Find a sequence of bytes and return the start position

Question

I have a large file, I need to search in it for a sequence of 7 bytes and return the position of that sequence in that files. I can't post any code because so far I was not able to write any decent code. Can anyone please point me in the right direction? Maybe is there a function that I don't know the existence of?

Example Given a file like that:

I want to find the position of F8 1E 13 B9 E4 28 88 which in this case is at 0x21

Answer 1

Here's a nice extension method to do it:

public static class ByteArrayExtensions
{ 
    public static int IndexOf(this byte[] sequence, byte[] pattern)
    {
        var patternLength = pattern.Length;
        var matchCount = 0;

        for (var i = 0; i < sequence.Length; i++) 
        {
            if (sequence[i] == pattern[matchCount])
            {
                matchCount++;
                if (matchCount == patternLength) 
                {
                    return i - patternLength + 1;
                }
            }
            else
            {
                matchCount = 0;
            }
        }

        return -1;
    }
}

Then you can find it as follows:

var bytes = new byte[] { 0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x010 };

var index = bytes.IndexOf(new byte[] { 0x03, 0x04, 0x05 });