Re: C++ PATCH to reject initializating flexible array members in constructors (PR c++/72775)

[Martin Sebor <msebor at gmail dot com>]

On 12/08/2016 01:28 PM, Marek Polacek wrote:
> On Thu, Dec 08, 2016 at 02:56:56PM -0500, Nathan Sidwell wrote:
> > On 12/08/2016 01:05 PM, Jason Merrill wrote:
> > > If the problem is the member initializer, we can diagnose that
> > > directly rather than wait until we're in a constructor.
> >
> > What about:
> > struct Foo {
> > int a;
> > char ary[];
> > Foo () : ary ("bob"){}
> > };
> >
> > ?  That ICEs in the same way.
>
> My patch would make GCC to reject this too, but the new 'else' needs to
> be removed from the patch, i.e.

Clang accepts this test case although it does reject the originally
submitted test case with the messages below.  I think GCC should
accept the latter case for compatibility.  If it is accepted then
rejecting the original test case will make the array initialization
irregular.  I think it would be nice if they both could accepted
but I don't know how much work it would be to make it work.

Martin

t.C:4:12: warning: in-class initialization of non-static data member is 
a C++11
      extension [-Wc++11-extensions]
  char a[] = "foo";
           ^
t.C:4:12: error: array bound cannot be deduced from an in-class initializer
t.C:3:8: warning: private field 'b' is not used [-Wunused-private-field]
  bool b;
       ^
t.C:4:8: warning: private field 'a' is not used [-Wunused-private-field]
  char a[] = "foo";
       ^
3 warnings and 1 error generated.