Member initialization of arrays of constants

[Michael Schwendt]

On Tue, 25 Jul 2000 llewelly@dbritsch.dsl.xmission.com wrote:

>I think we should move this discussion to comp.std.c++ .

Of course. I'll consider that depending on a reply from Borland's support (if any).

>> Error: Constant member 'A::c' in class without constructors
>
>I cannot find wording in the standard that disallows const members
>  from classes without constructors.
>
>(Nor have I ever found a C++ compiler that did not have a multitude of
>  bugs.)

Me neither. However, I find errors like this in commercial and popular compilers disgusting. I mean, I can't be the only one who has tried to port code which uses an aggregate with constant members as a character-based binary file header. On the other hand, a lot of C/C++ programmers seem to not like const-qualified types. So, most likely they work with non-consts in most places. ;-)

>> struct A
>> {
>>     const char c[4];
>>     const j;
>
>I presume 'const j' was intended to be 'const int j' .

Yes, a typo.

>I do think 12.6.1/4 makes this constructor ill-formed, however, your
>  previous examples did not contain user-defined constructors, and
>  were aggregates according to 8.5.1; this class is not.

Ack. I had tried a few alternatives. The most trivial one would be to remove all const's from the structure and make sure read-only values are not written to. This would be feasible, but hey, that const-portability issue bugs me.

>(gcc 2.95.2, and 2.96 20000626 both compile it without errors, and
>  that (I belive) *is* a bug, but it is different from your earlier
>  examples.)

Ack.

[snip]

>In your 'Example 2', the initialization was not in the class
>  declaration, and so I do not see how 9.2/4 applies.

Forget about it, please. What I had in mind was extending an aggregate to become a non-aggregate by adding constructors. Doing that, the new non-aggregate class would suffer a lot from lack of flexibility compared with the old aggregate. This move would force me to turn member aggregates static, and I'd also need to redesign a lot of other code because I couldn't initialize sub-aggregate arrays of constants easily.


<off-topic>

>> Yes. Whenever I add a constructor, I can forget about using the
>> brace-enclosed initializer-list. Hmmm...
>
>That is what 8.5.1/1 says.

This is where this entire issue turns out to get nasty.

>From this nice and *simple* aggregate

struct A1
{
    const char a[4];
    char b[4];
    // add members here
};

to

struct A2
{
    const char a[4];
    char b[4];
    // add members here

    A(const char*)  // error! ctor makes member 'a' illegal!
    { ; }
};

Hmm... =:-}

</off-topic>


Case closed. *g*

Regards,
Mike

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