c# - How to truncate a file down to certain size but keep the end section?

Question

I have a text file that's appended to over time and periodically I want to truncate it down to a certain size, e.g. 10MB, but keeping the last 10MB rather than the first.

Is there any clever way to do this? I'm guessing I should seek to the right point, read from there into a new file, delete old file and rename new file to old name. Any better ideas or example code? Ideally I wouldn't read the whole file into memory because the file could be big.

Please no suggestions on using Log4Net etc.

Answer 1

You don't need to read the whole file before writing it, especially not if you're writing into a different file. You can work in chunks; reading a bit, writing, reading a bit more, writing again. In fact, that's how all I/O is done anyway. Especially with larger files you never really want to read them in all at once.

But what you propose is the only way of removing data from the beginning of a file. You have to rewrite it. Raymond Chen has a blog post on exactly that topic, too.