[cfe-dev] Zero-initialization and explicit constructors

[Richard Smith]

On Mon, Jun 23, 2014 at 10:51 AM, Kuba Břečka <kuba.brecka at gmail.com> wrote:

> Hi,
> I would like to ask about the difference in behavior of C++11 explicit
> constructors, between Clang/LLVM 3.4 and current trunk version (3.5). The
> following:
>
>   #include <stdio.h>
>   struct Inner {
>     explicit Inner() {}
>   };
>   struct Outer {
>     Inner member;
>   };
>   int main() {
>     Outer s = {};
>     printf("%p\n", &s); // just to silence "unused variable" warning
>     return 0;
>   }
>
> compiles fine with Clang 3.4 using "clang++ -std=c++11 -Wall -Wpedantic",
> however using trunk version, this gives me "chosen constructor is explicit
> in copy-initialization" error. Is this the right (intended) behavior?
>

Yes. This reflects a recent bugfix to the C++ specification. Note that:

  Inner s = {};

was rejected before and after this change, as was

  Inner s = { {} };


> How can you zero-initialize such an object? I mean "Outer s = Outer{}"
> doesn't compile either.
>

  Outer s = Outer();

should work. In this case,

  Outer s;

should work fine too.
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