> controllable by a -Wxxx option.
By clicking “Sign up for GitHub”, you agree to our terms of service and > For an example of adding a new option see. 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. Learn more. a file program contained in a single .cpp file) get this warning warning: #pragma once in main file Makes sense does it not?
TLS_API_MACRO /* defined on the command line */, TASKING VX-toolset for TriCore: C compiler, "Games from Within: Even More Experiments with Includes", "The C Preprocessor: 1. #pragma once. > > g++ t.C -S Already on GitHub? Over-reliance upon either mechanism on the part of programmers by direct, unprotected use of #include directives without their own #include guard will lead to failure when using an include file that has not protected itself with either mechanism.
> I'm sorry if I am doing something wrong, but I do not see what. The compiler recognizes the include guard idiom, and implements the multiple-include optimization the same way as the #pragma once directive if no non-comment code or preprocessor directive comes before or after the standard form of the idiom: We recommend the include guard idiom when code must be portable to compilers that don't implement the #pragma once directive, to maintain consistency with existing code, or when the multiple-include optimization is impossible. Specifies that the compiler includes the header file only once, when compiling a source code file. Sign up for a free GitHub account to open an issue and contact its maintainers and the community. See: dense-analysis/ale#356. Sign up for a free GitHub account to open an issue and contact its maintainers and the community. #pragma once in main file In all headers included in a main file. Already on GitHub? `#pragma once` was originally intended to provide functionality that is a bit different from what include guards do.
See: dense-analysis/ale#356.
Using #pragma once allows the C preprocessor to include a header file when it is needed and to ignore an #include directive otherwise. You should be able to turn off the pragma warning with a flag in FlagsForFile. 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. privacy statement. Using #pragma once will delegate the task, of detecting subsequent #include statements for the same file, to the compiler. This can easily spread over a significant part of the workspace, which is quite irritating. This issue has appeared (and has been fixed) in other editor plugins making use of clang. Already on GitHub? > t.C:1:9: warning: #pragma once in main file 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. 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. Have a question about this project? `#pragma once` was originally intended to provide functionality that is a bit different from what include guards do. On the other hand, #pragma once is not necessarily available in all compilers and it… This wasn't YouCompleteMe's fault, it was Syntastic's... sorry! > Adding such an option is quite easy, and a good first contribution to GCC. 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. If the same file is included again, the preprocessor would realize it just by looking at the name. GitHub is home to over 50 million developers working together to host and review code, manage projects, and build software together.
Remarks. http://llvm.org/bugs/show_bug.cgi?id=16686, Workaround for annoying clang bug with pragma once. The most common alternative to #pragma once is to use #define to set an #include guard macro, the name of which is picked by the programmer to be unique to that file. Learn more. Moreover, the files using these headers are marked as being affected as well in the explorer sidebar, and so on and so forth. Have a question about this project? By clicking “Sign up for GitHub”, you agree to our terms of service and
Compilers may use a heuristic that compares file size, modification time and content. We use optional third-party analytics cookies to understand how you use GitHub.com so we can build better products. Learn more, We use analytics cookies to understand how you use our websites so we can make them better, e.g. 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? 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. However copy the .h file and save it with a new name.
This is a clang issue, not a YCM issue. > int main() {} > You haven't explained why do you need to use #pragma once in the main cpp Just place the directive in the first line of every header file. > conditional. [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. to your account. For more information, see our Privacy Statement.
Sign in Environment: * Ubuntu 12.04 amd64 * GCC 4.6.3 from Ubuntu repo To reproduce: $ unzip pragma-once-bom.zip $ make The contents of the archive are listed below for convenience of … [citation needed]. For an example of this design, see the
they're used to log you in. I'm sorry if I am doing something wrong, but I do not see what. There is more than just that for this bug.
they're used to log you in. You can always update your selection by clicking Cookie Preferences at the bottom of the page. We use optional third-party analytics cookies to understand how you use GitHub.com so we can build better products. It isn't part of the C++ Standard, but it's implemented portably by several common compilers. The idea was that `#pragma once` would permit the preprocessor to cache the names of already-included files. 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. This issue has appeared (and has been fixed) in other editor plugins making use of clang. This approach minimally ensures that the contents of the include file are not seen more than once. 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. 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. to your account. Such errors are unlikely to remain undetected but can complicate the interpretation of a compiler error report.
9 comments Labels. Sign in Successfully merging a pull request may close this issue. By using the pragma, the compiler should not need to open the file and scan for its contents, processing the include guards.
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. privacy statement. 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.
It would be great if that was an option, but I've searched before for a different similar project and could find no such flag (but it's a wanted feature for cases like this). Copy link Quote reply jhasse commented Jul 5, 2015. 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. We use essential cookies to perform essential website functions, e.g. I think SublimeClang, the Clang completer for SublimeText (a GUI editor, a bit vim-like) also explicitly filters out this warning. You signed in with another tab or window.
Put the same line in a .h file included in the main file No warning. After working for a while, lots of files are marked and I never know if these are "real" warnings or just pragma once virus spreading. Successfully merging a pull request may close this issue. GitHub is home to over 50 million developers working together to host and review code, manage projects, and build software together. Learn more. Searching the webs, I get the impression this has something to do with how gcc and clang (both give the same warning) compile for flymake. > #pragma once they're used to gather information about the pages you visit and how many clicks you need to accomplish a task.
> ^~~~ Comments. > you could work around this by wrapping the pragma in a preprocessor > In any case, I agree with confirming this as a bug: all warnings should be
Please provide a minimal test case and a sequence of steps that reproduces this issue. > controllable by a -Wxxx option. These difficulties, together with difficulties related to defining what constitutes the same file in the presence of hard links, networked file systems, etc. This is a valid error when compiling (since you don't directly compile headers) but not while syntax checking. Learn more, getting "pragma once in main file" error in header files, both gcc and clang. Since the pre-processor itself is responsible for handling #pragma once, the programmer cannot make errors which cause name clashes. For example. Nice, thanks!
By clicking “Sign up for GitHub”, you agree to our terms of service and Sign up for a free GitHub account to open an issue and contact its maintainers and the community. Specifies that the compiler includes the header file only once, when compiling a source code file. 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. #pragma once is accepted for compatibility with other compilers, and enables you to use other forms of header guard coding.
While editing a C++ header file that has #pragma once, YouCompleteMe emits only one error: "#pragma once in main file". If the same file is included again, the preprocessor would realize it just by looking at the name. once pragma. 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. 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. Learn more, We use analytics cookies to understand how you use our websites so we can make them better, e.g.
> #pragma once Not to mention that it is best not to use We use optional third-party analytics cookies to understand how you use GitHub.com so we can build better products. This makes YouCompleteMe useless on C++ header files that use #pragma once as header guards.