I think SublimeClang, the Clang completer for SublimeText (a GUI editor, a bit vim-like) also explicitly filters out this warning. This is a clang issue, not a YCM issue. 9.90 #pragma once Enable the compiler to skip subsequent includes of that header file. There's no advantage to use of both the include guard idiom and #pragma once in the same file. While editing a C++ header file that has #pragma once, YouCompleteMe emits only one error: "#pragma once in main file". > controllable by a -Wxxx option. Yet, since include guards appear very often and the overhead of opening files is significant, it is common for compilers to optimize the handling of include guards, making them as fast as #pragma once. See: dense-analysis/ale#356.

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. I recently switched from syntastic, where this problem did not occur, so it must be some misconfiguration of the makers. #pragma once in main file In all headers included in a main file. Include #pragma once in the main file (i.e. You can always update your selection by clicking Cookie Preferences at the bottom of the page. By clicking “Sign up for GitHub”, you agree to our terms of service and

By clicking “Sign up for GitHub”, you agree to our terms of service and 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 [2] On the other hand, #pragma once is not necessarily available in all compilers and its implementation is tricky and might not always be reliable. > For an example of adding a new option see.

This approach minimally ensures that the contents of the include file are not seen more than once. There is more than just that for this bug. Looks like this has been sitting quite a while. > you could work around this by wrapping the pragma in a preprocessor See: dense-analysis/ale#356. > int main() {} Hello, Successfully merging a pull request may close this issue. We use essential cookies to perform essential website functions, e.g. Not clear to me if this should be hidden always, then it could be done just through the errorformat. Since the pre-processor itself is responsible for handling #pragma once, the programmer cannot make errors which cause name clashes. > Adding such an option is quite easy, and a good first contribution to GCC.

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. Copy link Quote reply jhasse commented Jul 5, 2015. Have a question about this project? Warning: #pragma once in main file I do indeed use this pragma in the header files, but it seems that the compilers somehow think that the file is not a header. > conditional. Learn more, "pragma once in main file" warning reported in header files. It also helps to prevent violations of the one definition rule, the requirement that all templates, types, functions, and objects have no more than one definition in your code.

[1] 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. #pragma once. AtomLinter/linter-clang#120 Have a question about this project? Be careful not to use #pragma once or the include guard idiom in header files designed to be included multiple times, that use preprocessor symbols to control their effects. This issue has appeared (and has been fixed) in other editor plugins making use of clang. 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. For more information, see our Privacy Statement.

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. 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. You signed in with another tab or window. > #pragma once Oops. 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.

For example. You can always update your selection by clicking Cookie Preferences at the bottom of the page. [citation needed]. 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.

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#pragma once is accepted for compatibility with other compilers, and enables you to use other forms of header guard coding. to your account. Using #pragma once allows the C preprocessor to include a header file when it is needed and to ignore an #include directive otherwise. > t.C:1:9: warning: #pragma once in main file > #pragma once

Please provide a minimal test case and a sequence of steps that reproduces this issue. this problem still exists and there is not flag to disable this behaviour, its kind of annoying :/, Clang bug causing this: http://llvm.org/bugs/show_bug.cgi?id=16686. The #pragma once directive serves to avoid this by ignoring subsequent inclusions of grandparent.h. An option to disable warning "#pragma once in main file", > Testcase: We recommend the #pragma once directive for new code because it doesn't pollute the global namespace with a preprocessor symbol. Learn more, We use analytics cookies to understand how you use our websites so we can make them better, e.g. Yes, in the system I'm working on, there is no "main file", all C++ (xcpp files actually) are small C++ programs that I link with a generated main file.

Pragma directives and the __pragma keyword.

It can occur in complex projects when file system aliasing or aliased include paths prevent the compiler from identifying identical include files by canonical path. 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. If the same file is included again, the preprocessor would realize it just by looking at the name. Learn more, We use analytics cookies to understand how you use our websites so we can make them better, e.g. > > ^~~~ This can easily spread over a significant part of the workspace, which is quite irritating.

Just place the directive in the first line of every header file. Hi. It isn't part of the C++ Standard, but it's implemented portably by several common compilers.

It can do this efficiently and safely. Put the same line in a .h file included in the main file No warning. You should be able to turn off the pragma warning with a flag in FlagsForFile.

These difficulties, together with difficulties related to defining what constitutes the same file in the presence of hard links, networked file systems, etc. In this case, the direct determination for which API is available would make use of the fact that the include file had advertised itself with its #include guard macro. Nice, thanks! This makes YouCompleteMe useless on C++ header files that use #pragma once as header guards. 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.

However copy the .h file and save it with a new name. Such errors are unlikely to remain undetected but can complicate the interpretation of a compiler error report. We’ll occasionally send you account related emails. http://llvm.org/bugs/show_bug.cgi?id=16686, Workaround for annoying clang bug with pragma once.

once pragma. Compilers may use a heuristic that compares file size, modification time and content.

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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. I miss that too, as a workaround I use the localvimrc plugin for this to modify the makers.. Having this poblem too.. so, 3 yrs without a fix? See: A workaround would simply be to check the extension of the current fail and get rid of the diagnostic if it's an header. By clicking “Sign up for GitHub”, you agree to our terms of service and to your account. This wasn't YouCompleteMe's fault, it was Syntastic's... sorry! [7] Additionally, #pragma once can do the wrong thing if the same file is intentionally copied into several parts of a project, e.g. privacy statement. > We use optional third-party analytics cookies to understand how you use GitHub.com so we can build better products. 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. Sign up for a free GitHub account to open an issue and contact its maintainers and the community. It has an effect similar to the include guard idiom, which uses preprocessor macro definitions to prevent multiple inclusions of the contents of the file.

> For an example of adding a new option see, > In any case, I agree with confirming this as a bug: all warnings should be The use of #include guard macros allows dependent code to recognize and respond to slight differences in semantics or interfaces of competing alternatives. Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

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