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Date: Thu, 26 Dec 2002 13:46:00 -0000
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From: Manfred Spraul <manfred@colorfullife.com>
Subject: Re: c/9058: structure with flexible array member: offsetof() != sizeof()
Reply-To: Manfred Spraul <manfred@colorfullife.com>
X-SW-Source: 2002-12/txt/msg01301.txt.bz2
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The following reply was made to PR c/9058; it has been noted by GNATS.

From: Manfred Spraul <manfred@colorfullife.com>
To: "Joseph S. Myers" <jsm28@cam.ac.uk>
Cc: gcc-gnats@gcc.gnu.org, gcc-bugs@gcc.gnu.org
Subject: Re: c/9058: structure with flexible array member: offsetof() != sizeof()
Date: Thu, 26 Dec 2002 22:45:04 +0100

 Joseph S. Myers wrote:
 
 >On 26 Dec 2002 manfred@colorfullife.com wrote:
 >
 >  
 >
 >>Now sizeof(struct x) is 8, offsetof(struct x, c) is 6. That seems to
 >>contradice the C99 standard: section 6.7.2.1, constraint 16.
 >>    
 >>
 >
 >Please read the suggested TC in response to DR 282.  (See N983
 ><http://std.dkuug.dk/JTC1/SC22/WG14/www/docs/n983.htm> and the Santa Cruz
 >minutes <http://std.dkuug.dk/JTC1/SC22/WG14/www/docs/n987.htm> - the DR
 >log hasn't yet been updated.)
 >
 Thanks, I found the thread "C99 conformance bug in gcc-3.1" after filing 
 the bug report.
 What's the recommended approach to calculate the size for malloc calls? Is
 
     struct a {int a; char b; short c[]; };
 
     len = offsetof(struct a, c[nr_entries]);
 
 valid and portable?
 
     sizeof(struct a)+nr_entries*sizeof(short);
 
 would waste 2 bytes.
 
 --
     Manfred