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Re: Is a union a kind of class?

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On 12/22/2013 08:27 PM, news wrote:
>
> On 12/19/13 13:24, johnolithicsoftware@googlemail.com wrote:
> [snip]
>
>> The size of a union is equal to the size of it's largest data member
>> if I'm not mistaken.
>
> What about:
>
>   union dbl_charray
>   {
>       double dbl;
>       char [sizeof(double)+1] charray;
>   };
>
> IIUC, in order to satisfy the alignment requirements of the double,
> the size would have to be 2*sizeof(double), not just sizeof(double)+1.

Not necessarily. The minimum possible size will be sizeof(double) +
alignof(double), which could be smaller than 2*sizeof(double) - in
principle, it could be as small as sizeof(double)  + 1. The actual size
could be larger than the minimum - some implementations give all classes
the same alignment requirement, which would be alignof(max_align_t), and
could in principle be larger than 2*sizeof(double), though it's rather
unlikely.


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Is a union a kind of class? Seungbeom Kim <musiphil@bawi.org> - 2013-08-31 01:12 -0600
  Re: Is a union a kind of class? Daniel Krügler <daniel.kruegler@googlemail.com> - 2013-08-31 23:52 -0700
  Re: Is a union a kind of class? James Kuyper <jameskuyper@verizon.net> - 2013-08-31 23:52 -0700
  Re: Is a union a kind of class? johnolithicsoftware@googlemail.com - 2013-12-19 11:24 -0800
    Re: Is a union a kind of class? "news" <news@fx21.iad.highwinds-media.com> - 2013-12-22 19:27 -0600
      Re: Is a union a kind of class? James Kuyper <jameskuyper@verizon.net> - 2013-12-27 13:11 -0600
        Re: Is a union a kind of class? evansl <cppljevans@googlemail.com> - 2013-12-29 23:00 -0600
          Re: Is a union a kind of class? James Kuyper <jameskuyper@verizon.net> - 2013-12-31 17:45 -0600

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