Question

What is the fastest and most efficient way to prepend bytes at the beginning of a file? Basically, I want to open a file and then add a number of bytes to it. I thought of using a loop, but given that all of the bytes to prepend are the same, I don’t think it would be necessary.

Answer 1

This is about the most succinct way I could personally think of, but doesn’t avoid loops like you wanted:

int numberOfBytes = 100;
byte newByte = 0x1;

using ( var newFile = new FileStream( @"C:\newfile.dat", FileMode.CreateNew, FileAccess.Write ) )
{
    for ( var i = 0; i < numberOfBytes; i++ )
    {
        newFile.WriteByte( newByte );
    }
    using ( var oldFile = new FileStream( @"C:\oldfile.dat", FileMode.Open, FileAccess.Read ) )
    {
        oldFile.CopyTo(newFile);
    }
}

// Rename and delete files, or whatever you want to do

It could also use some error handling, but you get the idea.