Abl-electronic PIC Microcontrollers PIC16 Manuel d'utilisateur télécharger pdf (Page 93)

Introduction to Declarations

Declaration introduces one or several names to a program – it informs the compil-

er what the name represents, what is its type, what are allowed operations with it,

etc. This section reviews concepts related to declarations: declarations, definitions,

declaration specifiers, and initialization.

The range of objects that can be declared includes:

- Variables

- Constants

- Functions

- Types

- Structure, union, and enumeration tags

- Structure members

- Union members

- Arrays of other types

- Statement labels

- Preprocessor macros

Declarations and Definitions

Defining declarations, also known as definitions, beside introducing the name of

an object, also establish the creation (where and when) of the object; that is, the

allocation of physical memory and its possible initialization. Referencing declara-

tions, or just declarations, simply make their identifiers and types known to the

compiler.

Here is an overview. Declaration is also a definition, except if:

- it declares a function without specifying its body,

- it has an extern specifier, and has no initializator or body (in case of func.),

- it is a typedef declaration.

There can be many referencing declarations for the same identifier, especially in a

multifile program, but only one defining declaration for that identifier is allowed.

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Abl-electronic PIC Microcontrollers PIC16 Manuel d'utilisateur Page 93