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CHAPTER 2 CONSTRUCTS OF C LANGUAGE

User’s Manual U15556EJ1V0UM

2.3.2 Linkage of identifiers

The linkage of an identifier refers to the case when the same identifier declared more than once in different

scopes or in the same scope can be referenced as the same object or function. By being linked an identifier is

regarded to be one and the same. An identifier may be linked in the following three different ways: External linkage,

Internal linkage and No linkage.

(1) External linkage

External linkage refers to identifiers to be linked in translation (compiling) units that constitute the entire program

and as a collection of libraries.

The following identifiers are examples of external linkage.

•

The identifier of a function declared without a storage class specification.

•

The identifier of an object or function declared as extern, which has no storage class specification

•

The identifier of an object which has file scope but has no storage class specification

(2) Internal linkage

Internal linkage refers to identifiers to be linked within one translation (compiling) unit.

The following identifier is an example of internal linkage.

•

The identifier of an object or function that has file scope and contains the storage class specifier static.

(3) No linkage

An identifier that has no linkage to any other identifier is an inherent entity.

Examples of identifiers that have no linkage are as follows.

•

An identifier that does not refer to a data object or function

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An identifier declared as a function parameter

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The identifier of an object that does not have the storage class specifier extern inside a block

2.3.3 Name space for identifiers

All identifiers are classified into the following “name spaces”.

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Label name...................................................... Distinguished by a label declaration.

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Tag name of structure, union, or enumeration

Distinguished by the keyword struct, union or enum

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Member name of structure or union ................ Distinguished by the dot (.) operator or arrow (

→) operator.

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Ordinary identifiers (other than above)............ Declared as ordinary declarators or enumeration type constants.

2.3.4 Storage duration of objects

Each object has a storage duration that determines its lifetime (how long it can remain in memory). This storage

duration is divided into the following two categories: Static storage duration and Automatic storage duration.

(1) Static storage duration

Before executing an object program that has a static duration, an area is reserved for objects and values to be

stored are initialized once. The objects exist throughout the execution of the entire program and retain the

values last stored.

Objects that have a static storage duration are as shown below.

•

Objects that have external linkage

•

Objects that have internal linkage

•

Objects declared by the storage class specifier static

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