352

Can we convert a hex string to a byte array using a built-in function in C# or do I have to make a custom method for this?

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  • 2
    You can easily convert string to byte[] in one line: var byteArray = Encoding.ASCII.GetBytes(string_with_your_data); Commented Jun 6, 2013 at 22:02
  • 38
    @mik-T, a hex string is in some format like 219098C10D7 which every two character converts to one single byte. your method is not usable. Commented Dec 12, 2014 at 7:52
  • 5
    This question does not seem to be duplicate of selected question. this one converts FROM hex string to byte array, however other question converts byte array to hex. Commented Dec 12, 2014 at 7:53
  • 3
    A simple one-liner with: BigInteger.Parse(str, System.Globalization.NumberStyles.HexNumber).ToByteArray().Reverse().ToArray() Commented Mar 10, 2020 at 21:21
  • 3
    Convert.FromHexString Method learn.microsoft.com/en-us/dotnet/api/… Commented Jul 25, 2024 at 9:37

4 Answers 4

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607

Here's a nice fun LINQ example.

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();
}
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18 Comments

Good heavens!! Do you realize how INEFFICIENT that is??? Sure, it's fun, but LINQ is overused for things that should be done otherwise! LINQ code requires .NET 3.5 and requires referencing System.Core (which might otherwise not be needed). See the duplicate article for efficient solutions.
It's probably meant to be fun, not efficient
Continually impressed with LINQ's elegance and versatility
Came up with this to go the other direction. In case anyone else needs it... public static string ByteArrayToBinHex( this byte[] bytes ) { return bytes.Select( b => b.ToString( "X2" ) ).Aggregate( ( s1, s2 ) => s1 + s2 ); }
The shorter version would be, Enumerable.Range(0, hex.Length / 2) .Select(x => Convert.ToByte(hex.Substring(x * 2, 2), 16)) .ToArray()
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120

I did some research and found out that byte.Parse() is even slower than Convert.ToByte(). The fastest conversion I could come up with uses approximately 15 ticks per byte.

    public static byte[] StringToByteArrayFastest(string hex) {
        if (hex.Length % 2 == 1)
            throw new Exception("The binary key cannot have an odd number of digits");
        
        byte[] arr = new byte[hex.Length >> 1];
        
        for (int i = 0; i < hex.Length >> 1; ++i)
        {
            arr[i] = (byte)((GetHexVal(hex[i << 1]) << 4) + (GetHexVal(hex[(i << 1) + 1])));
        }
        
        return arr;
    }
    
    public static int GetHexVal(char hex) {
        int val = (int)hex;
        //For uppercase A-F letters:
        //return val - (val < 58 ? 48 : 55);
        //For lowercase a-f letters:
        //return val - (val < 58 ? 48 : 87);
        //Or the two combined, but a bit slower:
        return val - (val < 58 ? 48 : (val < 97 ? 55 : 87));
    }

// also works on .NET Micro Framework where (in SDK4.3) byte.Parse(string) only permits integer formats.

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21 Comments

I tried that, but somehow this is slightly faster. Maybe because the difference between the Heap and the Stack.
to answer that you would need to know a lot about how the compiler makes its decisions about automatic inlining
The bytes are in same order as hex chars on my side. What do you mean by reverse?
I just found this code pasted into a program I have to maintain. It no longer compiles and throws a CS0307 (variable 'i' cannot be used with type args) and a CS0118 ('hex' is a variable but used as a type). Using the bitwise shifting (instead of a plain old "/ 2") may seem cool but this is a clear case of premature optimization evil for 99.99% of developers who comes to this question.
@RobertSnyder - my point isn't about the compilation (though it was more or less broken overnight with no recent changes to the build server). We had a consultant copy paste this code into a program that did not need this level of performance. .
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65

The following code changes the hexadecimal string to a byte array by parsing the string byte-by-byte.

public static byte[] ConvertHexStringToByteArray(string hexString)
{
    if (hexString.Length % 2 != 0)
    {
        throw new ArgumentException(String.Format(CultureInfo.InvariantCulture, "The binary key cannot have an odd number of digits: {0}", hexString));
    }

    byte[] data = new byte[hexString.Length / 2];
    for (int index = 0; index < data.Length; index++)
    {
        string byteValue = hexString.Substring(index * 2, 2);
        data[index] = byte.Parse(byteValue, NumberStyles.HexNumber, CultureInfo.InvariantCulture);
    }

    return data; 
}
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3 Comments

Should it not be "for (int index = 0; index < HexAsBytes.Length; index++)" ?
68016101061B4A60193390662046804020422044204000420040402060226024676DB16 with this i am getting The binary key cannot have an odd number of digits
@Moeez And did you look at your input and the message you're getting?
13

I think this may work.

public static byte[] StrToByteArray(string str)
    {
        Dictionary<string, byte> hexindex = new Dictionary<string, byte>();
        for (int i = 0; i <= 255; i++)
            hexindex.Add(i.ToString("X2"), (byte)i);

        List<byte> hexres = new List<byte>();
        for (int i = 0; i < str.Length; i += 2)            
            hexres.Add(hexindex[str.Substring(i, 2)]);

        return hexres.ToArray();
    }
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