C# how convert large HEX string to binary

Question

I have a string with 14 characters . This is a hex represantation of 7bytes. I want to convert it to binary. I tried using Convert.ToString(Convert.ToInt32(hexstring, 16), 2); For small strings this works but for 14 characters it will not work because the result is too large. How can i manage this? Keep in mind that the output of the conversion should be a binary string with a lengeth of 56 characters (we must keep the leading zeros). (e.g. conversion of (byte)0x01 should yield "00000001" rather than "1")

Answer 1

You can just convert each hexadecimal digit into four binary digits:

string binarystring = String.Join(String.Empty,
  hexstring.Select(
    c => Convert.ToString(Convert.ToInt32(c.ToString(), 16), 2).PadLeft(4, '0')
  )
);

You need a using System.Linq; a the top of the file for this to work.

Answer 2

Convert.ToString(Convert.ToInt64(hexstring, 16), 2);

Maybe? Or

Convert.ToString(Convert.ToInt64(hexstring, 16), 2).PadLeft(56, '0');

Answer 3

Why not just take the simple approach and define your own mapping?

private static readonly Dictionary<char, string> hexCharacterToBinary = new Dictionary<char, string> {
    { '0', "0000" },
    { '1', "0001" },
    { '2', "0010" },
    { '3', "0011" },
    { '4', "0100" },
    { '5', "0101" },
    { '6', "0110" },
    { '7', "0111" },
    { '8', "1000" },
    { '9', "1001" },
    { 'a', "1010" },
    { 'b', "1011" },
    { 'c', "1100" },
    { 'd', "1101" },
    { 'e', "1110" },
    { 'f', "1111" }
};

public string HexStringToBinary(string hex) {
    StringBuilder result = new StringBuilder();
    foreach (char c in hex) {
        // This will crash for non-hex characters. You might want to handle that differently.
        result.Append(hexCharacterToBinary[char.ToLower(c)]);
    }
    return result.ToString();
}

Note that this will keep leading zeros. So "aa" would be converted to "10101010" while "00000aa" would be converted to "0000000000000000000010101010".

Answer 4

You can get a byte array from hex string using this code

 public static byte[] StringToByteArray(String hex)
    {
        int NumberChars = hex.Length;
        byte[] bytes = new byte[NumberChars / 2];
        for (int i = 0; i < NumberChars; i += 2)
            bytes[i / 2] = Convert.ToByte(hex.Substring(i, 2), 16);
        return bytes;
    }

Answer 5

My C++ background answer:

private Byte[] HexToBin(string pHexString)
{
    if (String.IsNullOrEmpty(pHexString))
        return new Byte[0];

    if (pHexString.Length % 2 != 0)
        throw new Exception("Hexstring must have an even length");

    Byte[] bin = new Byte[pHexString.Length / 2];
    int o = 0;
    int i = 0;
    for (; i < pHexString.Length; i += 2, o++)
    {
        switch (pHexString[i])
        {
            case '0': bin[o] = 0x00; break;
            case '1': bin[o] = 0x10; break;
            case '2': bin[o] = 0x20; break;
            case '3': bin[o] = 0x30; break;
            case '4': bin[o] = 0x40; break;
            case '5': bin[o] = 0x50; break;
            case '6': bin[o] = 0x60; break;
            case '7': bin[o] = 0x70; break;
            case '8': bin[o] = 0x80; break;
            case '9': bin[o] = 0x90; break;
            case 'A':
            case 'a': bin[o] = 0xa0; break;
            case 'B':
            case 'b': bin[o] = 0xb0; break;
            case 'C':
            case 'c': bin[o] = 0xc0; break;
            case 'D':
            case 'd': bin[o] = 0xd0; break;
            case 'E':
            case 'e': bin[o] = 0xe0; break;
            case 'F':
            case 'f': bin[o] = 0xf0; break;
            default: throw new Exception("Invalid character found during hex decode");
        }

        switch (pHexString[i+1])
        {
            case '0': bin[o] |= 0x00; break;
            case '1': bin[o] |= 0x01; break;
            case '2': bin[o] |= 0x02; break;
            case '3': bin[o] |= 0x03; break;
            case '4': bin[o] |= 0x04; break;
            case '5': bin[o] |= 0x05; break;
            case '6': bin[o] |= 0x06; break;
            case '7': bin[o] |= 0x07; break;
            case '8': bin[o] |= 0x08; break;
            case '9': bin[o] |= 0x09; break;
            case 'A':
            case 'a': bin[o] |= 0x0a; break;
            case 'B':
            case 'b': bin[o] |= 0x0b; break;
            case 'C':
            case 'c': bin[o] |= 0x0c; break;
            case 'D':
            case 'd': bin[o] |= 0x0d; break;
            case 'E':
            case 'e': bin[o] |= 0x0e; break;
            case 'F':
            case 'f': bin[o] |= 0x0f; break;
            default: throw new Exception("Invalid character found during hex decode");
        }
    }
    return bin;
}

Answer 6

You can do this.

I have put it in a class called UtilMath this is a good Idea as, if you ever use it in a different program you can use the class again. And as the name implies this is for all my Math functions.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace Math.Util
{
    class UtilMath
    {

        public static string hex2binary(string hexvalue)
        {
            // Convert.ToUInt32 this is an unsigned int
            // so no negative numbers but it gives you one more bit
            // it much of a muchness 
            // Uint MAX is 4,294,967,295 and MIN is 0
            // this padds to 4 bits so 0x5 = "0101"
            return String.Join(String.Empty, hexvalue.Select(c => Convert.ToString(Convert.ToUInt32(c.ToString(), 16), 2).PadLeft(4, '0')));
        }
    }
}

now before you use it you need to include it,

using Math.Util

then if you need to use it you can call it by going

UtilMath.hex2binary("FF");

Or

String hexString = "FF";
UtilMath.hex2binary(hexString);

Hope this helps.

Answer 7

Convert.FromHexString has been introduced in .Net 5

 var bytes = Convert.FromHexString("13AF3F")

Answer 8

What if you convert one character at a time? I'm can't test this out, but the idea should work.

//Convert.ToString(Convert.ToInt32(hexstring, 16), 2)

StringBuilder sb = new StringBuilder();
foreach( char c in hexstring.ToCharArray() ){
  sb.Append( Convert.ToString(Convert.ToInt32(c.ToString(), 16), 2);
}

Answer 9

How about using Int64 instead of Int32?

Convert.ToString(Convert.ToInt64(hexstring, 16), 2);

Answer 10

If you need a byte array, you can get it by:

Collection<byte> bytes = new Collection<byte>();
for (int i = 0; i < hexText.Length; i += 2) {
    byte bin = BitConverter.GetBytes(Convert.ToInt32(hexText.Substring(i, 2), 16))[0];
    bytes.Add(bin);
}

But if it is directly to save to a file, I would do it directly:

using FileStream fileStream = new FileStream(fileName, FileMode.Create, FileAccess.Write);
for (int i = 0; i < hexText.Length; i += 2) {
    byte bin = BitConverter.GetBytes(Convert.ToInt32(hexText.Substring(i, 2), 16))[0];
    fileStream.WriteByte(bin);
}
fileStream.Close();