Finding something after a search term

How can you determine if there are more bytes to a file after a certain string? I want to parse a file, find a certain combination of values, and then see if that's the end of the file or not. What will happen next depends on whether that's the end or not. Any ideas?

>>13
OP here. This isn't text processing, it's processing of binary data. I don't want to be too specific though. And no, it's not s spam not. I don't see how you could possibly misconstrue this as being for spam. But regardless, I'm not going to tell you what it's really for.