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Re: Alignment, placement new and struct with pointer to array of POD

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On Monday, December 14, 2015 at 8:00:20 AM UTC-5, Martin Bonner wrote:
> On Sunday, 13 December 2015 19:10:14 UTC+1, Daniel  wrote:

> > But what if we have 
> > 
> > struct B 
> > { 
> >     size_t length; 
> >     int *p; 
> > }; 
> > 
> > and wish to allocate storage for B and p with placement new from the
> > same storage? 

> I think you need to define:
>     struct BB { struct B b; int i[1] };
>     typedef typename std::aigned_storage<sizeof(B), 
>         alignof(B)>::type storage_type;
> 
>     size_t length = 10;
>     char* storage = new char[sizeof(storage_type)+(length-1)*sizeof(int)];
>     B* pb = new(storage)B();
>     auto pbb = reinterpret_cast<BB*>(storage);
>     pb->p = new(&pbb->i)int[length];
> 
Thank you very much! that definitely helps my understanding. But did you 
mean to write BB instead of B in the typedef for storage_type?

Best regards,
Daniel


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Alignment, placement new and struct with pointer to array of POD Daniel <danielaparker@googlemail.com> - 2015-12-13 12:01 -0600
  Re: Alignment, placement new and struct with pointer to array of POD Martin Bonner <martinfrompi@yahoo.co.uk> - 2015-12-14 06:52 -0600
    Re: Alignment, placement new and struct with pointer to array of POD Daniel <danielaparker@googlemail.com> - 2015-12-15 07:08 -0600
      Re: Alignment, placement new and struct with pointer to array of POD Martin Bonner <martinfrompi@yahoo.co.uk> - 2015-12-15 13:55 -0600
  Re: Alignment, placement new and struct with pointer to array of POD evansl <cppljevans@googlemail.com> - 2016-01-11 06:46 -0600
    Re: Alignment, placement new and struct with pointer to array of POD evansl <cppljevans@googlemail.com> - 2016-01-12 07:21 -0600

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