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| From | Shao Miller <sha0.miller@gmail.com> |
|---|---|
| Newsgroups | comp.std.c |
| Subject | Re: Unsequenced Side Effects on the Same Union |
| Date | 2013-01-17 17:50 -0500 |
| Organization | A noiseless patient Spider |
| Message-ID | <kd9v6r$ge3$1@dont-email.me> (permalink) |
| References | <kd570b$mvc$1@dont-email.me> <kd6f0b$fh4$1@dont-email.me> <50F6CF92.4090803@verizon.net> <kd745t$mm8$1@dont-email.me> <kfnfw1za4k2.fsf@x-alumni2.alumni.caltech.edu> |
On 1/17/2013 16:21, Tim Rentsch wrote:
> Furthermore it's easy to find an example where parts of a union
> can be modified separately in safety, eg,
>
> union {
> long x[100];
> short y[ sizeof (long[100]) / sizeof (short) ];
> } u = {0};
>
> u.x[10]++ * u.y[5]++; /* assume sizeof (long) >= sizeof (short) */
>
> The scalar object u.x[10] is not the same scalar object as
> u.y[5], so this expression is safe. (To be thorough, I should
> include a proviso that this code is run on a platform where
> all-bits-zero is the only representation of zero for both long
> and short, so the initialization produces object representation
> suitable for both members.)
>
It can be (and has been) argued that this is a violation of 6.5p7. In
fact, WG14 hasn't reached consensus. (I asked.)
--
- Shao Miller
--
"Thank you for the kind words; those are the kind of words I like to hear.
Cheerily," -- Richard Harter
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Unsequenced Side Effects on the Same Union Shao Miller <sha0.miller@gmail.com> - 2013-01-15 22:32 -0500
Re: Unsequenced Side Effects on the Same Union Nick Bowler <nbowler@draconx.ca> - 2013-01-16 14:55 +0000
Re: Unsequenced Side Effects on the Same Union Shao Miller <sha0.miller@gmail.com> - 2013-01-16 10:53 -0500
Re: Unsequenced Side Effects on the Same Union James Kuyper <jameskuyper@verizon.net> - 2013-01-16 11:04 -0500
Re: Unsequenced Side Effects on the Same Union Nick Bowler <nbowler@draconx.ca> - 2013-01-16 20:56 +0000
Re: Unsequenced Side Effects on the Same Union Tim Rentsch <txr@alumni.caltech.edu> - 2013-01-17 13:21 -0800
Re: Unsequenced Side Effects on the Same Union Shao Miller <sha0.miller@gmail.com> - 2013-01-17 17:50 -0500
Re: Unsequenced Side Effects on the Same Union Tim Rentsch <txr@alumni.caltech.edu> - 2013-01-18 11:25 -0800
Re: Unsequenced Side Effects on the Same Union Shao Miller <sha0.miller@gmail.com> - 2013-01-18 15:07 -0500
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