c/9058: structure with flexible array member: offsetof() != sizeof()

[manfred@colorfullife.com]

>Number:         9058
>Category:       c
>Synopsis:       structure with flexible array member: offsetof() != sizeof()
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    unassigned
>State:          open
>Class:          wrong-code
>Submitter-Id:   net
>Arrival-Date:   Thu Dec 26 04:36:01 PST 2002
>Closed-Date:
>Last-Modified:
>Originator:     Manfred Spraul
>Release:        gcc (GCC) 3.2 20020903 (RedHat Linux 8.0 3.2-7)
>Organization:
>Environment:
Linux i386
>Description:
See the attached test case:
struct x {int a; char b; short c[];};

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.

The problem occurs both with gcc and g++
>How-To-Repeat:
gcc -o simple simple.c
./simple
>Fix:
Workarounds:
- Do not assume that x_ptr->c == x_ptr+1
- Manually pad structure
>Release-Note:
>Audit-Trail:
>Unformatted:
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