Defining scope – visibility, extent, and linkage

Often, when the scope of a variable or function is mentioned, it is referring only to the visibility of the variable or function. Visibility essentially determines which functions or statements can see the variable to either access it or modify it. If the variable is visible, it can be accessed and modified, except—as you may recall from Chapter 4, Using Variables and Assignments—when it is declared as a const variable, it can only be accessed but cannot be changed. As we will see, visibility is but one component of a variable's scope. The other components of scope are extent (or the lifetime of the variable) and linkage (or in which file the variable exists).

The visibility, extent, and linkage of variables and functions depend upon where they are declared and how they are defined. However, regardless of how or where they are...