From mboxrd@z Thu Jan  1 00:00:00 1970
Message-ID: <4A5CB1C2.2000805@tecmav.com>
Date: Tue, 14 Jul 2009 18:26:42 +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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	<7144845a3c658a8194be95e64d69486f@coraid.com>
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Subject: Re: [9fans] C compiler question
Topicbox-Message-UUID: 203f5e96-ead5-11e9-9d60-3106f5b1d025

erik quanstrom wrote:
>> The point is how to compute the offset(s) of the last field at compile /
>> run time.
>>
>
> the offset of the last field is not in question.  i believe you mean the size?
>
It's really the same info.

struct
{
      .....     // total sizeof = 100
    int B[..];
}A;

offset(B) = 100,  &(A.B[7]) == address(A) + 100 + 7*sizeof(int).
The compiler accept the dirty but legal expression  A.B[-3]  because it
can compute
the address (or the offset with respect the beginnig of "A") of the B
"-3" cell.

But in this case

struct
{
      .....     // total sizeof = 100
    struct B B;
}A;

with B declared (just named), how 8c could determined the address of A.B.x ?
To accept the above definition of A, say in a global .h, means that every .c
should include the definition of B.
They could be - legally - different, so generating different offsets of
"x" with respect A
in the same program.


>> I prefer to have only the tricky but standard  "char  x[0]" tails.
>>
>
> i'd prefer not to have them, either.  but it's too late for that.
>
>
:-)   And what about

char x[...]  and   x[2] == 2[x]    :-)  :-)
>> Your patch will be included in the next distribution CD ?
>>
>
> no.  i haven't submitted it yet.
>
> - erik
adriano