has so far prevented the standardization of #pragma once. header1.h: Now you get not only a warning, but also a redefinition error. #pragma once in main file In all headers included in a main file. Successfully merging a pull request may close this issue. Nice, thanks! Comments. Oops. GitHub is home to over 50 million developers working together to host and review code, manage projects, and build software together. Even when #pragma once is used in an header file, the plugin incorrectly reports a diagnostic mentioning that it's being used in a main file. privacy statement. Is there a way to at least disable this in the IDE? Just place the directive in the first line of every header file. > #pragma once at all anywhere. This may occur several times within a single compilation unit, and is useful for evaluating macro-containing contents multiple times against changing definitions of the macro. xcpp programs can use other programs (xcpp files) or libs (xhpp files). AtomLinter/linter-clang#120. [6] Symbolic links and especially hard links may cause the same file to be found under different names in different directories. Learn more, We use analytics cookies to understand how you use our websites so we can make them better, e.g. Sign in Already on GitHub? > conditional. 08/29/2019; 2 minutes to read +1; In this article.

You can always update your selection by clicking Cookie Preferences at the bottom of the page. Sign in privacy statement. For example. > t.C:1:9: warning: #pragma once in main file [citation needed].

#pragma once in main file In all headers included in a main file. By clicking “Sign up for GitHub”, you agree to our terms of service and > #pragma once Moreover, the files using these headers are marked as being affected as well in the explorer sidebar, and so on and so forth. It can do this efficiently and safely. Such errors are unlikely to remain undetected but can complicate the interpretation of a compiler error report. `#pragma once` was originally intended to provide functionality that is a bit different from what include guards do. This issue has appeared (and has been fixed) in other editor plugins making use of clang. See: dense-analysis/ale#356. Learn more, getting "pragma once in main file" error in header files, both gcc and clang. Pragma directives and the __pragma keyword. when preparing the build. Then, the following warning and error appear: It appears that the error "#pragma once in main file" earlier was caused by the project using -Werror (sorry for that). The use of #include guard macros allows dependent code to recognize and respond to slight differences in semantics or interfaces of competing alternatives. Please provide a minimal test case and a sequence of steps that reproduces this issue. > compiling it as the TU itself? This is more verbose, requires greater manual intervention, and is prone to programmer error as there are no mechanisms available to the compiler for prevention of accidental use of the same macro name in more than one file, which would result in only one of the files being included. I'd like to use "#pragma once" in my .h files instead of the old fashioned #ifndef __FOO.H include guards, It seems to work, but I get the warning symbol and the complaint "#pragma once in main file" in the left margin of the editor, although there are no actually compiler warnings. Already on GitHub? The use of #pragma once can reduce build times, as the compiler won't open and read the file again after the first #include of the file in the translation unit. There's no advantage to use of both the include guard idiom and #pragma once in the same file. Using #pragma once allows the C preprocessor to include a header file when it is needed and to ignore an #include directive otherwise. Remarks. These difficulties, together with difficulties related to defining what constitutes the same file in the presence of hard links, networked file systems, etc. Another advantage of “#pragma once” mentioned in Wikipedia and some other sources is its supposed performance. In the absence of #include guards around #include directives, the use of #pragma once will improve compilation speed for some compilers since it is a higher-level mechanism; the compiler itself can compare filenames or inodes without having to invoke the C preprocessor to scan the header for #ifndef and #endif. When I open foo.hpp, I get the question whether I want to load ycm_extra_conf.py, I say "ok", and wait a moment.

It seems to be a combination of YCM and Syntastic: when either is unloaded, it doesn't happen; when both are loaded, it does. An option to disable warning "#pragma once in main file", > Testcase:

Even when #pragma once is used in an header file, the plugin incorrectly reports a diagnostic mentioning that it's being used in a main file. It requires less typing, is less distracting, and can't cause symbol collisions, errors caused when different header files use the same preprocessor symbol as the guard value. The C Preprocessor", "GCC 3.4 Release Series — Changes, New Features, and Fixes", "should_stack_file() function in GCC source code", "Comeau C++ Pre-Release User Documentation: Pragmas", "CCE 9.0.0 Release Overview Introduction S-5212", "GCC Bug 11569 - there's no substitute for #pragma once", "HP aC++/HP C A.06.29 Programmer's Guide; March 2016 (AR1603)", "Diagnostic 1782: #pragma once is obsolete. [3][4][5], Identifying the same file on a file system is not a trivial task. Thus, #pragma once serves the same purpose as include guards, but with several advantages, including: less code, avoidance of name clashes, and sometimes improvement in compilation speed. Whereas include guards would still protect from double definitions, #pragma once may or may not treat them as the same file in a compiler-dependent way.

In this example, the inclusion of grandparent.h in both parent.h and child.c would ordinarily cause a compilation error, because a struct with a given name can only be defined a single time in a given compilation. Include #pragma once in the main file (i.e. > source file, are you sometimes including it as a header and other times Created attachment 29594 Minimal example demonstrating the problem When an include file starts with a UTF-8 byte order mark and is included in a precompiled header, it is not protected against repeated inclusion. http://llvm.org/bugs/show_bug.cgi?id=16686, Workaround for annoying clang bug with pragma once. The idea was that `#pragma once` would permit the preprocessor to cache the names of already-included files. > controllable by a -Wxxx option.

Use #ifndef guard instead", https://msdn.microsoft.com/en-us/library/4141z1cx.aspx, "Oracle® Developer Studio 12.5: GCC Compatibility Guide", "MA160-800 (v6.2r2) March 13, 2018 page 92", P0538R0 A Qualified Replacement for #pragma once, https://en.wikipedia.org/w/index.php?title=Pragma_once&oldid=986187523, Articles with dead external links from September 2020, Short description is different from Wikidata, Articles with unsourced statements from January 2019, Articles with failed verification from September 2020, Creative Commons Attribution-ShareAlike License, Supported (depending on the underlying host compiler), This page was last edited on 30 October 2020, at 09:50. > #pragma once to your account.

Using VSCode 1.22.2 and C/c++-Extension 0.16.1 If I write a simple header file like Abc.h and insert a modern include-guard #pragma once I am getting the very annoying warning: #pragma once in main file. We’ll occasionally send you account related emails. If the same file is included again, the preprocessor would realize it just by looking at the name. Do you know if there is a way to pass project-specific flags to neomake like with the .syntastic_XYZ_config files? Learn more. By using the pragma, the compiler should not need to open the file and scan for its contents, processing the include guards. 9.90 #pragma once Enable the compiler to skip subsequent includes of that header file. Basically default settings: It would be nice if neomake offered something like the g:syntastic_quiet_messages variable which would allow you to filter out messages that you don't want.