wilmott.com

I swear I have written a file and read it at the same time, but I don't remember when. This is a standard feature of Linux, no?

Yes, you can open the file in read/write mode and have calls of both types intermixed, if that´s what you mean. If you intend to access the file concurrently from different processes/threads, then you may need to use some synchronization mechanism to guarantee data consistency.