hexString = "0CFE9E69271557822FE715A8B3E564BE";

File.WriteAllBytes("output.dat", StringToByteArray(hexString));

The StringToByteArray method is included below:

public static byte[] StringToByteArray(string hex) {
    return Enumerable.Range(0, hex.Length)
                     .Where(x => x % 2 == 0)
                     .Select(x => Convert.ToByte(hex.Substring(x, 2), 16))
                     .ToArray();
}

This example reads 6 bytes into a byte array and writes it to another byte array. It does an XOR operation with the bytes so that the result written to the file is the same as the original starting values. The file is always 6 bytes in size, since it writes at position 0.

using System;
using System.IO;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main()
        {
        byte[] b1 = { 1, 2, 4, 8, 16, 32 };
        byte[] b2 = new byte[6];
        byte[] b3 = new byte[6];
        byte[] b4 = new byte[6];

        FileStream f1;
        f1 = new FileStream("test.txt", FileMode.Create, FileAccess.Write);

        // write the byte array into a new file
        f1.Write(b1, 0, 6);
        f1.Close();

        // read the byte array
        f1 = new FileStream("test.txt", FileMode.Open, FileAccess.Read);

        f1.Read(b2, 0, 6);
        f1.Close();

        // make changes to the byte array
        for (int i = 1; i < b2.Length; i++)
        {
            b2[i] = (byte)(b2[i] ^ (byte)10); //xor 10
        }

        f1 = new FileStream("test.txt", FileMode.Open, FileAccess.Write);
        // write the new byte array into the file
        f1.Write(b2, 0, 6);
        f1.Close();

        f1 = new FileStream("test.txt", FileMode.Open, FileAccess.Read);

        // read the byte array
        f1.Read(b3, 0, 6);
        f1.Close();

        // make changes to the byte array
        for (int i = 1; i < b3.Length; i++)
        {
            b4[i] = (byte)(b3[i] ^ (byte)10); //xor 10
        }

        f1 = new FileStream("test.txt", FileMode.Open, FileAccess.Write);

        // b4 will have the same values as b1
        f1.Write(b4, 0, 6);
        f1.Close();
        }
    }
}