Use compiler's default standard version(s) when probing the compiler, if none was specified.

[ghuser404]

By default, gcc is using gnu C/C++ standard (gnu99, etc.). This means that __STRICT_ANSI__ is not defined. However, cpptools will always define __STRICT_ANSI__, unless otherwise specified with cStandard (specifying "cStandard": "gnu99" will correctly result in __STRICT_ANSI__ not being defined).

Consider the setup below. IntelliSense shows "__STRICT_ANSI__ defined", but running this program, it prints "__STRICT_ANSI__ not defined".

main.c

#include <stdio.h>

int main()
{
#ifdef __STRICT_ANSI__
    printf("__STRICT_ANSI__ defined\n");
#else
    printf("__STRICT_ANSI__ not defined\n");
#endif

    return 0;
}

c_cpp_properties.json

{
    "configurations": [
        {
            "name": "Win32",
            "compilerPath": "C:/mingw-w64/8.1.0/mingw32/bin/gcc.exe"
        }
    ],
    "version": 4
}

[Colengc]

Hi ghuser404 . Thanks for reporting this. It looks like we're adding the latest standard version when probing the compiler (and falling back to older standard versions if that fails). But, that is the wrong approach, as it overrides the default standard version of the compiler. We should instead be probing the compiler without a std version if none was configured.

[ghuser404]

Colen Garoutte-Carson (@Colengc) Thanks for looking into this. Really, this invalidates #2782 for me as I was hoping it would solve a handful IntelliSense errors in one of the libraries that we are using.

[Colengms]

ghuser404 Does providing the appropriate value for cStandard in your config work around the issue?

[ghuser404]

Colen Garoutte-Carson (@Colengms) The library is based on CMake. Specifying gnu standard in CMake configuration solves the problem, but we cannot do this in an external library. In my local tests choosing gnu standard via cStandard worked too.

[sean-mcmanus]

Should be fixed with https://github.com/microsoft/vscode-cpptools/releases/tag/0.30.0-insiders

[ghuser404]

Works with my original example. But sadly, doesn't work with cmake-tools extension, as it sets c11 by default, instead of gnu11. Maybe will be fixed with microsoft/vscode-cmake-tools#1152