Re[2]: Member initialization of arrays of constants

["Michael Schwendt" <mschwendt at web dot de>]

[re-sent because of MAPS blocking first attempt]

On Sun, 23 Jul 2000 llewelly@dbritsch.dsl.xmission.com wrote:

>There is nothing in 8.5.1 [dcl.init.aggr] that disallows initializing
>  a member array of constant type with a brace-enclosed initializer
>  list.

Then it seems, I've found a bug in both Borland C++ 5.5 and Visual C++ 5.0. They throw errors upon compilation of my code examples and further related tests.

In case of brace-enclosed copy-initialization (_dcl.init.aggr_) of an array of constant chars, BC says:

struct C
{
    const char c[4];
};

Error: Constant member 'C::A::c' in class without constructors

>In both of your examples, A is an aggregate, and can therefor be
>  initialized with a brace-enclosed initializer list. (See 8.5.1)

How's that possible, considering the extended example of a class with default constructor and, for instance, a non-static member constant of aggregate type?

If you say, it _can_ be initialized, shouldn't the following code be ill-formed then? Uninitialized const-qualified types, according to 12.6.1, 4:

#include <iostream.h>
#include <iomanip.h>

struct A
{
    const char c[4];
    const j;
    int i;

    A()
    {
        i = 42;
    }
};

void f()
{
    A a;
    cout << a.i << endl;  // okay, a.i is initialized
    cout << a.j << endl;  // oops?
    cout << a.c << endl;  // oops?

    const A b = { "foo", 1, 2 };  // error
    // b' must be initialized by constructor, not by `{...}'
};

>The fact that there are const-qualified types in involved does not
>  matter in either of your examples; const qualifed types can be
>  initialized the same way.

I'd be forced to make each array of constants static. Else I could not perform copy-initialization.

  9.2, 4

  A member-declarator can contain a constant-initializer only if
  it declares a static member (_class.static_) of integral or
  enumeration type, see _class.static.data_.

If you mean, that the brace-enclosed initializer-list is a special case which can only initialize static constant member aggregates, this would make sense.

>(If const-qualifed members could not be initialized, there would no
>  use for them.)

Well, const-qualified members can be initialized via the ctor's mem-initializer list. But what about member arrays of const-qualified basic types?

>(The rule you are probably thinking of is probably based on 12.6.2/4,
>  which does not apply to static data members, or to initialization of an
>  aggregate via a brace-enclosed intializer list.)

Yes. Whenever I add a constructor, I can forget about using the brace-enclosed initializer-list. Hmmm...

Regards,

Mike

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