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

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On Tuesday, 15 December 2015 14:10:17 UTC+1, Daniel  wrote:
> 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?

Yes!  

(and apologies to mod for failing to format correctly last time)


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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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