Re: [boost] reinterpret_cast : differents structs or classes with identical structural type

From: Sebastian Redl (sebastian.redl_at_[hidden])
Date: 2007-10-02 06:32:22

David Abrahams wrote:
> on Fri Sep 21 2007, "Marco Servetto" <marco.servetto-AT-gmail.com> wrote:
>   
>> struct A{
>>   int a1;
>>   double a2;
>>   int a3[3];
>>   };
>> struct B{
>>   int b1;
>>   double b2;
>>   int b3[3];
>>   };
>>
>> The question is: C++ grants that
>> A a;
>> a.a2=8.8;
>> assert(reinterpret_cast<B*>(&a)->b2==8.8);
>>     
> C++ guarantees very, very little about reinterpret_cast, and certainly
> not that.
>   
The rules about layout compatibility of POD structs seem to guarantee
exactly that. I don't know how else to interpret them - that is, how
else to even be in a situation where the compatibility rules apply,
except by using reinterpret_cast or a C-style cast.

Sebastian Redl