write in specific line in c++

[smsmsm]

Hi
I have a file with 1000 of '\n' ( I mean it has lots of line) I'm looking for a way to writ in specific line of it.

[LB]

With the way file systems work, you have to rewrite the whole file. If the new file is longer than the old file, you can get away with just overwriting starting at the first difference, but that isn't always the case.