Declaration (computer programming)

In computer programming, a declaration in a syntactic language construct is the process of specifying identifier properties for its initialization: it declares a word's (identifier's) meaning.

↑ For example, Java uses "declaration" (class declaration, method declaration), while Python uses "definition" (class definition, function definition).
↑ This distinction is observed in Pascal "units" (modules), and in conventional C and C++ code organization, which has header files consisting largely of pure declarations, and source files consisting of definitions, though this is not always strictly observed, nor enforced by the language.

References

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"A declaration specifies the interpretation and attributes of a set of identifiers. A definition of an identifier is a declaration for that identifier that:
- for an object [variable or constant], causes storage to be reserved for that object;
- for a function, includes the function body;
- for an enumeration constant, is the (only) declaration of the identifier;
- for a typedef name, is the first (or only) declaration of the identifier."
C11 specification, 6.7: Declarations, paragraph 5.
↑ Mike Banahan. "2.5. Declaration of variables". GBdirect. Retrieved 2011-06-08. [A] declaration [...] introduces just the name and type of something but allocates no storage[...].
↑ 7. Compound statements, The Python Language Reference

Declare vs Define in C and C++, Alex Allain
8.2. Declarations, Definitions and Accessibility, The C Book, GBdirect
Declarations and Definitions (C++), MSDN
"Declarations tell the compiler that a program element or name exists. Definitions specify what code or data the name describes."