Vscode-cpptools: Support gnu standard versions for querying compiler

Created on 7 Nov 2018 · 14Comments · Source: microsoft/vscode-cpptools

Hi, I am receiving the error identifier "CLOCK_MONOTONIC" is undefined from cpptools for the below code, which I don't receive when compiling with gcc. If I include "defines": ["_POSIX_C_SOURCE 199309L"] in c_cpp_properties.json then the issue is resolved and cpptools doesn't complain.

My question is, why is this behavior different when I compile with gcc? I believe the default C standard for gcc is gnu11, which doesn't require _POSIX_C_SOURCE to be defined. Is cpptools using a different standard, and if so is there a way to force using gnu11? I've tried adding -std=gnu11 to the compiler path, but that doesn't seem to solve the issue.

OS and Version: Ubuntu 16.04.3 LTS
VS Code Version: 1.28.2
C/C++ Extension Version: 0.20.1
Other extensions: none

#include <stdint.h>
#include <time.h>

uint64_t timer_diff(struct timespec *start)
{
    uint64_t diff;
    struct timespec now;

    clock_gettime(CLOCK_MONOTONIC, &now);

    diff = UINT64_C(1000000000) * (now.tv_sec - start->tv_sec) +
           now.tv_nsec - start->tv_nsec;

    return diff;
}

{
    "configurations": [
        {
            "name": "Linux",
            "includePath": [
                "${workspaceFolder}/**"
            ],
            "compilerPath": "/usr/lib/gcc",
            "intelliSenseMode": "gcc-x64",
            "browse": {
                "path": [
                    "${workspaceFolder}/**"
                ],
                "limitSymbolsToIncludedHeaders": true,
                "databaseFilename": ""
            },
            "cStandard": "c11",
            "cppStandard": "c++17"
        }
    ],
    "version": 4
}

workspace/didChangeConfiguration
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File exclude: **/CVS
File exclude: **/.DS_Store
File exclude: **/.vscode
Search exclude: **/node_modules
Search exclude: **/bower_components
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terminating child process: 5243
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Attempting to get defaults from compiler found on the machine: '/usr/bin/gcc'
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  Folder: /usr/lib/gcc/x86_64-linux-gnu/5/include/ will be indexed
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sending compilation args for /home/dan/Desktop/vscode-test/main.c
  include: /usr/lib/gcc/x86_64-linux-gnu/5/include
  include: /usr/local/include
  include: /usr/lib/gcc/x86_64-linux-gnu/5/include-fixed
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  other: --gcc
  other: --gnu_version=50400
  stdver: --c11
  intelliSenseMode: gcc
Checking for syntax errors: file:///home/dan/Desktop/vscode-test/main.c
queue_update_intellisense for files in tu of: /home/dan/Desktop/vscode-test/main.c
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Done parsing remaining files.
terminating child process: 5258
errorSquiggles count: 1
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Feature Request Configuration Language Service fixed (release pending)

Source

invedj

👍3

Most helpful comment

The gnu standards are supported now with https://github.com/microsoft/vscode-cpptools/releases/tag/0.28.0-insiders2 . Let us know if you hit any issues with that.

sean-mcmanus on 6 May 2020

❤2

All 14 comments

I repro the issue. It looks like _GNU_SOURCE needs to be defined for c files, not C++. Using gnu11 is supposed to work in terms of the defines that are used, but we could have a bug. You can workaround this bug via adding "_GNU_SOURCE" to the defines section of c_cpp_properties.json (or C_Cpp.default.defines in settings.json).

sean-mcmanus on 12 Dec 2018

But from what I read at https://exceptionshub.com/_gnu_source-and-__use_gnu.html it sounds like maybe users are expected to define _GNU_SOURCE themselves in their build process or code (I haven't verified that though).

sean-mcmanus on 12 Dec 2018

I have this same problem.

The underlying cause seem to be that when cpptools is querying the compiler defines, it passes something like -std=c11 (depending on what you configured in c_cpp_properties.json) to the compiler when it does the gcc -Wp,-v -E -xc -dD /dev/null trick.

The presence of -std=c11 on the command line puts gcc in "strict C mode", and means _GNU_SOURCE (and other important macros that are contingent on that, like _DEFAULT_SOURCE) don't get set. So Intellisense will see an inconsistent view of the world.

Perhaps you be able to set the cStandard in the json to gnu11, so -std=gnu11 can be passed? Or a mode where no standard is passed or something like that.

travisdowns on 2 May 2019

@travisdowns Ah, thanks for the info. Maybe we can add the gnu std versions when we add C++20 versions.

sean-mcmanus on 3 May 2019

@sean-mcmanus - thanks!

In the meantime it would be nice to have a bit more visibility into exactly how the cpptools extension is determining the args, e.g., in the debug log it the command line used to invoke gcc doesn't appear, but it would be very useful it it did (since various things are unclear, e.g., if you add to compilerPath an argument, how it gets positioned relative to the arguments that cpptools adds).

travisdowns on 3 May 2019

@travisdowns The user compilerPath args get added to the front of the args that we add, so any "-std" set by the user is overwritten by the one we set.

sean-mcmanus on 3 May 2019

👍1

It would be really nice if the generated -std argument was prepended instead of appended to the user-provided arguments. I have a codebase that requires __GNUC__ to be set and __STRICT_ANSI__ to be unset in order for the correct typedefs to exist. Because this extension forces gcc to report its definitions for an ANSI standard, I am unable to get that combination of definitions (and there also doesn't seem to be any way for me to manually undef __STRICT_ANSI__).

The only workaround I've found is to pass bogus arguments to the compiler so that it errors out and doesn't report any definitions at all. Then, I can set the ones I need manually.

tchebb on 10 Dec 2019

When the gnu options are supported will they auto configure from the compile_commands.json?

ie my project emits a compile_commands.json that includes -std=gnu11, will all the red squiggles go away once this is fixed? We expect the project to compile in glibc's -D_DEFAULT_SOURCE mode as is the default for all the -std=gnu* options. Not in STRICT_ANSI mode as vs code defaults to.

It is a significant, practicle differnce that was very hard to uncover as being caused by -std.

jgunthorpe on 14 Jan 2020

@jgunthorpe If your project uses one "std" then I believe it would work to just set that in the c_cpp_properties.json; however, if you require the "std" to be picked up in the compile_commands.json command arguments, then we would also need to fix https://github.com/microsoft/vscode-cpptools/issues/1755 (the workaround for that for non-std flags is to pass the arguments in the compilerPath or compilerArgs properties).

sean-mcmanus on 14 Jan 2020

The gnu standards are supported now with https://github.com/microsoft/vscode-cpptools/releases/tag/0.28.0-insiders2 . Let us know if you hit any issues with that.

sean-mcmanus on 6 May 2020

❤2

The gnu standards are supported now with https://github.com/microsoft/vscode-cpptools/releases/tag/0.28.0-insiders2 . Let us know if you hit any issues with that.

Thanks!

Can you give a one-liner one how to use it?

Is it like "cppStandard" : "gnu++17"? The release notes link back here so it would be good to have a brief note about how it's fixed.

travisdowns on 6 May 2020

The GNU standards were added as additional options to properties cStandard and cppStandard. The example you provide is correct usage:
"cppStandard" : "gnu++17"