From mboxrd@z Thu Jan  1 00:00:00 1970
Message-ID: <4A595F8D.1080408@tecmav.com>
Date: Sun, 12 Jul 2009 05:59:09 +0200
From: Adriano Verardo <a.verardo@tecmav.com>
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To: Fans of the OS Plan 9 from Bell Labs <9fans@9fans.net>
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Subject: [9fans] C compiler question
Topicbox-Message-UUID: 1be5c556-ead5-11e9-9d60-3106f5b1d025

Hi, all.

Yesterday I observed different sizeof() of a union in a library function
and in the main program. The reason seems to be a forgotten #include
in a library source.

union U
{
    struct
    {
          <fields of defined types>            //  sizeof = 100
          struct NeverDefined  nf;              //  Unknown, definition
not #included
    } S1

    struct
    {
          <fields of defined types>            //  sizeof = 20
    } S2
};

8c silently accept the above definition and sizeof(U) is 100.  ???
The sources which include the definition of "NeverDefined" are
regularly compiled too and sizeof(U) = 100 + sizeof(NeverDefined).

This happens only if the undefined field is the last of the structure.
If it is followed by other (defined or not defined) field(s), the compiler
correctly detects the error.

Is this behaviour correct ?

Thanks in advance.

a.verardo