How do you convert a byte array to a hexadecimal string, and vice versa in C#?

Below are two common approaches for converting byte arrays to hexadecimal strings and vice versa. One uses built-in .NET functionality with a bit of string manipulation, and the other relies on manual parsing.

Converting a Byte Array to a Hex String

One of the easiest ways to transform a byte array into a hex string is to use BitConverter.ToString(), then remove the hyphens:

public static string ByteArrayToHexString(byte[] bytes)
{
    // Produces something like "0A-1B-FF"
    string hexWithHyphens = BitConverter.ToString(bytes);

    // Remove hyphens => "0A1BFF"
    string hexWithoutHyphens = hexWithHyphens.Replace("-", "");

    return hexWithoutHyphens;
}

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Alternative: Custom Loop

If you need tighter control over the formatting, you can create a loop and manually format each byte:

public static string ByteArrayToHexString(byte[] bytes)
{
    StringBuilder sb = new StringBuilder(bytes.Length * 2);
    foreach (byte b in bytes)
        sb.AppendFormat("{0:X2}", b);  // Formats each byte in 2-digit uppercase hex

    return sb.ToString();
}

Converting a Hex String to a Byte Array

Reversing the process involves:

1. Ensuring your hex string has an even number of characters (each byte corresponds to two hex digits).
2. Parsing each pair of hex characters into a byte.

public static byte[] HexStringToByteArray(string hex)
{
    if (hex.Length % 2 != 0)
        throw new ArgumentException("Hex string must have an even number of digits.");

    byte[] bytes = new byte[hex.Length / 2];
    for (int i = 0; i < bytes.Length; i++)
    {
        string byteValue = hex.Substring(i * 2, 2);
        bytes[i] = Convert.ToByte(byteValue, 16);
    }
    return bytes;
}

Tips and Best Practices

• Validate Input: Always confirm the hex string has an even number of characters.
• Case Sensitivity: Convert.ToByte() handles both uppercase ("AF") and lowercase ("af").
• Performance: For large arrays, consider using StringBuilder or streaming approaches.
• Hyphens/Delimiters: If your hex string contains separators (e.g., "0A-1B-FF"), remove them before conversion.

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For free tutorials and discussions about system design and coding best practices, visit the DesignGurus.io YouTube channel. This knowledge can be particularly handy when dealing with low-level manipulations like string-to-byte conversions in real-world projects or interviews.