How to replace hexadecimal value in a binary file?

Question

Can you tell me how to replace the Hex value of a file with C#? Example: replace 62 61 72 ("bar") for 66 6F 6F ("foo").

Answer 1

You will need to process the bytes manually in the case of a binary file:

byte[] findBytes = { 0x62, 0x61, 0x72 };
byte[] replaceBytes = { 0x66, 0x6F, 0x6F };
List<byte> result;

using (var file = File.OpenRead(@"...origem..."))
{
    var allBytes = new byte[(int)file.Length];
    file.Read(allBytes, 0, (int)file.Length);
    result = new List<byte>(allBytes.Length);

    for (int itFile = 0; itFile < allBytes.Length; itFile++)
    {
        bool found = !findBytes
            .Where((t, i) => (i + itFile >= allBytes.Length)
                || (t != allBytes[i + itFile])).Any();

        if (found)
        {
            result.AddRange(replaceBytes);
            itFile += findBytes.Length - 1;
        }
        else
            result.Add(allBytes[itFile]);
    }
}

using (var file = File.Open(@"...destino...", FileMode.Create))
    file.Write(result.ToArray(), 0, result.Count);

This is a very crude implementation... that reads all bytes of the source and does all the processing in memory... in the case of very long files, you will probably have to subdivide the file and do the overwriting part by part.

Answer 2

There is an excellent explanation in an original Stackoverflow post in English:

https://stackoverflow.com/questions/3217732/how-to-edit-a-binary-files-hex-value-using-c-sharp

Translation adapted from the important part:

If you want to simply change the values of the bytes in the file, the most efficient approach in my opinion would be to open the file using a Filestream, find the appropriate position, and replace the bytes, as in the example below:

using (var stream = new FileStream(path, FileMode.Open, FileAccess.ReadWrite)) {
    stream.Position = 0;
    stream.WriteByte(0x66);
    stream.WriteByte(0x6F);
    stream.WriteByte(0x6F);
}

Answer 3

Try it like this: Hex p/ Decimal:

Convert.ToInt64(hexValue, 16);

Decimal p/ Hexadecimal:

string.format("{0:x}", decValue);