Initialization of an anonymous struct within a class

Clang Frontend
#1

Hi,

I'm not sure whether an anonymous struct within a class is standard, or
a GCC extension that clang attempts to support. In any case, the
following code snippet gives this error:

anonymous-struct.cc:9:16: error: multiple initializations given for non-static member 'y'
        Foo() : x(0), y(0) { }
                      ^~~~
anonymous-struct.cc:9:10: note: previous initialization is here
        Foo() : x(0), y(0) { }
                ^
2 diagnostics generated.

Just for comparison, I've also given code that does not use an anonymous
struct and does compile cleanly.

Thanks,
Shaun

#define DOES_NOT_WORK 1
#if DOES_NOT_WORK
struct Foo
{
  struct {
    int x;
    int y;
  };
  Foo() : x(0), y(0) { }
};
#else
struct Foo
{
  struct S {
    int x;
    int y;
  } s;
  Foo() : s((S){ .x = 1, .y = 2}) { }
};
#endif

#include <iostream>

int main()
{
  Foo foo;
#if DOES_NOT_WORK
  std::cout << foo.x << ' ' << foo.y << '\n';
#else
  std::cout << foo.s.x << ' ' << foo.s.y << '\n';
#endif
  return 0;
}

#2

It's definitely a Clang bug, and while I know I've seen this issue at least once before, it doesn't seem to be in our bug tracker. Could you file a bug on LLVM's Bugzilla?

  - Doug

#3

Hi Doug,

Is an anonymous struct like this one standard?

Bug 7855 - Initialization of an anonymous struct within a class
http://llvm.org/bugs/show_bug.cgi?id=7855

Cheers,
Shaun

#4

Hi,

I'm not sure whether an anonymous struct within a class is standard, or
a GCC extension that clang attempts to support. In any case, the
following code snippet gives this error:

anonymous-struct.cc:9:16: error: multiple initializations given for non-static member 'y'
      Foo() : x(0), y(0) { }
                    ^~~~
anonymous-struct.cc:9:10: note: previous initialization is here
      Foo() : x(0), y(0) { }
              ^
2 diagnostics generated.

Just for comparison, I've also given code that does not use an anonymous
struct and does compile cleanly.

It's definitely a Clang bug, and while I know I've seen this issue at least once before, it doesn't seem to be in our bug tracker. Could you file a bug on LLVM's Bugzilla?

  - Doug

Hi Doug,

Is an anonymous struct like this one standard?

No, anonymous structs are a GCC extension. We have reasonably good support for them in C, but not necessarily in C++.

Bug 7855 - Initialization of an anonymous struct within a class
http://llvm.org/bugs/show_bug.cgi?id=7855

Thank you!

  - Doug