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Groups > comp.lang.c > #11745

Re: Structure without a tag

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Максим Фомин <maxim@maxim-fomin.ru> writes:
> Consider this code:
>
> struct
> {
>    int x;
>    int y;
> }  one;
>
> struct
> {
>    int x;
>    int y;
> }  two;
>
> int main(void)
> {
>    one.x = one.y = 6;
>    one = two;
>    return 0;
> }
>
> Compiler rejects assignment of first structure to second
> ("incompatible types when assigning to type ‘struct <anonymous>’ from
> type ‘struct <anonymous>’").
>
> It seems to me that objects one and two have type struct {int x; int
> y} and therefore their types are equal.
>
> If not, which type they have?

If you had declared them with distinct tags:

    struct foo { int x; int y; } one;
    struct bar { int x; int y; } two;

they'd be of distinct and incompatible types, "struct foo" and "struct
bar".

Omitting the tags doesn't make them compatible.

If you want "one" and "two" to have compatible types, it's easy enough
to declare them that way, either:

    struct { int x; int y; } one, two;

or

    struct foo { int x; int y; };
    struct foo one;
    struct foo two;

-- 
Keith Thompson (The_Other_Keith) kst-u@mib.org  <http://www.ghoti.net/~kst>
"We must do something.  This is something.  Therefore, we must do this."
    -- Antony Jay and Jonathan Lynn, "Yes Minister"

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Thread

Structure without a tag Максим Фомин <maxim@maxim-fomin.ru> - 2011-10-15 13:20 -0700
  Re: Structure without a tag Eric Sosman <esosman@ieee-dot-org.invalid> - 2011-10-15 17:16 -0400
    Re: Structure without a tag Frederick Williams <freddywilliams@btinternet.com> - 2011-10-16 15:19 +0100
      Re: Structure without a tag Eric Sosman <esosman@ieee-dot-org.invalid> - 2011-10-16 10:30 -0400
      Re: Structure without a tag Keith Thompson <kst-u@mib.org> - 2011-10-16 13:54 -0700
      Re: Structure without a tag Jorgen Grahn <grahn+nntp@snipabacken.se> - 2011-10-16 22:09 +0000
        Re: Structure without a tag Eric Sosman <esosman@ieee-dot-org.invalid> - 2011-10-16 18:29 -0400
          Re: Structure without a tag "BartC" <bc@freeuk.com> - 2011-10-16 23:55 +0100
            Re: Structure without a tag blp@cs.stanford.edu (Ben Pfaff) - 2011-10-16 17:31 -0700
          Re: Structure without a tag James Kuyper <jameskuyper@verizon.net> - 2011-10-16 20:05 -0400
            Re: Structure without a tag Kaz Kylheku <kaz@kylheku.com> - 2011-10-17 17:02 +0000
              Re: Structure without a tag James Kuyper <jameskuyper@verizon.net> - 2011-10-17 13:53 -0400
                Re: Structure without a tag Robert Wessel <robertwessel2@yahoo.com> - 2011-10-17 13:38 -0500
                Re: Structure without a tag Максим Фомин <maxim@maxim-fomin.ru> - 2011-10-17 22:28 -0700
                Re: Structure without a tag gordonb.b1148@burditt.org (Gordon Burditt) - 2011-10-18 03:04 -0500
                Re: Structure without a tag Nick Keighley <nick_keighley_nospam@hotmail.com> - 2011-10-18 01:37 -0700
                Re: Structure without a tag James Kuyper <jameskuyper@verizon.net> - 2011-10-18 07:10 -0400
                Re: Structure without a tag gwowen <gwowen@gmail.com> - 2011-10-18 08:43 -0700
                Re: Structure without a tag James Kuyper <jameskuyper@verizon.net> - 2011-10-18 11:55 -0400
                Re: Structure without a tag "BartC" <bc@freeuk.com> - 2011-10-18 17:18 +0100
                Re: Structure without a tag Joe Pfeiffer <pfeiffer@cs.nmsu.edu> - 2011-10-18 15:09 -0600
                Re: Structure without a tag Patrick Scheible <kkt@zipcon.net> - 2011-10-18 08:59 -0700
                Re: Structure without a tag James Kuyper <jameskuyper@verizon.net> - 2011-10-18 12:54 -0400
                Attributions (was Re: Structure without a tag) Keith Thompson <kst-u@mib.org> - 2011-10-18 11:48 -0700
                Re: Structure without a tag Stephen Sprunk <stephen@sprunk.org> - 2011-10-18 16:20 -0500
    Re: Structure without a tag Tim Rentsch <txr@alumni.caltech.edu> - 2012-01-24 18:05 -0800
  Re: Structure without a tag Keith Thompson <kst-u@mib.org> - 2011-10-15 16:30 -0700
  Re: Structure without a tag Jean-Christophe <5.d@free.fr> - 2011-10-16 09:54 -0700

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