Programming :: Prepend To ASCII Text File In C?

To start off I would like to acknowledge that I am not a very good C programmer and pretty much everything I know has been self taught through mostly trial and error. So forgive me if there is an obvious answer to my question, or if I don't immediately grasp the concepts involved in the possible solution.

Basically, I'm writing an application which will be creating log file entries rather rapidly (potentially hundreds per minute), and I would like each new line to appear at the top of the log file, rather than the end. Opening a text file in append mode is easy enough, but I can't seem to find any obvious way to do the opposite.

I have been looking online and it seems that there exists no standard way to do this, and I have only been able to find a few mentions of how somebody might achieve it. The most common method seems to be using two files and copying the data back and forth between them. This seems like it would be insanely I/O intensive with the number of lines I'm likely to be generating. If this is the best method to use, I will give it a shot; though I am not 100% clear on how to implement it, I am also open to any other ideas as to how to accomplish this, and I don't have to worry about portability since the program already uses Linux-only libraries. So calling out to sed or something is not necessarily out of the question (though I imagine performance would also be an issue there).