_Generic compiles fine in c++ source

Clang Frontend
1

Hi, sorry to ask a daft question but why does the following code
compile fine with clang/clang++ ?

int main()
{
  int a = _Generic(1, int: 2);
  int &x = a;
}

As far as I know, it does not conform to either C or C++ ( I believe
_Generic is not supported by C++ ? ).
It fails to compile with g++.

Thanks and Regards,
Prathamesh

2

That appears to be a bug; if you'd like, you could file a bug report
at http://llvm.org/bugs on it.

Good catch!

~Aaron

3

Actually, I take that back, we treat it as a language extension (not
certain how I missed that). You should be seeing an extension warning:
"generic selections are a C11-specific feature" depending on your
compiler flags.

So I wouldn't file a bug just yet. What flags are you passing in to
the compiler?

~Aaron

4

Actually, I take that back, we treat it as a language extension (not
certain how I missed that). You should be seeing an extension warning:
"generic selections are a C11-specific feature" depending on your
compiler flags.

So I wouldn't file a bug just yet. What flags are you passing in to
the compiler?

I hadn't passed any flags initially. However when i passsed -Wc11-extensions,
i got the warning:
x.cpp:3:11: warning: generic selections are a C11-specific feature
[-Wc11-extensions]
  int a = _Generic (1, int: 2);
But when I pass no options, it compiles silently.

5

Actually, I take that back, we treat it as a language extension (not
certain how I missed that). You should be seeing an extension warning:
"generic selections are a C11-specific feature" depending on your
compiler flags.

So I wouldn't file a bug just yet. What flags are you passing in to
the compiler?

I hadn't passed any flags initially. However when i passsed -Wc11-extensions,
i got the warning:
x.cpp:3:11: warning: generic selections are a C11-specific feature
[-Wc11-extensions]
  int a = _Generic (1, int: 2);
But when I pass no options, it compiles silently.

~Aaron

That appears to be a bug; if you'd like, you could file a bug report
at http://llvm.org/bugs on it.

Good catch!

~Aaron

Hi, sorry to ask a daft question but why does the following code
compile fine with clang/clang++ ?

int main()
{
  int a = _Generic(1, int: 2);
  int &x = a;
}

As far as I know, it does not conform to either C or C++ ( I believe
_Generic is not supported by C++ ? ).
It fails to compile with g++.

The same thing is true for _Static_assert.
This compiled without any error/warning too (without passing any option):

int main()
{
    int a;
    int &x = a;
    _Static_assert(1, "hello world");
}

Are (most of) c11 features treated as language extensions ?

6

Yes, they appear to be. It seems that language extension diagnostics
are ignored by default, which is why you need to enable them
explicitly. For instance, with -pedantic, et al.

~Aaron