C++ Primer Plus

Scope and Linkage

Scope describes how widely visible a name is in a file (translation unit). For example, a variable defined in a function can be used in that function but not in another, whereas a variable defined in a file above the function definitions can be used in all the functions. Linkage describes how a name can be shared in different units. A name with external linkage can be shared across files, and a name with internal linkage can be shared by functions within a single file. Names of automatic variables have no linkage because they are not shared.

A C++ variable can have one of several scopes. A variable that has local scope (also termed block scope) is known only within the block in which it is defined. Recall that a block is a series ...