Which is an include guard?
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.
Which choice is an include guard for header file?
Use of #include guards In this section, the same code is used with the addition of #include guards. The C preprocessor preprocesses the header files, including and further preprocessing them recursively. This will result in a correct source file, as we will see.
Why do we need include guards?
Include guards are used to prevent a file, actually the contents of a file, from being included more than once. The header file above has an include guard.
What is a guard in a header file?
Header guards are little pieces of code that protect the contents of a header file from being included more than once. Header guards are implemented through the use of preprocessor directives. The C/C++ preprocessor directives all start with the # character. You are already familiar with some ( #include, #define).
Is #include a macro?
It doesn’t behave exactly like a macro would, but it can achieve some pretty macro-like results, since #include basically just dumps the contents of one file into another.
What happens if we include a header file twice?
If a header file happens to be included twice, the compiler will process its contents twice. This is very likely to cause an error, e.g. when the compiler sees the same structure definition twice. Even if it does not, it will certainly waste time.
What is a header guard in C++?
Header Guards in C++ are conditional compilation directives that help to avoid errors that arise when the same function or variable is defined more than once by the mistake of a programmer. According to C++, when a function or a variable is defined more than once, it yields an error.
What is the purpose of header guards also known as include guards?
Header guards are designed to ensure that the contents of a given header file are not copied more than once into any single file, in order to prevent duplicate definitions.
What do you mean by included?
1 : to take in or comprise as a part of a whole or group. 2 : to contain between or within two sides and the included angle. 3 : to shut up : enclose.
What is include Stdio h?
stdio. h is a header file which has the necessary information to include the input/output related functions in our program. Example printf, scanf etc. If we want to use printf or scanf function in our program, we should include the stdio. h header file in our source code.
What happens if header file is not included?
Even if it does not, it will certainly waste time. This construct is commonly known as a wrapper #ifndef. When the header is included again, the conditional will be false, because FILE_FOO_SEEN is defined. The preprocessor will skip over the entire contents of the file, and the compiler will not see it twice.
Should include guard name be same as header file name?
Without violating any of the above, the include guard name can be anything and doesn’t have to be the name of the header file. But usually the convention I have seen/used is to use same name as that of the header file name so that it doesn’t cause any unnecessary confusion.
How to name inclusion guards in a header?
From my own experience, the convention is to name the inclusion guards after the header file containing them with the exception that the name is all in caps and the period is replaced with an underscore. So test.h becomes TEST_H. Real life examples of this include Qt Creator, which follows this convention when auto-generating class header files.
What is the best way to name include guards?
Therefore, a project using #include guards must work out a coherent naming scheme for its include guards, and make sure its scheme doesn’t conflict with that of any third-party headers it uses, or with the names of any globally visible macros. For this reason, most C and C++ implementations provide a non-standard #pragma once directive.