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Jordan Abel wrote:
> On 2006-05-04, Ian Collins <ian-> wrote:
>
>>Jordan Abel wrote:
>>
>>>On 2006-05-04, Keith Thompson <kst-> wrote:
>>>>
>>>>I'm fairly sure it is, since the standard doesn't define what the
>>>>behavior is.
>>>
>>>
>>>I guess i'm used to thinking of UB as something that can at least in
>>>principle be identified by careful examination of the source. that is,
>>>for any given set of inputs ["inputs" including returns from library
>>>functions whose outputs are not fully determined by their inputs - e.g.
>>>malloc returning null or not], a program either does cause UB or
>>>doesn't. stack overflows are a big hole in this, and i think they're
>>>unique.
>>
>>Are they UB and are they unique?
>>
>>I'd categorise them as an environment constraint violation, another
>>example would be opening more files then the operating environment permits.
>
>
> That doesn't cause UB. It causes fopen to return a null pointer.
>
OK.
>
>>Stack size is environment specific, so a well formed program that
>>operates correctly in one environment might violate the constraints of
>>another.
>
>
> Which is unique among ALL things which cause UB.
>
How about dereferencing an odd address on a target the doesn't support this?

--
Ian Collins.

On 2006-05-04, Ian Collins <ian-> wrote:
> Jordan Abel wrote:
>> On 2006-05-04, Ian Collins <ian-> wrote:
>>
>>>Jordan Abel wrote:
>>>
>>>>On 2006-05-04, Keith Thompson <kst-> wrote:
>>>>>
>>>>>I'm fairly sure it is, since the standard doesn't define what the
>>>>>behavior is.
>>>>
>>>>
>>>>I guess i'm used to thinking of UB as something that can at least in
>>>>principle be identified by careful examination of the source. that is,
>>>>for any given set of inputs ["inputs" including returns from library
>>>>functions whose outputs are not fully determined by their inputs - e.g.
>>>>malloc returning null or not], a program either does cause UB or
>>>>doesn't. stack overflows are a big hole in this, and i think they're
>>>>unique.
>>>
>>>Are they UB and are they unique?
>>>
>>>I'd categorise them as an environment constraint violation, another
>>>example would be opening more files then the operating environment permits.
>>
>>
>> That doesn't cause UB. It causes fopen to return a null pointer.
>>
> OK.
>>
>>>Stack size is environment specific, so a well formed program that
>>>operates correctly in one environment might violate the constraints of
>>>another.
>>
>>
>> Which is unique among ALL things which cause UB.
>>
> How about dereferencing an odd address on a target the doesn't support
> this?

Things that would cause this to happen ALWAYS cause UB. UB doesn't
always mean something bad happens.

<> wrote in message
news: oups.com...
> hi,
>
> int main(void)
> {
> main();
> return 0;
> }
>
> wat does the standard says about the above code snippet?
>

This is allowed in C and performs the obvious useless recursive call. It is
forbidden however in the C++ standard

Robert Smith wrote:
> <> wrote in message
>>
>> int main(void)
>> {
>> main();
>> return 0;
>> }
>>
>> wat does the standard says about the above code snippet?
>
> This is allowed in C and performs the obvious useless recursive
> call. It is forbidden however in the C++ standard

In C it is of primary use in writing obfuscated code. C++ needs no
assistance in this respect, and thus can dispense with the
capability.

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said:

> hi,
>
> int main(void)
> {
> main();
> return 0;
> }
>
> wat does the standard says about the above code snippet?

Not a lot.

It's legal C, but eventually you'll run out of something or other, depending
on what system you are using.

--
Richard Heathfield
"Usenet is a strange place" - dmr 29/7/1999
http://www.cpax.org.uk
email: rjh at above domain (but drop the www, obviously)