Chapter 13: Persistent Data: File Input and Output

Overview

As a kid, I had to listen patiently, or not so patiently, to endless (so it seemed at the time) lectures from my parents on how I could be better, or do better. After I became an adult, I realized to my amazement that my parents more often than not were right. Indeed, after I became a parent, I realized to my horror that I was repeating their lectures to my own children, who, of course, today enjoy these talks about as much I used to.

One of my parents favorite lectures was about how important it is to be persistent. Once again, mom and dad showed true insight, because, though persistence is a very valuable trait in any person, it is particularly important in programmers.

Data, as well as programmers, should be persistent. By persistent, I mean the data should survive when the program is finished. Can you imagine if, after typing this chapter, when I exited Microsoft Word, everything I typed was lost?

With the programs we have written so far, this is exactly what would happen. Whatever values we have stored in variables do not persist, or survive, when the program is finished. Instead, the data is lost because the data is stored in RAM (random access memory), which is cleared when the program (or the computer) stops running.

Fortunately, Microsoft Word (and most programs for that matter) has the capability to save data to a file on the computer s hard drive or other storage medium so that data later can be retrieved when needed. That data persists after the termination of the program or even after the computer is turned off.

This chapter will show you how to make your data persistent by saving it to a file. Of course, saving the data accomplishes little unless you can later retrieve it, so this chapter also will show you how to retrieve data from a file.