C Pocket Reference

Categories and Scope of Identifiers

Each identifier belongs to exactly one of the following four categories:

• Label names

• The tags of structures, unions, and enumerations. These are identifiers that follow one of the keywords struct, union, or enum (see Section 1.10).

• Names of structure or union members. Each structure or union type has a separate name space for its members.

• All other identifiers, called ordinary identifiers.

Identifiers of different categories may be identical. For example, a label name may also be used as a function name. Such re-use occurs most often with structures: the same string can be used to identify a structure type, one of its members, and a variable; for example:

struct person {char *person; /*...*/} person;

The same names can also be used for members of different structures.

Each identifier in the source code has a scope . The scope is that portion of the program in which the identifier can be used. The four possible scopes are:

Function prototype

Identifiers in the list of parameter declarations of a function prototype (not a function definition) have function prototype scope . Because these identifiers have no meaning outside the prototype itself, they are little more than comments.

Function

Only label names have function scope . Their use is limited to the function block in which the label is defined. Label names must also be unique within the function. The goto statement causes a jump to a labelled statement within the same function.

Block

Identifiers ...