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Re: Is a union a kind of class?

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On Saturday, August 31, 2013 2:20:02 AM UTC-4, Seungbeom Kim wrote:
> In the taxonomy of C++ types, is a union a (kind of) class?
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> 9[class]/5 clearly says, "A union is a class defined with the class-key
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> union [...]". 5.1.2[expr.prim.lambda]/3 and 9[class]/10 also mention "a
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> non-union class [type]", and 5.9[expr.rel]/2 "provided their class is
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> not a union", all of which imply that a union is a class.
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> On the other hand, 3.9.2[basic.compound]/1 lists classes and unions
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> separately, which strongly implies that a union is not a class.
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> If a union is a class, I think 3.9.2/1 is confusing (at best) and should
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> be considered a defect.
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> --
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> Seungbeom Kim
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A union is like a struct except that each member variable is using the same memory spot, so unlike a struct or a class if you modify the value of one of them you modify the value of them all at once. They all share the same variable value but that value can be truncated if one of it's members is an int and the other is a char and you assign the int with the value 256 and reference it with the associated char member in a printf statement but it will still attempt to convey the memory associated with the int member. The size of a union is equal to the size of it's largest data member if I'm not mistaken.


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Thread

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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