How to reverse bytes in certain order in file in C#?

Question

I was wondering in my C# code how I can reverse bytes in a certain order in a file? Let me be more specific, I have a file and I need to reverse the order of some bytes inside of it (endian-swap).

So for example I could turn the bytes 00 00 00 01 into 01 00 00 00 or 00 01 into 01 00 and vice versa.

Does anyone know how I can achieve this in C# code? I am quite new to C# and I have been attempting this on my own however to no avail. Please help if you can, thank you.

Answer 1

You can reverse them with a simple utility function like this one:

public void ReverseBytes(byte[] array, int startIndex, int count)
{
    var hold = new byte[count];
    for (int i=0; i<count; i++)
    {
        hold[i] = array[startIndex + count - i - 1];
    }
    for (int i=0; i<count; i++)
    {
        array[startIndex + i] = hold[i];
    }
}

Use it like this:

byte[] fileBytes = File.ReadAllBytes(path);
ReverseBytes(fileBytes, 0, 4);  //reverse offset 0x00 through 0x03
ReverseBytes(fileBytes, 4, 4);  //reverse 0x04 through 0x07
ReverseBytes(fileBytes, 8, 4);  //reverse 0x08 through 0x0B
//etc....
File.WriteAllBytes(path, fileBytes);

Depending on your requirements you may be able to use a loop too:

for (int i=0; i<16; i+=4)
    ReverseBytes(fileBytes, i, 4);