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In the C and C++ programming languages, unistd.h is the name of the header file that provides access to the POSIX operating system API. [1] It is defined by the POSIX.1 standard, the base of the Single Unix Specification , and should therefore be available in any POSIX-compliant operating system and compiler .
[5] [6] [7] An X-Macro is a header file. Commonly, these use the extension .def instead of the traditional .h. This file contains a list of similar macro calls, which can be referred to as "component macros." The include file is then referenced repeatedly. Many compilers define additional, non-standard macros.
Another solution is to use an include guard in each header file. [4] The C standard library is declared as a collection of header files. The C++ standard library is similar, but the declarations may be provided by the compiler without reading an actual file. C standard header files are named with a .h file name extension, as in #include <stdio ...
In the event that header file is included a second time, the #include guard will prevent the actual code within that header from being compiled. An alternative to #include guards is #pragma once . This non-standard but commonly supported directive among C and C++ compilers has the same purpose as an #include guard, but has less code and does ...
The C POSIX library is a specification of a C standard library for POSIX systems. It was developed at the same time as the ANSI C standard. Some effort was made to make POSIX compatible with standard C; POSIX includes additional functions to those introduced in standard C.
Berkeley sockets originated with the 4.2BSD Unix operating system, released in 1983, as a programming interface.Not until 1989, however, could the University of California, Berkeley release versions of the operating system and networking library free from the licensing constraints of AT&T Corporation's proprietary Unix.
This suggests that unistd.h is part of the C or C++ language standards when actually it's part of the POSIX standards. To fix this, I would turn it around: > On POSIX operating systems, unistd.h is the name of the header file that provides system API declarations to programs written in the C or C++ programming languages.
In computer programming, a precompiled header (PCH) is a (C or C++) header file that is compiled into an intermediate form that is faster to process for the compiler.Usage of precompiled headers may significantly reduce compilation time, especially when applied to large header files, header files that include many other header files, or header files that are included in many translation units.