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In B, all variables must be declared, as one of auto, extrn, or implicitly as function arguments. [1] An external variable is defined outside functions, has a lifetime of the whole program execution, and introduced to function by the mean of extrn declaration. Using the following code in the tutorial as an example: [1]
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).
Forward-declaration is used to avoid unnecessary coupling which help reducing compilation time by reducing the number of header inclusion. This has a triple advantage: reduce the number of files opened by #include (hence the number of operating system calls) reducing the volume of the pre-processed files (as the header is not included)
An example of the printf function. printf is a C standard library function that formats text and writes it to standard output.. The name, printf is short for print formatted where print refers to output to a printer although the functions are not limited to printer output.
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 ...
While a variable or function may be declared many times, it is typically defined once (in C++, this is known as the One Definition Rule or ODR). Dynamic languages such as JavaScript or Python generally allow functions to be redefined, that is, re-bound; a function is a variable much like any other, with a name and a value (the definition).
Encapsulation is also possible in non-object-oriented languages. In C, for example, a structure can be declared in the public API via the header file for a set of functions that operate on an item of data containing data members that are not accessible to clients of the API with the extern keyword. [13]
[8] [9] Common Lisp; Compiled Native Interface (CNI), alternative to JNI used in the GNU compiler environment. One of the bases of the Component Object Model is a common interface format, which natively uses the same types as Visual Basic for strings and arrays. D does it the same way as C++ does, with extern "C" through extern (C++)