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The term "declaration" is frequently contrasted with the term "definition", [1] but meaning and usage varies significantly between languages; see below. Declarations are particularly prominent in languages in the ALGOL tradition, including the BCPL family, most prominently C and C++, and also Pascal.
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.
In C and C++, the line above represents a forward declaration of a function and is the function's prototype. After processing this declaration, the compiler would allow the program code to refer to the entity printThisInteger in the rest of the program. The definition for a function must be provided somewhere (same file or other, where it would ...
The term "function prototype" is particularly used in the context of the programming languages C and C++ where placing forward declarations of functions in header files allows for splitting a program into translation units, i.e. into parts that a compiler can separately translate into object files, to be combined by a linker into an executable ...
C preprocessor (CPP) conditional constructs can also be used to switch between different versions of a symbol. The difference from weak symbols is that weak symbols are interpreted by the linker. The CPP is run during the compilation of each translation unit before the C compiler.
The declaration informs the compiler that a variable by that name and type exists, but the compiler does not need to allocate memory for it since it is allocated elsewhere. The extern keyword means "declare without defining". In other words, it is a way to explicitly declare a variable, or to force a declaration without a definition.
This is an accepted version of this page This is the latest accepted revision, reviewed on 17 January 2025. General-purpose programming language "C programming language" redirects here. For the book, see The C Programming Language. Not to be confused with C++ or C#. C Logotype used on the cover of the first edition of The C Programming Language Paradigm Multi-paradigm: imperative (procedural ...
32-bit compilers emit, respectively: _f _g@4 @h@4 In the stdcall and fastcall mangling schemes, the function is encoded as _name@X and @name@X respectively, where X is the number of bytes, in decimal, of the argument(s) in the parameter list (including those passed in registers, for fastcall).