Re: Fwd: Bug#1050663: dar option --on-fly-isolate creates catalogue with broken slice_layout

Hi Denis,

I was somewhat confused about your finding concerning zero 
initialization of objects.

> What does a default constructor in C++ seem to do, depend on the C++ 
> standard (pivot at C++11) but the object should be zero-initialized, 
> that to say, the field slice_layout::older_sar_than_v8 should be set 
> to false according to this reference (unless I misread it):
>
> https://en.cppreference.com/w/cpp/language/value_initialization

Since I started programming in C++ about 30 years ago, I was shure that 
only static data gets zero-initialized. As far as I remember this is a 
heritage of C wher this also was true.

It took some time till I realized that "value initialization" is not the 
thing that happens if you declare an object without explicit 
initialization like

     MyTypeOrClass obj;

but seems to be the kind of initialization that is used if you declare 
an object using an empty initializer e.g.

     MyTypeOrClass obj {};

(Thanks for citing this article anyway. I dit not know that yet and It's 
fine to learn something new even being old ;-) )

I think the relevant article is the one about "default initialization":

https://en.cppreference.com/w/cpp/language/default_initialization

where you find the note:

"Default-initialization of non-class variables with automatic and 
dynamic storage duration produces objects with indeterminate values 
(static and thread-local objects get zero initialized 
<https://en.cppreference.com/w/cpp/language/zero_initialization>).

References and const scalar objects cannot be default-initialized."

Now my world is fine again :-)

> Cheers,
> Denis
>
A la tienne,

Rolf