fseek() by line, not bytes?

Question

I have a script that parses large files line by line. When it encounters an error that it can't handle, it stops, notifying us of the last line parsed.

Is this really the best / only way to seek to a specific line in a file? (fseek() is not usable in my case.)

<?php

for ($i = 0; $i < 100000; $i++)
    fgets($fp); // just discard this

I don't have a problem using this, it is fast enough - it just feels a bit dirty. From what I know about the underlying code, I don't imagine there is a better way to do this.

Answer 1

If you only have the line number to go on, there is no other method of finding the line. Files are not line based (or even character based), so there is no way to simply jump to a specific line in a file.

There might be other ways of reading the lines in the file that might be slightly faster, like reading larger chunks of the file into a buffer and read lines from that, but you could only hope for it to be a few percent faster. Any method to find a specific line in a file still has to read all data up to that line.

Answer 2

If I understand correctly, you want to seek to the specific line at some point after you have found an error. If that is the case, you probably store or print the line-number of the bad line somewhere, depending on what you mean by "notify".

Unless you really mean that you cannot use fseek()*, what you can do is to also store/print the position in the file where the bad line starts. Then you can fseek().

* How, in that case, would fseekbyline() be usable if it existed?