Delete File Contents?

I've created a program that runs a process then stores the results to a file on the server. I would like the file to contain only the most recent update, but it seems I can only append to my using fopen. Is there a way to open the file and overwrite the data in that file? I've considered deleting the file and creating a new one but that seems like a lot to do. It would be nice if there were a way to set a pointer to the top of the file and overwrite. Thanks, Chris