The correct title of this article is #include guard. The omission of the # is due to technical restrictions.
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In the C and C++ programming languages, an #include guard, sometimes called a macro guard, header guard or file guard, is a particular construct used to avoid the problem of double inclusion when dealing with the include directive.
The C preprocessor processes directives of the form #include <file> in a source file by locating the associated file on disk and transcluding ("including") its contents into a copy of the source file known as the translation unit, replacing the include directive in the process. The files included in this regard are generally header files, which typically contain declarations of functions and classes or structs.
If an #include directive for a given file appears multiple times during compilation (i.e. because it appeared in multiple other headers), the file is processed again each time. However, if certain C or C++ language constructs are defined twice, the resulting translation unit is invalid. #include guards prevent this erroneous construct from arising by defining a preprocessor macro when a header is first included, and detecting its presence to skip the file's contents on subsequent inclusions.
The addition of #include guards to a header file is one way to make that file idempotent. Another construct to combat double inclusion is #pragma once, which is non-standard but nearly universally supported among C and C++ compilers.
C and C++ programming languages, an #includeguard, sometimes called a macro guard, header guard or file guard, is a particular construct used to avoid...
include directives to the original file. Another solution is to use includeguards. Since C++20, headers can also be imported as header units, that is...
a single compilation. Thus, #pragma once serves the same purpose as includeguards, but with several advantages, including less code, avoidance of name...
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second would include the Imperial Guards of the Russian and German Empires prior to 1917–18. Monarchs frequently modelled their royal guards upon those...
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not include the vessels of the Islamic Revolutionary Guard Corps Navy. Iran portal List of equipment of the Navy of the Islamic Revolutionary Guard Corps...
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typically lines up on the line of scrimmage, opposite one of the offensive guards; however, he may also line up opposite one of the offensive tackles. Defensive...
antibacterial and water wicking. Some variations include the following: Cropped rash guard: A rash guard that is similar to a crop top and is made specifically...
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as guard labor include: management, guards, military personnel, and prison officers. Samuel Bowles has expanded the notion of guard labor to include IT...
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