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Re: Is this valid code or UB?

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* Joshua Maurice, on 24.05.2011 01:35:
> On May 23, 2:57 pm, "Paul"<pchris...@yahoo.co.uk>  wrote:
>> Yes I'm still arguing about arrays. Anyway consider the following:
>>
>> int main(){
>>   int (*p)[3]=0;
>>   std::cout<<*p<<std::endl;
>>   std::cout<<  typeid(*p).name()<<std::endl;
>>   std::cout<<  sizeof(*p);
>>
>> }
>>
>> Does a valid array type object exist?
>> Is it UB because it dereferences a null pointer?
>
> Add a missing #include<iostream>  for starters.
>

[snip long descent into standard]

He he.

There is a non-normative *comment* somewhere at the start of the standard that 
states pretty off-hand that dereferencing a null pointer is UB. Then there is 
normative text regarding typeid that says that it's OK for the typeid argument. 
Which makes sense, since the compiler can add checking there.

This is a well-known "almost-defect". I think but I am not sure that it has been 
fixed in C++0x.


Cheers & hth.,

- Alf

-- 
blog at <url: http://alfps.wordpress.com>

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Thread

Is this valid code or UB? "Paul" <pchristor@yahoo.co.uk> - 2011-05-23 22:57 +0100
  Re: Is this valid code or UB? Leigh Johnston <leigh@i42.co.uk> - 2011-05-23 23:05 +0100
  Re: Is this valid code or UB? Anand Hariharan <mailto.anand.hariharan@gmail.com> - 2011-05-23 16:04 -0700
  Re: Is this valid code or UB? Ian Collins <ian-news@hotmail.com> - 2011-05-24 11:15 +1200
  Re: Is this valid code or UB? Joshua Maurice <joshuamaurice@gmail.com> - 2011-05-23 16:35 -0700
    Re: Is this valid code or UB? "Alf P. Steinbach /Usenet" <alf.p.steinbach+usenet@gmail.com> - 2011-05-24 02:38 +0200
      Re: Is this valid code or UB? Joshua Maurice <joshuamaurice@gmail.com> - 2011-05-23 18:36 -0700

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