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In computer programming, a declaration is a language construct specifying identifier properties: it declares a word's (identifier's) meaning. [1] Declarations are most commonly used for functions , variables , constants , and classes , but can also be used for other entities such as enumerations and type definitions. [ 1 ]
C functions are akin to the subroutines of Fortran or the procedures of Pascal. A definition is a special type of declaration. A variable definition sets aside storage and possibly initializes it, a function definition provides its body. An implementation of C providing all of the standard library functions is called a hosted implementation.
Thus, calling f x, where f:: a-> b-> c, yields a new function f2:: b-> c that can be called f2 b to produce c. The actual type specifications can consist of an actual type, such as Integer, or a general type variable that is used in parametric polymorphic functions, such as a, or b, or anyType. So we can write something like: functionName:: a ...
A programming language specification can take several forms, including the following: An explicit definition of the syntax and semantics of the language. While syntax is commonly specified using a formal grammar, semantic definitions may be written in natural language (e.g., the approach taken for the C language), or a formal semantics (e.g., the Standard ML [3] and Scheme [4] specifications).
A declaration which creates a data object, instead of merely describing its existence, is commonly called a definition. Many find it convenient to draw a distinction between the terms "declaration" and "definition", as in the commonly seen phrase "the distinction between a declaration and definition ...", implying that a declaration merely ...
Semantics is concerned with the meaning of a program. The standards documents for many programming languages use BNF or some equivalent to express the syntax/grammar in a fairly formal and precise way, but the semantics/meaning of the program is generally described using examples and English prose. This can result in ambiguity. [8]
Declarative programming is a non-imperative style of programming in which programs describe their desired results without explicitly listing commands or steps that must be performed. Functional and logic programming languages are characterized by a declarative programming style.
The C language specification includes the typedef s size_t and ptrdiff_t to represent memory-related quantities. Their size is defined according to the target processor's arithmetic capabilities, not the memory capabilities, such as available address space. Both of these types are defined in the <stddef.h> header (cstddef in C++).