Overview of data declarations and definitions

A declaration establishes the names and characteristics of data objects used in a program. A definition allocates storage for data objects, and associates an identifier with that object. When you declare or define a type, no storage is allocated.

The following table shows examples of declarations and definitions. The identifiers declared in the first column do not allocate storage; they refer to a corresponding definition. The identifiers declared in the second column allocate storage; they are both declarations and definitions.

Declarations determine the following properties of data objects and their identifiers:

• Scope, which describes the region of program text in which an identifier can be used to access its object
• Visibility, which describes the region of program text from which legal access can be made to the identifier's object
• Duration, which defines the period during which the identifiers have real, physical objects allocated in memory
• Linkage, which describes the correct association of an identifier to one particular object
• Type, which determines how much memory is allocated to an object and how the bit patterns found in the storage allocation of that object should be interpreted by the program

The elements of a declaration for a data object are as follows:

• Storage class specifiers, which specify storage duration and linkage
• Type specifiers, which specify data types
• Type qualifiers, which specify the mutability of data values
• Overview of declarators, which introduce and include identifiers
• Initializers, which initialize storage with initial values

In addition, ILE C/C++ allows you to use attributes to modify the properties of data objects. Type attributes, which can be used to modify the definition of user-defined types, are described in Type attributes. Variable attributes, which can be used to modify the declaration of variables, are described in Variable attributes.

All declarations have the form:

Data declaration syntax
 
   .-----------------------------.  .--------------------.
   V                             |  V                    |
>>---+-------------------------+-+----+----------------+-+------>
     '-storage_class_specifier-'      '-type_qualifier-'
 
                   .-,---------------------------.
                   V                             |
>--type_specifier----declarator--+-------------+-+--;----------><
                                 '-initializer-'
 

Related information

• Function declarations and definitions