Re: [eigen] Alignment of a derived class

[Martin Sälzle <martin.saelzle@xxxxxxx>]

Am 19.07.2012 um 01:38 schrieb Gael Guennebaud:

> On Thu, Jul 19, 2012 at 6:48 AM, Christoph Hertzberg
> <chtz@xxxxxxxxxxxxxxxxxxxxxxxx> wrote:
>> On 18.07.2012 23:29, Gael Guennebaud wrote:
>>> 
>>> On Wed, Jul 18, 2012 at 4:18 AM, Martin Sälzle <martin.saelzle@xxxxxxx>
>>> wrote:
>>>> 
>>>> struct Base
>>>> {
>>>>   Eigen::Vector4f vec4f_base;
>>>>   EIGEN_MAKE_ALIGNED_OPERATOR_NEW
>>>> };
>>>> 
>>>> struct Derived1 : public Base
>>>> {
>>>>   Eigen::Vector4f vec4f_derived_1;
>>>>   EIGEN_MAKE_ALIGNED_OPERATOR_NEW
>>>> };
>>>> [...]
>>>> 
>>>> The final question is what would happen for Derived1 if Base does note
>>>> have EIGEN_MAKE_ALIGNED_OPERATOR_NEW?
>>> 
>>> 
>>> On a 64bits system nothing special. On a 32bits system with SSE
>>> enabled, an abort or segfault if you create a Derived1 on the heap
>>> using "new Derived1".
>> 
>> 
>> Actually, if Derived1 still has an EIGEN_MAKE_ALIGNED_OPERATOR_NEW, it
>> should be ok to use `new Derived1`, shouldn't it?
> 
> Sure!
> 
> gael
> 
>> Of course it is better to just add EIGEN_MAKE_ALIGNED_OPERATOR_NEW to the
>> base class -- and it won't harm if you add it to the derived classes as
>> well.
>> 
>> Christoph
>> 
>> 
>> 
>> 
>> 
>> --
>> ----------------------------------------------
>> Dipl.-Inf. Christoph Hertzberg
>> Cartesium 0.049
>> Universität Bremen
>> Enrique-Schmidt-Straße 5
>> 28359 Bremen
>> 
>> Tel: +49 (421) 218-64252
>> ----------------------------------------------
>> 
>> 
> 
> 

Hi Gael,

I have another question:

I saw that you define 
   typedef void eigen_aligned_operator_new_marker_type;
in the macro
   EIGEN_MAKE_ALIGNED_OPERATOR_NEW_IF
in Memory.h 

Do you have a structure in Eigen that checks if the typedef is defined, similar to the second example here:
http://en.wikipedia.org/wiki/SFINAE

If Eigen provides this I would not have to define it myself. 

Basically what I want to do is to use boost::conditional to check if I have to use the aligned allocator for a vector.

thank you,
Martin