Ivor Horton's Beginning Visual C++ 2012

UNDERSTANDING STORAGE DURATION AND SCOPE

All variables have a finite lifetime when your program executes. They come into existence at the point at which you declare them and then, at some point, they disappear — at the latest, when your program terminates. How long a particular variable lasts is determined by a property called its storage duration. There are three different kinds of storage duration that a variable can have:

• Automatic storage duration
• Static storage duration
• Dynamic storage duration

Which of these a variable will have depends on how you create it. I will defer discussion of variables with dynamic storage duration until Chapter 4, but you will be exploring the characteristics of the other two in this chapter.

Another property that variables have is scope. The scope of a variable is simply that part of your program over which the variable name is valid. Within a variable’s scope, you can legally refer to it, either to set its value or to use it in an expression. Outside of the scope of a variable, you cannot refer to its name — any attempt to do so will cause a compiler error. Note that a variable may still exist outside of its scope, even though you cannot refer to it by name. You will see examples of this situation a little later in this discussion.

All the variables that you have declared up to now have had automatic storage duration, and are therefore called automatic variables. Let’s take a closer look at these first.

Automatic Variables

The variables that ...