Why did initializer-list not value-initialize this struct?

[xml...@gmail.com]

The C++11 standard 8.5.4.3 says:

"If the initializer list has no elements and T is a class type with a default constructor, the object is value-initialized."

struct A
{
    int get() { return i; }

private:
    int i;
};

int main()
{
    A a = {};

    int n = a.get();
    // Here I can watch a.i is not value-initialized, 
    // instead is 0xCCCCCCCC when running in debugging mode.

    return 0;
}

Is this a bug of VC++? My VC++ is the latest Nov 2012 CTP.

[Daniel Krügler]

2012/12/16 <xml...@gmail.com>:

> The C++11 standard 8.5.4.3 says:
>
> "If the initializer list has no elements and T is a class type with a
> default constructor, the object is value-initialized."

Yes.

> struct A
> {
> int get() { return i; }
>
> private:
> int i;
> };
>
> int main()
> {
> A a = {};
>
> int n = a.get();
> // Here I can watch a.i is not value-initialized,
> // instead is 0xCCCCCCCC when running in debugging mode.
>
> return 0;
> }
>
> Is this a bug of VC++? My VC++ is the latest Nov 2012 CTP.

This looks like a compiler bug to me.

- Daniel

[xml...@gmail.com]

But GCC behaves like VC++. Both are stupid?

[Daniel Krügler]

2012/12/16 <xml...@gmail.com>:

> But GCC behaves like VC++. Both are stupid?

I'm running here gcc 4.8.0 20121209 (experimental) and it behaves as expected.

- Daniel

[Klaim - Joël Lamotte]

Doesn't the value initialization applies to A? 

Here the default constructors isn't user defined so it's using the default constructor which will never call the int constructor anyway.

Shouldn't

A a = {}; 

be equivalent to 
A a = A(); 

?

Joel Lamotte

[Klaim - Joël Lamotte]

Ignore my previous remark, I misread the cited standard sentence.

Joel Lamotte

[luca ciciriello]

I think that is a visualisation problem of the debugger.

I've tried this code with LLVM clang 3.1 and LLDB debugger. With the debugger I see a uninitialized value of n, but if I print n out with cout << n << endl; on the the standard output I can see n = 0

Luca

2012/12/16 <xml...@gmail.com>

--
 
 
 

[Mateusz Loskot]

On 16 December 2012 18:21, <xml...@gmail.com> wrote:
> struct A
> {
> int get() { return i; }
>
> private:
> int i;
> };
>
> int main()
> {
> A a = {};
>
> int n = a.get();
> // Here I can watch a.i is not value-initialized,
> // instead is 0xCCCCCCCC when running in debugging mode.
>
> return 0;
> }
>
> Is this a bug of VC++? My VC++ is the latest Nov 2012 CTP.

Does this example compile for you at all?
What is the exact version of the Visual C++ compiler?

I'm using the version 17.00.51106.1which throws the following:

error C2552: 'a' : non-aggregates cannot be initialized with initializer list
'A' : Types with private or protected data members are not aggregate

Best regards,
--
Mateusz Loskot, http://mateusz.loskot.net